Tbi swap build thread

[rfmaster]

Originally Posted by BigBlocksRule

Yet another newbie...
I have an '85 dually that I want to sell the engine and tranny out of and install a freshly rebuilt Gen 6 454 along with a 4L80E. I have a '95 that I'm using the cab and other parts for a different project, so I can strip the computer and harness out of it, this truck originally had a 350 and 4L80E. I have access to an '87 truck that I can snag a baffled TBI tank from and plan to install a transfer pump to move fuel from the unused tank into the one with the TBI fuel pump. I also have sourced a set of gauges from a '91 so I can use the electronic speedo.
What am I overlooking?

Welcome to the thread.

Donor drive train: 95 ( 2wd?) 454 + 4L80E (rear end ratio + tire size)
Recipient platform: Dually 85 (2wd?) (rear end ratio + tire size)

The 85 did not have 4L80E as OE - probably 350-700R4, 350 -350C or 350 -THM400 . You must keep the 454 + 4L80E + PCM as a unit to make swap simple. Make sure to take DRAC or VSB module from 95 donor as well. Take a look at VSS it should be where the old speedometer cable used to bolt into trany tail shaft.

I am not familiar with 91 speedometer - being electronic then it will take one of the DRAC outputs (4000 ppm) to drive it. Depending on rear end gear ratio/tire combination DRAC reprogramming maybe required to get speedometer indicate correct speed.

Late 454 TBI systems - 94 & 95 model years used higher fuel pressure over traditional 9-13 PSI used by SBC and earlier BBC TBI. Starting in '94 the 454 TBI fuel systems went from 9-13psi spec to 26-32psi. Use TPI or Vortec spec fuel pump in the 87 baffled tank:
AC Delco#: EP241
GM#: 25116163

Feed fuel line from the gas tank to the TB inlet should be 3/8" - use steel line with SAE 30R9J rated flexible lines. Original fuel line might be marginal due to its age (it was not designed for high fuel pressure operation - carburetor fuel pump operated in lift mode)

//RF

[BigBlocksRule]

Both are 2WD trucks.
All I pulled so far from the '95 was the engine, all the harness, etc. is still there. Fluid was dirty in the tranny but with less than 150K on the odometer, I'm going to flush it, swap the filter and run it. I have a second one from a '96 that I can use if needed, but since it's Vortec, I'm guessing I may have to swap an internal wiring harness?
I have two 454TBI's, will rebuild the best looking one of the two. I stripped an '88 with a 454 in it, snagged that TBI unit and wiring harness so I'll have plenty of wire ends, etc. but the computer is ECM, not PCM, so it'll be off to ebay with that one.
I'll probably go with something like a Holley Strip Dominator, single plane, since I'm swapping to late 60's closed chamber heads. Stock valve sizes, bowl cleanup ,etc., nothing major, I don't want to kill torque. I did manage to save the fuel pump assembly...but my TBI units are older, should I go with higher or lower fuel pressure pumps since my TBI units are older?

[rfmaster]

Sounds like you have this project under control.

Holley Strip dominator is not a good choice for TBI. TBI needs fully heated intake manifold - strip dominator is a cold intake due to its runner design. With cold ambient temperatures this intake will cause acceleration lean outs - stumbles during acceleration. Unfortunately, truck PCM does not have IAS which can be used to compensate for colder ambient temperatures.

You can use either 88 or 95 TB - just keep in mind that TPS connector is different between the two and FPR spring in 95 should be stiffer - to support higher fuel pressure. Also, the 95 TB internal fuel passages are slightly larger providing less restriction to fuel flow.

//RF

[BigBlocksRule]

Thanks for the info. I guess I've been reading too much at the 454SS site, they're more concerned with outright performance than towing. I'll find a good heated intake and go from there.
I appreciate your help, will probably need more, but that's what's great about the net - keeps us from all making the same mistakes!

[68 TT]

Originally Posted by BigBlocksRule

Thanks for the info. I guess I've been reading too much at the 454SS site, they're more concerned with outright performance than towing. I'll find a good heated intake and go from there.
I appreciate your help, will probably need more, but that's what's great about the net - keeps us from all making the same mistakes!

