Need help with odd lean issue.
05-16-2019, 11:08 PM
#1
Need help with odd lean issue.
I have a completely new motor, fitted with new dme, new dme harness, and new vitesse maf kit. I started having a random lean issue at idle but the kicker is that it comes and goes. Most of the time I get a normal 14.7 idle at about 17+ inhg and the car runs great. If I let the car idle for a few minutes I notice the car starts slowly getting leaner, eventually getting up into 16.5 or more. When it does this I seem to lose some vac pressure and the idle gets a bit low and rough. I view my vitesse logger and everything looks the same as when it idles correctly. The only thing I've noticed is when my high fans kick on it seems to cause some of this behavior described above . My high and low fans are working and my car has a Nissan alternator mod. The voltage overall never drops below 12v. I'm guessing the relay, wiring, resistor, grounds or fan is causes some type of electrical issue that's intermittent.
What ground locations directly link to the fans?. What can I test and check?
What ground locations directly link to the fans?. What can I test and check?
05-17-2019, 12:21 AM
#2
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A few things I would try:
- create some sort of a shield to block air filter from any air blown by fans. ( If somehow the fans are creating turbulence). I have seen odd behavior caused by the fan on a 944 where the air filter was not located all of the way toward the fender and the fans were causing all sort of issues.
- check MAF signal on monitor. Note any difference in MAF voltage between the different AFRs. Also keep an eye on the TPS, and battery Voltage.
- disconnect O2 sensor. Does it change the behavior.
Try each one at a time, so we know which is causing the lean AFRs.
If none of the above, I would look at a possible vacuum leak or a voltage issue.
Send me a picture of your MAF installation. I know you changed a few things, maybe I can spot something???
Try cleaning all engine grounds (by headlight mechanism, by battery and at bellhousing).
- create some sort of a shield to block air filter from any air blown by fans. ( If somehow the fans are creating turbulence). I have seen odd behavior caused by the fan on a 944 where the air filter was not located all of the way toward the fender and the fans were causing all sort of issues.
- check MAF signal on monitor. Note any difference in MAF voltage between the different AFRs. Also keep an eye on the TPS, and battery Voltage.
- disconnect O2 sensor. Does it change the behavior.
Try each one at a time, so we know which is causing the lean AFRs.
If none of the above, I would look at a possible vacuum leak or a voltage issue.
Send me a picture of your MAF installation. I know you changed a few things, maybe I can spot something???
Try cleaning all engine grounds (by headlight mechanism, by battery and at bellhousing).
05-17-2019, 01:02 AM
#3
A few things I would try:
- create some sort of a shield to block air filter from any air blown by fans. ( If somehow the fans are creating turbulence). I have seen odd behavior caused by the fan on a 944 where the air filter was not located all of the way toward the fender and the fans were causing all sort of issues.
- check MAF signal on monitor. Note any difference in MAF voltage between the different AFRs. Also keep an eye on the TPS, and battery Voltage.
- disconnect O2 sensor. Does it change the behavior.
Try each one at a time, so we know which is causing the lean AFRs.
If none of the above, I would look at a possible vacuum leak or a voltage issue.
Send me a picture of your MAF installation. I know you changed a few things, maybe I can spot something???
Try cleaning all engine grounds (by headlight mechanism, by battery and at bellhousing).
- create some sort of a shield to block air filter from any air blown by fans. ( If somehow the fans are creating turbulence). I have seen odd behavior caused by the fan on a 944 where the air filter was not located all of the way toward the fender and the fans were causing all sort of issues.
- check MAF signal on monitor. Note any difference in MAF voltage between the different AFRs. Also keep an eye on the TPS, and battery Voltage.
- disconnect O2 sensor. Does it change the behavior.
Try each one at a time, so we know which is causing the lean AFRs.
If none of the above, I would look at a possible vacuum leak or a voltage issue.
Send me a picture of your MAF installation. I know you changed a few things, maybe I can spot something???
Try cleaning all engine grounds (by headlight mechanism, by battery and at bellhousing).
05-17-2019, 01:05 AM
#4
Drifting
How do your wires look at the fans ballast resistors? The two ceramic round resistors tucked under the HVAC blower motor shroud next to the battery. I’ve yet to see wires in good shape that haven’t been replaced. Also you can clean your power distribution block. I did a write up on how easy it is.
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05-17-2019, 12:21 PM
#8
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Sounds like you might be on to something with the fans. One thing I noticed in your first post is that you said the voltage never drops below 12 volts. If it is really down to a true 12.0 volts, that's too low. The charging system should keep it near 13.8 (as I'm sure you know). You might put a volt meter on the battery when the car is running with the fan off and confirm you are well up into the 13's and then see what happens to the voltage when the fans kick on. If it drops to 12, it would suggest the fan circuit is drawing too much current.
