Limp home mode/ bad driving at low revs
19-02-2007, 12:08 PM
#1
Limp home mode/ bad driving at low revs
Still in search to why my sierra cosworth 4x4 (L8, non cat) is in the 'Limp Home Mode' all the time. I try to get the answer what triggers this mode?
Anyone with experience who knows?
Checked and measured all the sensors at the multiplug and they all show the right values. LED test also doesn't show any faults. Checked timing, altough it gets in this mode before the engine is running.
Still my fuel pump keeps pumping all the time when swithing to ignition. I checked the relay is being switch by the ECU. Also changed the chip but this also didn't solve it.
Looks like the ECU itself thinks there is a problem and therefor goes into the 'LOS' mode.
When I do start the engine it can hardly be moved like their is a short of fuel. CO now at 4.5% and fuel pressure at the 3 Bar at idle (pipe connected), so their shouldn't be any fuel starvation for driving away. At this CO setting it can be moved although still with hesitation.
But who knows what all the triggers are to get the ECU in this mode?
Hope someone can help me.
Anyone with experience who knows?
Checked and measured all the sensors at the multiplug and they all show the right values. LED test also doesn't show any faults. Checked timing, altough it gets in this mode before the engine is running.
Still my fuel pump keeps pumping all the time when swithing to ignition. I checked the relay is being switch by the ECU. Also changed the chip but this also didn't solve it.
Looks like the ECU itself thinks there is a problem and therefor goes into the 'LOS' mode.
When I do start the engine it can hardly be moved like their is a short of fuel. CO now at 4.5% and fuel pressure at the 3 Bar at idle (pipe connected), so their shouldn't be any fuel starvation for driving away. At this CO setting it can be moved although still with hesitation.
But who knows what all the triggers are to get the ECU in this mode?
Hope someone can help me.
19-02-2007, 09:17 PM
#2
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Not sure if this is the problem but i had a prob on me saph 2wd would not start so a mate plugged in his L8 went straight into limp mode turned out my altinator was goosed have you checked for that otherwise noy sure mate. 
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26-02-2007, 08:05 AM
#11
Well, as soon as I put it in the ignition mode, the fuel pump starts to run permantly. Normally it would run only for a few seconds. That's what my previous cosworths also did.
Stu told me then that if the fuel pump is wired up correctly (and I have checked and it is) when it constantly runs it means it is detecting something wrong and goes into this LOS mode. So thats how I know its in Limp home mode.
The car has been tuned with a MSD chip, greens, 3 bar mapsensor. But in standard trim it also goes into the LOS mode.
If it is any of you help here is an overview of the values I have measured at the connector (unplugged of the ECU L8 non-cat):
Tamb = 10 Degrees Celsius
Engine is cold
CTS= 6,1 kOhms (pin 11-29)
ATS= 5,8 kOhms (pin 11-31)
Injectors= 4,7-4,9 Ohms (pin 20-18/32/33/35)
Crankpully sensor= 654 Ohms (pin 3-4)
Phase sensor= 765 Ohms (pin 5-23)
Knocksensor= No ohms value (piezo element type) (pin 6-22)
Mapsensor (pin 11-30)= 377 ohms
Mapsensor (pin 11-15)= 4,35 kOhms
Mapsensor (pin 15-30)= 4,72 kOhms
TPS (pin 11-17 at closed throttle)= 43 Ohms (when pushing throttle it goes up to 425 Ohms without hesitations)
TPS (pin 17-30 at closed throttle)= 393 Ohms (when pushing throttle it goes down to 74,3 Ohms without hestitations)
Checked the fuel pressure and even installed a fuelpressure gauge incar and all looks good: 3,1 Bar at idle (pipe connected) then raised with the boost pressure when driving.
Renewed the wiring for the fuelpump to get a healty 12.9 Volt at the pump at idle (was 11,5 Volts).
Cut away the 3 connectors at the bulkboard and resoldered them.
So this LOS mode start witout starting the engine only by switching to ignition. Therefor it seems to detect something directly. Led test doesnt show any faults.
When I adjust the CO to 2,7% like it should be the engine runs fine at idle. As soon as you want to drive away the engine almost stalls and it wont go. Only when putting the CO at about 8-10 % the car still runs fine at idle but then it also want to drive reasonable.
Well hope to have given enough info off what I have done the last few months to find the fault.
