Various running problems - what to try next?
Discussion
Unplugged all the HT leads, and I'm pretty sure I had failed to get the rubber sheath slid down over the plugs. Removed a plug each side, and they were already quite badly sooted up. 
Decided to clean one up, and I can pass on a top tip: if using white spirit and a plastic toothbrush, you can kiss goodbye to the toothbrush:
I decided I couldn't be arsed to remove and clean them all, so I'll rely on them self-cleaning - which they should do being hotter plugs. I wiped the bodies of the plugs with kitchen paper and reconnected the leads making sure to slide the rubber sheath down properly this time.
I took the old girl for a run, including some full throttle blasts up to
mph to give the plugs a chance to sort themselves out. She's now running properly again, as good as before!
Might remove a plug once things have cooled down to see what it looks like.
Decided to clean one up, and I can pass on a top tip: if using white spirit and a plastic toothbrush, you can kiss goodbye to the toothbrush:
I decided I couldn't be arsed to remove and clean them all, so I'll rely on them self-cleaning - which they should do being hotter plugs. I wiped the bodies of the plugs with kitchen paper and reconnected the leads making sure to slide the rubber sheath down properly this time.
I took the old girl for a run, including some full throttle blasts up to
mph to give the plugs a chance to sort themselves out. She's now running properly again, as good as before!Might remove a plug once things have cooled down to see what it looks like.
Have you replaced your rotor and cap yet?
I had similar problems to what you are describing. I replaced plugs with Chimp's recommended plugs, ( the old
ones were very black) replaced the tempreture sender, and replaced the rotor with a Powermax Red rotor arm.
Been running great ever since. I personally suspected the main cause was the tempteture sender making it run too rich and making the plugs fowl up.
I had similar problems to what you are describing. I replaced plugs with Chimp's recommended plugs, ( the old
ones were very black) replaced the tempreture sender, and replaced the rotor with a Powermax Red rotor arm.
Been running great ever since. I personally suspected the main cause was the tempteture sender making it run too rich and making the plugs fowl up.
Dr Mike Oxgreen said:
Well, on Friday I drove it to work and it was running brilliantly - possibly better than it has ever run. Drove it at lunchtime and ditto.
But then when I started it to drive home I could immediately tell it was misfiring as soon as the engine was running, and it drove like an absolute pig - stuttering and misfiring really badly. It did improve very slowly, and by the time I'd got home it was almost back to how it had been earlier in the day.
What on earth could have caused it to change so dramatically when it was just sitting in the office car park for a few hours? Well, I do remember being in a meeting that afternoon and we could hardly hear ourselves over the rain drumming on the roof, so I'm suspecting water ingress. It's possible that I may have failed to get the rubber sheaths of the HT leads properly slid down over the body of the plugs - I found that the socks made it harder to feel what you're doing when fitting the leads to the plugs, and I'm wondering whether I may have slid the sock down over one or more of the plugs without sliding the rubber sheath as well.
The engine was too hot to check at the time, and I was busy with other things yesterday, so today I will check, clean the bodies of the plugs and refit the HT leads more carefully. I think that is the most likely explanation. I may have a tube of dielectric grease somewhere, so I'll consider putting a smear around the porcelain body of the the plugs.
Its not easy to see if the lead is fully home on the plug. Best to try it with a spare plug so you can see how far it needs to be to be fully on. You should then be able to see each plug (with some contortionist moves) to see if they are all the same. I've got this plug lead holder which is like a pair of ting with rubber handles and at the opposite end which helps get the sheath on fully.But then when I started it to drive home I could immediately tell it was misfiring as soon as the engine was running, and it drove like an absolute pig - stuttering and misfiring really badly. It did improve very slowly, and by the time I'd got home it was almost back to how it had been earlier in the day.
