Misfire . . . AGAIN!

[dayton.reed]

Hey folks, IIIIIIITS BAAAAAAACK!

(For the backstory, you can read viewtopic.php?f=18&t=20810&p=219345&hilit=misfire+mysery#p219345 and http://www.pontiacbonnevilleclub.com/fo ... 28687.html )

Short version, a few years ago, I had a misfire whenever I gave the car good throttle, like on a freeway onramp, etc. It went to the dealership, they goofed off and it magically fixed itself for a while. Then, it came back whenever I tried to go above about 1800 rpm, and turned into a catastrophic failure that misfired whenever the car was on--I diagnosed the coils with the resistance test and found a dead one, and the car was back to normal after replacement.

Now, it's back under light load, like it was before the initial magic fix. It came on about last week when I was trying to get up a steep, slick road. It wouldn't have been a problem to get up if people hadn't STOPPED ON IT!!!! but that's another story.

Let me roll out what I've done to try and fix this since the beginning, and other incidentals I feel might be important:


A While ago:
New EGR

Autolite 605's . . . I'll probably get new Delco Iridiums no matter what, as my gas mileage tanked after I added these. I get 24 max on the freeway, and about 12 around town. Blech. They may be worn out anyway, so that'll be part of my diagnosis, I'm sure. Not to mention there's a huge mail-in rebate from Rockauto right now that make them about the same price as the Autolites at Walmart.

Napa Belden wires

New fuel pump

BWD Select coil from Checker (now O'Reilly)

Just before 1000 mi trip for Christmas:
Dealership oil change (as opposed to doing it myself . . . it was about -20F for a while here, no exaggeration)

Cleaned MAF with specific MAF cleaner

Brand new K&N air filter

New cabin air filter

Everything went just fine on that trip.


Anyway, I'm leaning toward ICM, because in reading on the forum it seems to be associated with similar symptoms. I'm thinking of buying the cheapest one Rockauto has (about $80), because I'd have to limp quite a distance to get to a junk yard, and who knows if they'd have one anyway. Before I pull the trigger on that, though, anyone have any other ideas? I might try to take my ICM to AutoZone to be tested, but who knows if it's even worth the time, since my car starts and runs, so the problem isn't catastrophic, and those tests apparently aren't very reliable.

Help me Obi Wan Kenobis. Ya'll're my only hope.

[dayton.reed]

Oh ya, I had a new Magnaflow cat put on too same time as plugs, wires. That's important.

[gweg_b]

My problem was the ICM. Almost same problems you described, and I changed coils, plugs, wires constantly before I changed the ICM. Been going on 10 months, and no misfires.

I don't know about getting a cheap new one, but if you contact Andrew (harofreak00), he can get you a good used factory AC Delco ICM for cheap (I think it was something like $30).

[DaMaroon]

Whenever I have ignition problems I like to look under the hood at night. Near total darkness. It can be ...uh.. illuminating.

Here's a couple of links that seem to show logical testing methods.

http://easyautodiagnostics.com/gm_3800_ ... test_1.php
http://easyautodiagnostics.com/gm_ignit ... dule_1.php

At the end of the coil pack tests they list some other possible causes. Might make you sick. The one that caught my eye is the fuel pressure regulator. These going bad is very common.

[Nocrank]

I'd clean the Maf sensor first. K&N filters are notorious for getting it dirty, or oily causing it to read improperly. That is if you installed the K&N after you had already cleaned it.

[Mechtech]

If you can get access to a real scan tool (not just generic OBDII) GM provides a misfire counter, it includes a misfire history. If it just "feels like" a misfire you could have a marginal fuel supply problem causing a lean condition under heavy load, can be done with generic OBDII reader.. Have someone watch the short term fuel trim when the problem happens. MAF can cause all kinds of problems without setting a code. K&N cotton air filters don't play nice with MAF. I'm not sure why people use them.

[00Beast]

I've never had an issue with K&N's and MAF's, and I've had half a dozen vehicles with them.

[gweg_b]

Between me and family members, we have 8 running vehicles. Seven of them have K&N filters (mix of cones and drop-ins), and in all the years we've been using the filters, we've never had an issue with the MAF sensors. I have friends that have been using them for years as well without problems.

Of course, everything's possible, but in this case I don't think it's the filter.

[Mechtech]

Sorry was not my intention to start a pro/con K&N debate

[Nocrank]

Yeah, me neither just was stating facts. Its easy just do a search of K&N and MAF sensor problems and you will get tons of people complaining and proving that K&N's will in fact destroy a MAF or at least cause improper fueling due to continually dirtying the MAF sensor. What do you think oil on a heated sensor wire will do? You will also in fact see articles and testings of K&N trying to cover there butts, and B.S. so they don't lose sales etc. Or get sued. Don't get me wrong I love K&N filters I have used one on my built 91 Camaro, for 13 years now, but that does not have a MAF sensor.
It can't be just coincedence that so many peoples MAF sensors failed or at least needed a good cleaning shortly after install of the filter. With many of theses on new vehicles.

[gweg_b]

I've heard and read the horror stories as well. What I was saying was, at least personally, I've never seen issues with the MAF wires and K&N filters. Not saying it's not impossible, I've just never had issues. I did have a failing MAF sensor on my LeSabre in 2003, and the mechanic explained why, but I informed him the sensor was failing 6 months before I ever had any kind of K&N in there (didn't start modding it until 2004).

