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Recently finished my t2 swap and for the most part it's running good. However, while cruising the car leans out. Like 18+ afr kinda leaning out. Give it enough throttle and it'll jump back to stoich. It'll also jump back to stoich if I lift off the throttle enough.
What's been done-
Tps has been set to 1k ohms
Have rotated between stock and rtek 1.5 ecu with no change
Boost sensor and afm are in spec
Fuel pump is hooked up to battery through relay
FPR set to stock pressure levels
Fuel pressure gauge shows good pressure even when leaning
Can't find any more vacuum leaks
Now the one thing I found tonight that was really odd was when reading the o2 sensor voltage, it would drop into the negatives. Im not sure if I had the correct lead on the wire, but with the positive lead hooked up to the o2 sensor it would drop to upwards of -.6. When it wasn't leaning out the highest I saw .3.
I would wait for someone else to chime in to verify, but it sounds like a faulty O2 sensor. Our cars use a 1-wire sensor, so there is no outside influence. If it is not outputting between 0v and 1v, it is bad as that is the only range they should output. Are you measuing this while its unplugged? Just making sure nothing else is plugged in that could influence the voltage.
Also, the fact that it goes normal when you give it throttle also points to the O2 sensor. The ECU only uses the O2 sensor when cruising, and ignores it otherwise.
Question - how do you know it is leaning out? Is it based on the readings of that same O2 sensor, or do you have another sensor? Because if its the same sensor, then those readings probably aren't reliable.
I would wait for someone else to chime in to verify, but it sounds like a faulty O2 sensor. Our cars use a 1-wire sensor, so there is no outside influence. If it is not outputting between 0v and 1v, it is bad as that is the only range they should output. Are you measuing this while its unplugged? Just making sure nothing else is plugged in that could influence the voltage.
Also, the fact that it goes normal when you give it throttle also points to the O2 sensor. The ECU only uses the O2 sensor when cruising, and ignores it otherwise.
Question - how do you know it is leaning out? Is it based on the readings of that same O2 sensor, or do you have another sensor? Because if its the same sensor, then those readings probably aren't reliable.
I measured it while driving. I just back probed the o2 connector on the harness side and taped it in place. Something to note though is that this o2 connector has definitely been messed with. It's an s4 na harness but the o2 connector is a little black connector and I believe that was on the s5 cars. Also the o2 is a brand new Bosch direct fit replacement with only a few hours of run time on it.
I should have mentioned it in my first post but this lean condition happens with or without the o2 plugged in. I should have also mentioned that I have an AEM wideband.
I measured it while driving. I just back probed the o2 connector on the harness side and taped it in place. Something to note though is that this o2 connector has definitely been messed with. It's an s4 na harness but the o2 connector is a little black connector and I believe that was on the s5 cars. Also the o2 is a brand new Bosch direct fit replacement with only a few hours of run time on it.
I should have mentioned it in my first post but this lean condition happens with or without the o2 plugged in. I should have also mentioned that I have an AEM wideband.
^You answered what would have been my 1st question, what are you using to measure AFRs? So I gather you have a 2nd bung on your downpipe where the wideband O2 sensor for your AEM unit is mounted, correct? Assuming your AEM wideband is good, the 1st thing I'd look for is small exhaust leaks up or downstream from the WBO2 sensor -- any extra air getting into the exhaust stream will screw up your AFR readings, and give you the kind of lean readings you're seeing.
I'm running my FC on an AEM Infinity ECU and last year I had a very similar issue - getting crazy lean AFR readings on my CAN bus gauge, but the car was running fine. Turned out that my WBO2 sensor managed to work itself a little loose over many heat cycles in the year or so I had it, causing an air leak into the exhaust stream. Removed & reinstalled the WBO2 sensor and torqued it back down tight and the problem went away.
Another possibility is that the WBO2 sensor is just worn out - they do have a limited service life, and if you have lots of dyno time & tuning sessions on it, and run lots of premix, they tend to not last forever.
^You answered what would have been my 1st question, what are you using to measure AFRs? So I gather you have a 2nd bung on your downpipe where the wideband O2 sensor for your AEM unit is mounted, correct? Assuming your AEM wideband is good, the 1st thing I'd look for is small exhaust leaks up or downstream from the WBO2 sensor -- any extra air getting into the exhaust stream will screw up your AFR readings, and give you the kind of lean readings you're seeing.
