91 cav igntion problems

[ebritt]

i just replaced the head, crank sensor and ignition module. checked the timing chain and it's ok but i still have trouble with getting it running. sometimes it will start and run but it runs rough and you can hear it try to run right for a few seconds at a time. but sometimes it will not start just backfires through the throttlebody like the chain is off. On a good day I can get it started and take it down the road for a little while and actually get it up to 55. If you can get the rpm's up it runs better.

Any idears??

[richtazz]

check the EGR valve.

[ebritt]

would the egr make it backfire like that?

[public]

Yes,
And two possible easy fixes.
1. Remove and clean the IAC valve. Be carefull not to move the pintle in or out.
2. Also clean/check the fuel injector(s) as a sticking injector can cause the mixture in one cylinder to got rich or lean. TBI systems are kinda bad for this. My 89 (300,000 miles) has had this issue several times. Cleans right up and then runs great for a couple of years. Good Luck

[ebritt]

i dont beleive this car has an iac valve...at least i cant find it anyways



ooops..found the iac..i'll give it a try..thanks

[public]

Glad you found it. It can cause a world of problems when dirty, stuck, or broken. Good Luck.

[ebritt]

removed the iac...appears to be stuck open. also no vacuum on the line to the egr or evap can.

[public]

You can clean the IAC with carb cleaner and a toothbrush. Be careful not to move the pintle in or out. If you do then you will need to get the engine warm and drive for several minutes at 35 mph. BE CAREFUL the engine will idle VERY high making it hard to stop. You will then feel the motor idle down to a normal speed.

[ebritt]

i treid to drive it but never got out of the drive(my drive is almost half mile) when i got back to the house and put it into park it idled very high then calmed down. also the airhorn(?) on the throttlebody was really loose so i added a couple of washers to tighten it.Also no vacuum on the line to the egr valve, guess i need to pull the little plate to see if it is stopped up? This is getting very frustrating...one minute it will run smooth then like crap.
somedays you cant even start it without backfiring.
I beleive it may be time to go to the shop.

[public]

The idle coming back down is good. That is the IAC reseting. At idle on a cold engine there will not be vacuum on the EGR. You can test the EGR diaphram with a vacuum pump. I have blocked off EGRs on this engine without problems. It might be a cheap way to see if your EGR is stuck open. Cut a piece of gasket material to fit the bolt holes but leave the big holes blocked. Cut a piece of a soda can the same. Remove te EGR and install these instead if the "real" gasket. Then Test Drive. Again, Good Luck.

[ebritt]

i just noticed that when it back fires fumes shoot out of the throttlebody at the butterfly linkage on both sides. also maybe noteworthy, maybe backfire is wrong no flames but pressure and fumes shooting back.

[public]

The EGR system allows some exhaust back into the intake. A backfire caused by the EGR will be in the intake. As for smoke/fumes coming out around the butterfly. That is not supposed to happen. There must be a lot of wear around the butterfly shaft. This could cause a vacuum leak and improper airflow in the venturi.

[ebritt]

i beleive im gonna try a junkyard throttlebody.

[public]

I have done that in the past myself. Worked great.