What on earth could have caused it to change so dramatically when it was just sitting in the office car park for a few hours? Well, I do remember being in a meeting that afternoon and we could hardly hear ourselves over the rain drumming on the roof, so I'm suspecting water ingress. It's possible that I may have failed to get the rubber sheaths of the HT leads properly slid down over the body of the plugs - I found that the socks made it harder to feel what you're doing when fitting the leads to the plugs, and I'm wondering whether I may have slid the sock down over one or more of the plugs without sliding the rubber sheath as well.
The engine was too hot to check at the time, and I was busy with other things yesterday, so today I will check, clean the bodies of the plugs and refit the HT leads more carefully. I think that is the most likely explanation. I may have a tube of dielectric grease somewhere, so I'll consider putting a smear around the porcelain body of the the plugs.
Edited by Dr Mike Oxgreen on Sunday 20th September 07:54
I still had a hesitation at around 2000 revs which a new dizzy cap cured.
FFG
[quote=carbon14]
On the way from the lambdas to the ECU there are connectors (cylinder types) and in my case
one (there are in total 3 of them) was "oxydated" (sorry my english is poor), I just had to clean it properly, plug it again (firmly) and the whole crazy (like a rodeo horse) behavior disappeared....
I also have suspect lambda connections. I have found two of those connectors, one on each side about 9" from the sensor itself, but didn't know that there was a third. Would appreciate knowing where it is.
Thanks.
On the way from the lambdas to the ECU there are connectors (cylinder types) and in my case
one (there are in total 3 of them) was "oxydated" (sorry my english is poor), I just had to clean it properly, plug it again (firmly) and the whole crazy (like a rodeo horse) behavior disappeared....
I also have suspect lambda connections. I have found two of those connectors, one on each side about 9" from the sensor itself, but didn't know that there was a third. Would appreciate knowing where it is.
Thanks.
The lambdas are on extension cables on the TVR loom- you will find extra cylindrical connectors near the fuel rail on each side inside the V of the engine. A open circuit Lambda will case the ECU go go into fault mode, but you wont know as the ECU warning light does not work on most TVR's, so the car will just drive badly as the ECU cant work out the required fuelling.
FlipFlopGriff said:
Its not easy to see if the lead is fully home on the plug. Best to try it with a spare plug so you can see how far it needs to be to be fully on.
My technique, such as it is, is to retract the rubber sheath (stop sniggering at the back!) so that the metal connector is fully exposed, and push that onto the end of the plug until I feel and hear it click on. Then (and this the bit I failed to do properly first time) push the rubber sheath so that it slides down over the shaft (I'm warning you, you'll be in detention if you don't stop snickering!) of the plug. Then slide the 'sock' down so that it provides complete protection. And there's nothing funny about that.
Gaaahhhh!!! Buggeration!
"Dead throttle syndrome" came back.
I can't over-emphasise how beautifully the engine is now running 99.9% of the time. Absolutely no misfiring; it's pulling smoothly, keenly and without hesitation, and in the low-to-medium rev range it is particularly improved. The driveability and throttle response are excellent: it responds to every nuance of what I do with my right foot. It has been a joy to drive!
But on my way home last night, "dead throttle syndrome" came back.
Let me re-summarise the symptoms of this weird effect:
I am now thinking that this can't possibly be related to ignition. If it were an ignition issue, you'd either expect the engine to misfire or go lumpy (which it doesn't), or you'd expect it to go completely silent (which it doesn't). When this happens, it sounds exactly like I've just lifted right off the throttle.
So a question, particularly for Blitz or any other experts: What does the ECU use the throttle pot for? What would happen if you were driving along and the pot suddenly reports zero, or that the throttle is completely closed - either due to a sensor fault or a loom break? How would the ECU respond to that? Would it suddenly cut the fuelling to idle?
I guess a supplementary question would be the same question, but for the air mass sensor. What if that suddenly reported zero, or a ridiculously low value? Presumably the ECU would also cut the fuelling right down?
If I've understood correctly, the lambdas are only used to trim the mixture, so they couldn't have such a dramatic effect like this. Is that right?
Sorry to resurrect this thread, just when I thought everything was sorted!
