I've changed my cap, rotor, wires, fuel filter and my car still shakes on idle like it is only running on 7 cyl... My car also backfires on deceleration and has a loss of power and gas milage. I've had a bad injector before and this seems to be a little different. My car doesn't shake as bad as it did with the bad injector. Can a bad plug cause these symtoms??? I've checked the timing and it is right on. I've put some injector cleaner in the gas too hoping that maybe it is just a partial clogged injector but still did no good. The symtoms I've mentioned above started like a week ago. I have a check engine light popping up every now and then, I pulled the code and it is 32, EGR ****. I really don't think this is my culprit because I've had that engine code popping up before these symtoms. thanks
kyle

 

i had similar problems with vibrations and skipping, un plug the vaccum line from the egr and plug it then run it and see what happens.

 

Check the EGR system. You may have a stuck or leaking EGR valve.

You might also want to test fuel pressure. If pressure is O.K. (37 PSIG +/- 3 at idle), an injector power balance test might be a good idea.

Exhaust popping on decel is often a lean condition or intermittent ignition.

 

The EGR valve is under the plenum right?? Does the plenum have to come off to change that?? How do I test the fuel pressure?? And last, how would i do an injector power balance test?? Sorry for all the questions but I unfamiliar with some of this stuff. You guys are awesome for the help, thanks

 

'91,

The EGR valve can be located here:



Yes, the plenum has to be removed to access the EGR valve, as the photo depicts. It would be a shame to remove the plenum and NOT port the area behind the throttle body and match the runners better, at a minimum. The factory castings are not that accurately aligned, and can leave some significant restrictions in the intake tract. this even helps the "lowly" 305 to breathe better.

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Fuel pressure is read from the Schrader valve on the right fuel rail:



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Injector relative delivery flow (power balance) tests can be done fairly easily with only a little diagnostic equipment and some time.

If you are certain the ignition system is functioning and you have good compression on all holes, you need to perform a power balance test to locate the offending cylinder(s). I had a similar problem with my TPI and the test isolated the dead holes.

To perform a power-balance test, start the engine, allow it to reach operating temperature, then unplug the IAC electrical connector while the engine is idling. Unplug the electrical connector from one injector and monitor the engine RPM as it is disconnected. The drop in idle RPM should be relatively equal through the firing order. Replace the electrical connector and go on to the next injector. You need to realize that the ECM will sense the RPM drop and attempt to compensate by adjusting the IAC, which is why it was disconnected in the first place.

Compare the RPM drop at each cylinder. Don't forget to replace the IAC connector. If one or more injectors caused little or no change in RPM, it is not flowing fuel at the correct rate or if it has a poor spray pattern.

NOTE: This test will not be accurate if the ignition system is not in good order or compression is low on a cylinder.

This test allowed me to identify two defective injectors, and test results after removal of the injectors confirmed that - two of them had very poor spray patterns and low flow rates. The engine had 18,000 miles and I had already tried several types of injector cleaner in the fuel tank and a "professional" cleaning at the dealer with the pressurized fuel rail system, all with no improvement.

As always, if you discover a bad injector, I would recommend contacting Cruzin' Performance.

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"It will come to you, then you will bring it before me. I will turn it to the Dark Side. This is as I have foreseen..."

I'd invite you to roll it down for a look, but we're expecting 6-10" this afternoon, and that's NOT in the bedroom...

Later,
Vader

 

Thanks Vader, I really appreciate your help, hopefully one of these will clear up my problems. thanks again.
Kyle

 

Yes, a bad plug could cause it.