Incorrect Lambda reading - Rovergauge - AFM
Discussion
Hi All,
I hope the Chim-crowd reads here as well since they have the same engines.
I have a serp 500Griff from 1997 with CAT.
I recently found out with rovergauge, that my lambdas reading apparently rich and the 14CUX tried to correct that.
The long term fuel trim in rovergauge was all the way down to -100% both banks.
But the Lambdas were still working, since the short term values were still going up and down.
So I hooked the oscilloscope to the lambdas and really - the read lean (cycling rich-lean, but stayed on the lean side most of the time).
I read on here, that the reason may be a shot AFM. There is also a test described somewhere, that the sensing voltage of the AFM has to drop to 0.3V immediately after startup - mine didn't and took some seconds to end up at 0.5V. So I bought one off Rimmerbros called ERR 5198 and swapped it.
Now my long term trim values go all the way to +100% - wtf(?)! And it really runs rich at Idle and has misfires (which surely don't help).
1st Question: Is there an explanation, why a faulty AFM should make the Lambdas read wrong (or be misunderstood by the 14CUX)?
2nd Question: May the ERR-5198 be wrong? (It is not RR since there are only aftermarket versions available)
Anyone has experienced that?
The only thing I changed is the Rover distributor that I swapped to the 123Tune - could that be it?
I hope somebody can help!
Rgds,
Marvin
I hope the Chim-crowd reads here as well since they have the same engines.
I have a serp 500Griff from 1997 with CAT.
I recently found out with rovergauge, that my lambdas reading apparently rich and the 14CUX tried to correct that.
The long term fuel trim in rovergauge was all the way down to -100% both banks.
But the Lambdas were still working, since the short term values were still going up and down.
So I hooked the oscilloscope to the lambdas and really - the read lean (cycling rich-lean, but stayed on the lean side most of the time).
I read on here, that the reason may be a shot AFM. There is also a test described somewhere, that the sensing voltage of the AFM has to drop to 0.3V immediately after startup - mine didn't and took some seconds to end up at 0.5V. So I bought one off Rimmerbros called ERR 5198 and swapped it.
Now my long term trim values go all the way to +100% - wtf(?)! And it really runs rich at Idle and has misfires (which surely don't help).
1st Question: Is there an explanation, why a faulty AFM should make the Lambdas read wrong (or be misunderstood by the 14CUX)?
2nd Question: May the ERR-5198 be wrong? (It is not RR since there are only aftermarket versions available)
Anyone has experienced that?
The only thing I changed is the Rover distributor that I swapped to the 123Tune - could that be it?
I hope somebody can help!
Rgds,
Marvin
Thanks a lot guys!
I did contact Mark, lets see if he can come up with something.
Is it possible, that a new AFM may have its CO-trim value not adjusted and I have to do that?
I read two instructions:
1) With the AFM connected, make sure between the red/black cable and the red/blue cable are 1.8V (CAT car) - adjust the trim with the adjusting screw on the outside.
2) With the AFM disconnected, make sure the resistance between the outer two pins is 300Ohm. Again - adjusted by outside screw.
Anyone done that before?
Shouldn't the AFMs come with 1.8V out of the box?
I have currently no time to go to the garage and I will check that later.
Have fun!
Marvin
I did contact Mark, lets see if he can come up with something.
Is it possible, that a new AFM may have its CO-trim value not adjusted and I have to do that?
I read two instructions:
1) With the AFM connected, make sure between the red/black cable and the red/blue cable are 1.8V (CAT car) - adjust the trim with the adjusting screw on the outside.
2) With the AFM disconnected, make sure the resistance between the outer two pins is 300Ohm. Again - adjusted by outside screw.
Anyone done that before?
Shouldn't the AFMs come with 1.8V out of the box?
I have currently no time to go to the garage and I will check that later.
Have fun!
Marvin
Hi Mark,
Thanks a lot for your reply.
If I understand that correctly I have a Chinese copy and no genuine Lucas part. That is why the measured value is slightly off and therefore the 14CUX gets confused and messes with the long term trim.
Now can I do anything with the CO adjustment or will that not help?
Could I do anything in the cable, like adding a resistor?
Rimmer Bros advertised this AFM as "aftermarket" so at least they were not lying. Where do I get a real one and how do I recognize it?
Have fun!
Marvin
Thanks a lot for your reply.
If I understand that correctly I have a Chinese copy and no genuine Lucas part. That is why the measured value is slightly off and therefore the 14CUX gets confused and messes with the long term trim.
