poor running, misfire?
Discussion
following my thread 'won't rev past 2000rpm' i've had the wedge ('87 350i) into a TVR specialist who got the car running again by re-setting the fuel pressure, changing the plugs, replacing a broken coil, rebuilding the distributor (rusty trigger wheel) and replacing the ignition module. However the car now has a slight running problem, which i can't get to the bottom of!
When driving with the accelerator in a constant position the car seems to have a juddering or slight misfire, however it does rev quite freely and the 'hesitation' or 'juddering' doesnt seem to be there when accelerating?
The car has magnacor 8.5mm leads (not sure how old), i have swapped the airflow meter (Co etc set up)which made no difference, the dist cap and rotor have also been changed!
Any ideas out there?
When driving with the accelerator in a constant position the car seems to have a juddering or slight misfire, however it does rev quite freely and the 'hesitation' or 'juddering' doesnt seem to be there when accelerating?
The car has magnacor 8.5mm leads (not sure how old), i have swapped the airflow meter (Co etc set up)which made no difference, the dist cap and rotor have also been changed!
Any ideas out there?
johntom said:
TVR specialist got the car running again by re-setting the fuel pressure, changing the plugs, replacing a broken coil, rebuilding the distributor (rusty trigger wheel) and replacing the ignition module. However the car now has a slight running problem, which i can't get to the bottom of!
When driving with the accelerator in a constant position the car seems to have a juddering or slight misfire, however it does rev quite freely and the 'hesitation' or 'juddering' doesnt seem to be there when accelerating?
The car has magnacor 8.5mm leads (not sure how old), i have swapped the airflow meter (Co etc set up)which made no difference, the dist cap and rotor have also been changed!
Any ideas out there?
Wow! Were all those mentioned components faulty? When driving with the accelerator in a constant position the car seems to have a juddering or slight misfire, however it does rev quite freely and the 'hesitation' or 'juddering' doesnt seem to be there when accelerating?
The car has magnacor 8.5mm leads (not sure how old), i have swapped the airflow meter (Co etc set up)which made no difference, the dist cap and rotor have also been changed!
Any ideas out there?
No question, your latest symptoms point to the Throttle Pot!
Not necessarily expensive, it depend how you go about acquiring the replacement. Read all about the throttle pot in the PDF available from here:
http://www.vintagemodelairplane.com/pages/Rover_Te...
You can do tests to prove the need for a replacement before buying, or possibly even mend the one you've got at no cost.
Hi
i've spent nearly £600 and the car still doesn't run right ! I rang the Specialist again today and suggested the throttle pot, he said definitely not - i am going to try one all the same (might as well i've changed everything else)!
Are the throttle pots the same regardless of whether they have the white or black plug (mines white)?
i've spent nearly £600 and the car still doesn't run right ! I rang the Specialist again today and suggested the throttle pot, he said definitely not - i am going to try one all the same (might as well i've changed everything else)!
Are the throttle pots the same regardless of whether they have the white or black plug (mines white)?
I _always_ get the old parts back when I have things done.
Last time I had an intermittent cutting out which recurred during a service and they replaced the coil and ignition amp.
The cutting out came back weeks later, and all along it turned out to be the rev limiter.
So now I have a spare good coil and ignition amp, at least it wan't a tun down the drain.
BTW the throttle pot is easy to test, just clip on a voltmeter and watch that the voltage increases smoothly as you turn the throttle linkage. If the needle flickers or drops to zero, it's worn out.
Last time I had an intermittent cutting out which recurred during a service and they replaced the coil and ignition amp.
The cutting out came back weeks later, and all along it turned out to be the rev limiter.
So now I have a spare good coil and ignition amp, at least it wan't a tun down the drain.
BTW the throttle pot is easy to test, just clip on a voltmeter and watch that the voltage increases smoothly as you turn the throttle linkage. If the needle flickers or drops to zero, it's worn out.
Edited by adam quantrill on Friday 20th June 21:25
they are generally all 5000 ohm - 90 degrees rotation and interchangeable, but may rquire some rewiring of mounting plate modification.
the two normally encountered plugs are shown on page 9 of the PDF.
as are all the test details.
If you have already paid 600 moohlah and its not running OK its possible that the technician is mistaken again.
I assume you read this.
