98 gmc carb swap

[Jeremiahdavis]

I have a 98 Sierra 4.3 with a 96 5.7 I dropped in I am getting 8 or 9 mpg. It also has less power than the 4.3. The wiring is wrong the computer is wrong it shifts hard the o2s don't work. The mass air flow don't work the egr is no good. That's why I want to do a carb swap. I have everything I need I just need help with wiring. And the fuel pump. The simpler the better I was thinking turbo 350 trans.

[LynnJr]

What I have done on my truck is simply unhook what I am not going to use roll it up and cover it with black vinyl tape.On mine it sits on the inside of the valve cover.
I would remove the factory electric fuel pump in the tank and add a piece of fuel line to it so you still get to the bottom of the tank.A hacksaw and a hose clamp will help.
I would then put a $25 O'reillys electric pump inline under the cab and be done with it.
I went with points as wiring it is very simple but there are easy to use HEI instructions on here if you know how to find them.I don't so I bouht the system from Summit racing cheap.

[BigBlocksRule]

Why not replace the wiring harness and computer? There's plenty of 'em at junkyards. You're going to lose the advantages of injection AND overdrive...

[speedygonzales]

What distributor are you using?

Do you want to keep the fuel pump you have or replace it?

So we can help with wiring

Keep the trans you got and get this:
http://www.fuelairspark.com/fas/ez-t...85e-to-09html/

[LynnJr]

If I am not confusing the years his current trucks fuel pump puts out about 50 PSI and that is to much for a carburetor.
The cheapest and easiest route for the fuel pump in my opinion would be an inline electric pump.Very easy install and very easy wiring.

It sounds to me if he did replace the wiring harness and computer he would still need a lot of bolt-ons adding to the bill.

[Jeremiahdavis]

Thanks for the replies. I was going to use an in line fuel pump. Will it pump through the in tank pump without modification? I thought I might put the manual valve body in the 4l60e. I have the hei distributer. I was Gona wire the ignition to a toggle and push button and the fuel pump will be a toggle in the ash tray. All the harness I find are cut up and $250 And I have to try to make them work for.

[speedygonzales]

You can use the intank pump but you need a regulator that will bring the pressure down low enough for the carb you are using. Find the carb details. That's what I would do and when the intank pump quits, add a replacement in line later. Don't reinvent the wheel now, you have enough to do.

Forget using switches to power up anything. The first time you forget to shut it off will undo all the work you did. Use a switched power source to power up relays. Have them hold themselves in and then don't require the switched power source any longer. Then they drop out as soon as power is gone.

You can get harnesses from a few different companies with as many circuits as you need. Painless is one source.

Why bother with the manual valve body along with the work it involves? Plug and play brother.

BTW have you checked the bottom end of the engine to be sure it's in tip top shape? I'd hate to see you do all this work just to find out you have a bad cylinder.

One other thing, I assume you are keeping the vortec heads. If so, these intake gaskets are the only ones you should consider.
http://www.summitracing.com/parts/fel-ms98000t
I've only seen them in a kit like this and never on their own but they are worth every penny.
I have tried every conceivable vortec intake gasket made and these are the $H!T.

[BigBlocksRule]

I'm having trouble understanding why you're cobbling this together instead of correcting the wiring problems you have??? Ask the old farts around how much they enjoyed figuring out carb and ignition problems back in the day. By the time it's all over, you'll spend waay more with controllers, etc. that you would correcting what's there and you'll lose the benefits of a computer controlled drivetrain.

[LynnJr]

Originally Posted by BigBlocksRule

I'm having trouble understanding why you're cobbling this together instead of correcting the wiring problems you have??? Ask the old farts around how much they enjoyed figuring out carb and ignition problems back in the day. By the time it's all over, you'll spend waay more with controllers, etc. that you would correcting what's there and you'll lose the benefits of a computer controlled drivetrain.

All the harness I find are cut up and $250 And I have to try to make them work for.

If you can't get a complete harness and computer run and run fast.It will soon become the biggest headache in your life.
Yes you can leave the pump in the tank and simply add an inline electric.I have a friend who does it all the time.Myself I would remove it but it does work.
I have the push button and toggle in my Jeep and a blown chevy stepside and they both work flawlessly.

I am one of the old farts posted about earlier and will answer BigBlocksRule comment.
Today a HEI ready to go runs $39 on E-Bay.You can buy 3 of them for the price of a single ignition module and leave them in the box behind the seat.
A Holley 600 carburetor runs $300 to your door or the same price he will pay for a MAF sensor.
He can buy 3 Holley 600's and keep two brand new ones in the garage for the price of one fuel injection unit.The first time his carburetor hints at giving him a problem he can toss it in the garbage and install a brand new one while your shopping for a OBDII meter to read all of your error codes and he still has not spent a dime of extra money.
I like the computer controlled trucks as much as the next guy but once they start having problems and need diagnosing they become life-long projects that never again seem to run right and an endless money pit.
I would rather toss a carburetor in the garbage every 4 years than spend the time on a message board begging for help from those that don't have a clue and I am saving money.