I mentioned earlier that I agree with the OP's idea that his ICM might be going bad. I've seen a few of those fail recently. Getting it scanned can help, but when my ICM was bad, I had no codes, so I took the chance, and that was my problem.


To clear things up, I wasn't trying to start a debate with the K&N filters. As I said, everything's possible. It just seems to me that the problem seems to be electrical, and if coils, wires, and plugs were replaced, and not the ICM, there's a chance it could be that.

[dayton.reed]

Just to let you know, I cleaned the MAF and got the filter at the same time.

I bought a new ICM and some new Delco plugs (mail-in rebates right now, $2/plug back for iridium) this afternoon, and I plan on doing some work tonight after work. I was letting it limp for a while because I didn't feel like dealing with it, but on my way out of my parking lot today, the car felt like it didn't want to deal with life anymore. Constant misfiring now at any amount of gas. I have one aftermarket coil which has some good cracks in it, which I exchanged under lifetime warranty. I'll try replacing that first and see if that fixes the problem, then move onto installing the new ICM if the coil doesn't solve it.

If that doesn't work, I suppose I'll just start replacing stuff, like the crankshaft position sensor, fuel pressure regulator . . . right?

[dayton.reed]

New icm, coil, and plugs didn't solve it. It doesn't misfire at such low throttle anymore, but it still does under 2/3 or more on the gas. What am I missing? Old plugs smelled like gas terribly.

[dayton.reed]

How common is the harmonic balancer failing? I am reaching for any solution, I know, but I may hear a sound at certain RPMs and when starting the car that might be localized over there on the passenger side of the engine compartment that sounds like this http://www.youtube.com/watch?v=FCeMx18P2aM but not at idle and not NEARLY as loud.

Is a squeaky alternator pulley a clue? Would the crankshaft position sensor throw a code if it was failing? Should I even consider the camshaft position sensor? is there anything I'm missing here?

I'm just getting depressed now.

[1oldman]

there is a chance one of the replacement parts might be defective. Test them just to be sure. every once in a while I'll get two or three defective replacement parts in a row. It really make life difficult when you trying to repair something when the replacement parts are defective - BC

[DaMaroon]

Old plugs smelled like gas terribly.

Checked for leaking fuel pressure regulator membrane?

[DaMaroon]

Old plugs smelled like gas terribly.

Checked for leaking fuel pressure regulator membrane?

[vogie01]

I had this same issue for so long as well. I chased it down to first being a bad MAF, then bad coils, then replaced the ICM as it would go away for a while then come back. I too thought that the CPS or harmonic balancer was the issue. Finally, I noticed that I had burned a hole in the plastic on the wheel well that exposed my K&N. I changed out the MAF and it turned out that it had been acting up intermittently. I clean the entire FWI, throttle body, IAC, and replaced the MAF again.

I have yet to have an issue and found that a K&N can get really dirty and cause MAF issues.

Edit: Right before I fixed all of the above stuff, the car was running very rich and causing similar issues in your latest post.

[dayton.reed]

I had this same issue for so long as well. I chased it down to first being a bad MAF, then bad coils, then replaced the ICM as it would go away for a while then come back. I too thought that the CPS or harmonic balancer was the issue. Finally, I noticed that I had burned a hole in the plastic on the wheel well that exposed my K&N. I changed out the MAF and it turned out that it had been acting up intermittently. I clean the entire FWI, throttle body, IAC, and replaced the MAF again.

I have yet to have an issue and found that a K&N can get really dirty and cause MAF issues.

Edit: Right before I fixed all of the above stuff, the car was running very rich and causing similar issues in your latest post.

So, if I'm understanding you correctly, your MAF was acting up so bad, you had to replace it rather than clean it? I cleaned mine at the same time that I got the K&N drop-in, and smoothness was off the charts right after. Shifting was like riding on a cloud. I hadn't realized how bad I must have let it get. So now, I ought to clean it again, perhaps, or just replace it? I've only had the K&N and cleaned MAF since right before Christmas.

How should I clean the IAC? With carb/choke cleaner, maybe? How do you get that honeycomb-looking grill off to clean out the throttle body and not trash it?

Old plugs smelled like gas terribly.

Checked for leaking fuel pressure regulator membrane?

Is that where you take the T off and see if gas is leaking out? I could find none leaking, and I successfully broke one of the old, brittle connections to that T thing. I don't think it is making my problems, as they happened before I broke that, and I found that T disconnected after a 500 mile trip home when I first bought the car. It's electrical-taped at the moment.

[dayton.reed]

I cleaned the MAF last night and gave it a hard turn around the block. I noticed an improvement, for sure, but I still feel it misfiring. It'll dump almost 10 lbs boost in, but when it takes off, it feels like it's stumbling still. I haven't held the gas in to see if the SES light flashes, but I might try that today to make sure the roughness/stumbling is still a misfire and not something else.

I'm also going to see about cleaning the throttle body, the IAC, etc.

Is the MAF supposed to have any kind of gasket? There's a hiss coming from where the intake meets the throttle body, and I can't tell it it's some kind of leak of just air rushing past the honeycomb thing in there.