Stu told me then that if the fuel pump is wired up correctly (and I have checked and it is) when it constantly runs it means it is detecting something wrong and goes into this LOS mode. So thats how I know its in Limp home mode.
The car has been tuned with a MSD chip, greens, 3 bar mapsensor. But in standard trim it also goes into the LOS mode.
If it is any of you help here is an overview of the values I have measured at the connector (unplugged of the ECU L8 non-cat):
Tamb = 10 Degrees Celsius
Engine is cold
CTS= 6,1 kOhms (pin 11-29)
ATS= 5,8 kOhms (pin 11-31)
Injectors= 4,7-4,9 Ohms (pin 20-18/32/33/35)
Crankpully sensor= 654 Ohms (pin 3-4)
Phase sensor= 765 Ohms (pin 5-23)
Knocksensor= No ohms value (piezo element type) (pin 6-22)
Mapsensor (pin 11-30)= 377 ohms
Mapsensor (pin 11-15)= 4,35 kOhms
Mapsensor (pin 15-30)= 4,72 kOhms
TPS (pin 11-17 at closed throttle)= 43 Ohms (when pushing throttle it goes up to 425 Ohms without hesitations)
TPS (pin 17-30 at closed throttle)= 393 Ohms (when pushing throttle it goes down to 74,3 Ohms without hestitations)
Checked the fuel pressure and even installed a fuelpressure gauge incar and all looks good: 3,1 Bar at idle (pipe connected) then raised with the boost pressure when driving.
Renewed the wiring for the fuelpump to get a healty 12.9 Volt at the pump at idle (was 11,5 Volts).
Cut away the 3 connectors at the bulkboard and resoldered them.
So this LOS mode start witout starting the engine only by switching to ignition. Therefor it seems to detect something directly. Led test doesnt show any faults.
When I adjust the CO to 2,7% like it should be the engine runs fine at idle. As soon as you want to drive away the engine almost stalls and it wont go. Only when putting the CO at about 8-10 % the car still runs fine at idle but then it also want to drive reasonable.
Well hope to have given enough info off what I have done the last few months to find the fault.
26-02-2007, 08:09 AM
#12
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Sorry, didnt read your first post properly.
Can you answer a few questions please.
Does the car idle ok ?
Does it stall when you touch the throttle ?
Does this happen all the time or only when hot/cold ?
Can you answer a few questions please.
Does the car idle ok ?
Does it stall when you touch the throttle ?
Does this happen all the time or only when hot/cold ?
26-02-2007, 08:17 AM
#13
Originally Posted by SECS
Sorry, didnt read your first post properly.
Can you answer a few questions please.
Does the car idle ok ? Yes, the idle is fine.
Does it stall when you touch the throttle ? Yes, when setting the CO to the normal value of 2.7 % it almost want to stall when pushing the throttle.
Does this happen all the time or only when hot/cold ? Especially when its cold it wants to stall, when warm its less
Can you answer a few questions please.
Does the car idle ok ? Yes, the idle is fine.
Does it stall when you touch the throttle ? Yes, when setting the CO to the normal value of 2.7 % it almost want to stall when pushing the throttle.
Does this happen all the time or only when hot/cold ? Especially when its cold it wants to stall, when warm its less
When I adjust the CO to 2,7% like it should be the engine runs fine at idle. As soon as you want to drive away the engine almost stalls and it wont go. Only when putting the CO at about 8-10 % the car still runs fine at idle but then it also want to drive reasonable.
26-02-2007, 09:53 AM
#14
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Have you tested the fuel pressure while the engine is running at idle. ?
Also checked the pressure as you start to drive off ?
If the problem is electrical, it sounds like a map or TPS problem to me.
Here are some tests to try.
Switch ignition off.
Remove cover of the ecu connector and the re-connect ecu plug to ecu.
Switch ignition on - DON NOT START ENGINE.
Using a voltmeter on DC volts - range at least 5 volts.
Push the negative probe into ecu pin 11 where the wire
goes in the back of the connector.
Using the psotive probe,
TEST 1
Connect positive probe to pin 15 (map sensor)
Read the voltage.
TEST 2
Remove map tube from inlet manifold and apply a suction (mouth
)
Read the voltage.
TEST 3
Apply a slight pressure to map tube. (mouth again !)
Read the voltage.
TEST 4
Move the positive probe to pin 17.
