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06-16-2012, 10:08 AM #1
- Join Date
- Jun 2012
Strange starting/rough running issue - '96 5.7L
I'm a newb, appreciate any help. Been fighting a problem for a long time in my 96 Yukon 5.7, 2WD. It has about 180k miles.
The only mod I've done to the truck is the installation of an injector spider upgrade to the Auto Shop independent injectors (which I highly recommend). I did this mod in part because of the problems that I'm having, in hopes it might correct some issues. It definitely helped, but did not solve everything. I also have an all-aluminum high capacity radiator (replaced this after some heating issues that finally took out the old radiator).
Over a year ago I started blowing up starters - the engine would kick back so hard during starting, it just blew the starter head up. The timing was going way retarded, creating a kick-back. After much frustration (2 or three starters, new flywheel, crank sensor, distributor, etc.), the problem was found to be that the crank damper key had sheared, and the hub had turned about 90 degrees on the crank snout (I now wonder whether the broken key might not have been the cause, but was instead caused by some deeper issue).
After fixing the crank hub problem, the engine did start and run okay. Sometime after that, I started noticing sort of rough performance, sputtering, etc., and that's when I broke down and put in the injectors. The fuel pump and filter are also less than a year old.
Now, I'm back to the engine kickback on startup. It was also running like a rag intermittently. First thing my local mechanic wanted to do was replace the flywheel (grrrrr). Long story short, I did go ahead with new, heavy duty flywheel (he said the old one was cracked because of all the stressful starting and the HD one was needed because of this issue) and starter. Of course, that didn't solve the underlying problem. After running checks, he said both my head gaskets were blown (or, perhaps cracked heads or block). He said he got coolant blowing out of two spark plugs, and coolant system pressure test failed (needless to say, I'm still pretty ticked that he couldn't have got the truck started and done this diagnosis before installing a flywheel). Took the truck home. I was recommended something called Blue Devil. Supposed to fix cracks, gaskets, etc. I know, there are no real substitutes for real repair when it comes to something like BHG. But, I wasn't convinced that was the problem (I guess I'm at the point of second guessing my mechanic). I did experience an overheating episode a while back, due to bad water pump, so, I can't throw out the possibility of bhg or cracks.
After applying the Blue Devil. The situation seems to have improved, but on cold start, I still get kickback (usually on hot start, it's okay). Now, I took out all the plugs, and I don't see one drop of water coming out. I have no white smoke (mechanic said it was blowing white smoke, I never saw any, ever). No other symptoms of bhg. I bought the idea of water in cylinders causing the kickback, and the knock sensor retardation of the timing. But, I don't really buy it now. There's no water there. But the timing IS being retarded by something. I noticed that with even ONE or TWO spark plugs installed, the engine kicks back on start.
I am getting ready to try disconnecting knock sensor for diagnostic purposes. When I do this, do I need to ground the wire, put a resistor to ground, or what? How do I fool the ecm to thinking it's working ok?
I'm also confused as to why the engine ran like crap from time to time, but now is fine.
Any ideas and recommendations are greatly appreciated.
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