Providing the voltage change is slow and smooth the injectors may be heard firing or clicking just once as the assembly approaches full throttle. If the prior maximum voltage measurement is undesirably low then, obviously, this function cannot take place and the above mentioned full load fuel enrichment is denied.
• Open the throttle RAPIDLY and the injectors fire much sooner during rotation.
• This simulated fast acceleration, triggers supplementary injector firing to provide extra fuel needed as soon as possible during the period of acceleration demand.
• However if the voltage rise is erratic it is very likely that the injectors will be heard firing randomly or in sympathy with the sharply varying voltage reading even when slowly operating the throttle.
[b]__This is because the erratic voltage signal fools the ECU into thinking the throttle is moving swiftly when it is not, triggering unwanted fuel enrichment under casual driving conditions resulting in a randomly unstable fuel/air mixture leading to very lumpy engine performance with gross adverse affect on fuel consumption.
• This random injection of extra fuel may not occur when the car is cruising at constant speed with the throttle not moving. However even casual acceleration or deceleration can cause havoc with mixture control.__[/b]
• Alas, the potentiometer is prone to wear at the point where it is most used at normal driving speed so the effects on normal driving are at their most noticeable.
the two normally encountered plugs are shown on page 9 of the PDF.
as are all the test details.
If you have already paid 600 moohlah and its not running OK its possible that the technician is mistaken again.
I assume you read this.
Providing the voltage change is slow and smooth the injectors may be heard firing or clicking just once as the assembly approaches full throttle. If the prior maximum voltage measurement is undesirably low then, obviously, this function cannot take place and the above mentioned full load fuel enrichment is denied.
• Open the throttle RAPIDLY and the injectors fire much sooner during rotation.
• This simulated fast acceleration, triggers supplementary injector firing to provide extra fuel needed as soon as possible during the period of acceleration demand.
• However if the voltage rise is erratic it is very likely that the injectors will be heard firing randomly or in sympathy with the sharply varying voltage reading even when slowly operating the throttle.
[b]__This is because the erratic voltage signal fools the ECU into thinking the throttle is moving swiftly when it is not, triggering unwanted fuel enrichment under casual driving conditions resulting in a randomly unstable fuel/air mixture leading to very lumpy engine performance with gross adverse affect on fuel consumption.
• This random injection of extra fuel may not occur when the car is cruising at constant speed with the throttle not moving. However even casual acceleration or deceleration can cause havoc with mixture control.__[/b]
• Alas, the potentiometer is prone to wear at the point where it is most used at normal driving speed so the effects on normal driving are at their most noticeable.
Edited by honestjohntoo on Saturday 21st June 08:14
That is pretty much the definitive test of the potentiometer except it is possible to measure its resistance in a similar way, with the item disconnected and ignition off, and then do the same thing at the ECU multiplug. Therefor (apart from trying a good temporary substitute from a friend) you are probably looking for something else that can cause the problem described.
The majority of all Efi faults have two root causes: ie.
o Air leaks and
o Wiring/connection issues.
Both these are covered in detail on the mentioned website.
http://www.vintagemodelairplane.com/pages/Download...
o For Leaks - go to the plenum chamber article under Efi components..
o For Efi wiring/connector maintenance - see the main article index.
Wiring/connector issues will affect the ignition circuit also.
o An unusual problem, easily overlooked - the suppression capacitor, if there is one, across the coil may be breaking down.
o Has the Ignition amplifier been fitted with the correct thermal conductivity compound to prevent local overheating of the unit.
o Earth straps to the chassis can also be an issue as can the Efi system earth at the rear of the block below and behind the LH rocker cover.
o And quite a common issue is dry joints inside the ECU which can be addressed with the judicious use of a small soldering iron.
Unfortunately, now, I am getting trapped into my pet hate, the scattergun approach to problem solving, suggesting some likely things at random. Usually this process does not work unless by luck! In the long run its usually better to use a structured test program, whereby the whole system is reviewed/tested in a logical sequence.
Help can be found on the mentioned website index under Efi Testing and Adjustment Program.
To add further detail all the components mentioned in that essay are examined in detail under the Efi system components index.
Good luck.
The majority of all Efi faults have two root causes: ie.
o Air leaks and
o Wiring/connection issues.
Both these are covered in detail on the mentioned website.
http://www.vintagemodelairplane.com/pages/Download...
o For Leaks - go to the plenum chamber article under Efi components..
o For Efi wiring/connector maintenance - see the main article index.
