Acceleration problem

[LeesTruk]

Ok, I brought my 5.3L to life, and after taking care of some engine swap teething problems (leaking ATF line, and a faulty O2 sensor), the truck will idle cleanly and will easily rev in park/neutral. The problem occurs when trying to drive the truck. While trying to accelerate, it's like someone turns off the engine until I take my foot off the gas pedal, then it comes back to life. Does this sound like a TAC situation? Supposedly the TAC/PCM are from the same vehicle as the engine, as well as the pedal. The only code I have is a P0654 RPM code, but that's most likely my tach hook-up (bad ground), I've seen similar concerns here, but no reply on what cured the problems. Any guidance would be greatly appreciated. Thanks

Lee

[BR3W CITY]

What are u using to scan? You sound like your throwing a U0107 or other non "p" code. Some cheap scanners won't read trans, body, abs or other module codes.

If you key off/on, does it clear and go back to normal?

If you have HPt, you can command throttle% independent of the pedal itself and check if the tac or pedal is the problem.

You may also have the right tac but wrong pedal.

[LeesTruk]

Here I am, again. BR3W, I have no U codes, and I'm currently using a Bosch 1200 scan tool, which isn't bi-directional. I was able to borrow the Tech2 scanner from where I worked and was disappointed when it wouldn't "talk" with the trans (it's been dormant for several years, in storage at a Toyota dealership). Anyways, I bought a subscription to AllData (Very good info there), for my Tahoe powertrain and have been doing a lot of wiring diag. From what I'm gathering, limp mode is an electrical situation brought on by the PCM. I have switched B+ at my trans connector (pin E). If I disconnect C2 at the PCM, theoretically, I should be able to ground my shift solenoids to the battery, and, possibly hear solenoid activity, yes? Also, could it be possible that my p0654 DTC is causing the limp mode and I'm chasing a ghost? What concerns me is the fact that the engine shuts right off when trying to accelerate or during a power brake test. If I'm quick enough to get off the accelerator, the engine turns back on instantly. When in park or neutral, the engine will rev freely to any RPM I desire (sounds really good!!). Frustrating!!

[aknovaman]

Monitor fuel pressure when the issue occurs. Should be rock solid at 55-60psi all the time. Any car buddies local to you have HP tuners that can datalog what is happening?

[LeesTruk]

I have good and consistent fuel pressure (58-60 psi). As far as knowing someone with HPTUNE? Nope. I'm usually the car guy that my friends come to see with problems. This being my first foray into the LS arena puts a different twist to things. What I have come to realize in my last 30 or so years of auto mechanics is that the most frustrating problems are usually caused by the stupidest/simplest of reasons. It's just finding that reason that can be so infuriating and you hope that someone somewhere might chime in and say "Hey yeah, I've seen that before, and this is what I did..." The one thing that's giving me some hope, is that a diag. for the p0654 code shows that I may have a faulty PCM (no voltage out from C2 pin 10, engine speed signal). I'm having a new PCM being set up for my application and should have it in a few days. If that doesn't cure the problem, then.... Idunno!

[clinebarger]

The P0654 is not an issue! My 85 Suburban with a '04 5.3/4L60E had that code for the whole 10 years I drove the truck, Because it had no Tach....
P0654 doesn't even illuminate the MIL, And no drivability issues can be linked to the Circuit or Code.

[BR3W CITY]

Are you actually going into limp mode tho? The engine shutting down isn't limp mode. Limp locks you in like 2nd gear, you'll be down on power but it will still allow the truck to "limp home".

What your describing is either fuel or spark cutting out completely, the dbw system getting an intermittent failure/mismatch and shutting down to prevent runaway (unusual), or something tampered in the tune that shouldn't have been.

I'd like to log your pedal % vs your TB % and see if something like torque management is cutting all your power. The same log would belie an intermittent sensor failure, or say if the throttle scale had been messed with.

The intermittent failure is possible, but I'd think it wouldn't catch itself like you say...it would just shut down. The only thing I've seen do that is when I tossed U0107's from freaking electromagnetic interference.

[LeesTruk]

BR3W, I'm almost 70 and electronics is NOT my forte', and acquiring high end electronic test equipment, though necessary, just isn't in the cards at this stage of my life. It would be easier just to send you my PCM than to send you a datalog. Besides, I don't know how to do that. I have seen, with Toyotas (I'm retired Toyota/GM tech), that a glitch with the ect sensor would shut the engine down while driving. It was so intermittent and sporadic that that was a difficult problem to find, but when it became common knowledge through TSB, it became an easy fix. That's the one reason I'm here, looking to share common knowledge from "Been there, done that"

[LeesTruk]

After viewing the HP Tuners on ebay, it may be just as economical for me to buy one instead of a high end scanner. But, the question is, what's a credit? All the adds say you got some. For what?

