LS2 with GMPP harness quit on me-HELP!
Thread Starter
Joined: Jan 2008
Posts: 29
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From: Eastern Ontario, Canada
LS2 with GMPP harness quit on me-HELP! I started building this car about 3 years ago and I've had it running a couple weeks now and have been taking it for short drives when the weather permits and then working on fixing the bugs. Things have been going well and today was a great day, for this time of year. I set out for a little drive in the country and about 5 miles away, the engine started to run rough and after about a mile, quit on me. It behaved just like running out of gas but I knew there was lots in the tank.
I called a friend and a couple hours later we had the car trailered back home. Cranked the engine and it was the same as when it quit - it would fire feebly for a couple seconds, then quit. I loosened the fuel line at the engine - got a bath. No problem with fuel press. I kept cranking it and going through the startup/ run barely on 2- 7 cylinders/ quit, routine. Tried didling with the DBW gas pedal while it was wheezing -- no effect.
After about a dozen of these attempts, it cleared itself out-- sort of, and continued to run. It now will rev strong but does not seem right on idle -- slight miss.
Through all this, there has been no sign of smoke at the tailpipes and the check engine light only comes on during cranking.I think this is indicative of no touble codes set. I've been under it and looked for signs of problems with the cam and crank sensors. The only thing I've found is a slight coolant leak (Dexcool) at the temp gauge fitting which is right above the Crank sensor.
Have any of you experienced similar problems?
I called a friend and a couple hours later we had the car trailered back home. Cranked the engine and it was the same as when it quit - it would fire feebly for a couple seconds, then quit. I loosened the fuel line at the engine - got a bath. No problem with fuel press. I kept cranking it and going through the startup/ run barely on 2- 7 cylinders/ quit, routine. Tried didling with the DBW gas pedal while it was wheezing -- no effect.
After about a dozen of these attempts, it cleared itself out-- sort of, and continued to run. It now will rev strong but does not seem right on idle -- slight miss.
Through all this, there has been no sign of smoke at the tailpipes and the check engine light only comes on during cranking.I think this is indicative of no touble codes set. I've been under it and looked for signs of problems with the cam and crank sensors. The only thing I've found is a slight coolant leak (Dexcool) at the temp gauge fitting which is right above the Crank sensor.
Have any of you experienced similar problems?
Sounds like you might have been in REP mode. The DBW system is very sensitive to a bad ground. First thing I would do is check/tighten all grounds body, frame, and at engine and battery.
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Joined: Apr 2008
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Was your fuel system perfectly clean: new lines front to back, as well as a good filter? Even with new fuel lines we run a filter at the engine for new retrofits for a 1000 miles or so. Just in case there are scraps of dirt or metal or whatever that have made their way in.
Thread Starter
Joined: Jan 2008
Posts: 29
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From: Eastern Ontario, Canada
The fuel system is all new components and I pumped about a gallon of gas through to flush prior to connecting to the engines fuel rail(crate motor). Gas is fresh.
Today I fixed the leak and flushed the dexcool off the side of the engine with clean water. I've read a lot of negative stuff about dexcool. It definitely has the ability to leak thru the smallest holes imaginable. I wonder if it could find its way past the weatherpac seal and short out the crank sensor. Electrical conductivity of the stuff is unknown to me.
So far it now starts,idles and revs fine. I just need the weather and the nerve to road test it again.
Today I fixed the leak and flushed the dexcool off the side of the engine with clean water. I've read a lot of negative stuff about dexcool. It definitely has the ability to leak thru the smallest holes imaginable. I wonder if it could find its way past the weatherpac seal and short out the crank sensor. Electrical conductivity of the stuff is unknown to me.
So far it now starts,idles and revs fine. I just need the weather and the nerve to road test it again.
TECH Resident
Joined: Apr 2008
Posts: 828
Likes: 12
From: Right here, right now!
Cool. Sounds like your fuel feed is AOK.
When it was running bad, did you completely remove the power from the ECM at all? Have seen these go into what appears to be limp mode or at least a period of rough or borderline running with no MIL lamp, as well as wiring errors.
Assuming you are running full GMPP kit from pedal thru ECM, harness and an '08 throttle body.
When it was running bad, did you completely remove the power from the ECM at all? Have seen these go into what appears to be limp mode or at least a period of rough or borderline running with no MIL lamp, as well as wiring errors.
Assuming you are running full GMPP kit from pedal thru ECM, harness and an '08 throttle body.
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Thread Starter
Joined: Jan 2008
Posts: 29
Likes: 0
From: Eastern Ontario, Canada
You mean disconnect the power to re-boot the computer? It never occured to me at the time, but if it quits on me again, that'l be one of the first things I try. I just came back from the garage and had it running fine and I wiggled all the connectors for DBW and mass sensor and it didn't miss a beat.
You are correct: I'm using the full GMPP harness on the LS2 crate motor together with a GMPP 4l65e trans with the GMPP trans controller(T-COM). Car has a new Rock Valley, stainless tank with their pump inside. Pumping fuel thru a vette regulator/filter, mounted above the rear axle, thru braided stainless lines and everything was flushed as I said earlier. I was meticulous about grounds with braided cables everywhere using stainless lockwashers and dielectric grease after cleaning any paint from the connecting points. Everything is new in this car. Only the body metal and the license plate is old. I sent a bundle and 3 years labour thinking I could eliminate problems like this. Remember Murphy?
Thanks for your efforts to help me.
You are correct: I'm using the full GMPP harness on the LS2 crate motor together with a GMPP 4l65e trans with the GMPP trans controller(T-COM). Car has a new Rock Valley, stainless tank with their pump inside. Pumping fuel thru a vette regulator/filter, mounted above the rear axle, thru braided stainless lines and everything was flushed as I said earlier. I was meticulous about grounds with braided cables everywhere using stainless lockwashers and dielectric grease after cleaning any paint from the connecting points. Everything is new in this car. Only the body metal and the license plate is old. I sent a bundle and 3 years labour thinking I could eliminate problems like this. Remember Murphy?
Thanks for your efforts to help me.
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