Argh yet again... misfire over 5000rpm
08-27-2014, 09:31 PM
#16
Nordschleife Master
Thread Starter
08-27-2014, 09:45 PM
#17
Rennlist Member
FWIW
My car used to have a weird intermittent problem. It would on occasion just shut off as if you turned off the key. It would always restart and run fine for no determined time. I tried virtually everything. TPS, temp sensors, new s&r sensors, different DME , cap....on and on. Could never nail it down. Just knew it was electrical. I suspected that the harness in front that carries the voltage to the coil is so old and has built resistance in the wire. Anyway when I dynoed my 3.0 it was breaking up above 5k. Installed the MSD and now I haven't had the shut off issue or the misfire above 5k. About 1.5 years now and no problems...knock on wood.
08-27-2014, 11:02 PM
#19
Rennlist Member
08-28-2014, 04:34 AM
#20
Rennlist Member
The high side of the coil goes straight to +12V and comes on when you turn on the ignition switch.
Another thing to consider is that in the DME, the Darlington pair of power transistors that drive your injectors have their collector tied to +12V, so if your voltage is low, you may not get consistent current to your injectors. The injectors on a 951 are ~4.5 ohms, which require a fair amount of current.
Another thing to consider is that in the DME, the Darlington pair of power transistors that drive your injectors have their collector tied to +12V, so if your voltage is low, you may not get consistent current to your injectors. The injectors on a 951 are ~4.5 ohms, which require a fair amount of current.
08-28-2014, 01:14 PM
#21
Nordschleife Master
Thread Starter
Good point, you are indeed correct.
I guess I'll have to look into how the 6A wires into a 951. I figured it would've used the same stock coil wires.
That said - if it IS bad coil wires, I should be able to run fresh wires then and clear it up.
I agree^^
FWIW
My car used to have a weird intermittent problem. It would on occasion just shut off as if you turned off the key. It would always restart and run fine for no determined time. I tried virtually everything. TPS, temp sensors, new s&r sensors, different DME , cap....on and on. Could never nail it down. Just knew it was electrical. I suspected that the harness in front that carries the voltage to the coil is so old and has built resistance in the wire. Anyway when I dynoed my 3.0 it was breaking up above 5k. Installed the MSD and now I haven't had the shut off issue or the misfire above 5k. About 1.5 years now and no problems...knock on wood.
FWIW
My car used to have a weird intermittent problem. It would on occasion just shut off as if you turned off the key. It would always restart and run fine for no determined time. I tried virtually everything. TPS, temp sensors, new s&r sensors, different DME , cap....on and on. Could never nail it down. Just knew it was electrical. I suspected that the harness in front that carries the voltage to the coil is so old and has built resistance in the wire. Anyway when I dynoed my 3.0 it was breaking up above 5k. Installed the MSD and now I haven't had the shut off issue or the misfire above 5k. About 1.5 years now and no problems...knock on wood.
That said - if it IS bad coil wires, I should be able to run fresh wires then and clear it up.
08-28-2014, 01:14 PM
#22
Nordschleife Master
Thread Starter
09-01-2014, 08:27 PM
#24
Nordschleife Master
Thread Starter
Short update: while waiting for a spare M-Tune DME to arrive, I went ahead and ran brand new wires from the DME and fuse panel to the coil.
No change.
Fingers crossed the DME solves it.
EDIT: Thinking about this a little more last night... I think I'm going to go get a basic 12v solenoid, and run a 12v wire (through the solenoid) direct to the coil from the battery, taking the entire fuse box out of the loop. Easy enough to do and that eliminates one piece of the puzzle and should separate any sort of current draw between the headlights and the coil.
No change.
Fingers crossed the DME solves it.
EDIT: Thinking about this a little more last night... I think I'm going to go get a basic 12v solenoid, and run a 12v wire (through the solenoid) direct to the coil from the battery, taking the entire fuse box out of the loop. Easy enough to do and that eliminates one piece of the puzzle and should separate any sort of current draw between the headlights and the coil.
Last edited by User 52121; 09-02-2014 at 11:09 AM.
09-04-2014, 05:39 PM
#26
Rennlist Member
Jim,
I talked to a fellow 'lister that's suffering from low voltage reading at the gauge cluster but ~13.5V at the battery and has similar bucking and artificial rev limit. He is running a Tech GT stand alone but an OEM Bosch alternator. He reports whenever he sees below 13V on the voltage gauge he runs into problems when he's coming on boost and during WOT. Symptoms are a bucking that seems like fuel cut and an occasional rev limit around 5k.
I didn't get a chance to clean my grounds this weekend because it was just too damned hot to be in the garage for any length of time. Hoping to get to it soon and see if that cures the problem. My data logs from the Zeitronix show a consistent MAF signal during my "events" so I'm inclined to think my AFM connector is fine.
I talked to a fellow 'lister that's suffering from low voltage reading at the gauge cluster but ~13.5V at the battery and has similar bucking and artificial rev limit. He is running a Tech GT stand alone but an OEM Bosch alternator. He reports whenever he sees below 13V on the voltage gauge he runs into problems when he's coming on boost and during WOT. Symptoms are a bucking that seems like fuel cut and an occasional rev limit around 5k.
I didn't get a chance to clean my grounds this weekend because it was just too damned hot to be in the garage for any length of time. Hoping to get to it soon and see if that cures the problem. My data logs from the Zeitronix show a consistent MAF signal during my "events" so I'm inclined to think my AFM connector is fine.
09-04-2014, 06:44 PM
#27
Three Wheelin'
Two of the weirdest things I have ever found working on 951s.
-A bad alternator causing high rpm misfires. I disconnected the power wire at the alternator and the misfire went away. It was feeding AC voltage into the system and raising hell.
