Low Load Hesitation
15 February 2002, 10:59 PM
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I have posted about this problem before but I now finally got it cured - YIPEE!!
I decided to take the car to Power Engineering and am delighted to tell you all that they have resolved the problem completely!! I was very impressed with their service and Chris was very helpful and confident that he could resolve the problem.
As requested, I left the car with them for the day and when I returned, Chris had a big beaming smile on his face which meant that he had found the problem. It turned out to be the Lamda sensor as suggested by Stuart Brooks at the tail end of last year. The sensor had failed and this resulted in the engine running lean when in closed loop mode (i.e. at low RPM). Apparently, this does not show up on the Select Monitor which is a bit of a mystery to me as I believe that it has a fault code of 32 so I am surprised that the monitor does not read it? However, the gas emissions analyser run alongside the rolling road indicated that the engine was running lean in closed loop mode and a subsequent electrical test by Chris showed the sensor to have failed.
Replacing the Lambda sensor has completely resolved this problem and ended 6 months of frustration with this 'apparently intermittent' fault. I say 'apparently intermittent' because knowing what the fault was explains why it only happened under certain circumstances - i.e. at low load. low RPM after a fast drive.
The ECU being self learning, adjusts the engine on the fly at engine speeds over 3,000 RPM and the Lambda sensor is ignored. As the engine heats up, the mixture tends to 'lean out' but the ECU compensates for this as part of it's self learning protocol but as you slow down after a fast drive and get below 3000 RPM at low loads, the ECU switches to closed loop Lambda sensing mode and the faulty sensor then misreports the relatively lean mixture allowing the engine to run too lean, leading to hesistation. Not the best description perhaps but it is a summary from memory of what I was told on the day!
Thanks Chris and Power Engineering for resolving the annoying problem!
Steve
I decided to take the car to Power Engineering and am delighted to tell you all that they have resolved the problem completely!! I was very impressed with their service and Chris was very helpful and confident that he could resolve the problem.
As requested, I left the car with them for the day and when I returned, Chris had a big beaming smile on his face which meant that he had found the problem. It turned out to be the Lamda sensor as suggested by Stuart Brooks at the tail end of last year. The sensor had failed and this resulted in the engine running lean when in closed loop mode (i.e. at low RPM). Apparently, this does not show up on the Select Monitor which is a bit of a mystery to me as I believe that it has a fault code of 32 so I am surprised that the monitor does not read it? However, the gas emissions analyser run alongside the rolling road indicated that the engine was running lean in closed loop mode and a subsequent electrical test by Chris showed the sensor to have failed.
Replacing the Lambda sensor has completely resolved this problem and ended 6 months of frustration with this 'apparently intermittent' fault. I say 'apparently intermittent' because knowing what the fault was explains why it only happened under certain circumstances - i.e. at low load. low RPM after a fast drive.
The ECU being self learning, adjusts the engine on the fly at engine speeds over 3,000 RPM and the Lambda sensor is ignored. As the engine heats up, the mixture tends to 'lean out' but the ECU compensates for this as part of it's self learning protocol but as you slow down after a fast drive and get below 3000 RPM at low loads, the ECU switches to closed loop Lambda sensing mode and the faulty sensor then misreports the relatively lean mixture allowing the engine to run too lean, leading to hesistation. Not the best description perhaps but it is a summary from memory of what I was told on the day!
Thanks Chris and Power Engineering for resolving the annoying problem!
Steve
16 February 2002, 09:49 PM
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Steve did you experience the hesitation when slowly accelerating between 2-3000 rpm as I am experiencing this when the car is at normal operating temp. Also what MY is your vehicle? I would be very interested to hear your comments as it may answer my hesitation problem.
Thanks Stuart
Thanks Stuart
17 February 2002, 08:59 PM
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SNAP
hesitation at 2-3000rpm when runing norm temp ok on full
power but when steddy 2-3000rpm hesitation must book her in
to power engineering what did it cost must do some over time
car my93 wrx
Neil
18 February 2002, 09:10 AM
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Stuart/Neil,
The following is a summary of the exact features of my problem which has been completely cured after an exasperating 6 month search for a solution! My car is an Sti MY98 Ver IV Wagon.
