Intermittent Misfire - video included

[Mr95Gl]

Don't mean to sound like a **** (since i'm asking for help and all), but please read the description before responding.

I've been trying to troubleshoot this issue on my 92 (91K) for several weeks now to no avail. The car will randomly misfire in all conditions. They include:

With or without rain
Cold or warm weather
With the car at operating temperature or on start-up
In all gears

It's the exact same type of miss in all of these conditions with no variation.

If it misfires, up until 2K in 1st it'll run fine. Between 2K-4K it'll buck back and forth very violently at times, and clear up above that. Sometimes, I'll feel it misfire in the upper RPM range but it's only happened a couple of times.

Some nights I'll drive to work (I commute 33 miles each way), and it will run perfectly fine (cold, hot, rain, dry). I'll intentionally hit a bump to see if there's a change in engine operation, but nothing. I'll drive back home from work, and no issues. I can go several days without any issues. Other times, it'll miss on my way to work, but not on my way back home or vice versa. Sometimes it'll miss half way to work, then clear up.

The car is not stock. It has the following:

PRO-M 80MM MAF w/ SHO Shop Can
BBB's
UDP's (3 piece)
Catless Y (cat relocated after Y) w/ 2 1/2 inch exhaust
69MM TB

Here's the maintenance history (currently sitting at 91K):

Timing Belt/Valve Adjustment at 62.5K
Fuel Filter at 73K
Plugs and Wires (Bosch) at 73K
O2 sensors at 77.6K
TPS at 77.7K
Crank and Cam sensor at 78K

I've tried swapping out the MAF for a stock one, removed the bosch wires/plugs and put back in APP3924 plugs with the original wires, swapped out the coil pack for 2 others, and DIS module with a spare. Also did a fuel injection cleaning. All of the grounds look fine.

I'm still getting the EXACT same misfire (when it happens) which leans towards none of those parts being the issue. Only thing left would be the TB, but would that cause an intermittent miss?

Here's a video of what happens when the miss occurs:






Any suggestions?

 

[kikkinasphalt]

cam position sensor? mine had a miss like that when it was bad.

 

[SHO_ROLLER_2]

cam position sensor? mine had a miss like that when it was bad.

Mine too.

 

[Mr95Gl]

Hmmmm, ok. The orginal Cam sensor was replaced at 78K, but I guess this one could be defective. When yours was bad, did the CE ever come on? Mine hasn't (it works lol).

 

[SHO_ROLLER_2]

Hmmmm, ok. The orginal Cam sensor was replaced at 78K, but I guess this one could be defective. When yours was bad, did the CE ever come on? Mine hasn't (it works lol).

Mine gave no warning.

Started to misfire in traffic a few times. Didn't think anything of it. Few weeks later, she died and wouldn't crank for about 45 minutes.


My previous car,a 2005 SRT4, did it too. Little different, it would rev to about 2K rpms and then miss like a *****!

 

[rubydist]

My first thought was a sick tps.

 

[St Louis SHO]

I've seen 2 PCM's cause this exact issue as well...

 

[NotSoSlowSHO]

I see no mention of replacing the DIS... or did I miss it???

 

[Mrhappytuzi]

I see no mention of replacing the DIS... or did I miss it???

I would just take the DIS off and see if the grounding surface is all crapped up.

 

[whiteman_01]

You could do that, and also add a ground from the lower right bolt, right to the neg on the battery. I would try a new cam sensor, as they are decently cheap.

 

[Mr95Gl]

I see no mention of replacing the DIS... or did I miss it???

The DIS was replaced with a spare.

I would just take the DIS off and see if the grounding surface is all crapped up.

Swapped on a crossover tube from a spare intake I had.

You could do that, and also add a ground from the lower right bolt, right to the neg on the battery. I would try a new cam sensor, as they are decently cheap.

Already have a ground wire installed, but it's grounded to the same bolt that the wire coming from the negative battery cable is grounded to.


So far the consensus is a new Cam sensor, so I may have to try that.

 

[jonheese]

I had the same problem (random misfire, acted just like your videos), and it turned out to be the fuel pump. It was quite old (10+ years), so I replaced it and the problem was gone.

If replacing the cam sensor doesn't help, you might try the Paul Nimz method of ziptying a fuel pressure gauge to the windshield wiper (with the other end attached to the Schrader valve, obviously) and watching it while you attempt to reproduce the issue.

Good luck.

 

[moobypets]

i would definatly check fuel pressure cuz my 3.8 was doign soem weird thing until i put a new pump in

 

[SHOclass]

It might be a long shot but, My 95' MTX drove like crap and would have a similar "misfire" feeling when my MAF sensor was dirty.
IMO its worth a shot
MAF sensor cleaner is about 4 bucks, and if it doesnt work now you have a clean MAF

 

[DemonNeno]

Uhm.. Any codes? There are quite a few things (obviously, eh?) that could cause this. Start simple.

 

[shotime1994]

It might be a long shot but, My 95' MTX drove like crap and would have a similar "misfire" feeling when my MAF sensor was dirty.
IMO its worth a shot
MAF sensor cleaner is about 4 bucks, and if it doesnt work now you have a clean MAF

I does it with a known good maf also.

DemonNeno there are no codes.

 

[alvaro.noriega]

My '91 did the same exact thing. I replaced the cam sensor and it didn't change. then I noticed that two of my plug wires were arching. replaced those helped a little but it actually turned out to be the coil pack for the plug wires

 

[tool88]

Easy one if you think it might be the cam sensor just unplug it and drive and see if it happens again if it does it with the cam sensor unpluged then your cam sensor is not the problem.