T-Pot Readings: This is a strange one...
Discussion
My Tamora has been running very rich recently- thick soot on the exhaust tips, and the lugs well coked up. Anyway, I get the laptop plugged in to see whats what. With ignition on, but engine not running, the main screen on the diagnostics shows everything to be in order- not even anyt fault codes logged. Note- with throttle untouched, tpot readings were 10 and 12%, and both increase smoothly all the way up to 93% as the pedal is depressed fully. Next, I give the throttle a slight tickle, just enough to bring both banks up to about 15%, then start up the engine. Instantly, both tpot readings jump to over 30%!!?? Even with me lifting off the pedal completly (at which point the engien starts to die) the readings are still high 20's. Not surprisingly, both adaptive values are showing max leaning (-37.3 both banks).
So, I think I can safely say I've found the cause of the rich running, as thew engine is dumping in fuel equivelant to 30% throttle whilst its on idle. Problem is, whats causing this? it doesn't make sense to me that the tpots are just faulty, as they respond perfectly when the engine is off, and the fault, whatever it is, is affecting both of them.
Any ideas?
Admin guys: Can you delete my other post created last night- a glitch in the matrix seemed to cause it to save without a title. Thanks.
So, I think I can safely say I've found the cause of the rich running, as thew engine is dumping in fuel equivelant to 30% throttle whilst its on idle. Problem is, whats causing this? it doesn't make sense to me that the tpots are just faulty, as they respond perfectly when the engine is off, and the fault, whatever it is, is affecting both of them.
Any ideas?
Admin guys: Can you delete my other post created last night- a glitch in the matrix seemed to cause it to save without a title. Thanks.
Edited by brogenville on Monday 21st June 08:20
Very high +ve adaptives surely mean not enough air. Sounds like its just really out of adjustment and the throttles are basically sitting virtually shut and sealed at idle. Try cracking open the throttle adjust screw a wee bit, then start the car, then reset the throttle pots from the menu.
See what happens.
See what happens.
Strange one!
There are two possibilities:-
1 - The pots both recieve a 5 volt (Vref) signal from the ECU. The feedback from the pots gives the ECU your throttle positions.
It could be that this is less than 5 volts KOEO (Key On, Engine Off), and this is jumping to 5 volts when you start the car. This would increase the feedback voltage proportionally and give you your problem.
This would point to either a faulty voltage regulator in the ECU or a bad connection somewhere between the ECU and sensors.
You can check the voltage at the sensor end (KOEO) between pins 1 & 3...
2 - The throttle spindles are worn, so that when you start the engine, the vacuum behind the plates is sucking them open slightly.
Can you feel any wear? It would be quite noticable to go from 12% to 28%!
I'm assuming the throttle cable isn't binding slightly as you say it appears fine when the engine is not running.
Failing that it is possible that the throttle pots have worn tracks as they spend a lot of time at idle / slight throttle and usually wear at the same rate for both. They can do some strange things that appear normal on the laptop.
How many miles have they done?
For the sake of 60 quid and a quick reset I would do this (assuming the above is all OK) just for peace of mind and go from there.
HTH
There are two possibilities:-
1 - The pots both recieve a 5 volt (Vref) signal from the ECU. The feedback from the pots gives the ECU your throttle positions.
It could be that this is less than 5 volts KOEO (Key On, Engine Off), and this is jumping to 5 volts when you start the car. This would increase the feedback voltage proportionally and give you your problem.
This would point to either a faulty voltage regulator in the ECU or a bad connection somewhere between the ECU and sensors.
You can check the voltage at the sensor end (KOEO) between pins 1 & 3...
2 - The throttle spindles are worn, so that when you start the engine, the vacuum behind the plates is sucking them open slightly.
Can you feel any wear? It would be quite noticable to go from 12% to 28%!
I'm assuming the throttle cable isn't binding slightly as you say it appears fine when the engine is not running.
Failing that it is possible that the throttle pots have worn tracks as they spend a lot of time at idle / slight throttle and usually wear at the same rate for both. They can do some strange things that appear normal on the laptop.
How many miles have they done?
For the sake of 60 quid and a quick reset I would do this (assuming the above is all OK) just for peace of mind and go from there.
HTH
Mnay thanks nelly, good knowledge, I'll look into both suggestions this evening.
The car has done 29k miles, and I've no reason to believe that they aren't the original tpots. I may just replace both of them anyway for good measure, but given that it sems to be a problem commen to both, I have to suspect that they aren't the root cause. With this in mind, does anyone know if the ecu has separate voltage regulators for the different tpot banks? Or indeed is there just one 5v voltage reg that supplies all engine sensors?
