Misfire and TPS sensor question
Discussion
Hi all, having some trouble with my 97 4.5 AJP Cerb with original MBE ecu.
Ive had the car 3 years, but known it 15 before. Its ran well for my 3 years, slightly rich, but well. When plugged in to the diagnostic software on the laptop, it would however always show the map on the lhs bank higher the the right with about 5% in it.
Now on 100k miles, sent it into a specialist for 12k including clearance check - did not need adjustment
When i got it back it was idling a little high, with the specialist saying it was a bit tough to set. A little lurchy lower in the revs, but when pressed felt WAY quicker -good fun. Unfortunately not long after i got it back had master cylinder failure resulting in lots of fluid drawn into the engine and smoke. Now fixed and smoke cleared by its self once burnt off, however this seems to have exaggerated the above running trouble massively.
So the issue is:
- High idle even with the idle stop completely wound out the way. (about 1250rpm), but about 25% of the time will idle more normally but cant seem to influence when it settles high vs normal.
- When idling it will miss a beat a make a bang (backfire) on the rhs drivers side exhaust (worth noting each exhaust servs each bank only - straight). Also does this misfire under partial throttle.
- Really lumpy, missing, lurchy running under part throttle. Under full load - perfect, fast, amazing, no misses.
What ive done:
- Cant get my software to connect, it finds the correct coms port, but doesn't connect. Com port it looks at changes from 1 to 3 with the usb port on the laptop. (windows 11 - Bluetooth off. USB to 9 pin cable)
- But, to try and get some headway, with it running ive doused the throttle body area in degreaser, no change to revs = no air leaks in.
- I then unplugged the throttle position sensor from the drivers side bank - cable reads "evens", which i believe to be correct - this results in no change at all to the running. I do the same to the passenger side, misfires erratically then cuts out.
- So i swapped the plugs over to the other bank. Still the misfire and backfire is on the driver side bank. I unplugged the drivers bank again whilst running, engine misfired then cut out. plug in and restart, tried the passenger bank and no change and still running.
So the misfire remains on the driver bank even with swapping the TPS leads over BUT the none effect from unplugging moves with the lead rather than staying with the sensor. To my mind this means the cable for the drivers bank TPS is faulty but still not sure as to why the misfire remains on the drivers side.
My questions:
- Do people agree with my conclusion of faulty TPS lead on the Drivers bank.
- Any suggestions RE the connection to computer - i have ordered a new lead to rule that out, will try it this week when it arrives.
- Any other thoughts, suggests etc.
-Any ideas as to why the misfire remains on the same bank (my current theory being i have 2 separate issues, one with the TPS cable, and 1 with general setup - need to connect to the computer to find out)
(Worth mentioning, happy my specialist and the work he does, nothing negative there. he is very good, but suggested if trouble persists after a good drive trying joolz - he is more equipped and experienced with this sort of issue - knows joolz would get to the root much faster. If i have no joy or it gets more involved than bolt on parts and setup i will book in with joolz but would like to exhaust my abilities first, also with peaks to the beach just a week away... i wont get in that soon)
Ive had the car 3 years, but known it 15 before. Its ran well for my 3 years, slightly rich, but well. When plugged in to the diagnostic software on the laptop, it would however always show the map on the lhs bank higher the the right with about 5% in it.
Now on 100k miles, sent it into a specialist for 12k including clearance check - did not need adjustment
When i got it back it was idling a little high, with the specialist saying it was a bit tough to set. A little lurchy lower in the revs, but when pressed felt WAY quicker -good fun. Unfortunately not long after i got it back had master cylinder failure resulting in lots of fluid drawn into the engine and smoke. Now fixed and smoke cleared by its self once burnt off, however this seems to have exaggerated the above running trouble massively.
So the issue is:
- High idle even with the idle stop completely wound out the way. (about 1250rpm), but about 25% of the time will idle more normally but cant seem to influence when it settles high vs normal.
- When idling it will miss a beat a make a bang (backfire) on the rhs drivers side exhaust (worth noting each exhaust servs each bank only - straight). Also does this misfire under partial throttle.
- Really lumpy, missing, lurchy running under part throttle. Under full load - perfect, fast, amazing, no misses.
What ive done:
- Cant get my software to connect, it finds the correct coms port, but doesn't connect. Com port it looks at changes from 1 to 3 with the usb port on the laptop. (windows 11 - Bluetooth off. USB to 9 pin cable)
- But, to try and get some headway, with it running ive doused the throttle body area in degreaser, no change to revs = no air leaks in.
- I then unplugged the throttle position sensor from the drivers side bank - cable reads "evens", which i believe to be correct - this results in no change at all to the running. I do the same to the passenger side, misfires erratically then cuts out.
- So i swapped the plugs over to the other bank. Still the misfire and backfire is on the driver side bank. I unplugged the drivers bank again whilst running, engine misfired then cut out. plug in and restart, tried the passenger bank and no change and still running.
So the misfire remains on the driver bank even with swapping the TPS leads over BUT the none effect from unplugging moves with the lead rather than staying with the sensor. To my mind this means the cable for the drivers bank TPS is faulty but still not sure as to why the misfire remains on the drivers side.
