crazy missfire issue, has two mechanics stumped!

[Beefcake]

Well my car started missfiring real bad about a month ago, changed all three coil packs, wires and plugs. Plugs are gapped right, wires are snug, and coil pack are well...new. Car ran fine for about a day then went back to missing again after I changed all three. Last weekend for some reason the car ran fine all weekend, then it rained and the car was running horribly. Don't know if rain had anything to do w/ it. Throwing two codes for the knock sensor and one code for the crank sensor. One mechanic said if it was the crank sensor, the car would not start and if it was knock sensor the car would still run fine and I wouldnt even notice it. Another mechanic says my crank sensor is not bad, because its still sending a signal I guess, because he tested with a nice mechanics diagnostic tool. I guess its not operating within its specified range? If anyone has any advice or has a similar problem, any help would be greatly appreciated.

[Archer]

Re: crazy missfire issue, has two mechanics stumped!

wow, this one even has me stumped. majority of the time it has to deal with air, fuel, and spark... I dunno man, look like they'll have to hook her up to a machine and run a full diag on it.
Let us know
Archer

[flamingchicken]

Re: crazy missfire issue, has two mechanics stumped!

archer, i think it was you that told me that you had an injector connection that was bad, and fixed it and it worked.

If its a spark knock or an actual mis, the dealer has a scan tool that will say what cyl. its on and how many times it has missed...most "shops" use generic scan tools, and you may need a GM one to get the proper reading.

[Beefcake]

Re: crazy missfire issue, has two mechanics stumped!

We ran a full diagnostic, We drove the car around and he had it on the mode where you can see the missfires on each cylinder and not one single missfire registered. Weird, it may not be a missfire but the thing sure drives likes it missing. Could it not be getting enough fuel? but then why is it throwing knock and crank sensor codes?

[Archer]

Re: crazy missfire issue, has two mechanics stumped!

archer, i think it was you that told me that you had an injector connection that was bad, and fixed it and it worked.

If its a spark knock or an actual mis, the dealer has a scan tool that will say what cyl. its on and how many times it has missed...most "shops" use generic scan tools, and you may need a GM one to get the proper reading.

yup, which is part of the FUEL spark air. lol

but a diag would of picked that up.

Archer

[cam98aro]

Re: crazy missfire issue, has two mechanics stumped!

if the crank sensor was bad your car would not run, and would most likely shut off, the crank sensor is used so the DIS knows when to fire the plug

it is possible that there are bad spots on wherever the CPS gets its signal, and it cuts out for a second, but not enough time for the engine to stall, and it keeps on running..

when does it misfire, only underload? or will it at idle?

you need to get a timing light and test the cylinders to see if its a miss, a misfire here and there will not cause a misfire code right away

how long has this problem been happening? personally, it sounds like you got bad gas, and its predetonating, its trying to force your crank back down when its not ready to causing a knock, i would try and siphon the fuel out, put new fuel in, and change the fuel filter

[Beefcake]

Re: crazy missfire issue, has two mechanics stumped!

It misses at certain cruising RPM's especially around 3k when I shift. So its not the crank sensor? damn thats not a good sign...i feel even more in the dark now. It can't be bad fuel, I usually use 92-93 octane and I drive the car everyday so it cant be old gas or something. Fuel filter was changed probably 2 years ago so that cant be it. Oh I forgot, it misses really bad under load only sometimes, thats how I am beginning to think its not a missfire but a clogged injector, rail, bad fuel pump etc. Like the other day I raced a ford probe and the car ran well all through 1st-3rd, then I go to cruise home and its skipping like crazy. Its gotta be the most frustrating problem I've had with the car, and I've replaced plenty of parts in the cars 118k miles. And as for how long its been happening, It started probably 2 months ago, and every part I replace only seems to make the problem a little better but not fix it and its still throwing the same codes.

[Archer]

Re: crazy missfire issue, has two mechanics stumped!

get your plugs tested..

[nascar24jd]

Re: crazy missfire issue, has two mechanics stumped!

Have you checked the ignition control module?

[Beefcake]

Re: crazy missfire issue, has two mechanics stumped!

I was thinking it could be the ignition control module too, but thats an expensive part I dont want to buy unless I know for a fact that its gonna fix it. I think the cheapest I found one was like $185. I checked plugs also, all look fine.

Also, maybe this helps...whenever I try to start the car in the morning it wont start that first time unless I give it a quick rev to keep it from dying out. This is what is making me believe this is a fuel issue rather than a sensor issue or an ignition problem. After that first crank of the day the car starts fine but still randomly missfires throughout the drive. Like today it drove fine for like 6 miles straight, then once I stopped for the stop sign and started again it skipped all the way home...Like I said before this is the most annoying problem I've had with the car

[RadRacer]

Re: crazy missfire issue, has two mechanics stumped!

Have you changed anything besides what you listed? When it does run bad, does it stop if you put it to the floor?

Check your Engine sensor fuse (under the hood; 15A if I remember right); have you checked your MAF? My car ran similarly when my O2 sim melted and grounded the whole system; kept blowing the engine sensor fuse, but once I pull the sim off the car ran perfect, so you might have a break somewhere doing something similar.

[Beefcake]

Re: crazy missfire issue, has two mechanics stumped!

nope havent checked MAF, figured that would send a code and make the check engine light up. I wish I could figure it out, my car has been going through alot fuses now that I think about it, both under the hood and under the dash.

[RadRacer]

Re: crazy missfire issue, has two mechanics stumped!

MAF won't always throw a code; I'd check into the fuses first, as it sounds like an electrical problem to me.

[Kleenax]

Re: crazy missfire issue, has two mechanics stumped!

I had the same exact problem as you and I replaced plugs,wire,coil packs, ICM, knock sensor, crank sensor, camshaft pos sensor and then i replaced my fuel filter (just because) .. and my problem went away how many miles do you have on parts?

[Beefcake]

Re: crazy missfire issue, has two mechanics stumped!

probably 30k on fuel filter but I use seafoam and injector cleaner pretty regularly, and I've never changed any sensor except for an O2 sensor about a year ago. But then again its not throwing any sensor codes except for the knock sensor and crank sensor. knock sensors on banks 1 and 2. Also, this may be unrelated, but my gas gauge jumps around alot and I thought it was the sending unit but my automotive instructor from school said it was fuel pump on the way out and that I would be replacing it probably within a year. Today I also noticed when I had the car in neutral and tried to hold it at 3k rpm it would sputter and drop to the 2.1-2.2k range and then jump back to 3k, but if I held it at 2k, 4k and even 5k it ran like a top. Today on my way to work, it ran fine after it warmed up for maybe 5 miles and then ran terrible the rest of the day. Hopefully I can get this figured out, I am eventually going to sell the car and i don't want to drop the value of the car $600-$700 because of a part that might cost $20-$30. I might also try fuel filter since thats a pretty cheap part. Well thanks for the help guys, I am gonna check my under the hood fuses and see if that leads me anywhere.