I'm running my FC on an AEM Infinity ECU and last year I had a very similar issue - getting crazy lean AFR readings on my CAN bus gauge, but the car was running fine. Turned out that my WBO2 sensor managed to work itself a little loose over many heat cycles in the year or so I had it, causing an air leak into the exhaust stream. Removed & reinstalled the WBO2 sensor and torqued it back down tight and the problem went away.
Another possibility is that the WBO2 sensor is just worn out - they do have a limited service life, and if you have lots of dyno time & tuning sessions on it, and run lots of premix, they tend to not last forever.
Yep I have a 2nd bung for the wideband. I think there is an exhaust leak because there is a very audible ticking from the passenger side engine bay at idle and low rpm cruising. However, I've tightened down all the exhaust components more then once now. At first I tightened them to factory torque spec. Then I just tightened them as much as I comfortably could. I don't smell exhaust in the engine bay though.
My car definitely is actually leaning out and not just reading lean on the wideband though. Starts to misfire and loses all power until I give it more throttle. I honestly don't really care about the narrowband o2 working correctly either. This is my track car so the marginal fuel economy increase isn't a huge concern for me.
The fact that the o2 sensor being plugged in out not has no bearing on the lean condition tells me this runs deeper then the o2 itself as well.
So I took the afm off and tested it again. Everything checked out until I got to e2->Vs. When moving the plate the resistance jump around a lot. Is this normal?
Still struggling with this. Anyone have any ideas?
I've changed my tps with my old known working NA TPS but that didn't do anything. It has to be a sensor of some sort right? I believe I read the ecu only uses the related sensors during closed loop and as this problem immediately disappears once in open loop then I'm inclined to think it's sensor related.
I've checked all the sensors though and they seem to be in spec so I'm kinda confused on this.
I may be late to this conversation, but have you checked for vacuum leaks? Depending on where they are, they don't always do the same thing. I usually disconnect the MAP sensor, seal the turbo inlet, and use about 20psi to find the leaks.
I may be late to this conversation, but have you checked for vacuum leaks? Depending on where they are, they don't always do the same thing. I usually disconnect the MAP sensor, seal the turbo inlet, and use about 20psi to find the leaks.
It's possible. I was fighting vacuum leaks for awhile on this thing. Would a leak do that though? It isn't just running a little lean while cruising. It progressively gets more and more lean if I keep the same throttle position.
I've noticed changes in my engine from different vacuum leaks. Leaks that are pre-throttle behave differently than those post-throttle. Also, if you have the air bleeds blocked off, leaks unique to each rotor have different effects as well. Post-throttle leaks typically increase idle speed. Pre-throttle leaks, like those in the intercooler piping, drop idle sometimes. Either way, the computer isn't getting the correct air measurement from the intake, and is trying to compensate on an incorrect assumption.
On a side note, one thing I am doing along with color coding my vacuum lines is tracing where their vacuum source comes from. Some sources at the throttle body are pre-throttle, some are post throttle, and some use both.
I've noticed changes in my engine from different vacuum leaks. Leaks that are pre-throttle behave differently than those post-throttle. Also, if you have the air bleeds blocked off, leaks unique to each rotor have different effects as well. Post-throttle leaks typically increase idle speed. Pre-throttle leaks, like those in the intercooler piping, drop idle sometimes. Either way, the computer isn't getting the correct air measurement from the intake, and is trying to compensate on an incorrect assumption.
On a side note, one thing I am doing along with color coding my vacuum lines is tracing where their vacuum source comes from. Some sources at the throttle body are pre-throttle, some are post throttle, and some use both.
I don't have an air compressor to be 100% sure on leaks but I went through every hose and found a couple that were lose. Tightened the clamps on them and nothing really changed. I feel like this is an electrical thing just because of how it only happens at a certain throttle position. Hate to throw parts at the car but I read of a similar issue and it turned out to be a bad afm despite his afm speccing correctly.
I really though I replied to this already, but I don't see it, so I guess I never submitted it. From what you said the AFM is the likely culprit. The readings on any sensor should be linear. I don't have the specs in front of me, but if it jumps around that doesn't seem good. That could definitely cause the erratic readings you are seeing.
