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94 S-10 2.2 emissions problem

My son has just replaced the 2.2l engine on his '94 S-10 pickup with a 3rd party rebuilt. Practically everything under the hood is new (except for the starter, which just cooked on him for good measure), but he failed his emissions test for his sticker. The hydrocarbons were extremely high, but everything else passed. The truck seems to run fine, except I think the head on the rebuilt engine was planed enough to increase compression where he needs to run a higher octane to stop the pinging (which he did and it helped).

He is a junior at the local tech school in the Auto Technology program and has access to all kinds of equipment, but even his instructors are stumped at this one. They tried flushing the injectors, and that only made the problem worse when they put it back on the analyzer.

The only old parts left in the equation are the injection system and controls on the intake side and the catalytic converter on the exhaust side.

Any ideas would be appreciated since he's running on a reject sticker and doesn't have much time left to have it reinspected.

Thanks, GaryG

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GaryG
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Has anyone put a vacuum gauge on it yet? Why was the original engine replaced? First thing comes to my mind is too lean. Vacuum leak? Lean mix could cause it to ping as combustion chamber temps would be higher, but I don't know if higher octane would help the ping. Timing off on the cam? I had a service writer who failed because of a bad Catalytic Converter for high hydros on an Acura a year newer than your son's truck.

Whitelightning

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Whitelightning

He said they only ran an EGR test, but not a full vacuum test.

Original motor overheated and was seized. It was sitting in a field for over a year with a crankcase and cylinders full of coolant. He got it "dirt" cheap and figured he could come out on top doing most of the work himself with the school.

First thing comes to my mind is too lean.

Hmmmm..... When they cleaned the injectors, letting in more fuel, it got worse. I was thinking maybe too rich?

Vacuum leak? Lean mix

The manual states compression should be around 140-160 PSI and this engine runs 180-200 PSI making me think the original 8.5:1 is now more like 10:1 or higher. I think that's where the regular gas pinging is coming from.

Timing off on the cam?

Non-adjustable on the outside for timing, and he claims it's buttery smooth at idle and throughout the full power range, so he's doubting a timing problem.

His instructors checked the Cat and don't feel its the problem, but without actually changing it, I'm not too sure they can absolutely rule it out. Bypassing it wouldn't help in clearing up the hydrocarbons though and might make it read worse?

Thanks for the thoughts and ideas. He'll check vacuum and look into the timing and cat possibilities when he gets the cooked starter replaced and takes it back into shop.

GaryG

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GaryG

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