Wiring/connector issues will affect the ignition circuit also.
o An unusual problem, easily overlooked - the suppression capacitor, if there is one, across the coil may be breaking down.
o Has the Ignition amplifier been fitted with the correct thermal conductivity compound to prevent local overheating of the unit.
o Earth straps to the chassis can also be an issue as can the Efi system earth at the rear of the block below and behind the LH rocker cover.
o And quite a common issue is dry joints inside the ECU which can be addressed with the judicious use of a small soldering iron.
Unfortunately, now, I am getting trapped into my pet hate, the scattergun approach to problem solving, suggesting some likely things at random. Usually this process does not work unless by luck! In the long run its usually better to use a structured test program, whereby the whole system is reviewed/tested in a logical sequence.
Help can be found on the mentioned website index under Efi Testing and Adjustment Program.
To add further detail all the components mentioned in that essay are examined in detail under the Efi system components index.
Good luck.
Edited by honestjohntoo on Saturday 21st June 10:55
Edited by honestjohntoo on Saturday 21st June 10:57
O.3V at idle seems too low to me. Try this: Check the gap top and bottom of the butterfly plate inside the plenum. It should not be fully closed on a Wedge (unlike the Rover SDI). Set this to about 0.002" then recheck the throttle pot voltage and re-set this to 0.35V at idle.
It is quite common for people to adjust tickover wrongly by using the throttle linkage which in turn changes the thottle pot voltage.
It is quite common for people to adjust tickover wrongly by using the throttle linkage which in turn changes the thottle pot voltage.
Hi
i have tested the throttle pot again today and the control voltage was 4.41v, the green/red with ignition on was 0.8 (i am sure this was 0.3 prior to going in the garage) so i have adjusted this to give .35v, it only seems to rise to 3.99v though at full throttle? The butterfly gap is 0.002" as suggested.
I went around the block and it made no difference (even trickling along at a constant throttle in 1st gives a slight juddering feeling), further to this it makes no difference if i disconnect it all together? Why?
I have tested the amplifier as suggested in wedge pages (5b Module located on dist). With ecu plug off, voltmeter between -ve terminal on coil and lucar clip from amp - on cranking the engine this gives between 9 and 10v? according to the info it should be 6 - 9 volts, what could be wrong? The coil and amp were fitted by RTR last week.
Items replaced so far include fuel pump, fuel filter and pressure set. New plugs, rotor arm, lucas dist cap. New HT leads, new coil and amplifier. Distributor rebuilt/fitted by rtr.
i have tested the throttle pot again today and the control voltage was 4.41v, the green/red with ignition on was 0.8 (i am sure this was 0.3 prior to going in the garage) so i have adjusted this to give .35v, it only seems to rise to 3.99v though at full throttle? The butterfly gap is 0.002" as suggested.
I went around the block and it made no difference (even trickling along at a constant throttle in 1st gives a slight juddering feeling), further to this it makes no difference if i disconnect it all together? Why?
I have tested the amplifier as suggested in wedge pages (5b Module located on dist). With ecu plug off, voltmeter between -ve terminal on coil and lucar clip from amp - on cranking the engine this gives between 9 and 10v? according to the info it should be 6 - 9 volts, what could be wrong? The coil and amp were fitted by RTR last week.
Items replaced so far include fuel pump, fuel filter and pressure set. New plugs, rotor arm, lucas dist cap. New HT leads, new coil and amplifier. Distributor rebuilt/fitted by rtr.
Edited by johntom on Sunday 22 June 22:27
When testing the ignition amp (as per wedgepages efi test 5b) i am getting between 9 and 10 volts between the coil -ve and the lucar clip back to the ignition module (when cranking the engine, ecu plug removed), what would make it higher then the suggested 6 - 9 volts? should there be some sort of balast resistor (the coil/ ign. amp are new)?
johntom said:
Hi
i have tested the throttle pot again today and the control voltage was 4.41v, the green/red with ignition on was 0.8 (i am sure this was 0.3 prior to going in the garage) so i have adjusted this to give .35v, it only seems to rise to 3.99v though at full throttle? The butterfly gap is 0.002" as suggested.