If you are actually going to tow with this truck then the stock small port heads and intake will work pretty well for you, probably better than the passenger car large oval port heads will. It will save you a bunch of work too as the stock tune in the PCM will be much closer to right. The VE of the passenger car heads are far different than the peanut port truck heads and will take a bunch of tuning time to get the engine to run right with them and a different intake too. Throw in a cam change and you are pretty much starting from scratch tune wise with no factory tune available to borrow from or build upon that used the bigger port heads.

I say get the thing on the road with the stock heads, intake & cam to get the bugs worked out of the swap first. Too many variables all at once will make your swap a nightmare to get running right.

After it is on the road and running right if you feel it doesn't make the power you want then tear into it and do a cam change and upgrade the exhaust. The small port heads can do pretty well. They might surprise you with a good cam upgrade, headers and dual exhaust. If it is still not making the power you want then do the head & intake upgrade.

The big valve converted passenger car oval port heads are great and I run them on my street cars instead of rectangular port heads but for a tow rig the stock small port heads may be a better fit for you.

[BigBlocksRule]

There won't be much towing, maybe a car trailer from time to time. I plan to use this as a work truck more than a hauler. Part of the reason for the pass heads is compression bump. Plus, with 4.10 gears, I'll be in the meat of the torque band pretty much all the time.
I started thinking a few years ago about an "old fart truck" for my later years which are slowly creeping up on me. Something to drive around and get in the impatient young kid's way, white hairs sticking out of my ears and nose and a finger in their direction...sure would be nice to have a truck with some cojones as well for when they decide they can't bear to follow an old fart in an old ugly truck and try to pass. I'm actually looking at decals for the dually fenders, something like the old Gentleman Jim and Beau James, except mine will be "Fugg Lee"...
And as long as I stay away from rectangle port heads, I'll have plenty of torque by default, that's the big block way!

[GmtGmt]

can a computer and wiring harness from an early Astro van be used?

[rfmaster]

Originally Posted by GmtGmt

can a computer and wiring harness from an early Astro van be used?

Yes, Astro Van used 4.3L V6 and TBI injection which was controlled by 1227747 ECM - same as in C/K trucks. The harness length and layout is a bit different, but with a little bit of work it can be adapted. Now - if you are planning to use 4.3 (V6) TBI setup on 5.0 or 5.7 V8 you'll have to make several changes.

1) In the ECM EPROM and NETRES must be from V8 vehicle that best matches your engine (i.e 5.0 to 305; 5.7 to 350). It is easier to find matching ECM from V8 truck with correct calibration.

2) distributor must be from V8.

3) Injectors - 4.3L V6 used 46 lb-Hr injectors; 5.0L 55 lb-hr and 5.7L are 62 lb-hr.

4) KS and ESC module - should be of a V8 flavor.

//RF

[SLR_65]

Hi Guys,

I'm still reading through this entire thread, but I thought I'd take a break and outline a project I'm thinking about taking on.

I have two trucks -

A 1974 C-10. It's just an old beater but I love it. It's not pretty but I like that - I can haul anything and not worry about scratching the box! It was an old farm truck before I bought it on an auction. I bought it when my oldest son was 15 (he's now 22) and we spent a year fixing it up (it had sat for 8 years as the farmer had retired and pretty much just abandoned it in a shed). It has a 350 in it, the numbers say it's a four bolt main though we've never had the pan off, and it has 010 020 cast in the block in the timing chain area so it should be a high nickel block. Fixing it up was great fun, we put new heads on it (it had a burnt valve ('74 was the last year for regular gas heads)), an Edelbrock Performer cam and intake, a Mallory HEI distributor, rebuilt the quadrajet, and a few other things. It ran well and actually didn't do too bad on mileage after the cam change. unfortunately it's an old truck and it's developed a really nasty noise down deep so I'm afraid it's spun a bearing or something.

The other one is a 1989 Chevy 1500 with a 305 TBI in it. It also has a 700R4 transmission that has about 4,000 miles on a rebuild in it. This was my father's truck and I inherited it after he passed away. It was a decent enough truck too - I don't do any heavy hauling or anything so the 305 was just fine. Unfortunately I let my middle son drive it to work right after he turned 16 and on the way home he had a pop from McDonalds (he worked there) and it fell over so he reached to grab it and pulled the wheel while he reached . . . and ran right into the back of a parked truck! Unfortunately it's not worth fixing - it'll need a new front clip and some frame straightening and we just had liability on it so insurance isn't paying to fix it and I'm not inclined to want to spend as much as it needs out of pocket. I was able to get the sheet metal out of the way enough to see if it would start and it does start and run fine, the fan isn't bent or anything.