The symptoms that I was getting were that between approx. 2500 and 3000 RPM, the car lurched and hesitated under LIGHT throttle loads. More right pedal and the car took off like a dream; reach 3000 RPM and it was like someone turned on the sweet switch and she would be silky smooth again. My problem was 'intermittent' apart from the fact that over the six months that it was 'doing my head in', I got to analyse the circumstances under which it occurred. There were two sets of circumstances that would set the problem off.
1. After a hard drive of say five miles or so, slowing down to 'town speed' and just trundling along with a low load on the throttle, the engine would immediately start to misbehave. After 2 or 3 miles of gentle town driving, the problem would go away.
2. After a prolonged drive on a motorway (in excess of 7 or so miles at a speed of maybe 70-80 MPH) coming off at a slip road to join an ordinary local/town road, again just trundling along with a low load on the throttle, the engine would immediately start to misbehave. After 2 or 3 miles of gentle town driving, the problem would go away.
In both cases, the problem could be clearly felt in any gear at low load between 2500 and 3000RPM. Occasionally, if I had driven hard and fast for a prolonged period of time, the hesitation range would creep up to as high as 3500RPM and on a couple of occasions down to maybe 2200 RPM.
From start-up in the morning, the car would run beautifully and if I did not drive hard or fast at any time during the journey, all would be well.
The cost was £223.97 including VAT but that included a full rolling road check and the relevant graph printout as well as the replacement part (a universal Lambda sensor as an 'official' one was not available in time).
The car is now faultless again.
Hope this helps.
For what it is worth, the following is the power/torque plot:-
[Edited by Steve Richards - 2/18/2002 9:12:19 AM]
[Edited by Steve Richards - 2/18/2002 9:57:57 PM]
The following is a summary of the exact features of my problem which has been completely cured after an exasperating 6 month search for a solution! My car is an Sti MY98 Ver IV Wagon.
The symptoms that I was getting were that between approx. 2500 and 3000 RPM, the car lurched and hesitated under LIGHT throttle loads. More right pedal and the car took off like a dream; reach 3000 RPM and it was like someone turned on the sweet switch and she would be silky smooth again. My problem was 'intermittent' apart from the fact that over the six months that it was 'doing my head in', I got to analyse the circumstances under which it occurred. There were two sets of circumstances that would set the problem off.
1. After a hard drive of say five miles or so, slowing down to 'town speed' and just trundling along with a low load on the throttle, the engine would immediately start to misbehave. After 2 or 3 miles of gentle town driving, the problem would go away.
2. After a prolonged drive on a motorway (in excess of 7 or so miles at a speed of maybe 70-80 MPH) coming off at a slip road to join an ordinary local/town road, again just trundling along with a low load on the throttle, the engine would immediately start to misbehave. After 2 or 3 miles of gentle town driving, the problem would go away.
In both cases, the problem could be clearly felt in any gear at low load between 2500 and 3000RPM. Occasionally, if I had driven hard and fast for a prolonged period of time, the hesitation range would creep up to as high as 3500RPM and on a couple of occasions down to maybe 2200 RPM.
From start-up in the morning, the car would run beautifully and if I did not drive hard or fast at any time during the journey, all would be well.
The cost was £223.97 including VAT but that included a full rolling road check and the relevant graph printout as well as the replacement part (a universal Lambda sensor as an 'official' one was not available in time).
The car is now faultless again.
Hope this helps.
For what it is worth, the following is the power/torque plot:-
[Edited by Steve Richards - 2/18/2002 9:12:19 AM]
[Edited by Steve Richards - 2/18/2002 9:57:57 PM]
18 February 2002, 02:13 PM
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Thanks Steve
your info has helped alot booking the old girl in when back from Geneva motor show she has cost me £435 so far this month
but i love her so much (sad t**t)
Neil
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22 February 2002, 09:17 AM
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Scott,
Yes I do know which one it is. The original part fitted to the car by Subaru was supplied by Bosch even though there are excellent ones made by the Japanese themselves. Unfortunately, P E could not get a replacement that day and as I had come a long way for the session and they knew that I couldn't leave the car longer thana working day, they decided to fit the universal in it's place. This did have the advantage of being considerably less money though.