I really though I replied to this already, but I don't see it, so I guess I never submitted it. From what you said the AFM is the likely culprit. The readings on any sensor should be linear. I don't have the specs in front of me, but if it jumps around that doesn't seem good. That could definitely cause the erratic readings you are seeing.
Yeah I am inclined to think that myself. Weird part is my NA afm does the same thing. Not to say that that couldn't be defective too. Any chance anyone could measure their working afm between E2 to Vs while slowly opening the flapper door to see how it behaves? Just to be sure before I throw money at it.
Here's the s4 and s5 AFM pages from the FSM. It shows 50-500 resistance for both open and closed, so thats not exactly conclusive. I wouldn't buy anything until someone chimes in with a knows good measurement. Unfortunately I haven't had one for years, so I'm not much help there.
You are doing a test(sweep test) that is not mentioned in the book. You can't do a sweep test with a digital meter. It must be done with an oscilloscope or an analogue meter.
I've wondered why there is no mention of a sweep test in the manual. Then I wondered if the resistance test simply makes the sweep test redundant for some reason. Maybe the resistance values during the two states(fully closed & fully open) are all a technician needs to diagnose the AFM.
Maybe someone on here has been in the situation where resistance values tested good but failed a sweep test on an oscilloscope/ analog voltmeter. This would be interesting to know because it would confirm if a sweep test is even necessary.
Last edited by Rotary Alkymist; 08-26-19 at 05:15 PM.
I did test mine with an analog multimeter. The needle rises and falls multiple times within one sweep of the door. It's pretty much just a potentiometer isn't it? I've never heard of a potentiometer that is designed to have values rise and fall like that.
I'm pretty sure it also has to be powered. I believe it is a bit more complicated than a pot. It certainly doesn't behave like one when it is not powered. If I had to guess, your AFM is good. It seems to be behaving the way it should.
I have never tested one(with oscilloscope) but I do remember watching a youtube video of a guy testing one with an oscilloscope. IIRC he had a power supply hooked up to it.
Last edited by Rotary Alkymist; 08-26-19 at 05:25 PM.
Questions
Which O2 sensor is new?
How far away is your wideband bung from exhaust manifold?
If the O2 sensor is functioning then it should fix the lean condition. If your O2 sensor is bad the feedback system is disabled.
You mentioned that the problem persists with O2 connector unplugged therefore, in that state your feedback system is disabled... and you're still leaning out.
You mentioned that fuel pressure does not fluctuate in this state.
It almost sounds like you have a vac leak and faulty O2 sensor or O2 sensor circuit. I'm gonna think about this more later.
Ok, so given that it isn't any of those things it would have to be fuel pressure. Turn up your fuel pressure by like 1psi-2psi and see if the problem disappears.
Ok, so given that it isn't any of those things it would have to be fuel pressure. Turn up your fuel pressure by like 1psi-2psi and see if the problem disappears.
So I finally got around to this. Adding fuel pressure didn't help. It's at about 32 psi at idle now which puts it in the high 30s when the lean happens. Still leans out hard enough that my afr gauge can't display it anymore so about 18 or more afr.
Also if it was a fuel pressure thing wouldn't it be happening all the time and not just a specific throttle range?
I had an idea. Are you running a purge control valve? I'm wondering if it's leaking. Start your car and pull the large vac line off(probably easier to disconnect from the other end). Vacuum should not be felt below 2000rpm.
Also check the check valve close to AFM and be sure it's functioning correctly(one way only). Make sure it isn't in backwards either.
These are two possible leaks that would be hard to find.
Having a girlfriend who will put up with it is half the battle haha.
Last edited by Rotary Alkymist; 09-01-19 at 09:06 AM.
So I woke up and had a coffee and wondered "what if both valves test fine"?
If they do test fine this is what might be going on. I think I remembered you saying you have an exhaust leak. This could be giving you a false positive and your bucking could be totally unrelated.
The bucking could be because and an improperly adjusted throttle body. Your main might not be open enough. This is common when TPS is adjusted. Maybe your adjust screw isn't even touching. Your primary might be too closed. This will cause bucking.
Solution Open up the primary a bit then readjust the TPS(obviously).
08-14-19, 07:33 PM
