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Old 04-08-2011, 07:42 PM   #1
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Raw gas coming out of exhaust manifolds -- what could be the diagnosis?

Hi guys,

Engine is a 93 camaro, upgraded to 94/95 configuration -- using 94/95 injectors.

I've been doing a conversion project for a while -- had to drop the exhaust to access a stripped bolt elsewhere. I hadn't fired the car yet -- when i decided to give it a test fire, i smelled raw gas coming from somewhere.

upon inspection, i noticed that there was gas literally DRIPPING from the exhaust manifolds on both sides. I don't think a sticky injector could dump that much gas, but it is possible -- the car has been sitting for about 5 months so maybe one got gummed up.

i turned off the engine -- i didn't notice that it was running that rough. after about 20 seconds of running it (with lots of smoke from the gas) it seemed like it ran a bit better. when i turned it back on, there was the dripping gas again on start up.

What could it be? FI? Or fuel pressure regulator?
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Last edited by tylerwerrin; 04-08-2011 at 07:55 PM.
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Old 04-08-2011, 07:55 PM   #2
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Re: Raw gas coming out of exhaust manifolds -- what could be the diagnosis?

Were you running it with the exhaust manifolds connected to the exhaust or open header?
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Old 04-08-2011, 08:08 PM   #3
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Re: Raw gas coming out of exhaust manifolds -- what could be the diagnosis?

Sounds like he was playing with open headers for fun before bolting the exhaust back up.

An open injector pours a lot of fuel but having one in each side is wierd. I had one stick open on an old cavalier and when I pulled the head, the cylinder was gleaming clean. Fuel powerwash!

Seafoam it?? People are still raving how it cleans everything.
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Old 04-08-2011, 09:57 PM   #4
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Re: Raw gas coming out of exhaust manifolds -- what could be the diagnosis?

The reason I asked that is because if the O2 sensors saw all that air and thought it was really lean, they might add fuel and cause it to run very rich. If he had a leaky injector though, he could see that as the fuel pressure bleeding down when the engine was shut off. 5 months is no big deal though - my car sits for 5 months out of every year during Winter.
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Old 04-09-2011, 12:50 PM   #5
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Re: Raw gas coming out of exhaust manifolds -- what could be the diagnosis?

it's a conversion -- in the application i have to use "Rams Horns" style manifolds, the cast iron ones. After i put the engine into the car, i never bolted up the exhaust system, just torqued down the manifolds. The center dump is where the gas is coming from. One side looked "wetter" than the other, but it's hard to quantify :-/

The O2 sensors are brand new -- i cant imagine them being the fault. i have another set of injectors i could swap in -- i just dont know how to check which one is leaking -- i remember you apply voltage to each injector and have to see if it "clicks", because that tells you that it is pulsing. Any other suggestions?
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Old 04-09-2011, 08:24 PM   #6
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Re: Raw gas coming out of exhaust manifolds -- what could be the diagnosis?

If I understand this correctly, you have nothing bolted to the exhaust manifold flange. Where are the O2 sensors located? On the stock LT1 cast iron manifold, only the driver's side has the O2 sensor screwed into it.

And as Kevin has pointed out, if the O2 sensors are exposed to the air, or the backwash of air at the manifold flange, its going to tell the PCM the engine is running lean, and its going to start pouring excess fuel into it, that the engine doesn't need.
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Old 04-10-2011, 04:30 AM   #7
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Re: Raw gas coming out of exhaust manifolds -- what could be the diagnosis?

shoot i didnt even think of that -- the o2 sensors were hooked up, but they are welded into bungs on the downpipes, which are not on the car! derp. could that be enough to dump that much fuel though? thats nuts!
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Old 04-10-2011, 01:25 PM   #8
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Re: Raw gas coming out of exhaust manifolds -- what could be the diagnosis?

Do not run it any more. The O2 sensors are seeing pure air, and telling the PCM the engine is running totally lean. The PCM, in response is pouring extra fuel into the engine that it doesn't need. It will run rich enough to wash down the cylinder walls, destroy the rings, and dilute the oil to the point where its going to start taking out bearings.

Shut it down. Change the oil. Do not run it until you have the exhaust system back together.
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Old 04-10-2011, 07:23 PM   #9
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Re: Raw gas coming out of exhaust manifolds -- what could be the diagnosis?

yeah its not gonna be turned on til all of that is taken care of. I'll still check for a leaking injector. Its a shame I have to change the oil again -- it only had about 60 seconds of total use :-( Hopefully no real damage has been done. I don't think i have the heart to replace the engine for a 3rd time.
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Old 04-10-2011, 11:22 PM   #10
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Re: Raw gas coming out of exhaust manifolds -- what could be the diagnosis?

Hopefully the O2 sensors never got hot, unless as part of your 94/95 configuration, you used the 4-wire heated sensors. If the O2 sensors don't get hot enough, it won't go into closed loop, which is where the damage would occur.
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Old 04-12-2011, 01:07 AM   #11
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Re: Raw gas coming out of exhaust manifolds -- what could be the diagnosis?

i used the 4 wire ones :-/ they were listed as direct replacements on rockauto. i guess only time will tell. ugh, stupid mistake!
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Old 05-23-2011, 12:49 PM   #12
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Re: Raw gas coming out of exhaust manifolds -- what could be the diagnosis?

So i hooked the exhaust system back up -- I think the engine is still running incredibly rich. I came to this conclusion because after the engine was shut down, smoke would rise up from the manifolds -- plus i could smell that the car was running very rich.

I also noticed that after i shut the car down, and i flexed on the gas pedal a bit, more smoke would come up -- my guess is that more gas is being dripped into the combustion chambers which is then burning up.

I don't smell the raw gas anymore -- but that could be because the entire exhaust system is back together and what gas is dripping into the exhaust pipes is getting burnt up. I could hear that there tiny "pops" while the engine was running -- little back fires (probably due to whatever gas was dripping down the pipes).

Anyways, does anyone have any other ideas? Another thing I should mention, I'm using a 96 harness on an engine that was from a 93 (i swapped intakes with a 96) I know there are other emissions equipment on the 96 that the 93-95s didn't have -- plus there is a vacuum hose that connected to the Opti (i plugged the hose).
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Old 05-23-2011, 12:49 PM
 
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