I have a 1996 Blazer LS 4x4. I only took 1 year of auto in a tech school and everything I've ever done was 'back yard' mechanic stuff (figured I'd go ahead get that out of the way and in the open). I purchased my Blazer a month ago. They read out the codes when I got it. They told me they replaced the distributor cap, button, and plug wires. Told me the code itself, but I can't remember. Only thing that popped up was 'Slight Misfire'. No specific cylinder. Check engine light was on. I drove it the hour and a half trip back. Everything worked great. Didn't even take a hit on gas mileage much. Was pretty impressed. I get back home and change the plugs, since it was the cheapest option first. I no longer have a check engine light on.. But the truck misses even worse than it did now. Was told by the auto parts store that they wouldn't be able to tell me much more than that, and that theirs would have spit me the same codes. Any advice of what to try? Had a guy tell me it could be as simple as them putting the wires on in the wrong order. I thought it wouldn't even turn over if that was the case.. But I still got a diagram and checked. There's a few "O2 sensors" on it so I'm not sure which one they mean or if they're talking about the mass air flow. Any insight or tests to try.. I would really appreciate it!

I searched and searched before I posted a new thread. If this happens to be a duplicate, I apologize and you can delete it. Sorry for any inconvenience!

 

What brand are the rotor, cap and wires? AC delco / delphi are the only brands that work in these vehicles for some reason. Plug wires could be wrong, but they would only misfire those specific cylinders, not all.

 

I'll message them and get back to you when they reply. Thank you for the response. I'm at all loss!

 

+1 on Thogert -




When I "acquired" my '99, it had some "off-brand" cap and rotor (wells?),
no-name wires (store stock?) and Champion plugs. It started, ran like s&%^, but enough to get it on a trailer.


After un-loading it, put AC-Delco Cap, Rotor, and Plugs, and Accel Wires on, heck of a lot better starting * (cold and damp) You MAY get by without AC-D wires, like I did, but DON'T go for the $20 specials...


P.J.




* - after reading the Captain's fuel system check, unknown state of the truck at the time, and was sitting for a year+, it did give me and edge/known good product for my base troubleshooting/diagnostics.. (Fuel pump leak-back, poor grounding, MFI/SFI leaked 2-quarts of fuel into oil [head-bang], etc... )

 

If you can still feel it missing and the SES light is not on, the the misfire detection system is not working.

FYI #1 and #3 plug wires are switched in comparison to what you might think on the cap. The cap should be labeled with the corresponding cylinder. I would run each wire to it's destination. Still the SES light should be on. Start with the wires. If that is good, then pull all the plugs and check for cracked porcelain (especially #3 behind the steering shaft). Avoid the urge to just replace stuff and hope that it fixes your problem.

 

Get a spray bottle and water. Start hitting things till you find what makes it run better/worse. I found a bad coil this way on my wife's Blazer that had a miss and was hard starting/ no starting some days. New coil and good to go!

 

Sprayed it last night. Not much success with that. But it did make the check engine light finally come back on to where my uncle could check the codes himself. The owners before me could only tell me they bought everything at Napa and that they don't remember the brand. They got mad when I asked and said brand doesn't matter. Same parts. So I'm going to take that and assume.. All of them were probably the cheapest products available. I didn't want to just keep replacing piece after piece and keep having the same end result. Gonna run a few more tests here in a min and see if I can come up with more info. Finally got the break issue out of the way. Everyone pointed to the break booster or the ABS module. (No lights on dash to go by) I paid $54 for a wheel speed sensor. Problem solved. Thanks guys!

 

If the misfire detection is off, wouldn't that indicate that the camshaft retard timing is over 7 degrees ( I think that was the number)? I know that should throw a code, but my Bravada was about 10 degrees or so before I swapped my distributor and it wasn't throwing a code...that may be why he isn't getting the misfire code.

 

The PCM requires correct camshaft position sensor, and crankshaft position sensor data to detect, and accurately identify cylinder misfire. If the data from either sensor is incorrect, cylinder misfire DTC's will not be accurate. When diagnosing a misfire, it really helps to know which cylinder is misfiring

If the crankshaft position sensor relearn data is incorrect, the engine will still start and run, but injector and ignition timing will be incorrect. There will be no DTC's set, and no check engine light.


If camshaft retard is out of spec, (zero degrees +or- 2 degrees) it will cause crossfire inside the distributor cap, (engine misfire) and it may or may not set a DTC. If it does, chances are the cylinder identified is incorrect. If camshaft retard is off more than ~25 degrees, DTC P1345 will be set in memory, and the check engine light will be illuminated, (distributor gear not timed correctly with the camshaft gear).


Diagnosing a misfire requires that all of the most
basic items are correct, FIRST:
Correct AC Delco spark plugs, with the correct gap.
AC Delco distributor cap & rotor in good condition.
Good quality spark plug wires.
Correct crankshaft position sensor relearn data in the PCM.
Camshaft retard within spec.
Fuel pressure and leakdown within spec.