[aknovaman]

It comes with 8 credits so 2 credits per VIN to tune 4 vehicles. Scanning is unlimited, no credits required.

[BR3W CITY]

Lee - Unfortunately, sending me the ECM wouldn't allow me to log the running functions of the vehicle, only check that the tune or ecm itself isn't experiencing failure.

You don't have to license the ECM (aka buy credits) just to scan/read, so if someone in your area has it, they can view the tune without any cost. You just can't make changes.

[LeesTruk]

Would it be worth my while, then, to purchase a Tuner, instead of, say, a used OTC Genisys? I need more than just a "reader" to trouble shoot properly

[aknovaman]

Yes. I would. I have 4 interfaces.

[LeesTruk]

BR3W, I don't wanna retune the truck, just be able to drive it. I appreciate your help and encouragement. This thing sounds so sweet idling in the garage!!

[aknovaman]

I may have a buddy near you with HPT. Still in Manchester? I just sent him a message asking if he can help.

[aknovaman]

He is 5 minutes from you. Pm me your email and i can have him get ahold of him and he can datalog your issue. He is in pittsburgh till wed. I just pm you his email to contact him

[LeesTruk]

PM sent in return. Many thanks

Lee

[terrylgreenjr]

I had kinda the same issue when I started mine. I ordered a ecm over the net and I was going to run it without a MAF sensor and only off the MAP. The tuner I ordered from had the wrong tune on the ECM. I added the MAF and everything cleared up. Might not be our issue but thought I'd mention it

[Jer64]

Sounds like the exact same problem i had on my conversion. i have an '06 5.3 w/ a plastic pedal assy and it would rev fine and idle fine until i tried to drive it. Turns out the ECU was tuned for an 05 5.3 which has a metal pedal assy. Not sure if you said what year yours is but i sent my ecu back and had it retuned. works perfectly now.

[LeesTruk]

Thanks for the response, Gents. I'm leaning towards a PCM issue, myself, but have no way to prove it yet. I will be having someone come to my house that can help to sort out my issue. I'll post the results when things have been corrected.

My engine came as a "drop-out", complete with PCM, TAC, harness and pedal, from a '05 Tahoe, so I have to assume that everything is correct for the application. The one thing I did notice when checking the pin-outs at the PCM, connector C1 (blue) has a yellow wire in location #59. The Tahoe doesn't use this pin location (empty), and on the LT1SWAP web site, Brendan says this wire is not needed for '03-'06 harnesses. BUT... the '99-'02 harness uses this location with a yellow wire for serial data. I don't know what this yellow wire is run to, in my harness, and am thinking I should just go ahead and sever it

[aknovaman]

Its not needed.

[LeesTruk]

Did some research on the yellow wire/ckt 710, pin #59 at C1 (blue). It's used on Chevy Silverado's and other like trucks (maybe more applications) as serial data that goes to connector C100 and ultimately terminates at the instrument cluster. The Tahoe doesn't use this so I'm going to delete that wire from my harness

Also, according the Brendan at LT1Swap, the white tach wire (pin 10 at C2-green) needs to have a switched 12vdc source and 1K ohm resistor added to it for the tach to function. Gonna try that and see if p0654 goes away and my tach starts working

[ls1nova71]

Not sure what year your truck is or if you have a factory tach, but here's the easiest way to add the resistor to a 67-72 factory tach. Just ignore the fact I don't have a printed circuit, but just put the resistor between the two terminals. You'll also have to change the tach resolution from 6 to 3 in the tune for it to be accurate.

[BR3W CITY]

I think either TR or Cline had a thread a while back called "Conventional Tach on LS2". Where he detailed a bunch of the "why" for the pullup resistor etc.

I still have a couple of them laying around somewhere...I think they only come in 4 packs most of the time...but for $1 who cares.

[LeesTruk]

I'm using a Sun Tach, from the 60's-'70's era. It's been reworked, incorporating new electronics. I had Williamson's Instruments in Arkansas do the restoration and I told them that the tach would be used with an LS swap. They, in turn, programmed the tach to accept the 4cyl. signal that the PCM puts out



BTW, my truck is a 1980 C10