My questions:
- Do people agree with my conclusion of faulty TPS lead on the Drivers bank.
- Any suggestions RE the connection to computer - i have ordered a new lead to rule that out, will try it this week when it arrives.
- Any other thoughts, suggests etc.
-Any ideas as to why the misfire remains on the same bank (my current theory being i have 2 separate issues, one with the TPS cable, and 1 with general setup - need to connect to the computer to find out)
(Worth mentioning, happy my specialist and the work he does, nothing negative there. he is very good, but suggested if trouble persists after a good drive trying joolz - he is more equipped and experienced with this sort of issue - knows joolz would get to the root much faster. If i have no joy or it gets more involved than bolt on parts and setup i will book in with joolz but would like to exhaust my abilities first, also with peaks to the beach just a week away... i wont get in that soon)
Check that the throttle cable is running free and slack when at idle position. If the cable is snagging on something, badly adjusted at the throttle bodies or the pedal is fouling on something then it can hold the idle high and the throttle cam does not even touch the stop screw. You say it idles normally for 25% of the time but is unpredictable. Disconnect the cable from the engine and turn the throttle cam by hand - see if it is a more consistent idle and the cam rests on the stop screw.
For the computer - Open the Device Manager in Windows and delete all listed COM ports.
Then with the USB cable unplugged - reboot the machine. When Windows has started plug in the USB cable and windows should reload the device. Make sure Bluetooth is turned off and then try to connect to the MBE. Also try a different USB port on the computer.
The misfire is more likely to be a bad HT lead on the even bank and the TP sensors are a red hearing. Check the HT leads for loose/broken connectors in the the spark plug end. At my last service I found a bad lead and replaced the set. It now runs much smoother.
One other thing - and I don't want to scare you, but 100k miles is a high number. When was the engine last rebuilt? I know they're all different, but mine needed a rebuild at just over 50k when it became untunable. If all else fails have it compression checked. It might just be tired.
For the computer - Open the Device Manager in Windows and delete all listed COM ports.
Then with the USB cable unplugged - reboot the machine. When Windows has started plug in the USB cable and windows should reload the device. Make sure Bluetooth is turned off and then try to connect to the MBE. Also try a different USB port on the computer.
The misfire is more likely to be a bad HT lead on the even bank and the TP sensors are a red hearing. Check the HT leads for loose/broken connectors in the the spark plug end. At my last service I found a bad lead and replaced the set. It now runs much smoother.
One other thing - and I don't want to scare you, but 100k miles is a high number. When was the engine last rebuilt? I know they're all different, but mine needed a rebuild at just over 50k when it became untunable. If all else fails have it compression checked. It might just be tired.
Hi, thanks for the fast responses:
- I will try with the hose clamped and then with the throttle cable disconnected tonight. The throttle cable however has been changed alongside the brake servo (whilst pedal box is out) and the issue existed to some extent before - but worth a check for how easy it is to do.
- I will also retry with the above steps on the computer.
- On general engine health, it is on its original engine, never rebuilt. at 75k miles ish it was tuned by joolz and performed well at 409bhp. Still goes like hell on flat out, and prior to this issue (200 mile ago tops) drove really well all round and doesn't burn much oil (or at least... not much for a TVR). At last valve clearance check (just the other month) the specialist also commented the shim levels are not too bad. But yes, i know the day will come and it is on borrowed time at 100k.
- I will try with the hose clamped and then with the throttle cable disconnected tonight. The throttle cable however has been changed alongside the brake servo (whilst pedal box is out) and the issue existed to some extent before - but worth a check for how easy it is to do.
- I will also retry with the above steps on the computer.
- On general engine health, it is on its original engine, never rebuilt. at 75k miles ish it was tuned by joolz and performed well at 409bhp. Still goes like hell on flat out, and prior to this issue (200 mile ago tops) drove really well all round and doesn't burn much oil (or at least... not much for a TVR). At last valve clearance check (just the other month) the specialist also commented the shim levels are not too bad. But yes, i know the day will come and it is on borrowed time at 100k.
Another theory . The brake fluid has ruined the driver’s side lambda sensor. This can cause high idle, lumpy running below 3k rpm with part throttle (but not at higher revs or wider throttle openings).
After swapping it out, it may take a little while for the ECU to learn the right adaptives so it will continue to run a bit lumpy for a bit.
. The brake fluid has ruined the driver’s side lambda sensor. This can cause high idle, lumpy running below 3k rpm with part throttle (but not at higher revs or wider throttle openings).After swapping it out, it may take a little while for the ECU to learn the right adaptives so it will continue to run a bit lumpy for a bit.
So had a play last night,
- sadly still the computer refuses to connect
but my hope is the new cable will fix this... whenever it arrives
- Ive ordered some new plugs and leads, the ones on do look quite old. however feeling the cables.... ive not had a shock, but they could be poor inside.
- Started up and ran with the throttle cable disconnected, idles low and nice, but then once warmed up started to rise again.
