I have an 87 IROC 5L, 5Sp that has had a hard time getting through CT emmisions. Here is the problem (been trying to adjust timing to make it pass), when the timing is set to factory setting (6BTC) and the computer wire is hooked back up (have to disconnect this wire to set timing) the advance is going to about 20BTC which is well off the timing plate! Is this normal? Even with timing set at 4BTC, it is going to the same place (20BTC) when I hook that computer wire back up. Does it sound like I have a computer problem? Upon hard acceleration am getting some knocking which based on emmisions points to the EGR, could this be the culprit??


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SG,

Yup. The timing marks (if you can find them) might even be jumping around a bit at idle, but this is completely normal since the ECM and EST are seeking the greatest possible advance without causing detonation and power loss.

Incidentally, the EGR shouldn't be active on accelleration. If it were stuck closed at cruise, the chambers might be a little hotter thatn they are supposed to be, contributing to detonation, but the knock sensor shoudl be retarding spark once it senses the condition. If your fuel volatility is too high, or the octane is too low, no measure of spark retard that the ECM/EST can apply will correct the problem.

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

 

I've always gone to the ALDL connector and shorted the two upper right-hand terminals to put the ECM into diagnostic mode before I set my timing. If the timing is advanced or retarded, the ECM won't go back to 20', but will flutter around the new setting.

I've given my two-cents many times on an old trick that seem to help people get through the smog test. Overdrive the smog pump! Go find a pulley about half the size of your stock pulley. You may have to take it to a machine shop to have new holes drilled so it will fit your pump. Anyway, that pump will end up pumping so much fresh air into the exhaust that it will usually fool the smog sniffer. Be sure not to let the diverter valve open and dump any air. There's a vacuum hose that controls the diverter valve; pull it so the pump is always pumping into the exhaust. After you're done at the smog station, put everything back the way it was.

 

Thanks for the info guys. My question is would you recommend disconnecting the computer (one wire, near the distributor) when it goes for emissions testing? This way the car would be running at truely 6BTC rather than about 20 or more when idling/accelerating (test is on dynomometer and done around 25 MPH). Could doing this make the emissions worse? I want to point out that the knock only occurs under hard acceleration and is not that bad. If you accelerate normally it is fine. Wonder if the leaking valve seals have carbonized the piston tops and that is causing the predetonation? Anyways, thanks for any input.

 

Don't disconnect the wire to go through emissions. DO disconnect it, and ground the ALDL like jrr said, then adjust your timing. Try 8-10*. (mine is 10) As for your knock, try replacing the knock sensor. And if you havent done it in a while, replace the O2 sensor too.

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Rob
'86 TA 305 TPI