Help! I really need ideas... (Full Version)

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Help! I really need ideas...

  

saulgood -> Help! I really need ideas... (8/1/2006 12:22:20 PM)

My '89 Caprice 9c1 has a 5.7 and throttle body injection. One day the motor was purring and it suddenly got "choppy" while I was driving -like it was missing on a couple of cylinders at all rpms (very steady).

I thought it would be an easy fix, so I checked for a vacuum leak. Then I replaced the plugs, wires, cap, rotor, and filters and checked the timing.

It still runs exactly the same, low power, steady miss.

Two of the spark plugs on the passenger side were black and sooty when I changed them, the rest were just kind of brown but looked like normal wear under poor running conditions.

Finally I checked for trouble codes, even though the ses light never came on. It might be "old", but it is flashing a "42". Hayne's manual says this is a problem with the EST, or electronic spark timing. Apparently it is an open circuit or grounded out. It also says it could mean a "faulty HEI". What it doesn't say is how I should proceed with testing/repairs. Auto electric is not my strong suit -let alone computers - so If you have any advice about using a tester (I have one), speak slowly.

Any other informed theories will be appreciated too. thanks

  
uncle bill -> RE: Help! I really need ideas... (9/2/2006 12:38:52 AM)

What the code means is that Your engine timing is not moving when needed. In the old days, the ignition timing was controlled by a vacuum advance. As the engine RPM's go up, the timing should retard. It appears Yours is stuck in the retard position, thus the choppiness at idle. The ignition thinks ( computer ) that it's at a higher RPM. Once the engine RPM reaches the compatibility of the ignition, it's happy. The problem is either in the distributor, harness or computer. I can only diagnose it that far. First test the wiring and see if it tests the same at both ends of the connection. If that's ok, Replace the ignition module ( the part the harness is connected to between the distributer and computer ) if it still persists, then have the computer tested. thanks for listening.

saulgood -> RE: Help! I really need ideas... (9/2/2006 1:38:13 AM)

finally, an answer...
thank you so much for your reply. When you say, "test the wiring and see if it tests the same at both ends of the connection." Which wires do you mean, exactly? Also, are you talking about a simple resistance test? Sorry for the ignorance - but I've always had trouble with auto electric (I know it's pretty simple in theory but I have a mental block for some reason). Thanks again!

uncle bill -> RE: Help! I really need ideas... (9/2/2006 9:49:14 AM)

I'm sorry I didn't make that clearer. The lead from the distributer module to the computer that controls it is the wire I mean. An ohm test should do.

  

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