The car has done 29k miles, and I've no reason to believe that they aren't the original tpots. I may just replace both of them anyway for good measure, but given that it sems to be a problem commen to both, I have to suspect that they aren't the root cause. With this in mind, does anyone know if the ecu has separate voltage regulators for the different tpot banks? Or indeed is there just one 5v voltage reg that supplies all engine sensors?
Its worth checking your throttle bodies for wear whilst you are doing the throttle pot change, look for any slop between the butterfly spindles and bodies
It doesnt sound typical of worn bodies but its worth checking -30k is a common time for them to show signs of wear. Also, if they are worn, your throttle pots wont last long
It doesnt sound typical of worn bodies but its worth checking -30k is a common time for them to show signs of wear. Also, if they are worn, your throttle pots wont last long
brogenville said:
Hmmm... so with that being the case, I should be looking for all sensors readings jumping up/down when the engine is started. It sounds unlikley that I wouldn't have noticed this before, but I'll have to check to be sure.
The only other sensor to use Vref is the MAP sensor.The temp. sensors are just resistances WRT Sigrtn.
The injectors coils and lambdas are powered by +12v and the CPS is an inductive sensor.
Does the MAP reading alter between KOEO and KOER?
Good sleuthing nelly (many thanks good sir); vref sits nicely on 5.01V with engine off, but for god knows why, it drops to 4.2V with the engine running, gradually rising to about 4.5V.
I take it this is outside acceptable parameters?
Given that this is something that alters precisely with the engine starting, I'm going to rule out a wiring fault (earth, bad connections etc.). Sadly this leaves but one culprit... mr ecu. Cock. Any chance you think this could be reparable?
Dont suppose anyone knows if all speed six ecu's are compatible with each other? I seem to have the later style mbe ecu (2002 car), so would this one on ebay from an '01 tuscan work out? (obviously I'd swap chips over):
http://cgi.ebay.co.uk/tvr-tuscan-speed-6-engine-ec...
I take it this is outside acceptable parameters?
Given that this is something that alters precisely with the engine starting, I'm going to rule out a wiring fault (earth, bad connections etc.). Sadly this leaves but one culprit... mr ecu. Cock. Any chance you think this could be reparable?
Dont suppose anyone knows if all speed six ecu's are compatible with each other? I seem to have the later style mbe ecu (2002 car), so would this one on ebay from an '01 tuscan work out? (obviously I'd swap chips over):
http://cgi.ebay.co.uk/tvr-tuscan-speed-6-engine-ec...
Edited by brogenville on Monday 21st June 21:46
Edited by brogenville on Monday 21st June 21:54
Isn't there any place local (specialists / fellow owners) that could lend you a spare ECU to test this hypothesis before dropping £150?
Shame you're not a bit closer than Edinburgh!
BTW - the Vref signal should be bang on 5v all the time, and while this does point to the ECU, I'd make double sure that something is not dragging the voltage down before weighing out on a replacement.
A back-back comparison with another vehicle is the only way to be sure.
Shame you're not a bit closer than Edinburgh!
BTW - the Vref signal should be bang on 5v all the time, and while this does point to the ECU, I'd make double sure that something is not dragging the voltage down before weighing out on a replacement.
A back-back comparison with another vehicle is the only way to be sure.
Edited by nelly1 on Monday 21st June 23:35
Alas it could well be more than £150, as I removed my ecu, and it has a completely different style of connector to the one in the ebay add above, so no luck there.
Racing Green have an ecu on their website though... £1,333.63 ha ha! Think I might shop around a bit before I go with that option.
Actually might not be so bad if i was in Edinburgh.... as it is I'm actually in Aberdeen these days. I know there are a few trev's about these parts, but not belonging to anyone I know.
Think I'll give MBE a call tomorrow and see if they offer any kind of repair/diagnosis service.
On a brighter note, my throttle spindle was tight as a drum. Ho hum...
Racing Green have an ecu on their website though... £1,333.63 ha ha! Think I might shop around a bit before I go with that option.
Actually might not be so bad if i was in Edinburgh.... as it is I'm actually in Aberdeen these days. I know there are a few trev's about these parts, but not belonging to anyone I know.
Think I'll give MBE a call tomorrow and see if they offer any kind of repair/diagnosis service.
On a brighter note, my throttle spindle was tight as a drum. Ho hum...
Is yours this type... with the three square-ish connectors?
If so, try plugging / unplugging the connectors a couple of times and give your engine a go again.