Sooooo, I have an old truck that needs an engine and I have a newer truck that has an engine but is totaled otherwise. My thoughts are to combine the two to get a truck back running. I thought about just rebuilding the 350 in the old truck but I hate to just toss the good engine/tranny/fuel injection from the newer truck and, some day, I'd like to do a t-bucket roadster and the 350/th350 could work well in that. My next thought was to just toss the tbi and use an Edelbrock carb conversion manifold, strip the newer engine down to a long block and install all the pulleys and accessories off the old 350 on to it and then just bolt it up to the th350 and go. I think the only real mod beyond the intake and carb would be to use an electric fuel pump as it seems to me the newer block doesn't have provisions for a mechanical fuel pump (I'll have to hop out to the shed we have it stored in to confirm though). It'd be pretty straight forward I think, but I kinda like serptentine belts and I kinda like throttle body injection and . . . I literally have ALL the parts! I just can't see tossing them! Soooo, I'm in the process of doing some research (I bought the Jags That Run book and have been surfing the net a good bit) trying to talk myself into this project . . . maybe you guys can help with that! ;->

Some random notes so far:

Transmission:
*) I should be able to use the 700r4 tranny.
*) The column linkage on my '74 will work, just the gear indicator will be off?
*) I will probably have to cut the drive shaft? There are several articles on the net on driveshaft shortening, it looks doable.
*) I may need to build or adapt a tranny crossmember.
*) The donor truck is an '89 so the DRAC is part of the instrument panel so I will need to replace it with a separate unit, or is the DRAC separable from the instrument panel?
*) If I can salvage the original DRAC the books says it's programmable - is that easy to do? I think the gear ratios and tire sizes are different between the two trucks. If I can't use or can't reprogram the original one then I'll need to get a DRAC that matches the gear ratio/tire size of the truck it's going into.
*) The Jags that Run manual says all TBI engines thru '92 used a two pulse VSS but on the next page they say that all Chevy trucks with rear wheel anti-lock brakes 1989 and newer use the 40 pulse per driveshaft revolution sensor and I'm sure the donor truck has rear abs brakes.
*) The older truck has a cable driven speedometer so I will need to accomdate that.
*) Jags That Run carries a reluctor ring sleeve assembly that allows for cable drive speedometer gears and a 40 pulse reluctor ring. In addition to this assembly I will need a modified tail house that allows for the relocated 40 pulse sensor. Both items will run $130 delivered.
*) Where is the park neutral switch at? On the transmission or up in the steering column gear indicator?

Wiring:
*) I would like to save some bucks and use the original harness. I'm comfortable with control / sensor wiring and troubleshooting as I do it in my job all the time.

*) After market harnesses are expensive, but the MegaSquirt people have an interesting option - they make do it yourself wire kits for less than $100 and the wires actually have the sensor designation stamped on them (it's just the wire though, no connectors). This would be nice, but the wire colors don't match the stock GM wire colors and I think there's value in maintaining the stock wiring colors so I'm back to trying to salvage my harness.

*) I have a laser printer and they make laser print outdoor labels so I'm thinking I'll just print labels and use them to tag the harness connectors.

Fuel System:
*) I don't know if an '87 fuel tank would work in my '74 truck as they are slightly different body styles and the tanks have different part numbers in the LMC truck catalog (I'm sure that's because of the baffles and stuff, but my older truck is also a different part number than the later '82 -'86 carbureted trucks). I can get a used '87 tank for $65 at the local junk yard (minus fuel pump, darn it!) though.

*) If I can use the '87 fuel tank the fuel pumps are expensive and it's a pain to change them when they go out, so I'm thinking an external pump set up would be better? External pump would entail two pumps and a small reservoir, but all in all I think it would be slightly cheaper and easier to work on in the future.

*) Update, it appears the fuel pump in the '89 could be used in an '87 tank - LMC truck says part number 32-4048 works on '87-'89 models! Though external pumps would be easier to service, if you don't habitually run the tank low in tank pumps usually last quite a while and not having to buy a pump/sending unit combined with a $65 junk yard tank is the cheapest option.

*) Is the fuel gauge sending unit compatible with the gauge in the '74 truck?