The fans might also be pointing you to a more general electrical issue. On my car, there was a time when I could change the AFR at idle by turning on the headlights and hvac blower fans. Cleaning all the grounds seemed to eliminate that. So you might try loading up the electrical system that way to see if it gives the same effect as the fans, just so you're not wasting time on that one thing if it's really just related to overall current draw.
The fans might also be pointing you to a more general electrical issue. On my car, there was a time when I could change the AFR at idle by turning on the headlights and hvac blower fans. Cleaning all the grounds seemed to eliminate that. So you might try loading up the electrical system that way to see if it gives the same effect as the fans, just so you're not wasting time on that one thing if it's really just related to overall current draw.
05-17-2019, 01:19 PM
#9
Sounds like you might be on to something with the fans. One thing I noticed in your first post is that you said the voltage never drops below 12 volts. If it is really down to a true 12.0 volts, that's too low. The charging system should keep it near 13.8 (as I'm sure you know). You might put a volt meter on the battery when the car is running with the fan off and confirm you are well up into the 13's and then see what happens to the voltage when the fans kick on. If it drops to 12, it would suggest the fan circuit is drawing too much current.
The fans might also be pointing you to a more general electrical issue. On my car, there was a time when I could change the AFR at idle by turning on the headlights and hvac blower fans. Cleaning all the grounds seemed to eliminate that. So you might try loading up the electrical system that way to see if it gives the same effect as the fans, just so you're not wasting time on that one thing if it's really just related to overall current draw.
The fans might also be pointing you to a more general electrical issue. On my car, there was a time when I could change the AFR at idle by turning on the headlights and hvac blower fans. Cleaning all the grounds seemed to eliminate that. So you might try loading up the electrical system that way to see if it gives the same effect as the fans, just so you're not wasting time on that one thing if it's really just related to overall current draw.
05-17-2019, 01:53 PM
#10
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Based on the pictures, I do not suspect the air flowing by the fans is the cause. To rule it out 100% test the shield theory. A cardboard will do.
Look at the Monitor and notice what changes when the fans kick in. It's sounding as an electrical issue.
Look at the Monitor and notice what changes when the fans kick in. It's sounding as an electrical issue.
05-17-2019, 02:00 PM
#11
I had issue with my fans as well with vitesse maf, air turbulence would cause maf reading to be off, but I would go rich instead, not much, but would drop to 14.3 or so at idle when fans cycle. Check voltage at maf plug when running perhaps. And having maf plugged into crusty diagnostic port or having dedicated wire might make a difference, John would know.
05-17-2019, 05:10 PM
#12
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Your issue was caused by a bad ground. The electrical load (fans, lights, heater fan) would cause positive voltage on engine/chassis grounds. So sensors signals were higher than should have been.
A few years ago, I changed the MAF setup, so it is not as sensitive to bad grounds.
However bad grounds affect many sensors, not just the MAF. Good clean grounds are a must!!!
With the Motronic Monitor, he should be able to tell if any sensor is quickly changing value when the fans kick in.
A few years ago, I changed the MAF setup, so it is not as sensitive to bad grounds.
However bad grounds affect many sensors, not just the MAF. Good clean grounds are a must!!!
With the Motronic Monitor, he should be able to tell if any sensor is quickly changing value when the fans kick in.
I had issue with my fans as well with vitesse maf, air turbulence would cause maf reading to be off, but I would go rich instead, not much, but would drop to 14.3 or so at idle when fans cycle. Check voltage at maf plug when running perhaps. And having maf plugged into crusty diagnostic port or having dedicated wire might make a difference, John would know.
05-18-2019, 06:58 PM
#13
Is it reasonable to say that if the maf was picking up more air from the fans I'd see a rich condition? I suspect my issue is electrical related to the fans, not my other accessories. Where do the fans get their ground from so I know I'm checking fan related things
05-19-2019, 05:04 PM
#14
It looks like my fan's resistor wiring is pretty bad. Is there a source for that harness new?
Also, I believe a maybe getting some hot air pushing towards the maf, not from the fans but from the alternator. Since I use a Nissan alternator it has a internal fan that pushes air out the front. I can feel a slight breeze from it near the maf but I'm not sure that it's actually causing any issues. I will replace all the fan resistor wiring, including the resistors, and the fan relay and see if I get any more issues. If so I'll custom make a shield to block the maf filter from under hood air. I'm thinking this might be where I tackle the dashboard cracks to expose the wiring underneath.
Also, I believe a maybe getting some hot air pushing towards the maf, not from the fans but from the alternator. Since I use a Nissan alternator it has a internal fan that pushes air out the front. I can feel a slight breeze from it near the maf but I'm not sure that it's actually causing any issues. I will replace all the fan resistor wiring, including the resistors, and the fan relay and see if I get any more issues. If so I'll custom make a shield to block the maf filter from under hood air. I'm thinking this might be where I tackle the dashboard cracks to expose the wiring underneath.
