Thank you. I really want to solve this misfire and enjoy y Blazer. I will plan on doing a compression test on #2 tomorrow to rule out that aspect.

 

Hey there, sorry you're having all sort of troubles with your blazer. I was reading all the responses and looks like you have covered a lot of things. One thing I didn't see was the throttle body. If they are corroded with gunk the throttle plate does not close properly and can cause several issues like hard starting, surging in rpms can also throw codes for misfires. Also with the throttle body there is a deflector plate that can get severely junk up and cause issues. There is a way to delete this and IMO helps a lot. I did mine several years ago and did wonders for just how it runs and throttle is must more responsive. Anyways I would try removing the TB and clean it and inspect it for gunk. Do not spray carb cleaner on it. Get some brake clean and spray away. wipe it clean and then reinspect the throttle plate for any gaps between the plate and the wall of the TB. Another thing is the gasket around the TB air cleaner top. Sometimes these don't always seal up right and can cause issues.

 

OK lets get back to work.

First lets talk about misfires. A misfire is registered when a momentary change in crankshaft rotation speed occurs and then the PCM registers a misfire for the cylinder that was firing at or near that time. This can be a lot of things. I will not list all of the possibilities but it can be fuel, ignition, mechanical problems, sensors, wiring, grounds, modules, PCM, etc.

One of the possibilities is distributor cross fire which can be caused by CMP retard being out of spec. This might also cause the wrong cylinder to get the misfire assigned to it causing you to chase your tail.. We need to get your CMP retard value and then adjusted it if needed. Then you need to make sure that you don't have ignition leakage outside the distributor by misting everything with water in the dark while the truck is running. Also inspect the old distr cap for carbon traces as evidence of cross fire.

You need to travel with a spark tester and fuel pressure gauge so that when it won't start we can find out which it is. The fact that it only starts sometimes when the gas pedal is floored suggests clear flood mode where the injectors are shutoff which suggests a flooded engine which may be leaking injectors. Have you done the complete fuel pressure and leak down test? Have you measured fuel pressure when it runs like crap?

George

 

I’m a little lost on CMP. Can my scanner detect this. I guess I’m looking at some progress cause I’m down to just one serious misfire cylinder. I have not done a fuel pressure yeast since I replace the spider system so that will happen hopefully today. Trying to let the outside temperature drop to something tolerable today cause I want to check compression on #2. I got it to TDC and it appears all timing marks are where they should be.

 

CMP retard is a measure of the distributor position relative to the crankshaft. Timing chain, cam gear and distr gear play makes this spec drift out of bounds and when far enough you can get distr crossfire and improper misfire cylinder reporting. Not all scanners can read this parameter but we have cost effective ways to do it here on the forum. Pretty much the standard advice you will get here with any of the wonky problems (rough idle, misfires, runs like crap) will be the complete fuel pressure test and CMP retard. If that doesnt do it then we move on.


George



George

 

 

#2 is definitely the misfire poster child. 1/3/5 have very low count misfires. I will get the compression test for #2 , ohm the new plug wire just in case it’s bad. I did see a data pic for advanced timing for #1 cylinder at 17.5/18,6, is that the CPM retard? I now have a decent scanner so if you need any certain data I’m more than glad to gather what you need. I did discover the rear tiny screw for the cap was too loose so I cut new threads in both to hold the cap secure, unfortunately it had no effect on the misfires.

 

No, CMP retard is its own parameter, getting it within spec makes certain that's its really cylinder #2 and/or might even improve the misfire. The members here have found low cost ways to measure it as well as other parameters and graphing:

https://blazerforum.com/forum/genera...-offset-92677/

Compression testing especially on an older engine needs all cylinders compared to each other to draw conclusions.

For that #2 problem try swapping plugs and wires and looking for arching in the dark while misting with water. Also look for crossfire under the distr cap.


George

 

Here is a comprehensive look at misfires that may be of value:

https://blazerforum.com/forum/2nd-ge...72/#post732722


Because you have a high count on a single cylinder I would concentrate on the individual cylinder causes:

Ignition
Injector firing
Mechanical problems (compression)


George

 

I just noticed those sky high short term fuel trims. They need to be captured with long term trims:

https://blazerforum.com/forum/2nd-ge...-trims-102906/

Also, can you graph your two precat O2 sensors (B1S1 and B2S1)?:

https://blazerforum.com/forum/2nd-ge...82/#post733375


George