Engine wont run, need help
Jul 30, 2010 | 10:02 PM
#1
Thread Starter
Joined: Jan 2006
Posts: 16,282
Likes: 438
From: Huntsville, AL
Engine wont run, need help
A friend and I just put an LQ4 from a salvage yard into his OBS tahoe and we have everything hooked up but the engine dies shortly after starting. Here is a video:
http://www.youtube.com/watch?v=rHT0ajwO0IM
Sparkplugs after that:
I attached the hptuners log. Its a stock lq4 with lq9 injectors. I corrected the tune with the proper injector data. It is running open manifolds right now, so no O2 sensors, but I have it in open loop so it shouldnt make a difference. If you watch the log, MAP goes from ~45 kpa right after starting and slowly increasing to near 100kpa, but the idle decreases from around 800 down to 200 where it finally dies. My first thought was vacuum leak, but the idle should go up, not down...
Pulled the oil dipstick. Oh ****. Its a light brown milky color...****, we reused the stock headgaskets (non-mls style), and this explains the white smoke we sometimes get from the exhaust. So my theory, is the engine is pushing water into the cylinders because the headgaskets have failed, so drowning the spark and causing a loss in vacuum. So current plan is to pull the heads, clean the mating surfaces really good, and reinstall with new mls headgaskets and bolts.
...any other suggestion?
http://www.youtube.com/watch?v=rHT0ajwO0IM
Sparkplugs after that:
I attached the hptuners log. Its a stock lq4 with lq9 injectors. I corrected the tune with the proper injector data. It is running open manifolds right now, so no O2 sensors, but I have it in open loop so it shouldnt make a difference. If you watch the log, MAP goes from ~45 kpa right after starting and slowly increasing to near 100kpa, but the idle decreases from around 800 down to 200 where it finally dies. My first thought was vacuum leak, but the idle should go up, not down...
Pulled the oil dipstick. Oh ****. Its a light brown milky color...****, we reused the stock headgaskets (non-mls style), and this explains the white smoke we sometimes get from the exhaust. So my theory, is the engine is pushing water into the cylinders because the headgaskets have failed, so drowning the spark and causing a loss in vacuum. So current plan is to pull the heads, clean the mating surfaces really good, and reinstall with new mls headgaskets and bolts.
...any other suggestion?
Jul 30, 2010 | 10:19 PM
#4
it sounds like boiling water lol... are all the fuel lines ok.. fuel pump etc.. try the LQ4 injectors... i would put new gaskets in there.. i never ever replace gaskets maybe the exaust manifold anyways.. and new plugs i guess lol..
Last edited by supercharged680; Jul 30, 2010 at 10:40 PM.
Jul 30, 2010 | 10:22 PM
#6
I suspect the injectors aren't what you think they are, or maybe the injector data you used isn't so proper. Mine had the same starting problem when I had way too little idle air.
Jul 31, 2010 | 03:45 AM
#7
Thread Starter
Joined: Jan 2006
Posts: 16,282
Likes: 438
From: Huntsville, AL
He bought the stock lq9 injectors from 2004sss since his were stuck shut. I found a sss tune file in the hpt repository i got the injector data from. I will get him to get the part number off of them to make sure they are lq9 data. I couldnt tell any difference in idle quality from using the lq4 injector tune vs the lq9.
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Jul 31, 2010 | 01:24 PM
#9
He bought the stock lq9 injectors from 2004sss since his were stuck shut. I found a sss tune file in the hpt repository i got the injector data from. I will get him to get the part number off of them to make sure they are lq9 data. I couldnt tell any difference in idle quality from using the lq4 injector tune vs the lq9.
Can you get it to run if you fiddle with the throttle or "two foot" it? Were any of those plugs wet, sounds like there's a miss, or maybe a gaping vacuum leak...