Edited to add: Does the ECU use the 'rate of change' of the throttle pot, rather than its position? In other words, is it used merely to richen the mixture when you kick down on the throttle to stop the engine stumbling? If so, that might partly explain why 'booting' the throttle causes the engine to snap out of 'dead throttle syndrome'...
"Dead throttle syndrome" came back.
I can't over-emphasise how beautifully the engine is now running 99.9% of the time. Absolutely no misfiring; it's pulling smoothly, keenly and without hesitation, and in the low-to-medium rev range it is particularly improved. The driveability and throttle response are excellent: it responds to every nuance of what I do with my right foot. It has been a joy to drive!
But on my way home last night, "dead throttle syndrome" came back.
Let me re-summarise the symptoms of this weird effect:
- Usually (perhaps always?) happens at low-to-medium throttle positions.
- Happens randomly.
- Engine abruptly goes to idle power for a random period of time, sometimes half a second, sometimes 4 or 5 seconds.
- Sometimes it does this just once, sometimes lots of times in succession before it mysteriously stops happening.
- Doesn't misfire, and it continues to make a normal engine sound. Engine does not go silent, and stays totally smooth (apart from the abrupt reduction in power). No pops or bangs.
- RPM gauge registers normally (I think).
- During the 'dead' period, the engine totally ignores moderate throttle movements.
- If I disengage the clutch and give it a large boot of throttle, the engine responds and revs up normally - this temporarily clears the problem.
- If I do nothing, the engine will abruptly return to normal power at some random time (usually just a few seconds).
I am now thinking that this can't possibly be related to ignition. If it were an ignition issue, you'd either expect the engine to misfire or go lumpy (which it doesn't), or you'd expect it to go completely silent (which it doesn't). When this happens, it sounds exactly like I've just lifted right off the throttle.
So a question, particularly for Blitz or any other experts: What does the ECU use the throttle pot for? What would happen if you were driving along and the pot suddenly reports zero, or that the throttle is completely closed - either due to a sensor fault or a loom break? How would the ECU respond to that? Would it suddenly cut the fuelling to idle?
I guess a supplementary question would be the same question, but for the air mass sensor. What if that suddenly reported zero, or a ridiculously low value? Presumably the ECU would also cut the fuelling right down?
If I've understood correctly, the lambdas are only used to trim the mixture, so they couldn't have such a dramatic effect like this. Is that right?
Sorry to resurrect this thread, just when I thought everything was sorted!
Edited to add: Does the ECU use the 'rate of change' of the throttle pot, rather than its position? In other words, is it used merely to richen the mixture when you kick down on the throttle to stop the engine stumbling? If so, that might partly explain why 'booting' the throttle causes the engine to snap out of 'dead throttle syndrome'...
Edited by Dr Mike Oxgreen on Thursday 24th September 08:51
I do believe that a faulty track on the the throttle pot can cause this, as if the throttle pot voltage drops low, the ecu will go into idle mode- having said that the ECU is smart enough to work out that if the AFM is showing high airflow- then the throttle pot cant be closed- so it will throw a fault code. You can do some easy throttle pot tests as suggested- but you may not see anything wrong as the fault is intermittent. You really do need an access to an ECUmate or RoverGauge cable to check for errors. Throttle pots are available from Britpart for about £70, or I think a "TVR" one is nearer £200, not that I condone swapping bits blindly- it could also just be a fractured wire under the throttle pot where it enters the plastic housing.
Basic 14CUX manual here:
http://www.g33.co.uk/images/PDFS/14cux_fuel_inject...
http://www.paddockspares.com/etc8495-potentiometer...
Basic 14CUX manual here:
http://www.g33.co.uk/images/PDFS/14cux_fuel_inject...
http://www.paddockspares.com/etc8495-potentiometer...
Edited by blitzracing on Thursday 24th September 13:18
Thanks - that's great. I think you're right - it's time I invested in a RoverGauge cable or similar.
The fact that booting the throttle seems to bring the engine back to life possibly indicates that it's an internal fault with the throttle pot rather than a simple broken wire: physically sweeping the pot rapidly might clear some dodgy connection internally, but I wouldn't expect it to have any effect on external wiring. That's my guess.