[BigBlocksRule]

While you're wrenching and throwing $39 Chinese dizzy's on your engine, I'll continue to drive my 200,000+ engine that's had nothing changed but plugs. The one in my work truck is almost 300K, same thing. O'Reilley's and AutoZone will shoot codes for nothing.
If all the OP is finding is hacked up harnesses, he needs to find another recycling facility, there are plenty around here. A new harness isn't going to cost any more than a new carb. Then you've got to spend the coin on something to run that overdrive tranny AND you'll have to have a TPS on the carb. And a new fuel pump.
I understand the OP's frustration, but he does admit it has the wrong harness and computer - there's NO WAY that everything -O2 sensors, MAF sensor, etc. quit working at once. Take the time to eliminate the problems and you'll end up with a truck that'll get better fuel economy and will have some resale value.

There's a reason that everyone's gone to injection and gotten away from carbs!!!

[speedygonzales]

Originally Posted by BigBlocksRule

I'm having trouble understanding why you're cobbling this together instead of correcting the wiring problems you have???

3 reasons.

one is

Originally Posted by Jeremiahdavis

I have everything I need I just need help with wiring.

He doesn't want the headache of dealing with a 5.7 vortec BS. He wants mechanical distributor and carb. Simple no issues. No B.S. "spider" injection that is crap. No plastic distributors that are crap. (I own a Vortec and have the new style fuel injectors and a billet distributor). The new carburetors are light years ahead of carbs just 10 years ago. Some can even deal with E85. Lets see a first gen Vortec do that.

Third, that's the question. Answer it. If he wanted us to talk him out of this, he would have titled the thread "Tell me why I shouldn't do this".

[BigBlocksRule]

I guess you "simple" carb guys don't remember how many folks we used to see with the hood up, scratching their heads, trying to figure out why they can't get it to run. Simple and no issues my butt - maybe you're having trouble remembering what it was like back in the day.

As for carbs being light years ahead - maybe if you're talking about high-end race carbs. Edelbrock and Holley haven't redesigned anything for street duty in years and years.

My prediction is that he'll spend more money and end up with some of the same problems he has now. And if he gets that carb set up too lean, it'll eat that engine in a heartbeat - seen it done more than once. Fuel injection calculates and targets an air:fuel ratio for ALL driving conditions. Let's see your carb do that.

[LynnJr]

BigBlocksRule does have a point.If its not your money please waste it freely.

Go to the dealership and order up a new harness and all the broken old malfunctioning sensors.It shouldn't run more than $3500

Now have the same dealership attempt to install it and the certified mechanic will say only if we put a 4.3 back in there for you at an additional $7000

I also wouldn't use as $40 dizzy when you can buy the most expensive MSD box on the planet for your street truck.If its less than a grand its gotta be junk.

Now ask yourself which way would be easier?

[BigBlocksRule]

If that's how you spend money on your stuff, that's your business. My dealer doesn't screw me like that, what did you do to piss yours off?
He could replace the harness and every sensor for under a grand. You'll be out a dizzy, intake (can't bolt that carb onto a Vortec intake), carb, controller for your tranny and harness for it and a ton of TIME, plus troublehshooting and trying to figure out why it still gets 9 mpg after all that time and work. And you'll end up with a truck that every potential owner will pass on as soon as the hood is lifted and see that it's been taken back in time 20 years.

[Jeremiahdavis]

I had no problems with this truck until 200,000 miles. The head cracked on my 4.3 I thought it was time to do a 5.7 swap. I built a 5.7 and dropped it in it took me a long time to build the wiring harness and get the computer out of limp mode. The computer is still not the corect one for my truck. I have put on 4 mass air flows 2 egrs 4 fuel pumps. Everything I build for racing, mud trucks, rock crawlers and hot rods are all carbureted. There are lots of people in my area that drive carbureted trucks and cars as daily drivers. When I was in high school me and all my buddies drove carb cars and trucks. I don't really know anyone that has much trouble with carbs. I have 5 hei distributed 2 superchargers 3 sets of aluminum heads lots of edelbrock intakes and carbs headers cams and transmissions. And anything else I need I probly know someone with a 350 that owes me a favor. I would like a 700r4 but my 4l60e can be turned into one. I think you guys answered my questions. Thank you

[Jeremiahdavis]

Oh and I think as it sits it is worth about 800 dollars right now. It's flat black the body is rough. It's a 2 wheel drive single cab. Work truck/daily driver.