1993 Chev S10 - 2.8L Driveability Issue

[Tim Martin]

I got this 93 S10 PU with a TBI 2.8L and a manual trans with 2 wheel drive. Issue is that it runs very poorly. Starts fine, no miss, no cel. As engine temperature goes up, performance and power drop. Under acceleration at operating temperature it will shoot fire out the tbi. Once up to operating temp, the engine will hardly start. Turns over good though. Compression shows 150-160 psi. Vacuum is 14-15". Timing is right on. Fuel pressure is 13psi.

I thought the timing chain might be stretched so I set the timing mark to 0 and have only 2 degrees of crankshaft movement till distributor shaft begins to move. Pretty much this rules out timing chain or am I wrong? What am I missing? I am thinking the low vacuum is a clue - but what?

[fortknoxx]

disconnect the exhaust before the cat, or take out an 02 and see if it gets better. is it cherry?

[ricmorin]

Right. The vacuum readings are too low. Double check timing and check for a possible restricted cat. You're close!

[Tim Martin]

disconnect the exhaust before the cat, or take out an 02 and see if it gets better. is it cherry?

The cat is not cherry but the exhaust coming out the tailpipe is extremely hot.

[fortknoxx]

Did we open up the exhaust?

[Tim Martin]

Not yet. Am working on a ford stroker.

[ricmorin]

I have one of those backpressure testers that screws in the O2 hole. Love it! No questions when you use that tool.

backpressure tool

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[Tim Martin]

ya got a tool number for that back pressure tester?

[ricmorin]

OTC 7215

[Tim Martin]

Thanks. Will check it out.

[DCC]

First how many miles are on the vehicle, pull the distributor cap and rotate engine to show timing mark on crankshaft to TDC, turn the engine backwards watching the distributor rotor, as soon as the rotor starts to move stop rotating and check how far the timing mark indicator has moved from TDC ( this will check how much play you have in the timing chain) if the free traval is more than 17-20 degrees this could be your culprite, but without some more data on the current conditions it hard to say at this point. Oh one other point you may want to check your EST circuit and make sure it is electronical advancing your timing.

[steven kiser]

disconnect the exhaust before the cat, or take out an 02 and see if it gets better. is it cherry?

The cat is not cherry but the exhaust coming out the tailpipe is extremely hot.

take out the front 02's. have fun. they have to come out to get a good feel. make sure there isn't any flammable material near by. i have a mig welder and on occasion will just bore a hole in the pipe if the sensor isn't cooperating and just weld a patch on it. i'll let the customer know what i'm doing all along the way. personally i've never run into a bad chain on one of these baby's. usually the chain slop will wear through the front cover and leak oil before it will jump. you mentioned cherry and exhaust is extremely hot. the cat being trashed may just be a result of something else. i'd look into a plugged egr port.

[Tim Martin]

yea steve, a plugged egr port wouldn't make low vacuum would it?

[steven kiser]

not so much at idle cold but if the engine isn't breathing properly is may effect it at idle warm. a jammed cat will and i'm leaning towards that but i still think if it's plugged it's the result of something else. i would cut the cat inlet pipe as close to the case as possible and see if honey comb is plugged or melted and fused at the top.

[ricmorin]

yea steve, a plugged egr port wouldn't make low vacuum would it?

Tim,

I'm willing to bet lunch that plugged EGR ports would have absolutely no effect on engine vacuum under any circumstance. Stuck open EGR yes. Plugged closed no.