Anyway, I need to have a look for fault codes. If I understand you correctly, if the ECU sees both a zero throttle pot and a non-zero air mass reading, then it would still go to idle mode but would also set the fault code to log the mismatched readings - is that right?
Edited to add: I suppose it's possible that this problem actually only occurs when I lift off the throttle completely, maybe during a lazy gear change, thus the engine actually does go to idle speed and puts the ECU into idle mode, and then when I put my foot back down the faulty throttle pot fails to tell the ECU that the throttle has opened again. Maybe. Dunno.
The fact that booting the throttle seems to bring the engine back to life possibly indicates that it's an internal fault with the throttle pot rather than a simple broken wire: physically sweeping the pot rapidly might clear some dodgy connection internally, but I wouldn't expect it to have any effect on external wiring. That's my guess.
Anyway, I need to have a look for fault codes. If I understand you correctly, if the ECU sees both a zero throttle pot and a non-zero air mass reading, then it would still go to idle mode but would also set the fault code to log the mismatched readings - is that right?
Edited to add: I suppose it's possible that this problem actually only occurs when I lift off the throttle completely, maybe during a lazy gear change, thus the engine actually does go to idle speed and puts the ECU into idle mode, and then when I put my foot back down the faulty throttle pot fails to tell the ECU that the throttle has opened again. Maybe. Dunno.
Edited by Dr Mike Oxgreen on Thursday 24th September 15:42
For idle mode it needs a low throttle pot, and a low speedo (below 3mph), but a low throttle pot on its own will cut most of the fuelling as its like its on the overrun- but in this case a high AFM reading should cause it to trip a code as the engine is drawing lost of air with the throttle closed, and that cant happen physically.
Right, I've got my RoverGauge cable, and I've been playing with it.
Some interesting results, I think.
First off, I did a reading of fault codes - quite a few! Some of these might be from the time when my car was misfiring and having all sorts of issues:
But interestingly, the "throttle pot low, MAF high" one is there, which I believe might be consistent with my "dead throttle syndrome".
I cleared the codes and went for a drive. At the end of the drive, all the fault codes were still clear. With the engine idling, I captured a screenshot with the long-term lambdas. Surely they shouldn't both be at -100%? Whilst driving, I could see out of the corner of my eye that the short-term trims were also negative for virtually all of the time, sometimes seeming to go almost to -100%.
So, do those long-term lambdas indicate that I've still got some kind of fuelling problem? Does it mean that the base fuel map is giving an over-rich mixture which is having to be leaned right down? Should I reset them and try again? To reset them, is it a case of disconnecting the battery, or would they have reset during a nice long drive anyway?
Some interesting results, I think.
First off, I did a reading of fault codes - quite a few! Some of these might be from the time when my car was misfiring and having all sorts of issues:
But interestingly, the "throttle pot low, MAF high" one is there, which I believe might be consistent with my "dead throttle syndrome".
I cleared the codes and went for a drive. At the end of the drive, all the fault codes were still clear. With the engine idling, I captured a screenshot with the long-term lambdas. Surely they shouldn't both be at -100%? Whilst driving, I could see out of the corner of my eye that the short-term trims were also negative for virtually all of the time, sometimes seeming to go almost to -100%.
So, do those long-term lambdas indicate that I've still got some kind of fuelling problem? Does it mean that the base fuel map is giving an over-rich mixture which is having to be leaned right down? Should I reset them and try again? To reset them, is it a case of disconnecting the battery, or would they have reset during a nice long drive anyway?
Edited by Dr Mike Oxgreen on Sunday 4th October 12:04
Just tested my MAF sensor.
With just the ignition on, the voltage peaks at about 0.8V, and then takes about 15 seconds to settle back to about 0.3V.
As I understand it, it should settle quickly back to about 0.3V - is 15 seconds normal?
When starting the engine, it settles at about 1.8V.