Read the voltage.
TEST 5
Depress the throttle half way
Read the voltage
TEST 6
Depress the throttle all the way to the floor
Read the voltage
Also checked the pressure as you start to drive off ?
If the problem is electrical, it sounds like a map or TPS problem to me.
Here are some tests to try.
Switch ignition off.
Remove cover of the ecu connector and the re-connect ecu plug to ecu.
Switch ignition on - DON NOT START ENGINE.
Using a voltmeter on DC volts - range at least 5 volts.
Push the negative probe into ecu pin 11 where the wire
goes in the back of the connector.
Using the psotive probe,
TEST 1
Connect positive probe to pin 15 (map sensor)
Read the voltage.
TEST 2
Remove map tube from inlet manifold and apply a suction (mouth
)Read the voltage.
TEST 3
Apply a slight pressure to map tube. (mouth again !)
Read the voltage.
TEST 4
Move the positive probe to pin 17.
Read the voltage.
TEST 5
Depress the throttle half way
Read the voltage
TEST 6
Depress the throttle all the way to the floor
Read the voltage
26-02-2007, 11:12 AM
#15
Wauw, what an answer!! Glad finally someone can help me further!
I will do these test today so I can give your the results.
I will now printout your reply and do the measurements incar.
Glad finally someone can help me further!
Originally Posted by SECS
Have you tested the fuel pressure while the engine is running at idle. ? Yes, it was measured running at idle.
Also checked the pressure as you start to drive off ? Yes, it didnt dip or did something strange in my opinion.
Also checked the pressure as you start to drive off ? Yes, it didnt dip or did something strange in my opinion.
I will now printout your reply and do the measurements incar.
26-02-2007, 12:01 PM
#19
Well, here are the results:
TEST 1
Connect positive probe to pin 15 (map sensor)
Read the voltage. => 1,537 Volts
TEST 2
Remove map tube from inlet manifold and apply a suction (mouth )
Read the voltage. => 1,0 Volts
TEST 3
Apply a slight pressure to map tube. (mouth again !)
Read the voltage. => 1,7 Volts
TEST 4
Move the positive probe to pin 17.
Read the voltage. => 0,192 Volts
TEST 5
Depress the throttle half way
Read the voltage => 3,3 Volts
TEST 6
Depress the throttle all the way to the floor
Read the voltage => 4,76 Volts
The sucking and blowing was done by my wife
(really, no joke as I had to measure!) and its all average off course. We did all the tests 3 times to see if there were no strange differences between them.
So now I hope you can tell me more with these results!
TEST 1
Connect positive probe to pin 15 (map sensor)
Read the voltage. => 1,537 Volts
TEST 2
Remove map tube from inlet manifold and apply a suction (mouth )
Read the voltage. => 1,0 Volts
TEST 3
Apply a slight pressure to map tube. (mouth again !)
Read the voltage. => 1,7 Volts
TEST 4
Move the positive probe to pin 17.
Read the voltage. => 0,192 Volts
TEST 5
Depress the throttle half way
Read the voltage => 3,3 Volts
TEST 6
Depress the throttle all the way to the floor
Read the voltage => 4,76 Volts
The sucking and blowing was done by my wife
(really, no joke as I had to measure!) and its all average off course. We did all the tests 3 times to see if there were no strange differences between them.So now I hope you can tell me more with these results!
26-02-2007, 12:45 PM
#20
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Those readings look about right to me. 
I presume that you have a 3 bar map sensor on that car ??
Having said that, maps sensors can fail and still give an in range
signal so the ecu fault code generation wont pick it up.
This is relatively rare though.
See if you can borrow a map sensor to try.
Can you rev the car gently and cleanly on the spot ?
Does the rev counter move smoothly when the problem happens ?
Also, have a look inside the distributor at the phase sensor to see
if the wires insulation has not fallen to pieces.
I presume that you have a 3 bar map sensor on that car ??
Having said that, maps sensors can fail and still give an in range
signal so the ecu fault code generation wont pick it up.
This is relatively rare though.
See if you can borrow a map sensor to try.
Can you rev the car gently and cleanly on the spot ?
Does the rev counter move smoothly when the problem happens ?
Also, have a look inside the distributor at the phase sensor to see
if the wires insulation has not fallen to pieces.