The pins on that sort of ECU are tiny, and the plugs are filled with a gel to prevent corrosion - this can cause a dodgy connection - and could be the root cause of your problem :fingerscrossed:
If so, try plugging / unplugging the connectors a couple of times and give your engine a go again.
The pins on that sort of ECU are tiny, and the plugs are filled with a gel to prevent corrosion - this can cause a dodgy connection - and could be the root cause of your problem :fingerscrossed:
Edited by nelly1 on Tuesday 22 June 06:15
Yeah, thats the type that I have. Seems like a really poor quality product too- really cheap and nasty feeling enclosure compared with the older style mbe.
I'll have a good check of the loom tonight before I commit to spending any more money. In the last few hundred miles I've done a 12k service, new ally rad, new racing red nitrons, new light weight flywheel, new clutch and slave. The car just seems to be gobbling up money at a crazy rate right now.
Keep those fingers crossed for me!
I'll have a good check of the loom tonight before I commit to spending any more money. In the last few hundred miles I've done a 12k service, new ally rad, new racing red nitrons, new light weight flywheel, new clutch and slave. The car just seems to be gobbling up money at a crazy rate right now.
Keep those fingers crossed for me!
Has any work been done on the car where the wire looms or HT leads might have been moved in the engine bay?
I had a problem with my SP6 Cerbera that was caused by positioning of the engine loom versus the HT leads. The HT leads did disturb the signals from the sensors and the engine did a lot of strange things, such as big hesitation, felt as the ignition was switched of at 5000 rpm and the adaptive maps was all over both high and low. The car did not pass the emission test at MOT.
In my case the engine loom wasn´t put back in the correct position after a rebuild of the engine, this disturbed signals from both the throttle pots and crank sensor. It took some time to find the problem but it was easy to solve when found. Just rerouted the engine loom and the car has worked fine since (4 years ago).
If you have a instrument where you can see how the signals look (oscilloscope)it could be possible to trace the problem.
I had a problem with my SP6 Cerbera that was caused by positioning of the engine loom versus the HT leads. The HT leads did disturb the signals from the sensors and the engine did a lot of strange things, such as big hesitation, felt as the ignition was switched of at 5000 rpm and the adaptive maps was all over both high and low. The car did not pass the emission test at MOT.
In my case the engine loom wasn´t put back in the correct position after a rebuild of the engine, this disturbed signals from both the throttle pots and crank sensor. It took some time to find the problem but it was easy to solve when found. Just rerouted the engine loom and the car has worked fine since (4 years ago).
If you have a instrument where you can see how the signals look (oscilloscope)it could be possible to trace the problem.
The earth is rising!!!
As reccomended to me on here, I put the voltmetre across the ground termainl on the tpot plug and the engine block: 6.5mV with engine off (which is easily just the error in my cheap digital multimetre), but a whopping 0.4V with the engine on. in fairness, this doesnt totally explain why the voltage read across the 5V Vref and Tpot ground drops by up to 0.7V, but its certainly of note.
Secondly, and I'm ashamed not to have picked up on this before, but the air and water temps read on the laptop both drop by about 6 degrees when the engine is started, and looking at the wiring diagram, they both use the same ground as the tpots.
Thirdly, i notice that the reading on the baro sensor doesnt budge when the engine is started, and seemingly this uses the same 5V Vref as the tpots.
Sooooooo... could I just have a bad earth? An earth which grounds the engine bay sensors, but not the baro sensor in the cabin???
[I'm quite glad that its looking slightly less likely that I wont need a new ECU. ]
As reccomended to me on here, I put the voltmetre across the ground termainl on the tpot plug and the engine block: 6.5mV with engine off (which is easily just the error in my cheap digital multimetre), but a whopping 0.4V with the engine on. in fairness, this doesnt totally explain why the voltage read across the 5V Vref and Tpot ground drops by up to 0.7V, but its certainly of note.
Secondly, and I'm ashamed not to have picked up on this before, but the air and water temps read on the laptop both drop by about 6 degrees when the engine is started, and looking at the wiring diagram, they both use the same ground as the tpots.
Thirdly, i notice that the reading on the baro sensor doesnt budge when the engine is started, and seemingly this uses the same 5V Vref as the tpots.
Sooooooo... could I just have a bad earth? An earth which grounds the engine bay sensors, but not the baro sensor in the cabin???
[I'm quite glad that its looking slightly less likely that I wont need a new ECU.
]The main loom earth point is to the gearbox just behind the CPS (Crank Sensor). Airbox off job but easy once that's done.
However - the main earth (0v) is not where the sensors return to - this is Sigrtn to the module.