Cooling System:
*) I bought the Jags That Run Fuel Injection manual - they had a point I hadn't considered, is the fan, shroud, etc. going to be properly placed to provide adequate cooling? My thoughts are yes, or with a few tweaks it could be made to work correctly. Worse comes to worse I revert back to the old separate pullys, fan, shroud, etc. so this shouldn't be a big issue, just something to keep in mind while it's coming together.

All in all, this looks doable. It's not "easy", but it's not hard either. No real fabrication work, more just getting parts that work and switching them out.

I'd be interested in any and all comments, suggestions, ideas, whatever - I'd really like to make this a smooth going project if I decide to take it on.

Back to reading the thread . . .

Steve

[Chad77]

Well its been a while again! I have my TBI set up running with a hiccup when I had started it for the first time it started and idled good, well scene then I have started it here and their and to day I rerouted the gas lines and topped off the coolant I started it up and now it wont idle unless I have my foot on the gas pedal I dont have a air breather for it and I have yet to drill and weld in the bung for the O2. any suggestions?

[Jonboy]

Steve, I think you are overthinking it. I just did the same swap: http://67-72chevytrucks.com/vboard/s...d.php?t=433689 , and it isn't that hard. I used a harness from www.fuelinjectionconnection.com ($245 shipped), to save the hassle and headaches of making a harness and using 20+ year old wires. That harness deletes the emissions, making the installation easier.

I used the 700R4 trans, relocated the crossmember back a little bit, and the driveshaft fit perfectly. I also used the 2PRS VSS from JTR ($75), and that will solve the hassle of the DRAC, tailhousing, etc. That will also let you use your existing gauge cluster with no problems. I did use the '74 column shifter, but added a quardant out of a later model truck. P/N switch is at the bottom of the column, inside of the truck. I bought a later model one (for an '87), and moved a few wires around. It's not currently in use, but that's my own fault. That will be fixed when I get the truck back.

I used the accessories from the '74, as I wanted it to look original. That's just my own weirdness there, but it wirks. The fan will fit in the shroud just fine, no matter which set of accessories you choose. I also used an '87 fuel tank, but mainly because I had one. I previously had a '79 C10 with an LT1 in it, and they used an external pump. It was a little noisy for my taste, but it worked fine, with no external sump. I had planned to fix that, but sold the truck first.

My project stretched out over a month, but that was due to a few external factors also (I got my wisdom teeth a pulled, got the flu, it was freakin cold, Christmas and New Years holidays, and then some). I did quite a bit extra too, but figure a couple of weekends to get it done, start to finish. There was a lot of head scratching involved, but I also have a talent for making my own headaches. For whatever reason, I redid almost everything at least twice.

[rfmaster]

Steve

Welcome to the board (and the thread)

1) Use in tank fuel pumps if you can - despite the small cost differential they do last longer. In tank fuel pumps are cooled by fuel and tend to be less noisy. Use baffled tanks from 87 (Spectra Premium part number GM1C; fuel sender FG05M driver side, FG05N passenger side, fuel pump Delphi FE0115). IRC, the fuel fill inlet diameter is different than the 73, but should fit existing inlet. If you have 20 Gallon tanks the new 20G gas tank should be a drop in replacement for OE non EFI tanks. In fact you should (must) replace you gas tanks - god only knows ho much crud you have in there (unless previously cleaned out). Also, modern gas (E10, E15) is a nasty mix of ethanol/methanol blend and tends to rot fuel systems from inside out. Not a good thing at all for us trying to keep older vehicles running.

2) 700R4 overall length is 30 3/4”. THM-350 came with three different tail shaft lengths: 6, 9, 12. Passenger cars were equipped with 6" tails while trucks (for the most part) were equipped with 9 or 12". Dim A: for 9" tail is 30-11/16.
http://www.tciauto.com/Products/TechInfo/trans_dims.asp
Measure your THM 350 - if it has 9" tail no drive shaft cutting will be required. Slide the cross member - you'll need extra long drill bit.

//RF

[SLR_65]

HI Jonboy,

Yeah, I tend to overthink things!

