LM7 DBW Issues, Now Won't Run
 

Hope it isn't a problem to cross post but I'm desperate. 5.3 LM7 swapped into my 1966 Skylark. Was running great until I hit full throttle for the first time and it threw DBW codes. Managed to get it started and got home, now will start, cough, and die. I've done the wrong thing and thrown a bunch of parts at it but to no avail. Any help is appreciated.

More here:
https://ls1tech.com/forums/conversio...eshooting.html

What codes? Did you use the donor vehicle TAC module and throttle pedal into the Skylark? Can you post a copy of your tune and a log file with the vehicle running?

Rick

Bump for ya...

Here's the opening post from the one I linked in case it helps.
To answer, I have the PCM from the swap vehicle but the TAC and pedal from PSI (matched to the PCM and harness).
The tune is from mailordertuner and I don't have a way to data log (unless the torque app does?).
In addition to the initial list of what I've done below I've replaced the filter/regulator, re-grounded the battery to the head (it's trunk mounted), and some other trouble-shooting.
The trouble shooting to date is outlined in the other thread.
Appreciate any help.


Been working on swapping this LM7 into my 1966 Skylark for a little over a year. I got it started up a month or so ago and it has been running well, although I've been taking it really easy to make sure I can work the kinks out. Finally got confident enough to drive into town (5 miles or so) and add some gas. On the way back I was feeling really good about how it was going and gave it full throttle for the first time. As soon as the pedal was all the way down it went into limp mode. I pulled over and didn't see anything immediately wrong. Turned the car off, and it restarted no problem. Drove home and put it in the garage. Torque Pro showed P1125 and P2125 for throttle/pedal position sensor issues.

I went back a few days later to try to troubleshoot and it cranks but won't start. It coughs a little like it wants to, but nothing happens. Now it shows different codes - P0220 and P2135, both for the throttle/pedal position sensors. With key on, the throttle body clicks and does a brief, small cycle where the blade opens slightly, but with the key still on the blade does not move when you press the gas pedal at all.

Here's what I have done:
-replaced the throttle position sensor
-checked the ignition/neutral safety switch relay (swapped a new one in, same result)
-pumped some of the fuel out to see if it was a bad batch. I don't see any water separating, so seems ok?
-I don't have a fuel pressure gauge but the pump primes and disconnecting the fuel line at the rail pumps into a container fine.
-Checked the plugs, connections at the pedal, TAC, PCM, throttle body
-Checked the crank sensor wires for damage since I have headers - they are fine (sensor is new)

I also called PSI since I have their swap harness and they said the motor should still start and idle even with the pedal/throttle codes so job #1 is just getting it started before I start trouble shooting the codes. He suggested ether into the throttle body to see if it fires. If so, it would be a fueling issue. This is my first LS and I'm not sure where to go next. When I crank it over I smell fuel so it feels like that's not the issue? I pulled a spark plug and it smelled like gas making me think ignition.

Would a faulty throttle body and these codes prevent start up? I'm just confused because everything worked great for 15 miles or so, which makes me think it's not a compatibility issue with pedal/TAC/PCM, etc. Any ideas on where to go from here? If the car should start even with these codes I'd hate to go through a trouble shooting tree if that won't even get the car started.

If it helps, here is what I have:
LM7 from a 2006 Silverado - cam and headers
4l60e from the same donor truck
Blue/Green PCM from the same truck - tuned by mailorder tuner to remove VATS, tune for the engine mods
PSI Conversion harness (HAR-1014)
the PSI C10 swap pedal ((ACC-1049) with pedal harness (HAR-1022)
New TAC purchased from PSI when I got the pedal
Corvette style filter/regulator - new with swap
255lph fuel pump - new with swap
New DW injectors

What do the spark plugs look like? Oily, wet, rich or sooty? Any OBD2 trouble codes from your Torque app? How many pounds per hour fuel flow with those injectors and did your mail order tune guy know about those injector parameters? What other engine mods?

Rick

Thanks for the help. Spark plugs smell like fuel and are pretty dark. The new injectors are 460cc/min and were accounted for in the tune, along with the cam and headers.
Only codes being thrown are P0220 and P2135 as mentioned above, both throttle position sensor codes. This was before and after I replaced the TPS. When I clear them they just come back.

Going from memory here, which might be faulty:
I've run into various DBW problems in LS swaps I have done. IIRC, even with the pedal disconnected from the TAC, and possibly with even the TAC disconnected, the engine would start just fine.
The initial limp mode at WOT was likely because the TAC received different signals from the two (or three) potentiometers in the pedal.
Have your tried disconnecting the battery for a bit to let the PCM and TAC reset? Be happy to let an expert correct me, but I don't think those two codes are preventing a start.

Update: I spent some time over the weekend checking on stuff and I was able to get it started. The only difference was adding an alligator clipped ground wire from the TAC module to the chassis (it had been sitting on the floorboard previously). Somehow or another that let me clear the DBW codes and get it started. I'd read and been told over and over that the motor should start with the pedal disconnected, the codes I had, etc. but it looks like that somehow didn't apply to my set up?

I also have no idea why grounding the TAC would make a difference now because when it was running before I was able to start, run, and drive before the limp mode at WOT. Very strange.

I took it for a drive and while it idles and revs just fine it's pretty rough under load at partial throttle and was bucking quite a bit (didn't do that before). I'm going to throw new plugs in just in case my efforts to start it over the last few months fouled them out.

Going to blame my faulty memory, or I would have reminded you to ground the TAC module. On a swap the GM dealer mechanic suggested running a good ground from the TAC case to chassis. The TAC is grounded through a small wire going to the PCM, but because the TAC is checking for small voltage differences between the potentiometers in the pedal, evidently if its ground floats a bit the TAC commands limp mode or even a shutdown. So I run a ground wire from the bolt which mounts the TAC to a main ground point.
Glad you got it figured out and thank you for the update.