Now can I do anything with the CO adjustment or will that not help?
Could I do anything in the cable, like adding a resistor?
Rimmer Bros advertised this AFM as "aftermarket" so at least they were not lying. Where do I get a real one and how do I recognize it?
Have fun!
Marvin
Hi again and thanks for your help!
Especially Mark, who was a great help!
In fact it was only a broken AFM. I got a used one now that works.
So here is what we learned:
-if you long term lambda trim values are high or low (beyond 60%) your AFM is probably dead.
-The Chinese copies are crap.
-When you have a cat car, the trim value is ignored (as Mark stated before).
I ordered a new one from Rimmers and it is a Chinese copy and it goes all the way rich in idle.
I measured the trim value and it was 1.9V (instead of the 1.8V for cat cars).
I adjusted the trim value and nothing changed.
Now I want to have something I can monitor the lambda values. Can someone tell me where I can get the plugs for the harness? And what part number they have?
Thanks!
Marvin
Especially Mark, who was a great help!
In fact it was only a broken AFM. I got a used one now that works.
So here is what we learned:
-if you long term lambda trim values are high or low (beyond 60%) your AFM is probably dead.
-The Chinese copies are crap.
-When you have a cat car, the trim value is ignored (as Mark stated before).
I ordered a new one from Rimmers and it is a Chinese copy and it goes all the way rich in idle.
I measured the trim value and it was 1.9V (instead of the 1.8V for cat cars).
I adjusted the trim value and nothing changed.
Now I want to have something I can monitor the lambda values. Can someone tell me where I can get the plugs for the harness? And what part number they have?
Thanks!
Marvin
I fixed it!
I had the same problem with a new (used original TVR) AFM (too low Lambda trim).
Than I realized that the AFM works fine with the bonnet open. I first thought it is due to the heat.
But later I realized I had worn off the insulation of the cable to the connector. When the bonnet was closed there was a short circuit on the aluminum heat shield under the bonnet.
Insulating the cables with electric tape cured all my problems!
Guys, check your cables. I know the original harness insulation is brittle, so that may cause all sorts of problems.
Have fun!
Marvin
I had the same problem with a new (used original TVR) AFM (too low Lambda trim).
Than I realized that the AFM works fine with the bonnet open. I first thought it is due to the heat.
But later I realized I had worn off the insulation of the cable to the connector. When the bonnet was closed there was a short circuit on the aluminum heat shield under the bonnet.
Insulating the cables with electric tape cured all my problems!
Guys, check your cables. I know the original harness insulation is brittle, so that may cause all sorts of problems.
Have fun!
Marvin
Hi,
I have to revise my last post. It is not fixed. I figured that is the heat. I wrapped up the AFM in heat reflecting foil and it stayed cooler. That made it read more air and let in more fuel.
However, there are some problems:
A) I cannot really insulate the AFM, after some time it will always getting hot and act up. I don't know how to keep it cool.
B) I am not sure if it is just the case of some old AFM or if they are always like that? Is it possible that they become heat sensitive when aged (happened to my Grandma)?
Finally: Does anyone ever opened one and maybe I can tune it to compensate for that effect? Because hot environment is normal and being a bit rich when cold would be ok.
Marvin
I have to revise my last post. It is not fixed. I figured that is the heat. I wrapped up the AFM in heat reflecting foil and it stayed cooler. That made it read more air and let in more fuel.
However, there are some problems:
A) I cannot really insulate the AFM, after some time it will always getting hot and act up. I don't know how to keep it cool.
B) I am not sure if it is just the case of some old AFM or if they are always like that? Is it possible that they become heat sensitive when aged (happened to my Grandma)?
Finally: Does anyone ever opened one and maybe I can tune it to compensate for that effect? Because hot environment is normal and being a bit rich when cold would be ok.
Marvin
Hi Mark,
Honestly I am not sure if it is the AFM or not. What I see is that the ECU has a long-term fuel trim of 20% to -35% as long as things stay cool. Whenever I go a bit faster (fast mountain roads etc) the AFM gets really hot and ECU long term trim goes to -100%.
Car runs so lean that it misfires. The misfires I can feel as part-load hesitation.
I suspect the AFM, because whenever I let her idle with open bonnet, the AFM stays cooler and everything works fine. If I drive her after idling for a while, no part-load hesitation.
Also, If I reset the ECU (by switching power to the ECU off and on again) and fuel maps are default, she runs fine and I have no part load hesitation.
