Megasquirt Random Engine Stuttering
06-22-08, 10:11 PM
#1
Random Engine Stuttering
When driving, occasionally the engine will stutter around a certain RPM and throttle position. It will act like its hitting a soft rev limiter or partial spark cut for a second or so. Usually it disappears if you return to the point a little later, and most of the time you can "push through it" and it will disappear. A couple times when this stuttering is happening, the redline buzzer will go off or the tach will momentarily jump around.
It's happened at approx 4k rpm and 100 kPa, 3.2k rpm and 80ish kPa, 3k rpm and 120ish kPa, 2k rpm and 70-80ish kPa, and a few other points around there. Its usually during periods of light to moderate acceleration.
I havent noticed abnormal noise on the CAS signals, but I havent been able to catch it when I'm datalogging or even have the laptop plugged in. It had been happening before, but only when the alternator belts were slipping a lot and squealing (headlights on, sometimes when wet). I've since replaced the alternator belts, but it still does it at times. Nothing abnormal shows up on the wideband gauge. At the same time as i replaced the alt belts, I also played around with the timing maps (generally just adding a little bit of advance, but less than in BDC's maps) and had enabled launch control (with the clutch switch thru an additional switch, so it would only see ground when the clutch is in and the other switch is pressed, so it shouldnt be active any of the times that this has happened). I went through the car and cleaned up the ECU ground, the ground under the trailing coil, and the engine harness ground to the drivers strut tower. I havent done the engine harness to engine ground yet, but that was off recently when I pulled the transmission and I think it was pretty clean.
Any other ideas as to what to check? I'll try to bring the computer into the car each time I go somewhere in hopes of catching it in a log.
It's happened at approx 4k rpm and 100 kPa, 3.2k rpm and 80ish kPa, 3k rpm and 120ish kPa, 2k rpm and 70-80ish kPa, and a few other points around there. Its usually during periods of light to moderate acceleration.
I havent noticed abnormal noise on the CAS signals, but I havent been able to catch it when I'm datalogging or even have the laptop plugged in. It had been happening before, but only when the alternator belts were slipping a lot and squealing (headlights on, sometimes when wet). I've since replaced the alternator belts, but it still does it at times. Nothing abnormal shows up on the wideband gauge. At the same time as i replaced the alt belts, I also played around with the timing maps (generally just adding a little bit of advance, but less than in BDC's maps) and had enabled launch control (with the clutch switch thru an additional switch, so it would only see ground when the clutch is in and the other switch is pressed, so it shouldnt be active any of the times that this has happened). I went through the car and cleaned up the ECU ground, the ground under the trailing coil, and the engine harness ground to the drivers strut tower. I havent done the engine harness to engine ground yet, but that was off recently when I pulled the transmission and I think it was pretty clean.
Any other ideas as to what to check? I'll try to bring the computer into the car each time I go somewhere in hopes of catching it in a log.
06-23-08, 08:57 AM
#2
Engine, Not Motor
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If the tach is jumping, then I'm willing to bet it's interference. Something bad is happening to cause it. A ground has fallen loose, or perhaps a coil wire is arcing over. What is the condition of the connector to the CAS? Any pins loose?
06-24-08, 06:27 PM
#5
It was doing it really badly earlier today, it would just start at about 2500 RPM with anything more than very gentle throttle use. Then I got more gas (I still had about 5 gallons in the tank) and it seemed to clear right up. I filled it at the same place, 93 octane each time, who knows.
I have since changed the spark plugs (the ones in there were getting to be a little old) and the fuel filter, and cleaned up the last battery ground. Hopefully that'll keep the stutter away.
I have since changed the spark plugs (the ones in there were getting to be a little old) and the fuel filter, and cleaned up the last battery ground. Hopefully that'll keep the stutter away.
06-26-08, 07:37 AM
#7
It was definitely misfiring, since I know the same amount of fuel was going in as other times (same PW), but the AFR would go completely lean. It also produced some "cough-of-God" backfires.
The gas tank had seemed to draw a pretty big vacuum when i opened the cap to fill up. It has done this a little for as long as I remember (but without the misfires), but maybe it's gotten worse and I need a new gas cap. Or it could just have been bad gas (although it was at a local BP, and I filled up there again which seemed to fix the problem, so who knows)
The gas tank had seemed to draw a pretty big vacuum when i opened the cap to fill up. It has done this a little for as long as I remember (but without the misfires), but maybe it's gotten worse and I need a new gas cap. Or it could just have been bad gas (although it was at a local BP, and I filled up there again which seemed to fix the problem, so who knows)
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06-26-08, 05:18 PM
#9
Man, not to scare you - but I've blown 5 engines running a piece of **** E6X that does the same thing.
Extra sheilding on the harness, no brakes or bad connections....
Sort this out soon if you haven't chipped a seal already (exhaust note....whats it pulling for vaccum?)
Extra sheilding on the harness, no brakes or bad connections....
Sort this out soon if you haven't chipped a seal already (exhaust note....whats it pulling for vaccum?)
