Misfiring engine, check engine light flashing

[scooberu]

My 02 SE presumably had new spark plugs and wires a year ago when I got it. A couple months ago, it misfired a few times after going through deep puddles, or in wet conditions. I replaced the spark plug wires with good results. Around a week ago, it started misfiring consistently with the check engine light flashing.

I immediately bought 6 new spark plugs and a new coil. I replaced all the plugs. One cylinder (not sure of the number) was full of un-burned gas; I could smell it as soon as I loosened the plug. The CEL stopped flashing momentarily while I took it for a test drive, but started flashing again, and the misfiring resumed. I replaced the coil feeding the offending cylinder with no improvement.

I suspected that my fuel injectors are bad, or that one of them is. I bought some gumout fuel system cleaner and put it in. After running it through, there was some improvement. At idle and under no load, the motor seems to run fine. When accelerating, the motor misfires and the CEL flashes. I can ease it up to around 25 mph without the CEL flashing, but no more. When decelerating, the flashing stops at 30 mph. I can shift into neutral at higher speeds so the rpms go down around 1000, but the CEL continues to flash. So... it is both speed related and load related. BTW, the CEL flashing feels consistent with the misfiring, except that the engine wobbles enough to move the car when it is stopped and idling (CEL on/not flashing, like normal ) Also, there is an odd burning smell somewhat like an electrical fire along with a smell of unburned gas.

Today, after reading about 200 forum posts for more clues, I messed with it some more. I replaced 2 vacuum lines that broke off in my hands, but no improvement. All the other vacuum lines appeared to be ok. I sprayed the coils with water until they were drenched, but the idle maintained. I saw that I have my original upper intake manifold (2001 date), but with no signs of damage. I'd like to back burner that one for a few months at least.

I still feel like a fuel injector could be plugged, but...not sure what to do about it. where to go now? It's possible I damaged a spark plug wire when I changed the plugs, but how to check that without risking further damage? Its also possible that I damaged a new plug when I checked the gap, or that I bought a bad one...? I was very gentle with them, but they were iridium (NGK I think) with very fine tips.

So injector(s), ICM, MAS, Vacuum, cat converter? Please help. Thank you all very much

[96 SSEi]

hi, the missing is causing the cel to flash!!
if you continue to drive while it flashes, you stand a great chance of killing your cat.

you must address the missing immediately!!

recheck the gap on every plug.....060 inch

check the terminal that clips to the boot of wire - you should hear a click when you connect the wire's boot to plug
squeeze the boot gently to close the gap of connector - if you wiggle it, there should be no play if its secure


do you have access to a scanner?
it may narrow down the issue to a specific cylinder

I had the flashing and it was #3 wire was broken by boot - easy fix

[scooberu]

Thank you 96SSEi. After reading your post, and also a very informative site on diagnosis ( http://troubleshootmyvehicle.com/gm/3.8 ... re-codes-1 ), I headed to O'Reilly's to narrow down the misfire. This is (hopefully) the conclusion to the story.

The codes that came up were:
-Fuel mix too rich
-Random multiple misfires
-Cylinder 5 misfires (Previously bad cylinder was #2)
-Coolant thermostat below temp

I purchased a spark plug tester and tested #5 in the O'Reilly's parking lot. The test seemed to indicate that both the ignition system and the fuel system were working properly. However, I noticed that the wire to #5 was burned about halfway up. The wires were under lifetime warranty, and less than 3 months old. I got a new set, put #5 in immediately and will put the others in as soon as the engine cools off. The misfire is gone. I believe the fuel mix and random misfires were a result of the consistent misfire in 5 (fingers crossed).

Coolant Thermostat? Whats that about? is there another forum on that?

My inclination is to consider "new" parts to be good, and to look elsewhere for the problem. Also, I like to blame the previous owner for my car's problems. These biases both led me the wrong way here. The nudge from 96SSEI to go back to the plugs and wires was what I needed.

[dougtoth]

Your inclination that new parts should be good is correct but not true.
I have had bad new parts such is ICM,Coils Wheel Bearings,MAF and Thermostats.
Unfortunately most of these parts are made in China or Mexico.
While the price might be inexpensive or cheaper the quality in a lot of cases is sub standard.

[96 SSEi]

coolant thermostat is the valve that controls flow of coolant from block to rad and back - when its closed, the engine warms faster and when open, the rad cools the temp faster - the car sees that the engine is taking too long to reach a predetermined engine temp. so a code is thrown.

does the car take a long time to warm up? , please check the thermostat, it may be stuck open. you can test it with a cup of boiling water:

water boils at 100c/212f

put thermostat in cup/glass

pour freshly boiling water on it to cover it - it should open up fully

as soon as the temp of water gets below 190f, it should start to close - I suspect it is staying open to some degree.

cooking/turkey thermometer will help you here - replace if faulty.


good thing you got on this missing issue pronto.........
little risk of premature wear on cat - and yes, #5 was missing so the unburnt fuel was being dumped into the exhaust manifold and the 02 sensor sees it as way too much fuel/rich - it should be fine now.

[MKMike]

Your inclination that new parts should be good is correct but not true.
I have had bad new parts such is ICM,Coils Wheel Bearings,MAF and Thermostats.
Unfortunately most of these parts are made in China or Mexico.
While the price might be inexpensive or cheaper the quality in a lot of cases is sub standard.

So sad, but entirely correct.


Scooberu, I would do an oil change.
When a cylinder consistently misfires, fuel gets into the oil.

When you do replace the upper intake, do yourself a favor and change the lower intake gaskets and coolant elbows, too.
(Assuming they're the original black LIM gaskets.)
Full instructions here, though the pics are not.
Looks like Photobucket requires acct mods for the images to reappear--and since the OP no longer visits the forum, that probably won't happen.
http://www.pontiacbonnevilleclub.com/fo ... c3591.html
FWIW, used a Dorman UIM.