26-02-2007, 01:48 PM
#21
Originally Posted by SECS
Those readings look about right to me.
I presume that you have a 3 bar map sensor on that car ?? Yes
Having said that, maps sensors can fail and still give an in range
signal so the ecu fault code generation wont pick it up.
This is relatively rare though.
See if you can borrow a map sensor to try.
The 3 bar mapsensor is brandnew. And I also switched it back to the standard 2 bar map sensor and chip, but no difference, still in LOS mode.
Can you rev the car gently and cleanly on the spot ?
When the engine is cold and you try to rev it instantly than it hesitates very much. As soon as the engine has warmed up its only a little. But thats now at a too high CO setting so I can drive it. When it is set at 2.7% CO the revs go up and down when cold and you cant drive it away.
When I gently rev it to higher rpm than there is no problem all the way up.
Does the rev counter move smoothly when the problem happens ?
Yes, no strange jumping of the rev counter.
Also, have a look inside the distributor at the phase sensor to see
if the wires insulation has not fallen to pieces.
Yes, I already checked that and those wires also look new..
I presume that you have a 3 bar map sensor on that car ?? Yes
Having said that, maps sensors can fail and still give an in range
signal so the ecu fault code generation wont pick it up.
This is relatively rare though.
See if you can borrow a map sensor to try.
The 3 bar mapsensor is brandnew. And I also switched it back to the standard 2 bar map sensor and chip, but no difference, still in LOS mode.
Can you rev the car gently and cleanly on the spot ?
When the engine is cold and you try to rev it instantly than it hesitates very much. As soon as the engine has warmed up its only a little. But thats now at a too high CO setting so I can drive it. When it is set at 2.7% CO the revs go up and down when cold and you cant drive it away.
When I gently rev it to higher rpm than there is no problem all the way up.
Does the rev counter move smoothly when the problem happens ?
Yes, no strange jumping of the rev counter.
Also, have a look inside the distributor at the phase sensor to see
if the wires insulation has not fallen to pieces.
Yes, I already checked that and those wires also look new..
26-02-2007, 01:50 PM
#22
Can you also explain what all the triggers are for the ECU to get in the LOS mode? Maybe that can give me a new clue to look for.
Because when it is in LOS mode does it do some kind of 'emergency' program where values are made different from the basic chip just to keep it running?
Because when it is in LOS mode does it do some kind of 'emergency' program where values are made different from the basic chip just to keep it running?
26-02-2007, 03:28 PM
#25
I also had done the "Basic Fault Findings for Cossie ECUS" by you.
In your last sentence it says "If however, the pump is wired correctly and working properly, if it runs continuously when the ecu is plugged in only, then the ECU and/or chip may have failed."
Well already changed the chip too.
OK, thanks Simon for all you have done for me and I am waiting for your reply. The answer for this fault cant be far away I quess..
In your last sentence it says "If however, the pump is wired correctly and working properly, if it runs continuously when the ecu is plugged in only, then the ECU and/or chip may have failed."
Well already changed the chip too.
OK, thanks Simon for all you have done for me and I am waiting for your reply. The answer for this fault cant be far away I quess..
27-02-2007, 03:27 PM
#26
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It is a mystery this one. ?????????????????
Its hard to diagnose faults like this remotely over the internet.
I would try another ecu first ! I dont have one I can lend you unfortnately.
Its hard to diagnose faults like this remotely over the internet.
I would try another ecu first ! I dont have one I can lend you unfortnately.
27-02-2007, 03:47 PM
#27
Originally Posted by SECS
It is a mystery this one. ?????????????????
Its hard to diagnose faults like this remotely over the internet.
I would try another ecu first ! I dont have one I can lend you unfortnately.
Its hard to diagnose faults like this remotely over the internet.
I would try another ecu first ! I dont have one I can lend you unfortnately.
Do you know if it is possible to change the ECU from a non-cat version (red label) to a cat-version (green label) just for a try?
Or is it possible to do a test with an ECU from a cat-version but than put my non-cat version chip in it?
27-02-2007, 03:57 PM
#29
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Could it not be something more 'mechanically orientated'? i mean it sounds like the fuel supply is fine...but maybe the injectors are duff? (unlikely tbh)
or maybe a significant air leak?
just stabbing in the dark really, but it sounds like all of the electrical avenues are covered, bar the ECU of course
or maybe a significant air leak?
just stabbing in the dark really, but it sounds like all of the electrical avenues are covered, bar the ECU of course
27-02-2007, 04:36 PM
#31
PassionFord Post Troll
Wim...do you live nearby...i have an L8 like you...so we could check if your ECU is faulty..
