I am so close to giving up. It idles perfectly, accelerates OK, and boosts fine. However when at 10% throttle it bucks and randomly goes lean over and over. It does not matter if this is closed or open loop. So.. the O2 sensor is NOT bad.

The setup is..

KA-T
Enthalpy tune
AEM UEGO
Fully built

I have tried the TPS.. the voltage is normal. With the TPS removed, it behaves very similarly, but the same problem persists.

The MAF is getting normal voltage. I'm seeing ~1.3V at idle. I can't see what it is under load but I would assume that it's normal. If I unplug the MAF with the car running, it will die immediately. If I try to start it again, it won't start.

The ECT is working normally, and the car will not start or run with it removed.

I'm seeing 14ish to 15ish at idle AFR's and about 13-14 under acceleration, less depending on throttle position. It has dipped down to 10-11 out of boost, so it's not lean under acceleration.

I recently redesigned the intake so that I have a 35 degree angled reducer to a 12x3" pipe with the MAF at the end of it, so it's not too close. I don't think that some weird vortex is causing this, but I guess it's possible.

I have never messed with IAT because I have not suspected it. It has not been touched and the car ran great before the new intake setup.

I am 99% sure it's not a fuel issue. Given that it accelerates, idles, and boosts just fine it can't be. Granted, whatever the issue it is causing a lean scenario it is not the fuel system itself, it is the control side.

I can't pull codes. The ECU I was given only has one light, and I can't hook up a Consult.

Please help me. I have searched over and over and cannot find the solution. I have tested damn near everything. I don't think the MAF is bad. I know the wiring is OK because I have tested it and re-soldered it and tested it again. I don't think it's because of the new intake because the MAF is further from the turbo than it's ever been.

Why are you so sure it's not an O2 sensor? Under cruise is exactly when it would give problems. They are cheap enough to change, just use any single wire bosch unit.

You could disconnect the O2 sensor and see if the problem changes.

for the record the car should start with the maf or cts not plugged in. Runs bad but works.

Is your bov recirculated?

I had a perfect idle at 15.5:1 and was good everywhere except low load cruise(off boost) it was lean. Recirc fixed it but gave me a leaner idle.

If your o2 is saying youre pig rich it will cut a good bit of fuel until the ecu reads a stoich~ish value. I hate o2 feedback, a good tune doesn't need it(but thats with map tracing)

Does your ecu have a screw ? You can read codes if it does.
Why can you not use consult?

WDRacing wrote:Why are you so sure it's not an O2 sensor? Under cruise is exactly when it would give problems. They are cheap enough to change, just use any single wire bosch unit.

You could disconnect the O2 sensor and see if the problem changes.

Partly because it's only about 200 miles old and also because it does not matter if it's in closed loop or open loop. I only have one bung in the exhaust currently so the O2 is usually unplugged for the UEGO.

neverlift wrote:for the record the car should start with the maf or cts not plugged in. Runs bad but works.

Is your bov recirculated?

I had a perfect idle at 15.5:1 and was good everywhere except low load cruise(off boost) it was lean. Recirc fixed it but gave me a leaner idle.

If your o2 is saying youre pig rich it will cut a good bit of fuel until the ecu reads a stoich~ish value. I hate o2 feedback, a good tune doesn't need it(but thats with map tracing)

Does your ecu have a screw ? You can read codes if it does.
Why can you not use consult?

I know.. which is why I am hoping that leads to clues. It's not like it tries to run. It just straight dies. It might be because I have 750's but the car should run with the ECT unplugged.

No, it is not. But I have good vacuum at idle. Now that I think about it, I am at pretty low vacuum during cruise if that helps. However, if it was a BOV leak, I would run rich not lean. In order for it to be lean I need to be registering less air than I am getting, or drawing in air behind the MAF, but given that I have good vaccum at idle the latter is unlikely.

You're right, it doesn't. Which is why mine is pretty much always not in the car. I only have a few month old Bosch unit for diagnostic purposes.

It does have a screw, but only one light. I don't know.. I tried plugging one in and it did not communicate.

IF your car boosts fine i dont believe u have a leak cause you would defnitly notice a problem when boosting. Is this s14 or s13? I can only think 2 things in ur situation, bad tune (enthalpy i hear is good but people make mistakes) or the cas if faulty under min load. On s13 the crank sensor is built into the distributor. On s14s i believe its on the back of the engine on the bellhousing. hope some of this info helps u out

chillmieste wrote:IF your car boosts fine i dont believe u have a leak cause you would defnitly notice a problem when boosting. Is this s14 or s13? I can only think 2 things in ur situation, bad tune (enthalpy i hear is good but people make mistakes) or the cas if faulty under min load. On s13 the crank sensor is built into the distributor. On s14s i believe its on the back of the engine on the bellhousing. hope some of this info helps u out

Correct.. I would have vacuum or boost issues if there was a leak, which I do not. I'm pulling like 18-19in of vacuum and can put out 14+ psi of boost.

I don't think it would be the CAS because I would have starting issues, and the timing seems to be OK.

I am going to try the tune.. at this point I'm thinking it's that or the ECU. I accidently told Enthalpy that I had 550cc injectors (what the previous owner told me) and I actually have 750's. I'm going to swap the 750 chips out for the 550's and see if that helps.

yeah that would do it.

neverlift wrote:yeah that would do it.

Sorry, I might not have been clear.

I have 750's, but was told I had 550's by the last owner and that's what I told Enthalpy. They sent out the 550 tune, and then subsequently sent out the 750 tune, which is what I have in now. The tune is good, but I wondered if putting in the old 550 tune would richen it up enough to make it driveable. Unfortunately it didn't.

I figured it out though. I don't f*** believe it. The intake setup I had (which I will provide pictures for) created a vortex that would only cause issues at atmospheric pressure. I can't really explain it, but it would cause the AFR's to go out of whack and bounce all over the place. That's why I had no problems under vacuum or boost but I did at cruise. I added a second 4" elbow to the 4>3 reducer and the problem went away. Oh how fun it is to work on cars.

EDIT: AAAHHHHH!!! I cut the intake down so it would actually fit, and even with 5-6+" before the MAF and 9" inches behind it it started f*cking up even more. Now I have no throttle response and coming into boost I'm running near stoich.. it has to be a bad MAF..

I had the same symptoms. My car does fine in idle and boost, but under cruise the AFRs bounce around and the car bucks. I see 18 inHG vacuum at idle. Stumped, I tested for boost leaks and found one. I'm working on fixing that now, and I bet that takes care of the issue.

I'm not sure why people are saying that if it boosts fine, there can't be any leaks. That's just not true. Build yourself a boost leak tester and I bet you end up finding some leaks you didn't know about.