It's possible that where these all join in the loom, you may have issues a la this thread...
:fingersstillcrossed:
ETA - The module could not generate a stable Sigrtn without a secure ground, so it'll be easier to check this first before attacking your loom with a Stanley knife!
However - the main earth (0v) is not where the sensors return to - this is Sigrtn to the module.
It's possible that where these all join in the loom, you may have issues a la this thread...
:fingersstillcrossed:
ETA - The module could not generate a stable Sigrtn without a secure ground, so it'll be easier to check this first before attacking your loom with a Stanley knife!
Edited by nelly1 on Wednesday 23 June 23:57
Been spending the last few hours checking different grounds. Sadly, everything looks sound (though everything got cleaned up as I went anyway). It is interesting what you were saying about the ecu ground, as this wire did have to come off when I changed the clutch recently. Truth is, when I put everything back together with the clutch fitting, I couldn't remember exactly which bolt held tihs wire on, so I just bolted it on with one of the starter motor bolts. I can't imagine this would matter though, since any induced voltage the starter could cause would stop as soon as the starter stops (though I guess there will be a fairly hefty magnet in the starter solenoid)? Out of interest then, what bolt would this ground normally be connected to?
See picture below for where I have the ecu ground connected to:
So, you think its possible that a connection to this ground inside the loom could be corroded, meaning when the engine starts running, and the ecu starts using more current, it struggles to get a stable ground? There was a post recently where someone traced an injector fault to corrosion inside the sealed loom.
Hmmmmm....
See picture below for where I have the ecu ground connected to:
So, you think its possible that a connection to this ground inside the loom could be corroded, meaning when the engine starts running, and the ecu starts using more current, it struggles to get a stable ground? There was a post recently where someone traced an injector fault to corrosion inside the sealed loom.
Hmmmmm....
Edited by brogenville on Thursday 24th June 00:24
brogenville said:
It is interesting what you were saying about the ecu ground, as this wire did have to come off when I changed the clutch recently. Truth is, when I put everything back together with the clutch fitting, I couldn't remember exactly which bolt held tihs wire on, so I just bolted it on with one of the starter motor bolts...
Is this when your problem started, or was it evident before the clutch change?The loom (and therefore ECU) earth should be sited away from the starter body.
When you start the engine, the heavy current from the starter will try to earth anywhere it can - this should be via the bellhousing / engine block to the heavy gauge engine earth (have you checked this BTW?).
It's possible the current surge may have damaged the ECU.
I would definitely move the loom earth away from the starter body to a bellhousing bolt, and if the problem persists, you really need to try a different module IMO.
That earth could be the problem, should be on the highest bell housing bolt.
other things:
-Balance throttles and reset adaptives and throttle via laptop.
-Check lambda's aren't being 'lazy', just being curious but wat do they read?
-Just go Omex
other things:
-Balance throttles and reset adaptives and throttle via laptop.
-Check lambda's aren't being 'lazy', just being curious but wat do they read?
-Just go Omex
Edited by -Jamie- on Friday 25th June 17:38
Ok, problem solved... sortof. I did first look to try and reinstate the ecu ground where it was previously, however given that I tightened this bolt up with a ratchet whilst the gearbox was off, there is now very limited room to get at this bolt with anything with the same leverage. The upshot is that I couldn't shift the bell-housing bolt where I wanted to put the earth. In any case, I tested the engine with the earth pressed against the bell-housing at the same location, and it didn't seem to make any difference. So, I checked all earths (one at front of car, one at OS engine mount, one behind battery, one in pass foot well)- all fine. Then I started to look for corrosion in the loom; I didn't want to chop the whole lot up but I opened a few bits and fond nothing a-miss. Getting annoyed at this point I decided to just cheat. So, I mounted the ecu earth in a new location, and installed some new earths to the same location that have been spliced into the ground connection for each of the t-pots (just behind the sensors themselves). The result is that all sensors show the same values with the engine on or off. Glorious. Speaking as an engineer however, this is not a neat solution, and particularly frustrating as I still don't really know whats caused the electrical problems in the first place. However, the sun is shining outside, and this gets me going again.
Actually, its not quite that simple. All the over-fueling has buggered the lambda's, so I've whipped them out and ordered a couple of new ones this evening. The fun just keeps on coming!
Thanks to all for the helpful suggestions.
Actually, its not quite that simple. All the over-fueling has buggered the lambda's, so I've whipped them out and ordered a couple of new ones this evening. The fun just keeps on coming!
Thanks to all for the helpful suggestions.
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