-A similar scenario to yours, misfiring with the headlights, ended up being a mushroomed pickup bolt on the flywheel. The last guy who did the clutch butchered it. Replacing the flywheel solved the misfire.
I really hate troubleshooting random high rpm misfiring on cars with very limited diagnostic capabilities... it would be so much easier on a newer car where you can actually see the live data...
Oh and another thing, I once found a faulty MBC on a 951 that momentarily allowed the boost to reach 28psi and cause a nasty backfire. It was hard to catch since the gauge was in the center console and would sit at 15 psi revving through the lower gears. But... once it was deep into 3rd gear, the boost crept up. A new MBC solved the issue.
Best of luck
-A bad alternator causing high rpm misfires. I disconnected the power wire at the alternator and the misfire went away. It was feeding AC voltage into the system and raising hell.
-A similar scenario to yours, misfiring with the headlights, ended up being a mushroomed pickup bolt on the flywheel. The last guy who did the clutch butchered it. Replacing the flywheel solved the misfire.
I really hate troubleshooting random high rpm misfiring on cars with very limited diagnostic capabilities... it would be so much easier on a newer car where you can actually see the live data...
Oh and another thing, I once found a faulty MBC on a 951 that momentarily allowed the boost to reach 28psi and cause a nasty backfire. It was hard to catch since the gauge was in the center console and would sit at 15 psi revving through the lower gears. But... once it was deep into 3rd gear, the boost crept up. A new MBC solved the issue.
Best of luck
09-07-2014, 04:48 AM
#28
Rennlist Member
Hi.
I am having almost the same issues on my -89 Turbo Cup car. Fresh rebuilt engine and vitesse stage 3r fitted. We have gone through most of the car but still have to fully check alternator and DME/KLR function.
My car drives nice when on low or part throttle but with load it stumbles around 4500, 5500 and it will not rev past 6000 were it bucks and misfires.
My volt guage at the cluster is showing about 12,8-13 but I have 13,2 at the battery and 13,8 at the alternator.
I will try to disconnect the power to the alternator and see what happens.
I will follow your progress with great interest and I will report back if I have any luck.
Regards
Peder Fallbom, Sweden
I am having almost the same issues on my -89 Turbo Cup car. Fresh rebuilt engine and vitesse stage 3r fitted. We have gone through most of the car but still have to fully check alternator and DME/KLR function.
My car drives nice when on low or part throttle but with load it stumbles around 4500, 5500 and it will not rev past 6000 were it bucks and misfires.
My volt guage at the cluster is showing about 12,8-13 but I have 13,2 at the battery and 13,8 at the alternator.
I will try to disconnect the power to the alternator and see what happens.
I will follow your progress with great interest and I will report back if I have any luck.
Regards
Peder Fallbom, Sweden
09-07-2014, 11:02 AM
#30
Nordschleife Master
Thread Starter
Thanks guys for the responses so far.
Lee - alternator? Ugh! Man I hope that's not it - this alternator probably doesn't have 10k on it (Nissan Quest alternator). As for the mushroomed ref sensor tab - hmmm. I've got a SPEC flywheel, the ref sensor pickup is a little threaded stud that hasn't been touched in years (red thread locker holding it in). Still, it's something in the back of my mind (something with the ref sensor signal) but based on everything I've read, they're either gapped properly, or not gapped properly (meaning - it runs, or it doesn't.) The sensors themselves were done at the same time I did the alternator. Still, I'll probably pull and inspect them.
I ran new coil wires - in multiple configurations, and have had 0 improvement (down to wiring the + coil straight to the battery so it's "hot" all the time). So I'm pulling all that stuff back out, will reconnect the stock stuff (no need to have extra wiring in there if I'm not using it).
Car developed an odd, new problem yesterday while road-testing a coil wire fix - car stalls while cruising. 70mph cruise... dead. 4-5 seconds later, comes back to life. Tach drops to 0. DME still sees RPM (thanks Rogue Logger!) so I'm not sure what's going on there. Figuring I must've bumped/nudged something when installing my temp coil wires, hopefully after I put it back to stock stuff the random stalling will at least go away.
Talked to a friend on the phone for a bit... he suggested it might be the KLR. Going to steal one out of another friend's car later tonight and see how that works.
If that doesn't fix it then my next step will be to rip out the engine wiring harness and throw my old crusty one back in.
Lee - alternator? Ugh! Man I hope that's not it - this alternator probably doesn't have 10k on it (Nissan Quest alternator). As for the mushroomed ref sensor tab - hmmm. I've got a SPEC flywheel, the ref sensor pickup is a little threaded stud that hasn't been touched in years (red thread locker holding it in). Still, it's something in the back of my mind (something with the ref sensor signal) but based on everything I've read, they're either gapped properly, or not gapped properly (meaning - it runs, or it doesn't.) The sensors themselves were done at the same time I did the alternator. Still, I'll probably pull and inspect them.
I ran new coil wires - in multiple configurations, and have had 0 improvement (down to wiring the + coil straight to the battery so it's "hot" all the time). So I'm pulling all that stuff back out, will reconnect the stock stuff (no need to have extra wiring in there if I'm not using it).
Car developed an odd, new problem yesterday while road-testing a coil wire fix - car stalls while cruising. 70mph cruise... dead. 4-5 seconds later, comes back to life. Tach drops to 0. DME still sees RPM (thanks Rogue Logger!) so I'm not sure what's going on there. Figuring I must've bumped/nudged something when installing my temp coil wires, hopefully after I put it back to stock stuff the random stalling will at least go away.
Talked to a friend on the phone for a bit... he suggested it might be the KLR. Going to steal one out of another friend's car later tonight and see how that works.
If that doesn't fix it then my next step will be to rip out the engine wiring harness and throw my old crusty one back in.