The manufacturer of my replacement was the Japanese manufacturer NTK (distributed by Commercial Ignition). NTK are the same people as NGK who make the spark plugs!
The cost was £65.61 plus vat but being 'universal', it comes without a Subaru 'plug'. Not a problem though as it does come with some good quality crimp connectors.
I am very happy with mine and very grateful to Power Engineering for sorting it.
[Edited by Steve Richards - 2/22/2002 9:20:37 AM]
Yes I do know which one it is. The original part fitted to the car by Subaru was supplied by Bosch even though there are excellent ones made by the Japanese themselves. Unfortunately, P E could not get a replacement that day and as I had come a long way for the session and they knew that I couldn't leave the car longer thana working day, they decided to fit the universal in it's place. This did have the advantage of being considerably less money though.
The manufacturer of my replacement was the Japanese manufacturer NTK (distributed by Commercial Ignition). NTK are the same people as NGK who make the spark plugs!
The cost was £65.61 plus vat but being 'universal', it comes without a Subaru 'plug'. Not a problem though as it does come with some good quality crimp connectors.
I am very happy with mine and very grateful to Power Engineering for sorting it.
[Edited by Steve Richards - 2/22/2002 9:20:37 AM]
24 February 2002, 08:02 PM
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Steve,
I have a STI 3 with a 4 lump fitted & have been experiencing a similair intermittent problem, it became a lot worse recently when I ran a couple of tanks of esso SUL instead of Optimax, I put this down to a lower octane & had intended to try octane booster to cure it. My local garage had guessed the Lamba sensor was probably at fault but were not sure why no fault code showed.
Anyway thanks for the answer & new sensor will go on ASAP
Regards
Stuart
I have a STI 3 with a 4 lump fitted & have been experiencing a similair intermittent problem, it became a lot worse recently when I ran a couple of tanks of esso SUL instead of Optimax, I put this down to a lower octane & had intended to try octane booster to cure it. My local garage had guessed the Lamba sensor was probably at fault but were not sure why no fault code showed.
Anyway thanks for the answer & new sensor will go on ASAP
Regards
Stuart
25 February 2002, 10:39 AM
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There is no fault code shown for this device unless it is measuring outside the accepted range (.1v to .9v) and on my one, it was 'stuck' at .3v so as far as the ECU was concerned, all was well!
I hope your problem is cured satisfactorily.
Steve
I hope your problem is cured satisfactorily.
Steve
25 February 2002, 10:56 AM
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Steve
How did you tell it was stuck at .3 what did you check it with or was it PE that checked it for you?
Also I have enquired about buying a universal CO sensor and the motor factors I have asked have said they do sell them and the only difference is the number of wires they have, but when I told them the car it was for they said CO sensors for japanese cars are different so you have to buy them from the main dealer.
Stuart
How did you tell it was stuck at .3 what did you check it with or was it PE that checked it for you?
Also I have enquired about buying a universal CO sensor and the motor factors I have asked have said they do sell them and the only difference is the number of wires they have, but when I told them the car it was for they said CO sensors for japanese cars are different so you have to buy them from the main dealer.
Stuart
25 February 2002, 05:36 PM
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Stuart,
PE did the diagnostics on the rolling road and determined the fault from the gas analyser which showed that I was running lean on 'closed loop' (i.e. when the lambda sensor is in use). They were then able to measure the actual voltage output of the sensor and they discovered that it remained constant at .3v all the time whereas it should be jumping about.
I would dispute the info. from the factors about the sensor as mine is now perfect and apparently PE often fit this type if they cannot get hold of the OEM version.