With just the ignition on, the voltage peaks at about 0.8V, and then takes about 15 seconds to settle back to about 0.3V.
As I understand it, it should settle quickly back to about 0.3V - is 15 seconds normal?
When starting the engine, it settles at about 1.8V.
Edited by Dr Mike Oxgreen on Sunday 4th October 13:05
Set the MAF reading to direct- its far more accurate at low airflows, and check its within tolerance:
1.62 volts for a 3.9 litre engine 32.4 %
1.75 volts for a 5 litre engine =35%
Heres a plot of the turn on spike for the AFM at less than 1 second, followed by by starting the car at 1.62 volts on the 3.9
So yours is not correct. An over high AFM will cause the fuel trim to remove fuel as the high AFM voltage will cause the fuel load point to be lower in the map, so too much fuel goes in , in the first place. If you unplug the ECU the trims will go back to zero, and then the short term should start to cycle again- but it will not cycle around the mid point, it will be on one side. Then over about 2-3 minutes at idle (hot engine) the long term trim should start to move bit by bit. If alls well it will then stop, and the short term trim will then be cycling around its mid point- somehow I dont think this will happen how ever.
1.62 volts for a 3.9 litre engine 32.4 %
1.75 volts for a 5 litre engine =35%
Heres a plot of the turn on spike for the AFM at less than 1 second, followed by by starting the car at 1.62 volts on the 3.9
So yours is not correct. An over high AFM will cause the fuel trim to remove fuel as the high AFM voltage will cause the fuel load point to be lower in the map, so too much fuel goes in , in the first place. If you unplug the ECU the trims will go back to zero, and then the short term should start to cycle again- but it will not cycle around the mid point, it will be on one side. Then over about 2-3 minutes at idle (hot engine) the long term trim should start to move bit by bit. If alls well it will then stop, and the short term trim will then be cycling around its mid point- somehow I dont think this will happen how ever.
Edited by blitzracing on Sunday 4th October 18:43
I was reading the MAF voltage using a multimeter and a couple of straightened paper clips shoved into the MAF connector, with Mrs Oxgreen operating the ignition. I will try using the MAF readout on Rovergauge as well.
It also occurred to me that I can't remember when I last replaced the battery in my meter, so I might do that and repeat the test to make sure my readings were accurate. Unless of course RoverGauge gives a voltage readout in "direct MAF" mode, in which case I'll ditch the multimeter and use that instead. (Edited to add: I think it just gives a percentage, but I assume I can convert that to a voltage by taking it as a percentage of 5V).
What I think is clear from your oscilloscope trace is that the power-on spike should settle back to 0.3V very quickly indeed, within a second or two. That isn't happening on mine - it takes well over 10 seconds.
I'm pretty sure my short-term trims were spending all their time in the left-hand half of the bars as well; I'll try logging it to confirm that.
To disconnect the ECU, it's a case of pulling off the big long connector that goes along one side, right? Does it just pull off?
It also occurred to me that I can't remember when I last replaced the battery in my meter, so I might do that and repeat the test to make sure my readings were accurate. Unless of course RoverGauge gives a voltage readout in "direct MAF" mode, in which case I'll ditch the multimeter and use that instead. (Edited to add: I think it just gives a percentage, but I assume I can convert that to a voltage by taking it as a percentage of 5V).
What I think is clear from your oscilloscope trace is that the power-on spike should settle back to 0.3V very quickly indeed, within a second or two. That isn't happening on mine - it takes well over 10 seconds.
I'm pretty sure my short-term trims were spending all their time in the left-hand half of the bars as well; I'll try logging it to confirm that.
To disconnect the ECU, it's a case of pulling off the big long connector that goes along one side, right? Does it just pull off?
Edited by Dr Mike Oxgreen on Monday 5th October 12:01
The direct mode reading is a percentage of the voltage where 5 volts = 100% so the maths is is not too complex! When you unplug the ECU, you will see a thumb clip at one end you depress, to release and then pivot the connector away- you will see the bracket it pivots on at the other end.
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