Boy, your '74 is a whole lot prettier than mine! Mine is just plain ugly, but I love my ugly old truck! I can haul compost for the garden, or lumber, or the equipment I use for public fireworks displays without worrying about scratching or denting things. And, it's relatively cheap and easy to work on (not that it ever really needed worked on much). It's just been a great old truck! I thought I had some pics on the computer but I can't find them, I'll try to snap a couple tomorrow so you can see what ugly is! ;->

First off, I'm cheap - and I freely admit that! Second off, I'm a do it yourself kinda guy and wiring doesn't intimidate me in the least, in fact I kind of enjoy it, so utilizing the '89s wiring harness is something I'd like to try. If it gives me problems though I think I would look at a prebuilt harness - from what I've dug up on the net it looks like it's hard to find vendors to sell small quantities of the various wire colors needed and the cost of the plugs add up too, so in the end building a harness from scratch, though maybe a fun project for a weekend, probably isn't really justifiable. (you could vary the wire colors but I think there's value in keeping the wiring the same colors just to get away from any confusion in the future)

I actually like the serpentine belt setup and can't really see spending the effort to switch them out. If the fan was going to be an issue though I could - again, the nice part of this swap is that I have both vehicles complete so no nickel and dime junk yard shopping! 8->

I'm going to have to read up on the VSS stuff again. How do you drive your cable driven speedometer with the 2PRS? I thought it screwed in to where a speedometer cable would go but just gave a two pulse output? And it needs internal gears like a speedometer, doesn't it? I see they have a 4 pulse unit that give the output and provides for a cable, but I didn't know if my computer would be happy with that. It may be though as the DRAC is in the speedometer of my '89, it may only use that high 40,000 count signal for the ABS brakes and output a lower count to my computer - I need to find out what the computer is expecting for input. My 700r4 is from a truck with ABS brakes so it has the 40,000 pulse reluctor thingie in it so it doesn't even have the gears to drive a speedometer type setup. It's just got the reluctor ring and the sensor for it plugs into the hole where the speedometer cable would go, at leat I think that's the way it works. I need to dig into this a bit further!

This will probably be an all summer project! I'm a power plant boiler operator and they're saving money by reducing staff so any time anyone is sick, on vacation, at training, etc. my schedule goes nuts. But this isn't my daily driver and it's already out of commission so time doesn't really matter much.

Thanks so much for the help! I'll keep ya posted as I progress into the project (yeah, I've decided I'm going to do it!).

Take care,

Steve

[SLR_65]

Hi RF,

Thanks so much for the reply!

I'm glad to hear I can use the '87 tank in my '74. And yeah, I have the 20 gallon tank (only one - driver's side mounted).

I'll try to check out the transmission tailshaft length tomorrow, but it's a 90% chance of rain all day tomorrow so I may not get the chance.

I'm glad the crossmember will work too - though fabbing a new one wasn't an insurmountable job (I just suck at welding. If I practice for a while I get ok at it, but I gotta practice. Once I quit practicing the skill evaporates and the next time I gotta start all over practicing before I work on my project . . . oh how I envy those who can just pick up a gun and start welding!)

I'm getting excited about this!!!

Take Care,

Steve

[Jonboy]

I thought the '89 might have used a cable driven speedometer. I've never owned one of that body style, it's still a new truck to me. You could locate the cluster out of a 90 4wd or 91 Suburban, and use it. Those use an electric speedometer, and will bolt in place. You will have to repin the connector and run a new wire to the speedometer, though. I've used them with newer engine swaps (LT1) that have the buffer in the PCM, so you will probably have to reuse the DRAC with that cluster.

There is nothing wrong with being cheap (although I prefer the term thrifty), but I also like to think I know when to pick my battles. I went ahead and bought the harness I did because mine was in pieces, and it was only $245. I need to reflash the ECM when I get my truck back to change tire size and kill the emissions inputs, but that is only another $60.

[rfmaster]

Steve

*) Where is the park neutral switch at? On the transmission or up in the steering column gear indicator? - It should be on the steering column next to the firewall.

GM used 90 Ohm fuel level sending since 50's - newer sending units with in tank fuel pump will be compatible.



2PRS is an inline unit, it screws into speedometer cable output port (at the transmission) and speedo cable bolts into the VSS. Run two wires from it - one goes to signal ground while the other is tied directly to pin A10 (assuming 1227747 C3 ECM)

//RF

[SLR_65]

Hi Jonboy,

No such luck, the '89 used an electronic speedo and the DRAC is built into the cluster pcb so it appears to me that I will need to get a separate DRAC also.