Why not give PE a call, they were very helpful and they may sell you the correct one for you to fit yourself although you will need to cut of the socket from your loom and use the crimp connectors supplied with the new sensor.
Steve
PE did the diagnostics on the rolling road and determined the fault from the gas analyser which showed that I was running lean on 'closed loop' (i.e. when the lambda sensor is in use). They were then able to measure the actual voltage output of the sensor and they discovered that it remained constant at .3v all the time whereas it should be jumping about.
I would dispute the info. from the factors about the sensor as mine is now perfect and apparently PE often fit this type if they cannot get hold of the OEM version.
Why not give PE a call, they were very helpful and they may sell you the correct one for you to fit yourself although you will need to cut of the socket from your loom and use the crimp connectors supplied with the new sensor.
Steve
25 February 2002, 07:38 PM
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Steve, the plot thickens
I have contacted NGK Technical direct. They have said "The sensors we import are not universal, They are all supplied with correct length leads & correct block connectors to fit straight in vehicles loom. We do not have a sensor listed for an Impreza. Please check, however the sensor fitted may be an NTK sensor, it may have a number on the body, let us know number & we may be able to help " etc etc
I know you said you could not see part no, but do you have a phone no for Commercial ignition or do you know where they are based so I can try directory enquires
Sorry to be a pain
Stuart J
I have contacted NGK Technical direct. They have said "The sensors we import are not universal, They are all supplied with correct length leads & correct block connectors to fit straight in vehicles loom. We do not have a sensor listed for an Impreza. Please check, however the sensor fitted may be an NTK sensor, it may have a number on the body, let us know number & we may be able to help " etc etc
I know you said you could not see part no, but do you have a phone no for Commercial ignition or do you know where they are based so I can try directory enquires
Sorry to be a pain
Stuart J
25 February 2002, 08:58 PM
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Stuart,
No pain at all I promise you. The part is definitely an NTK (NOT NGK)although they are, I believe the same company. However, I will attempt to get a part number for you off mine at an early opportunity - no offence but it is hissing with rain here at the moment so I will not offer to try tonight!!
The good news is, I have the address of Commercial ignition for you:-
Commercial Ignition
Newman Street
Burton Latimer
Kettering
Northamptonshire
NN15 5SH
East Midlands
Phone no. 01536 724662
Try them and let me know how you get on. I will try and get a part number for you as well though (from memory though, it has 4 wires and I saw a brand new one in its box at PE and it definitely had 4 pink (really!) crimp connectors on it indicating that it really was a universal).
Good luck.
I decided to get wet as it is such a good cause!! There is a number on the HEX part of the sensor that says 8B12. When conditions are better I will remove the sensor and have a look for any more markings.
Steve
[Edited by Steve Richards - 2/25/2002 9:09:49 PM]
No pain at all I promise you. The part is definitely an NTK (NOT NGK)although they are, I believe the same company. However, I will attempt to get a part number for you off mine at an early opportunity - no offence but it is hissing with rain here at the moment so I will not offer to try tonight!!
The good news is, I have the address of Commercial ignition for you:-
Commercial Ignition
Newman Street
Burton Latimer
Kettering
Northamptonshire
NN15 5SH
East Midlands
Phone no. 01536 724662
Try them and let me know how you get on. I will try and get a part number for you as well though (from memory though, it has 4 wires and I saw a brand new one in its box at PE and it definitely had 4 pink (really!) crimp connectors on it indicating that it really was a universal).
Good luck.
I decided to get wet as it is such a good cause!! There is a number on the HEX part of the sensor that says 8B12. When conditions are better I will remove the sensor and have a look for any more markings.
Steve
[Edited by Steve Richards - 2/25/2002 9:09:49 PM]
26 February 2002, 07:45 PM
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Thanks for all your help Steve,
I will contact Commercial later this week.
Iwill also email the ref No you gave me to NTK, they may be able to identify it from that.
Regards
Stuart
I will contact Commercial later this week.
Iwill also email the ref No you gave me to NTK, they may be able to identify it from that.
Regards
Stuart
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