Skip to main content
Topic: Troubleshooting persistent misfire (Read 9385 times) previous topic - next topic

Re: Troubleshooting persistent misfire

Reply #45
Won't get to datalogging today, but I did get the QH installed again. Injured 4th finger out of 5 on my right hand with more upholstery work...

J3 all cleaned up and installed with dielectric grease.

1988 Thunderbird Sport

Re: Troubleshooting persistent misfire

Reply #46
Here is a 15 minute cold-to-warm datalog.

Binary Editor Log
1988 Thunderbird Sport

Re: Troubleshooting persistent misfire

Reply #47
The first thing that really pops out at me is the amount of electrical noise that's being picked up, may just be your cable but might be worth looking into. You could scope the tps signal and see if its just as dirty. 90% of the time when I have electrical noise causing issues its due to aftermarket equipment or an alternator. The first thumbnail is from your datalog the second is one from my car a few weeks ago. I'll keep looking but that's the very first thing I see.



Re: Troubleshooting persistent misfire

Reply #48
Wow, that version of BE looks so different than my ancient BE2010!

And useful no doubt.

The only aftermarket electronics that I can think of are LEDs in various locations with their own driver boards (all powered off for the datalog), hid ballasts for my headlights (off), Mark VIII electric fan and DCControl PWM controller (not sure it ever turned on for this datalog), my old Viper alarm, Baumann 4r70w computer and innovate wideband, and the Quarterhorse Alternator was just replaced and it didn't change how the car ran, but obviously that's another potential source. Battery was replaced less than a year ago.

No car stereo/audio in there right now.

Edit:
Look at the scale differences. I know my tps was jittering mostly between 0.98-0.99V at CT. The scale you have of mine is 0.8-1.7V. Your scale is 0-5.3V, so the graph will hide noise, being 5 times wider.

Red herring?
1988 Thunderbird Sport

Re: Troubleshooting persistent misfire

Reply #49
Got my new BE version working, Not sure yet on how to mess with the scaling on this newer software, but I got this close. With A 0~5 scale, my TPS graph also looks clean.



Not sure this is any problem area to look into.
1988 Thunderbird Sport

Re: Troubleshooting persistent misfire

Reply #50
Can I see how your spark timing looks at idle? I would think the computer may mess with fuel and spark timing to aim for closed loop, but perhaps mine is swinging more than it should on the timing?

 I also would think the computer wouldn't know that SPOUT disconnect is happening, and continue to try to adjust spark and fuel, making the engine run rougher - pulling SPOUT may not be enough of a test to smooth out the idling motor.

Locking timing via tune would be smarter, but may only work okay in open loop.




Valleys and peaks of 16-25 degrees.

1988 Thunderbird Sport

Re: Troubleshooting persistent misfire

Reply #51
Oh look, a thread from me 10 years and 15 days ago trying to solve this issue: https://www.eectuning.org/forums/viewtopic.php?t=15381

Back then:
"The basics are a 306 with gt40 intake, gt40p heads, ho cam, 2.5" exhaust, still stock 60mm TB and 55mm mass air sensor with panel air filter, 19lb injectors, A9P ecu, distributor at 10 degrees."

I always google issues and stumble across my own threads from years long past  :frown:
1988 Thunderbird Sport

Re: Troubleshooting persistent misfire

Reply #52
You're right, I didn't even notice the scale difference I've compared the same PIDS on a lot of datalogs and its never done that to me thats weird. After work I'll find one with a good spark log and mess with the scaling of mine to see how dirty it comes out just out of curiosity.

Re: Troubleshooting persistent misfire

Reply #53
Ok so long story short I don't currently have any datalogs of idle with spark in it somehow. I have a lot of driving but not enough at idle to give any definitive result, although what I see in your log looks strange. As of right now my car is down, didn't notice my oil line to the turbo slid over against my manifold ended up burning a hole in it, talk about a mess. I just got the new line today should have it running this weekend and I'll get some logs of idle with spark. I did change the scaling of my TPS log and I don't see near as much noise also strange.  It could just be your USB cable and we are chasing ghosts. Do you happen to have any ferrite beads to put on it? I know mine came with them but I never had to put them on.

 

Re: Troubleshooting persistent misfire

Reply #54
My USB cable is the supplied replacement with ferrite, which Moates sent after the initial release cables performed poorly.

Don't think that's it.

cgrey8 over at eectuning is thinking I should take a look at the actual timing events of the cam. Well alluding to it. I still think a stock cam, crank, and timing set should be a drop-in-affair without a degree wheel, but retarded timing would help explain my idle/low load issue.
1988 Thunderbird Sport

Re: Troubleshooting persistent misfire

Reply #55
Well if its not the cable its either a strange issue or just my imagination but I have yet to see that kind of electrical interference out of one of these but it may be normal. I've had GMs at work that had so much noise you would think they were possessed, wipers going at random times, flashers randomly going off, fun to diagnose but like I said usually when I removed the random aftermarket stuff it would clean up the CAN signal and everything would go back to normal.


Is he referring to your timing table?  How would you check actual timing events of the cam?


Re: Troubleshooting persistent misfire

Reply #56
Sitting here thinking about it I remember a few years back I had a somewhat similar issue could not for the life of me get my idle to be steady but also on accel my tach needle would randomly jump all over, ended up playing the swap parts game until my cap finally fixed it, I keep a spare distributor with cap and rotor in my trunk now I've gone though 3-4 distributors and countless tfi modules the msd pro billet I have now has lasted the longest surprisingly enough.

Re: Troubleshooting persistent misfire

Reply #57
Yeah, the EDIS-8 conversion would allow me to ditch the distributor and TFI altogether.

Still trying to get a stock crank pulley for the project, for less than $50.
1988 Thunderbird Sport

Re: Troubleshooting persistent misfire

Reply #58
Someone today suggested that if I'm pulling the intake off to degree the cam, I should temporarily convert to carb to see if the issue persists. Seems like a reasonable plan, if the parts can be found cheaply enough.

Anyone know of the cheapest options to try such a thing? Would need the intake and carb obviously, and could just use a pump to pump from a gas can. igniton box. Sounds like I should have access to everything to test this, except the 4 barrel intake.

Really curious if the idle would smooth out by ditching all of the electronics, and this could potentially be a huge diagnostic test.
1988 Thunderbird Sport

Re: Troubleshooting persistent misfire

Reply #59
You have a stock cam in it right? Personally never had an issue but I also know all cams are different from one another. Is it possible yours is different enough to cause an issue, maybe but seems unlikely. Youre right though putting a degree wheel on it is the only way to know for sure but seems like a long shot to me. I personally would start with different plugs cap and rotor the maintenance stuff that has to be done eventually anyway. Cant say I've ever had a set of plugs last me more than a year even when I was N/A, now days I go through a set of ngk 5673-7 in about 3 months at most.  I would also try and set base idle by unplugging the battery and clearing KAM unplugging the IAC reconnect battery starting it and adjusting the throttle plate until it idles where I want then shut it off and plug the IAC back in start it and let it run for a while sometimes Ive had to do it a few times after replacing my throttle body to get idle back to normal. You said it acts up at 2000 rpm right? Like its misfiring?