- Tried clamping off the vac pipe for the servo, didn't make any difference (cant believe how much this pulses with engine beat)
- Removed the airboxes and short induction pipes - didnt make note of which goes where, i feel like future me will regret that on reassembly.
- Checking the flows at idle (around 900 rpm at point of test as still a little cold), Drivers bank (misfiring) measures 3, passenger side running cleaner measures 7. So im well out of balance. BUT, with the idle stop on the drivers bank completely out of the way, it must therefor be stopping at bottom on the passenger bank.... so how is this still flowing so much more!?!?
- Also... just a note, the passenger bank when running, splashes fuel up out of the top, where as drivers bank is far far less.
- Also... another observation, the drivers bank is free from dirt or deposits on the trumpets and TBs, the passenger side is quite blackened, particularly on the middle 2 (one of these also popped back when revved).
Not sure what sense can be made of this.... the computer would be most helpful...
Ref the lambda, that would make sense, however the bank it draws vacuum from is passenger side.
My thoughts on next steps:
- Remove the link rod, and see what happens to the flow on the passenger side with no influence. HOPEFULLY this will then go lower and allow me to set both up to match at idle, then set the idle with the screw.
- I will then NEED the computer to adjust the throttle pots and reset adaptive.
- Test drive.... hope its fixed. If not, then change HT leads (looks fiddly - cant even see how to get the plugs out)
What do people think, all opinions welcome :P
Video link below
https://drive.google.com/file/d/1hmHepLOgQTvp4iPaK...
- sadly still the computer refuses to connect
but my hope is the new cable will fix this... whenever it arrives- Ive ordered some new plugs and leads, the ones on do look quite old. however feeling the cables.... ive not had a shock, but they could be poor inside.
- Started up and ran with the throttle cable disconnected, idles low and nice, but then once warmed up started to rise again.
- Tried clamping off the vac pipe for the servo, didn't make any difference (cant believe how much this pulses with engine beat)
- Removed the airboxes and short induction pipes - didnt make note of which goes where, i feel like future me will regret that on reassembly.
- Checking the flows at idle (around 900 rpm at point of test as still a little cold), Drivers bank (misfiring) measures 3, passenger side running cleaner measures 7. So im well out of balance. BUT, with the idle stop on the drivers bank completely out of the way, it must therefor be stopping at bottom on the passenger bank.... so how is this still flowing so much more!?!?
- Also... just a note, the passenger bank when running, splashes fuel up out of the top, where as drivers bank is far far less.
- Also... another observation, the drivers bank is free from dirt or deposits on the trumpets and TBs, the passenger side is quite blackened, particularly on the middle 2 (one of these also popped back when revved).
Not sure what sense can be made of this.... the computer would be most helpful...
Ref the lambda, that would make sense, however the bank it draws vacuum from is passenger side.
My thoughts on next steps:
- Remove the link rod, and see what happens to the flow on the passenger side with no influence. HOPEFULLY this will then go lower and allow me to set both up to match at idle, then set the idle with the screw.
- I will then NEED the computer to adjust the throttle pots and reset adaptive.
- Test drive.... hope its fixed. If not, then change HT leads (looks fiddly - cant even see how to get the plugs out)
What do people think, all opinions welcome :P
Video link below
https://drive.google.com/file/d/1hmHepLOgQTvp4iPaK...
Edited by Car.Fool.James on Tuesday 23 June 11:04
Hi. I think you're best to wait until you get the software running. It should point you in a better direction.
If one side gets more fuel than the other that does suggest either throttle pot or injector issues and you're right in suspecting the TPs first. It might be that the even side TP has started to go bad in the low range and needs replaced. Either the software or perhaps a multi meter will verify if the pot has gone noisy.
I'm not sure removing the link rod and trying to fix the idle will work (without the software). Remember the bad side will always be affecting the good side and without seeing the values it's kind of just a stab in the dark. Also - the stored adaptive values will probably be throwing everything off. Especially if it updated the values while burning off oil etc. Before trying to balance/setup the engine you really should zero the adaptives.
e.g I've just fixed a loose connection with my lamda1 - which recorded the following. Idling was problematic and it would always stall until warm. . .
Guess which values were screwing up the idle
https://www.pistonheads.com/gassing/topic.asp?h=0&...
If one side gets more fuel than the other that does suggest either throttle pot or injector issues and you're right in suspecting the TPs first. It might be that the even side TP has started to go bad in the low range and needs replaced. Either the software or perhaps a multi meter will verify if the pot has gone noisy.
I'm not sure removing the link rod and trying to fix the idle will work (without the software). Remember the bad side will always be affecting the good side and without seeing the values it's kind of just a stab in the dark. Also - the stored adaptive values will probably be throwing everything off. Especially if it updated the values while burning off oil etc. Before trying to balance/setup the engine you really should zero the adaptives.
e.g I've just fixed a loose connection with my lamda1 - which recorded the following. Idling was problematic and it would always stall until warm. . .
Guess which values were screwing up the idle
https://www.pistonheads.com/gassing/topic.asp?h=0&...
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