> I've never owned one of that body style, it's still a new truck to me.

LOL! It was/is to me too! Remember, I inherited it!

I thought about an electronic speedometer but wanted the dash guages and stuff to stay matching (why, I dunno . . . again, this beast is ugly!). I hadn't thought of finding a used one. I'll dig into that.

So the VSS you have from JTR feeds the cable drive through? It just doesn't seem to say that on their web site, the only one that mentions doing both is the 4 pulse one, but even at that I'm pretty sure that I'm reading that my tranny doesn't have the speedometer / VSS drive gears in it, they've been replaced by the reluctor ring, so I can't just pull the sensor out of my tranny and put a new one in as there's nothing to drive it. It looks like I could put the drive gears back into it though and then use the 4 pulse cable feed through one and a stand alone DRAC. If the 2 pulse one feeds the cable through though then all the better - no DRAC needed! I gotta dig a little more on this . . . still, no matter what, it's not a project killer - it's definitely solvable one way or the other and wont cost a fortune either.

Thrifty, yeah, that's it! I'm just so used to the wife and kids calling me cheap that I've forgotten the proper term! 8->

Picking your battles is definitely a good idea! Time is a big factor in those decisions for me as when I work for myself I work pretty cheap :-> . With this project I have plenty of time so I'm willing to do as much as I can.

I've been playing with tuner pro as at first I thought I would have to have a new chip due to the tire size difference between the two, but now it seems if I get the drive right on the VSS then it will be accurate and no fudging in the chip will be necessary . . . correct?

Turning off EGR in the chip looks like duck soup. Turning off the AIR injection is something of a curiosity to me though. From what I gather many just remove it as it's not supervised by the computer so it wont set a check engine code. However I read on one of the boards that it isn't that simple because when the AIR is turned on the computer fudges the O2 reading coming in - it decreases it because they know it's going to read the extra oxygen they are pumping into the exhaust and that would throw the calculations off so they apply a correction factor to the reading coming in to deal with that. From what I gather the way to deal with it is to raise the Minimum Temp For AIR parameter to the maximum, doing so will keep the computer from ever turning the AIR pump on and thus the correction factor will never be applied. Though I read that it's not noted that way in the xdf file I have for the chip, so if that's true for the 7747 I dunno.

I actually thought about buying a programmer if I needed a new chip as it was about the same price as buying a chip and then I could play if I wanted to. I'm very comfortable with this as I used to play with electronics, pics, eproms, etc. years ago. In fact I still have a programmer but it wont run under Windblows - it wants DOS . . . it's THAT old! I doubt if I will now though as I don't think I absolutely need one to make this project work and I don't really care much to disable the EGR or AIR (maybe if it were free to do so, but I'm not paying much just to do that . . . especially since they keep bringing up emissions testing every couple years. The idea usually gets killed quickly, but you never know. If it ever does get implemented I don't want to have to scramble to find/put back stuff I took off).

TTYL,

Steve

[SLR_65]

RF - THANKS soooo much! I LIKE pictures!!!

[SLR_65]

OK, did a little poking around and I can find the Suburban speedo pretty easily on the net for around $75 delivered.

Finding a DRAC is a bit more of a challenge though! ONE guy on fleaBay is selling them for $100. Couldn't find anything else on the net.

I just need to hit the local salvage yards I think (though they were crushing LOTS of cars a few months ago when scrap metal prices were high). What's a good price on a DRAC? I have no problem installing the jumper switches and doing the calibration myself. Our local salveage guys like to haggle and it's kind of hard when you have no idea of the value!

I like the replacement speedo / use a DRAC idea - just no hassling with the tranny, leave it stock.

[Jonboy]

Check the classifieds here, too. By becoming a supporting member, you can post "want to buy" ads as well.

I would pull the extension housing off of your trans and have a look. If you can run a gear and a speedo cable, the 2PRS will get you all set, without a DRAC. I know you can just disconnect the AIR on an early TPI engine, so I am sure TBI is similar. It will not set a code.

[SLR_65]

Hi Jonboy,

I'm certain I have no VSS drive gears since I have the reluctor ring, though I will continue to dig a bit deeper into this when I have a bit more time.