I tested that with a second AFM, which seemed to be ok. But after some hot runs the other AFM does the same - Now I don`t know if the AFM is shot also or if my error is somewhere else.
I also tried a Chinese copy of the AFM and it makes the ECU go over rich from the start ( +100% fuel trim).
Could it be something else?
Does anyone have a known to be good AFM somewhere?
What else can I test (I tested the voltages at the AFM, but both tested ok).
What can I do?
Thanks!
Marvin
Honestly I am not sure if it is the AFM or not. What I see is that the ECU has a long-term fuel trim of 20% to -35% as long as things stay cool. Whenever I go a bit faster (fast mountain roads etc) the AFM gets really hot and ECU long term trim goes to -100%.
Car runs so lean that it misfires. The misfires I can feel as part-load hesitation.
I suspect the AFM, because whenever I let her idle with open bonnet, the AFM stays cooler and everything works fine. If I drive her after idling for a while, no part-load hesitation.
Also, If I reset the ECU (by switching power to the ECU off and on again) and fuel maps are default, she runs fine and I have no part load hesitation.
I tested that with a second AFM, which seemed to be ok. But after some hot runs the other AFM does the same - Now I don`t know if the AFM is shot also or if my error is somewhere else.
I also tried a Chinese copy of the AFM and it makes the ECU go over rich from the start ( +100% fuel trim).
Could it be something else?
Does anyone have a known to be good AFM somewhere?
What else can I test (I tested the voltages at the AFM, but both tested ok).
What can I do?
Thanks!
Marvin
Hi Mark,
Thanks for your help.
Here is what happened. Had 25°C outside today and started her up. After initial warm-up and O2 sensors started switching the ECU immediately went to -100% fuel trim (long term). Even the short term was around -70% to -90% on top of that.
MAF reading was 39% to 40% at idle (850 to 950 RPM)
After running a bit and getting stuck in a traffic jam, reading dropped down to 36% to 37%.
Long term trim recovered to -47% to -64%.
Car ran nice all the time!
Since I have a 123Tune ignition, I reduced the vacuum advance by 2° to 8°@14"Hg. I had almost no part load hesitation.
Is it possible that I am chasing a phantom problem? Maybe everything is ok? I am just worried that if some adjustment values are maxed out, something is not quite right?
Marvin
P.S. Mark, I read your comment on adapting the 20AM to the 14CUX and your problem with the electronics at 130°C. If they worked at 130°C but could not cope with the temp swings between cold start-up and said 130°, there is one solution: Heat them up to 130°C.
A friend of mine develops electronics for a living and he told me that. If you have temperature sensitive electronics, heat them to a value (controlled electric heat circuitry) that ambient temps do not reach. Than they will be stable all the time.
Thanks for your help.
Here is what happened. Had 25°C outside today and started her up. After initial warm-up and O2 sensors started switching the ECU immediately went to -100% fuel trim (long term). Even the short term was around -70% to -90% on top of that.
MAF reading was 39% to 40% at idle (850 to 950 RPM)
After running a bit and getting stuck in a traffic jam, reading dropped down to 36% to 37%.
Long term trim recovered to -47% to -64%.
Car ran nice all the time!
Since I have a 123Tune ignition, I reduced the vacuum advance by 2° to 8°@14"Hg. I had almost no part load hesitation.
Is it possible that I am chasing a phantom problem? Maybe everything is ok? I am just worried that if some adjustment values are maxed out, something is not quite right?
Marvin
P.S. Mark, I read your comment on adapting the 20AM to the 14CUX and your problem with the electronics at 130°C. If they worked at 130°C but could not cope with the temp swings between cold start-up and said 130°, there is one solution: Heat them up to 130°C.
A friend of mine develops electronics for a living and he told me that. If you have temperature sensitive electronics, heat them to a value (controlled electric heat circuitry) that ambient temps do not reach. Than they will be stable all the time.
PH430:
Yes, I checked the ignition with a timing light, it sits at 8°BTDC at idle.
The difference in map and multiplier seems odd to me, since I never touched the ECU. Is it possible that it was swapped for a standard 3.9? By somebody who didn't know what is different?
And I don't even try to change anything. I only want it to run right...
Marvin
Yes, I checked the ignition with a timing light, it sits at 8°BTDC at idle.
The difference in map and multiplier seems odd to me, since I never touched the ECU. Is it possible that it was swapped for a standard 3.9? By somebody who didn't know what is different?
And I don't even try to change anything. I only want it to run right...
Marvin
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