The engineer who set it up failed to notice that your throttle does not fully open so he adjusted the pot to give the higher voltage and upset the lower voltage. The below extract is from the article mentioned in my prior post:i have tested the throttle pot again today and the control voltage was 4.41v, the green/red with ignition on was 0.8 (i am sure this was 0.3 prior to going in the garage) so i have adjusted this to give .35v, it only seems to rise to 3.99v though at full throttle? The butterfly gap is 0.002" as suggested.
If it proves impossible to get near the maximum voltage with the throttle fully open then inspect the throttle quadrant and throttle assembly, the cruise control quadrant (especially because it can foul it’s own mounting bracket), accelerator pedal, driver’s side floor carpet and automatic transmission kick down cable.
Correct any faults at these locations as they can prevent full throttle opening.
Whilst not desirable, some set-ups may fall slightly short of the full voltage, say 3.7 to 4.1 volts, but it does not affect the system operation during normal driving. However, full load driving (i.e. throttle wide open) may be adversely affected.
johntom said:
I went around the block and it made no difference (even trickling along at a constant throttle in 1st gives a slight juddering feeling), further to this it makes no difference if i disconnect it all together? Why?
The throttle pot only modifies the behaviour of the ECU, disconnecting it does not generally stop the system running, but sometimes it does.However the acceleration enrichment circuits and full load enrichment cicuits will NOT work with the pot disconnected.
johntom said:
I have tested the amplifier as suggested in wedge pages (5b Module located on dist). With ecu plug off, voltmeter between -ve terminal on coil and lucar clip from amp - on cranking the engine this gives between 9 and 10v? according to the info it should be 6 - 9 volts, what could be wrong? The coil and amp were fitted by RTR last week.
Its probably not an issue because you are actually measuring voltage pulses and your meter may react differently depending upon its hysteresis response. Also the battery voltage may be quite good to start with.johntom] said:
Items replaced so far include fuel pump, fuel filter and pressure set. New plugs, rotor arm, lucas dist cap. New HT leads, new coil and amplifier. Distributor rebuilt/fitted by rtr.
I can only reiterate the advice given in my prior post. You have lots of testing yet to do, I'm afraid.Hi
thankyou for your response. In your previous post you mentioned the 'supression capacitor', i have noticed two small cylinders near the coil which were previously lucar clipped to the old coil - now the lucar clip is unconnected? is this the 'supression capacitor' and should this go to the +ve or -ve terminal?
many thanks for your help and patience.
prior to going into the garage the car ran very smoothly, it just wouldn't rev past 2000rpm. I think this new fault is possibly connected to the repair work on the previous fault, ie distributor rebuild, new ignition module, coil etc?
thankyou for your response. In your previous post you mentioned the 'supression capacitor', i have noticed two small cylinders near the coil which were previously lucar clipped to the old coil - now the lucar clip is unconnected? is this the 'supression capacitor' and should this go to the +ve or -ve terminal?
many thanks for your help and patience.
prior to going into the garage the car ran very smoothly, it just wouldn't rev past 2000rpm. I think this new fault is possibly connected to the repair work on the previous fault, ie distributor rebuild, new ignition module, coil etc?
Edited by johntom on Monday 23 June 22:50
I've not come across two capacitors being used it very much depends upon what was originally on the car and if it has been modified.
it could be someone fitted a replacement and did not remove the original.
One end will be earthed and the other would go to coil positive, iirc, its job is to suppress radio frequency interferance and voltage spikes generated by the ignition coil low tension cct.
It has no effect on the ign cct unless for some reason it goes faulty. Being disconnected may upset the amplifier function, but I dont know that for sure.
connect it and see what happens.
it could be someone fitted a replacement and did not remove the original.
One end will be earthed and the other would go to coil positive, iirc, its job is to suppress radio frequency interferance and voltage spikes generated by the ignition coil low tension cct.
It has no effect on the ign cct unless for some reason it goes faulty. Being disconnected may upset the amplifier function, but I dont know that for sure.
connect it and see what happens.
pwd95 said:
adam quantrill said:
I can't believe no-one has mentioned the engine temperature sensor. While this is usually implicated in warming-up bad running problems, it's a relatively cheap fix and, well, you never know....
Holy smokes Batman...nail & head spring to mind. 
but then all the other mentioned components have been randomly replaced at considerable cost - why not the temp sensor too?
Personally I would favour the testing approach before spending the money - but then I'm living on a modest pension.
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