Uneven running while decelerating
Discussion
Hello, I’ve recently had my TVR Griffith converted to use the canems ecu. The car runs really well during acceleration and general cruising but suffers from some uneven running when letting the car slow down with the gear. This effect makes driving in slow traffic and slow B roads annoying. The effect is like applying the breaks on and off very lightly during deceleration. It’s very subtle and probably wouldn’t be noticed by most!
I’ve checked the plug leads and spark plugs and all appears well. I’m thinking it’s not the plug leads as this would be noticeable at cruising and acceleration. I was thinking transmission slack but surely this would show up at cruising speeds and the transmission should be under constant load when decelerating.
Just wondering if anyone else has experienced this with the standard car or with canems?
The car is so close to perfect that it hurts! I’d return it to the installer again but they will charge for a rolling road diagnostic test and its bloody miles away! Lesson learnt there.
Any help or advice really appreciated.
I’ve checked the plug leads and spark plugs and all appears well. I’m thinking it’s not the plug leads as this would be noticeable at cruising and acceleration. I was thinking transmission slack but surely this would show up at cruising speeds and the transmission should be under constant load when decelerating.
Just wondering if anyone else has experienced this with the standard car or with canems?
The car is so close to perfect that it hurts! I’d return it to the installer again but they will charge for a rolling road diagnostic test and its bloody miles away! Lesson learnt there.
Any help or advice really appreciated.
Canems has been installed about 6 months. It's all under manufacturers warranty. I'm really hoping it's just a vacuum leak. Stepper motor has been removed for the canems conversion. Stepper motor Hole has been plugged. Some mechanics use smoke to detect the vacuum leak!
Edited by lancelin on Monday 10th July 22:05
Thanks Alun. So was it powersperformance that did your canems conversion? They are closer to home for me.
Out of interest is your car smooth even when cold? The uneven running is considerably worse when cold. Have you had any erratic cooling fan switching? sorry for all the questions.
Out of interest is your car smooth even when cold? The uneven running is considerably worse when cold. Have you had any erratic cooling fan switching? sorry for all the questions.
Thanks everyone for the suggestions. Thats my weekend sorted! I'll report back with any findings. I'm a big fan of closing out problems and reporting back with the fix. I have no clue about engine mapping so might leave that to the experts. This car has been one hell of a journey for me.The car has so much sentimental value I cant let it go! I just want a smooth ride.
Thanks for all the information. I've completed all the basic checks outlined in the post. I still have uneven running on the overrun! The strange thing is it gets a bit worse when the cab heater and lights are on! I'm starting to think its electrical interference. I also have New ceramic plug leads which DONT use the plug extenders. I have a new alternator and battery and the earth connections measure ok. I'm at the point of returning it. I don't want to mention who did the work. I'm tempted to try the suggested canems ecu map changes but don't want to invalidate the warranty.
Using an oscilloscope, I have observed switching noise on the ecu 12V supply. Perhaps this is interfering with the canems Operation. Interestingly, switching the cab heater on near the cooling fan switching point influences when it switches. All this makes me think the ecu is not immune to switching transients. If the warranty wasn't an issue I would put a 12v noise filter on the 12v supply to the ecu. This filter is basically a low noise 12V linear regulator and a bunch of inductors and capacitors to filter out nasty electrical transients upsetting the ecu. I could use an otter switch to eliminate the fan switching problem but the ecu should be capable of doing this and the problem has inadvertently highlighted the fact that the ecu is not immune to switching transients. This is a fact and it's happened eversince the car was converted. they didn't do enough testing.
Using an oscilloscope, I have observed switching noise on the ecu 12V supply. Perhaps this is interfering with the canems Operation. Interestingly, switching the cab heater on near the cooling fan switching point influences when it switches. All this makes me think the ecu is not immune to switching transients. If the warranty wasn't an issue I would put a 12v noise filter on the 12v supply to the ecu. This filter is basically a low noise 12V linear regulator and a bunch of inductors and capacitors to filter out nasty electrical transients upsetting the ecu. I could use an otter switch to eliminate the fan switching problem but the ecu should be capable of doing this and the problem has inadvertently highlighted the fact that the ecu is not immune to switching transients. This is a fact and it's happened eversince the car was converted. they didn't do enough testing.
Interesting comment on spark plugs, I'll check. I'm hoping they check the system free of charge. The car may have left their workshop perfect but it shouldn't be playing up within a few weeks of being delivered. I'll stand corrected if it's not a problem with the canems system. The erratic fan switching is definitely a canems issue. The guys that did the work are very knowledgable.
I'd love to drive a smooth TVR. Perhaps they don't exist. :-).
I'd love to drive a smooth TVR. Perhaps they don't exist. :-).
Interesting comment on spark plugs, I'll check. I'm hoping they check the system free of charge. The car may have left their workshop perfect but it shouldn't be playing up within a few weeks of being delivered. I'll stand corrected if it's not a problem with the canems system. The erratic fan switching is definitely a canems issue. The guys that did the work are very knowledgable.
I'd love to drive a smooth TVR. Perhaps they don't exist. :-).
I'd love to drive a smooth TVR. Perhaps they don't exist. :-).
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