I'm sure I can install gears with a JTR kit but it'll probably be cheaper to just find a DRAC (or Buffer as they are also called) and change the speedometer. I'm sure my local salvage yard will have something that will work, or Dakota Digital makes a unit that I'm sure will work for $85.

I don't think removing the AIR injection without disabling it in the computer is a good idea whether it's tpi or tbi - basically AIR drumps air into the exhaust so the O2 sensor is going to see more air. To avoid erroneously adjusting for that extra air the computer shaves a little off the input when it's calling for the AIR to be injected (not all the time, just when it calls for the AIR). The AIR is not supervised so it wont set a code. i.e. it's just sending a signal out to open the valve and it's assuming that's being done - whether it is really being done or not. Since it thinks it's being done it then invokes the O2 fudge factor.

I think this is like the use a VSS or not situation - the engine will run and for many people it will run just fine without a VSS but it's simply not running as well as it could be.

Personally I think I'll leave the AIR hooked up for now. If it creates a problem later down then road then maybe I'd look at just disabling it in the chip by raising it's minimum activation temperature. I have the AIR pump already on the engine, it's already in the wiring harness, and the engine runs fine so I'm not going out of my way to mess with it as I just don't see much need to.

Here's an interesting thread on it at the 3rd gen camaro forum:

http://www.thirdgen.org/techboard/di...-pump-air.html

The above is on a different ecu, but somewhere I have a thread on the 7747s and it said literally the same thing.

TTYL,

Steve

[Jonboy]

VSS will trigger more than AIR will. VSS input operates TCC, Evap, EGR, and a couple more acronyms I have forgotten. I think it is much more important than AIR, but that's me.

I had an '81 El Camino that I swapped a 305 TPI into that I drove through most of college. We didn't hook up the AIR, and it ran fine. No code, no problem. My speedo cable had broken at one point, and the CEL set almost immediately. It also ran hotter from the TCC not engaging. Didn't take long to see the need of fixing that.

[rfmaster]

Steve

1) AIR is only active when engine is cold and operating in open loop (O2 is not providing feedback). If you have 7747 ECM there is no AIR related DTC.

2) EGR function can be easily disabled by increasing EGR Temp On parameter to 155C (255 counts). To completely disable EGR DTC in TunerPro uncheck Malf Flag 32 in your Bin file and save.

3) I use flash chips AT29C256 or 27SF512 with a slightly modified G2-0.6 adapter (with ZIF socket) in my 7747, 8746 ECM's. A29C256 is still available from Future Electronics:

http://www.futurlec.com/Memory/AT29C256pr.shtml

4) For greater flexibility I prefer to use GQ-4X Willem Programmer from MCUmall. It is more than you need and BURN2 Chip Programmer from Moates will work just fine for you.

5) I use 2PRS in my conversions - Dakota digital should work as well. IRC, they have auto calibration capability so that you do not have to worry about having correct speedometer gear combination. It can be a real PITA trying to get a right pair of gears for speedometer to indicate correct speed. However, if you have OE mechanical speedometer (73) you must select correct gears. It is not as bad as it sounds - you need to know:

Drive gear teeth count (inside tail housing)
rear end ratio
tire diameter.

plug into equation

http://www.tciauto.com/Products/Tech...eedo_gears.asp

driven gear tooth count.
//RF

[SLR_65]

Hi RF,

Thanks for the reply - though I don't forsee a need to mess with my computer chip, I may just for fun once I get it running.

I don't have speedo gears in my tranny. I can put them in with a JTR kit (just talked to them), but I think the easiest approach is to simply find a DRAC/VSS Buffer and then set the jumpers for my tire size / rear gears. Then just use an electronic speedo since an OEM one that will match my dash both physically and appearance wise is easily available.

I think the DRACs are just a low failure item so there's not much demand for them and they're buried in the dash so the salvage places don't dig 'em out - I'm sure if I go salvage shopping I should be able to dig one up. I'm hoping to do that later this week.

I'm starting to feel pretty comfortable with this - it doesn't seem like there's any major hurdles . . . famous final words, eh?

TTYL,

Steve

[Chad77]

OK so I have my TBI all hooked up including the O2 and I have found out that the 350 TBI injectors are to big for my 283 so Iam looking for 305 injectors GM5235279*RPD Id even take a set from a 4.3L GM 5235203*RPD. I have a set of working 350 TBI injectors Id trade! The only thing Iam not 100% positive on the #.