I have a 2002 blazer 4wd that been a pain. I received it not running with 105xxx miles on it about a 2 months ago. It had been sitting for years. Put a battery in it and would crank but not start. Checked fuel and wasn’t getting anything. Removed and replaced the pump, fuel filter and clean tanked. It would start. Seem to run alright. Check engine light came on for Evap issues. Replace purge valve and canister. Light went off. Ran fine for a week. Drove around and it started to have a slight misfire at idle and park. Did a tune up with NGK platinum plugs, Acdelco cap and rotor, and standard wires. No change. Changed the IAC, TPS, ignition module, and coil since it had been sitting for a long time. Did a fuel pressure check. Pegs and 60 with key on drops to 55 and holds. Figured it might be an injector issue. Removed and replaced injector assembly. No change. Double checked for vacuum leaks. Couldn’t find anything. It won’t set a cel for anything. But show misfire on live date on cylinder 1 & 3. Figured I try the crankshaft sensor. Removed and replace it. Use my snap on scanner to do the relearn. No change at first. Drove it around and seem to start clearing up at idle. Shut it off and start back up. Code P0351 primary coil a. Started misfire again. This only misfires at idle and park. Driving down the road is smooth. I’ve done all this work within 1000 miles of driving it. It broke down twice once while driving. 1st it stalled and had to pull over. Second time I was at a pump and it wouldn’t start back up. Let it sit for a few each time and would fire up and get back home. Any ideas on where to start? Thanks in advance!

 

Do you feel the misfire or only see it on your scanner?

We need to get CMP retards within spec to make sure that the misfire counter is accurate.

Your misfires are driver bank specific. Can you graph O2 sensors in live data? What are your 4 fuel trims at idle and 2500 rpm in park?

Regarding P0351 I would start with the power and ground to the coil and ICM, especially at rough idle.

Any recent compression test?

What did the plugs look like?


George

 

You can feel the misfire at idle. Never while driving. I can watch it on my scanner when it misfires. The plugs are less than 500 miles on them. Haven’t pulled them to check the condition since. I replaced them cause the vehicle was had been sitting for a long period of time. Didn’t think to look at the old plugs before tossing them. I graphed the O2 sensors. They seem to be switching back and fourth. So I guess they are working. I’ll snap a photo of that to get a second opinion. I can’t remember the fuel trims off the top of my head. I’ll snap a photo of that as well at idling and at 2500 rpms in park. I think I have a shorted wire at the coil connector. Have a replacement on the way and should be here Wednesday. I havent done a compression check yet just because it completely clears while driving and with 106XXX miles on it I wouldn’t think that is the issue but I could be wrong. Plan on doing that Wednesday as well though. Just seems like something simple I’m over looking. I won’t have access to the blazer until Wednesday afternoon. Thanks for the reply.

 

If you want something simple that might help then get CMP retard within spec and check those ignition
voltages and grounds.


George

 

what is the CMP spec supposed to be?

 

CMPR is the relationship between the crank and cam position as dictated by the timing chain and distr drive gear. As the engine wears this spec starts to drift and as a result you get improperly reported misfire cylinders and eventually distr crossfire problems. You try for as close to 0 as possible, the spec is +/-2 degrees. anytime you are chasing a misfire issue this is your first stop.

George

 

I think that is going to be my issue. I can’t remember what it was reading but I know you wasn’t +/-2 degrees from 0. I didn’t think the distributor on these had much adjustment. But after reading I see people modify the hold down or replace it with an old school SBC one.

 

I went this route:



George

 

When you get this back in spec then we can chase any remaining misfire problem. Be interesting to see if you still have a bank 1 problem.

George

 

Here are the readings on my scanner. Didn’t have time to adjust the distributor yet. Doing that Friday.