06-26-08, 06:56 PM
#10
The vacuum its pulling is fine, same as it always was. i think I found the problem though... the gasket between the turbo and downpipe has fallen apart and mostly disappeared. Thats at least the new exhaust note (and why all of a sudden today the wideband was reading significantly leaner than usual). I think I managed to blow out all the pieces that could have fallen into the exhaust stream and been restricting the exhaust, its just a bit louder than normal until I make a new gasket, which will prob happen on saturday.
Maybe that was the reason why it was stuttering? Just random natural frequencies through the turbo from the hanging gasket that were choking the engine at different flow rates/RPMs? Maybe its wishful thinking, but it didnt seem to do it anymore after it got louder.
Maybe that was the reason why it was stuttering? Just random natural frequencies through the turbo from the hanging gasket that were choking the engine at different flow rates/RPMs? Maybe its wishful thinking, but it didnt seem to do it anymore after it got louder.
06-27-08, 09:40 AM
#11
Engine, Not Motor
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The gas tank had seemed to draw a pretty big vacuum when i opened the cap to fill up. It has done this a little for as long as I remember (but without the misfires), but maybe it's gotten worse and I need a new gas cap. Or it could just have been bad gas (although it was at a local BP, and I filled up there again which seemed to fix the problem, so who knows)
06-27-08, 11:28 AM
#12
Yea, thats what I figured it was doing... How should I check the gas cap? Is that something they should be able to do at autozone/murrays/napa etc?
I have the tank vent running up to the charcoal canister... i never checked if its actually clear back to the tank though.
I have the tank vent running up to the charcoal canister... i never checked if its actually clear back to the tank though.
07-01-08, 08:27 PM
#13
Well, it started doing it again... but at a much more dangerous time for the engine this time (6 psi boost, higher RPMs). I got a datalog of it this time, and it's happening at 705 seconds and 833 seconds, where the mixture suddenly becomes lean (to like 17 or 18:1) while in boost. What looks like noise right before the occurance at 833 seconds is just the launch control. This is really starting to get annoying, since it doesnt seem like theres anything out of the ordinary (at least thats getting logged) that would be causing this. Plus, it happened in 3rd gear both times, but didnt happen in the two gears before each, even tho the same conditions were present.
07-03-08, 05:07 PM
#17
If your tach still drops when the event occurs, its not a lean misfire. Presuming your tach is still getting its signal from the trailing coil as per stock - then its a trigger issue.
I battled this issue through different alternators (read the haltech section for the thread by wankel7) through many engines, through more re-wiring then I can count, through different CAS's, through countless amounts of shielding/different wire routing and could never make it go away *fully*. At one point, I drove the car for nearly 6 weeks with no issues - then it came back.
Best of luck man.......
I battled this issue through different alternators (read the haltech section for the thread by wankel7) through many engines, through more re-wiring then I can count, through different CAS's, through countless amounts of shielding/different wire routing and could never make it go away *fully*. At one point, I drove the car for nearly 6 weeks with no issues - then it came back.
Best of luck man.......
07-03-08, 06:51 PM
#18
No, the tach hasnt done any odd stuff since I replaced the plugs and re-ran some of the alternator wires. Next weekend I'm going to rewire the fuel pump since it seems like an intermittant low fuel pressure issue, as well as ground the crap out of everything in sight, and hopefully that'll do it
07-03-08, 09:24 PM
#19
Rotary Enthusiast
Sure looks like it's running out of fuel. Have you considered adding a fuel pressure sensor in the system? Datalogging fuel pressure is pretty straightforward, and gives great comfort that the pump and regulator are working as intended.
On another note, why is the battery voltage log so noisy?
On another note, why is the battery voltage log so noisy?
07-03-08, 10:18 PM
#20
I dont know why the battery voltage log is noisy. I am using an FD alternator, so it should be able to provide enough current. I dont know its history though (it was bolted to the engine when i got it), but it seems to work fine.
The alternator did recently do something odd; all the idiot lights came on randomly while driving, then shut off again after a couple seconds, which could only be the alternator signal wire. Whether this was due to a loose connection or the alt going bad, i'm not sure. It seems to always put out enough voltage though, so I dont know.
The alternator did recently do something odd; all the idiot lights came on randomly while driving, then shut off again after a couple seconds, which could only be the alternator signal wire. Whether this was due to a loose connection or the alt going bad, i'm not sure. It seems to always put out enough voltage though, so I dont know.
07-07-08, 08:29 AM
#21
Well, the fuel pump and wiring appeared to be in perfect condition. No voltage difference between battery posts and across the fuel pump, and minimal (unreadable on the analog multimeter I had) resistance on the ground (back to battery) and power (from the circuit opening relay) wires to the pump. I also attempted to clean out the sock on the end of the fuel pump (its a walbro 255 lph pump, installed new about 2 years ago), but it was pretty clean and nothing was coming out. I replaced the fuel filter 2 weeks ago.
Is there a way of testing the fuel filler cap?
Is there a way of testing the fuel filler cap?
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