Mrcorvette91

O' Ye Knowledgable ones...I have did everything I know to do, I have changed plugs, plug wires, fuel filter, fuel pump, checked distributor cap and rotor, still missing at all speeds..idling, WOT, and all areas in between. Possibly be an injector? Could anyone let me know how to check the injectors? Thanks..and all other opinions welcomed and begged for....I hope everyone had a GREAT Thanksgiving!!! :confused:

jeffie86/96

Did you make a compression test, mine sported a blown head gasket when my father bought it (long story). :cry

FU

Hope that your Thanksgiving was good also. Have you checked all of the ground's ?

ShawnZR-1

You say you "checked the distributor cap and rotor". I had a 77 Skylark (let the jokes begin) and had a similiar problem, everything looked good, but the cap was cracked. I couldn't see it, but a replacement solved that problem. I actually pulled each plug out one by one to see if there was a spark. One of them simply didn't spark at all. Traced back to the cap.

AquaMetallic94LT1

Compression test is a good idea.

You can also try to narrow it down to which cylinder is giving you trouble by pulling each plug wire while the motor is running and see if the rpm drops. You should see a noticeable drop in rpm if the cylinder is working okay when you pull the plug. Check the resistance of each injector. They should be around 12 -15 ohms.

SunCr

Are you losing coolant? Can you describe the condition of the plugs you removed - any fouled or any with rust on the threads? Best to isolate the cylinder with the problem first. You can pull the injector harnesses or the spark plug wires one by one, but first disconnect the Idle Air Control Motor. Otherwise, it can maintain idle and it will be difficult to find the bad cylinder. Once you know the bad cylinder you can check the injector harness by simply swapping two adjacent ones (assuming you're an L98 Batch fire). If the bad cylinder moves, it's in the harness. If not, you can check compression and perform a leakdown test as you can get a good compression reading and still have a problem or you could have a radiator shop check for combustion gasses in the coolant. If the miss is really bad and you're losing coolant, bring the offending cylinder to top dead center with the plug removed. Coolant will probably flow out if it's a blown head gasket. If those tests are normal then you might want to remove the valve cover and measure the lift of the rocker arms. Comparing Intake to Intake and Exhaust to Exhaust, they should have the same lift. If any differ, the cam or lifter is worn.

65Z01

Since it misses at idle there's an easy test to see if it's due to ignition.

Put a timing light on each wire in turn, pull the trigger and see if the miss coincides with the light missing on any or all plugs. I used this to diagnose two bad wire connectors at the dist.

Bob Hovey

I know I'm comparing apples to oranges, but when my daughter's '90 Corsica was missing badly I took it in to a good diagnostic technician. He found that two of the 3 coil packs were gone. So he replaced all 3. The coil packs control the firing of the motor and basically the car was running only on 5 cylnders. Take it to a good electronics diagostics guy. I bet it's an electronics problem. :)

Bob


[Modified by Bob Hovey, 4:42 PM 11/23/2001]

PeteL

Well, since we are into the "it could be anything" catagory. Why not start the car up with the hood open at night and see of you can find any little blue sparks?

Comparing plugs will be a real benefit. Look for wet plugs, black plugs, oily plugs, melted plugs, cracked plugs; that sort of thing.

Any codes? SES light?

Describe "miss" in terms that we can compare. Is is rough, does it make noises, does it bog when you hit the gas, backfire / cough, or just a little rough?

Hold one palm couple inches from the right exhaust tip and other palm couple inches from the left exhaust tip. You should feel even pulses, are pulses missing or is one pulse much stronger then the others?

Put vacuum gauge on un-ported source and check against standard vacuum troubleshooting chart (lots on web do google search).

Good Luck,

Pete

Frank C

I'd also bet it's electrical. 65Z01 has a great idea there with the timing light as long as it's rhythmic and happens also at idle.