Car misses. Getting frustrated. PL file inside.

[NVRL8]

I have an intermittent problem that only occurs at highway speed. The car will cruise along fine and then randomly "missfire". The rpms sink, car goes lean, it will buck and surge, and occassionally backfire through the exhaust. The car idles fine, accelerates under boost fine, and slow cruises fine. Here is what I have eliminated and why:

Coil pack/module (tested good with caspers tester and at auto store)
Plugs/wires (replaced with new)
ECM (replaced with known good)
Chip (replaced with known good)
Grounds (checked them)
Fuel pump (replaced with new)
Fuel filter (replaced with new)
MAF (eliminated with speed density)
NB o2 (eliminated with speed density)
WB o2 (running in open loop)
TPS (no dead spots on PL)

I think that leaves cam or crank sensor, but I'm not sure how to tell. Since it's intermittent I can't use the no start tree.

The PL file is a highway cruise. Things get crazy starting on frame 6990. Any help would be welcomed!

 

[BlackBandit]

if it was cam or crank sensor your car wouldn't run. If it's miss firing do to a lack of spark you should see rich spike on your wideband from the unburned fuel in the exhaust. (I can't look now because i'm out and about and using my phone to type this) When you say checked grounds do you mean took them apart and cleaned them? If your not seeing rich spikes in the exhaust you might consider a sticky/parially plugged injector. How bad and how consistent is the miss?

 

[TurboBuRick]

It could very well be crank or cam sensor.

Check to make sure none of the blades are hitting the crank sensor. Make sure balancer bolt is tight as you can get it with a jack handle on 1/2 bar.

What brand sensors are you running? Stock?

IMO nothing works as good as AC/Delco sensors.

HTH

 

[mikestertwo]

Looks like a bad ignition module or wiring related to the ignition module. Lean spiking on the O2's is plug missfire. Your timing is also spiking. Try a known good ignition module. Just because it tests good on a tester it still could be bad. May be heat related. Check all your connectors for corrosion or a spread female pin connector. Just for the heck of it reseat the connector on the computer.

 

[NVRL8]

It goes from lean immediately to rich and then bounces back and forth between lean and rich. If its misfiring from lack of spark couldn't I also see a lean spike from unburned o2? When I checked the grounds I looked for corrosion and gunk and tightened them. I did not physically clean them. I will hit them with a wire brush if you think that may help.

The miss can be a barely noticable hesitation (sometimes only evident on the datalog) to violently bucking the car and backfiring with 1500 rpm swings. The log I posted was a bad one. I have others. Also, fuel pressure remains constant during the event.

 

[NVRL8]

It could very well be crank or cam sensor.

Check to make sure none of the blades are hitting the crank sensor. Make sure balancer bolt is tight as you can get it with a jack handle on 1/2 bar.

What brand sensors are you running? Stock?

IMO nothing works as good as AC/Delco sensors.

HTH

I will check the blades and tighten balancer. Sensors are original.

Looks like a bad ignition module or wiring related to the ignition module. Lean spiking on the O2's is plug missfire. Your timing is also spiking. Try a known good ignition module. Just because it tests good on a tester it still could be bad. May be heat related. Check all your connectors for corrosion or a spread female pin connector. Just for the heck of it reseat the connector on the computer.

Will do and post up.

 

[TurboBuRick]

Check the wheel inside the cam sensor make sure it's tight as well.

You can try throwing in batch fire see if anything changes.

Original sensors are 23 years old now. I would not put it past one of them to be on the fritz.

I would get some new AC/Delco units while the gettins good.

 

[BlackBandit]

if it's a crank sensor you'll know soon enough. They don't "go on the fritz" for long before they stop working. A cam sensor ring changing position is possible and you can throw it into batch to find out if that's it. FWIW a missfire from spark should cause a rich condition which the computer will correct for. Check your plugs and see if they look lean.

Edit: While I stand by this statement after looking at the power logger logs it does look like there may be a problem with the crank sensor or the circuit. Like maybe you're loosing the crank pulses because I doubt it's going from 1500 rpm to 500 rpm and back to 1500 in 2 tenths of a second. I could see that sending you're timing and load variables all over. I still don't see how it would only happen during highway cruise though.

 

[J-B Racing]

Cam Sensor related problem.

 

[NVRL8]

Thanks for all the input. I will start working on all the above tomorrow, hopefully. I have put the car into batch fire, and it ran smooth. I was not sure if this was coincidence just because the problem is intermittent.

Here is a PL file of the batch fire test. At one point it goes very lean when I let off the gas. I'm not sure how to read this data. I noticed no driveability issues.

Also, at no time does it throw a code (except when I unplugged the cam sensor).

 

[Chuck Leeper]

End play on the crank is??

 

[NVRL8]

You guys are good. I started going through the list of checks you guys gave me. The balancer bolt was loose. I could unscrew it with fingers only. The balancer has never been off the car, so kinda weird. I'm betting that was the problem. I will let you know how the test drive goes.

 

[NVRL8]

The nightmare is over!

I drove the car to the ends of the earth today. It was smooth as silk. It's always nice when the fix is free. Thanks to everyone for all the help!

 

[TurboBuRick]

So many times this is the case with these cars but everyone likes jump and blame the coil pack and module. Not to say they are perfect or anything but for the most part they either work or they don't. It's the mechanisms that trigger that are usually the culprits.

Hopefully some of the others with this issue reads this thread.

O, and your welcome. :biggrin:

 

[Chuck Leeper]

Did you take it off and check for damage?
If not, B4 I drove it again, I'd pull it and check for cracks, bad threads.
Something caused it to come loose.

 

[Razor]

Balancers are known for cracking/splitting in the key way area.

If nobody has ever touched the car there.. it would be something to make sure its not an issue.

 

[NVRL8]

Did you take it off and check for damage?
If not, B4 I drove it again, I'd pull it and check for cracks, bad threads.
Something caused it to come loose.

Balancers are known for cracking/splitting in the key way area.

If nobody has ever touched the car there.. it would be something to make sure its not an issue.

Good points. I will definitely give it further attention.