For the experts...can this be a problem for my own ECU...if i change with his ECU...
oh...ehh..i have a cat version...but i have no cats anymore..and my lambda isnt working either....so i have a program without lambda..hehehe
For the experts...can this be a problem for my own ECU...if i change with his ECU...
oh...ehh..i have a cat version...but i have no cats anymore..and my lambda isnt working either....so i have a program without lambda..hehehe
28-02-2007, 03:34 PM
#33
First of all I want to say sorry and a BIG thanks to all the people who have helped me with this topic. 
Today I found what the problem was. After founding a wiring diagram of the car I started to study it. Then I saw that the fuel pump relay was powered by the fuel injector relay. The fuel injector relay is switched direct to the power when you put it in ignition mode and stays powered. So there I thought maybe I have wired the fuel pump to the wrong relay. And it was
At the time I did the new wiring to the fuel pump I didnt have a wiring diagram. I did knew where the fuelpump relay was located. So therefore I unplugged only the relays with thick wiring under the dashboard untill the fuel pump stalled and other items kept working. Unfortannelly I had pulled out the relay from the fuel injectors before I could pull out the one from the fuel pump, but I didnt know at the time. So when the fuel pump stalled I thought I had found the right relay an wired it up from that relay, the fuel injector one. I did find it strange at the time that I did had to connect the old wire to keep it running. But now with the diagram it all came to pieces..
It now primes only for a moment when you put it in the ignition mode.
So no LOS mode at all!!
Well, still do have the original problem with fuel starvation though. Engine only runs fine when CO set to about 8-10%. And that was the problem where it all started. Setting it to the right 2.7% CO it idles fine (when hot) but runs shit when just driving away and it very very lean thoughout the whole rev range (Ive got an rolling road done and made good power with this very weak mixture).
So if anyone has a tip for me where to look at I am open to that!
Today I found what the problem was. After founding a wiring diagram of the car I started to study it. Then I saw that the fuel pump relay was powered by the fuel injector relay. The fuel injector relay is switched direct to the power when you put it in ignition mode and stays powered. So there I thought maybe I have wired the fuel pump to the wrong relay. And it was
At the time I did the new wiring to the fuel pump I didnt have a wiring diagram. I did knew where the fuelpump relay was located. So therefore I unplugged only the relays with thick wiring under the dashboard untill the fuel pump stalled and other items kept working. Unfortannelly I had pulled out the relay from the fuel injectors before I could pull out the one from the fuel pump, but I didnt know at the time. So when the fuel pump stalled I thought I had found the right relay an wired it up from that relay, the fuel injector one. I did find it strange at the time that I did had to connect the old wire to keep it running. But now with the diagram it all came to pieces..
It now primes only for a moment when you put it in the ignition mode.
So no LOS mode at all!!
Well, still do have the original problem with fuel starvation though. Engine only runs fine when CO set to about 8-10%. And that was the problem where it all started. Setting it to the right 2.7% CO it idles fine (when hot) but runs shit when just driving away and it very very lean thoughout the whole rev range (Ive got an rolling road done and made good power with this very weak mixture).
So if anyone has a tip for me where to look at I am open to that!
28-02-2007, 05:21 PM
#38
Limp home mode solved, but not the main problem..
Originally Posted by Stu @ M Developments
Originally Posted by YBJ
Well, it has green injectors, a new 3 bar mapsensor and a MSD chip for this set up. So cant go wrong there i suppose.
For me I just bought the car in Italy with standard injectors,map sensor and chip. But of course that doensnt mean some previous owners had done something to it that I dont know of. Have written the former owners a letter and asked them all of the history of the car. Unfortannelly none of the four has written back..
Is there a way to find out if the compression rate is standard with een compression test? I mean how to see if the compression is different from standard?
28-02-2007, 05:26 PM
#40
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Ok they seem correct for a stage 3 conversion. 
It all points to a map or fuel pressure problem but those have been checked
Its a mystery....My guess is still the ecu itself is the suspect.
It all points to a map or fuel pressure problem but those have been checked
Its a mystery....My guess is still the ecu itself is the suspect.