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Post by emptywallet on Jul 26, 2008 21:12:24 GMT -5
a friend asked me to look at his 96 cavalier cause it was acting up.we got it running great by new plugs/wires/coils fuel pump.it is a 96 cavalier 2.2 multiport OBDII automatic trans with 216K miles.then 2 weeks later he got a fillup and parked the car for night and when he got in and started next morning the engine went immediately to 3-4-5k rpm!it stayed there for 2-3 minutes and then dropped to 4-500rpm with a rythmic pulse up and down.then ran like that for a couple minutes and slowly died out completely!i t has codes P0108 and P0507.when it runs at 4-600 rpm it rhythmically rises and falls and backfires a little thru manifold?when it runs at 5k it sounds more normal but has a slight rhythm/pulsation to it.when the codes are set it does not go to 5000.erase codes and it does.there are no detected vacuum leaks!and manifold vacuum is very weak at 4-500 pulsing rpm.brake booster holds vacuum.fuel pressure is 45 at 5000 and 60+at 500 pulsing.when engine is cranking compression sounds even.tried plugging/blocking all known engine air sources and it still runs the same.during original tuneup we had to remove plenum to get to coilpack.we ended up placing coilpack in front of engine on trans bolt as a convenience measure.splitting open the wiring harness allowed for move.also on change of fuel pump,inserted shrader valve test port by tank.i am puzzled by the EGR valve setup?i havn't worked on this model motor this scrutinizing before.hope someone can make suggestions on what to look for.we have had the coils and module tested at auto zone.they passed.i am a self trained 30 yr family mechanic.thanks!
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Post by idol on Aug 4, 2008 18:44:23 GMT -5
Hello emptywallet, from your description, it sounds to me like you have an idle circuit , fuel flow issue. Based upon all that you have done so far I believe you need to check all of the following components for proper operation, beginning with the Throttle Position Sensor (TPS). Usually a fluctuating idle occurs on fuel injected engines when the TPS is either slow or not functioning at all. Have it checked out, or you can check it with a multimeter. If this item passes the test, then next item to check would be a the mass airflow sensor. These items at times, especially on high mileage engines, burn out and when they fail you'll get the same symptom you're describing.
I read that you removed the plenum. When you reinstalled it did you make absolutely sure you sealed it throughly? Because in any engine , older types and new, a fluctuating idle is most commonly caused by and air leak; a very serious leak. Usually it will be found somewhere on , near or around the intake manifold. So my friend, check those items I mentioned and also give your engine a good looking over. Find a vacuum gauge and attach it to the intake and see what your vacuum is being measured at. This will also help you determine if you have a leak or not.
Let us know what you learn....or if we can help further.....IDOL
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Post by emptywallet on Aug 5, 2008 15:10:30 GMT -5
come to find out it was a plenum gasket leak!!it literally blew a chunk out completely!!it was brand new!!(gasket).it turns out that the design of the plenum is poor.it has a widely spaced bolt pattern that SHOULD require a metallic sandwiched gasket!!!like the head to intake 1.and furthermore,the original factory gasket had silicone strips between holes on BOTH sides of gasket for better adhesion while the replacement(felpro) did NOT!!(one side only!!the space between holes on the frontside of plenum under throttle/butterfly assy protrusion is especially wide!!over 8 inches!!!any warpage/looseness would be potentially failure prone there!!which is what happened??blew out the whole 8" stretch!!so i plane sanded both pieces/surfaces,added some peen marks along edge and applied new gasket with orange silicone.its working so far!!i have posted on several boards and this one is the only 1 to have correct answer/tip!!although i found it myself before reading the reply.thanks!!
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Post by idol on Aug 5, 2008 16:30:36 GMT -5
Glad we could help. Guess I'll need to log in more often to be sure our guests get timely advice. But thanks for telling us that we gave the RIGHT advice. ......IDOL
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