RB26 - Wont idle, running extremely rich

[drew6]

Hello all,

I have an RB26 that's having some frustrating issues.

Back story: I just finished putting the engine back in. About 10km (yes, ten kilometers) previous to pulling the engine I had replaced my R32 GTR MAFs with Z32 MAfs (R32 MAFs were in REALLY rough shape and were getting funny when it was raining out). I only got to start it a few times with the Z32 MAFs; It stalled a bunch of times on cold starts but once it warmed up it seemed to smooth out. I had a problem with my clutch and had to pull the engine so I never got to explore it any further than this.

Back to now: Whenever I start the engine it will run extremely rich, bouncing around from 10.5-11.5 AFR, and the idle will automatically raise and fall from about 850-1400 rpm over and over again. After about 20 seconds of running like this it will stall with an AFR of about 10.0. If I blip the throttle it will stay running, but very rich and very rough. I decided to start with a fresh new tune, so I loaded up the bin file for the car and started over. I changed the MAF to Z32 and halfed the values I also unplugged my O2 sensors as well as set the feedback temp to max value. The K constant was at 332 (the car has stock injectors), however, while at 332 the engine wont rev up so I doubled that to 664 and it now allows it to rev up. Still no change in the idling or the over all running condition of the engine though. So after triple checking for leaks or any thing obviously mechanical I put the stock MAFs back on. Same thing exact thing.

Now, the baffling part to me is this: if I pull the MAF plugs off the engine idles happy as can be with an AFR of 11.5 (Engine is now in limp mode), and besides the rich limp mode AFR it is just as smooth and steady as can be - no rising or falls rpms or small backfires... What gives?!

I've been at this for 2 days now and am flat out of ideas.

As a side note, I updated Nistune to the latest "stable" release, however, it sometimes crashes while syncing with the ECU. Also, twice tonight, I got an error when the car stalled "Check pin failed on board". I've never seen that before.

Really appreciate any help.

[Matt]

What you have done is correct (and doubling K constant after)

Keep adjusting K constant until your AFRs are happier. Both MAFs must be reading correctly (ie good condition) for it to work properly. Prior customer had similar issues and using second hand MAFs. Swapped to new ones and problem sorted. Only takes one to read bad and will cause issues. If it leans / richens as revs increase then they are not reading properly

I've fixed a bunch of crash bugs since the last stable build. The current test build will be re-released as the next stable after going through the latest reports collected when I get time. So use that test build instead

Pin failed error may be due to corruption on the consult line when initially connecting. Check the diagnostics guide

[drew6]

Matt,

Appreciate the heads up on the nistune test release. I'll try that today.

After work I'm going to try and clean those MAFs, reinstall the Z32 ones and play around with the K constant again.

Two questions:

1) If the K constant was wrong, would that explain the engine rpm going up and down by itself? I didn't think it would.

2) Do you think both sets of MAFs are gone bad? It seems odd to me that over the course of a winter both sets of MAFs would go back from sitting on a shelf.

[Matt]

No the MAFs shouldnt go bad if they were working fine previously

Having K constant in the wrong place will cause the engine to hunt around idle and timing to fluctuate trying to maintain the target idle RPM

It may be too rich or too lean which is why the AFRs need to be monitored with O2 feedback disabled until you get K around the correct value. I tend to tick the auto button and +/- the percentage until AFRs are around stoich

Then put some load on it and keep watching the AFRs

[drew6]

Matt,

I've been working flat out on this thing and am getting no where. I'm completely stumped. Can you please take a look at the below series of events and provide your thoughts?

1) This car is an R32 GTS4 that has an RB26 from an R33 GTR swapped in to it. Everything seems to be legit on the swap, except the "middle harness connector" will not connect together. This is for the IAC, Air regulator, knock sensors ect. As long as I have ever own the car it has been like this and posed no issues, except that when coming from mid-high load to complete throttle close it has a tendency to stall. I was planning to fix this by cutting out the connectors and putting butt connectors in place, however, I ran in to this issue.

2) When I had the engine out I degreed the stock cams to have intake open/exhaust close at 0* TDC @ 0.040". Last night I changed this back to the stock settings. It seems to be slightly more stable but the idle rpms (800-1400) are still rising and falling with AFR going every which way.

3) I tried both the stock R33 MAFs and the Z32 MAFs with nistune with no change in what the engine is doing.

4) I tried the stock R33 MAFs, with stock cam timing, with the stock R33 ECU and it is doing the same thing.

5) With both Nistune and the stock ECU when I unplug the MAFs the engine runs very smooth and steady. (Although very rich). When the MAFs are plugged in changing the K constant does seem to lean out or richen the mixture, however, does not stabilize the RPM or the AFR.

6) I've checked for intake leaks a dozen times and cannot find one.

7) I'm using an MTX wideband, which has a narrowband output, however, I do not have this hooked up to anything right now. The one stock O2 sensor in the car is unplugged.

The rpms and afr tend to be fairly stable (rich) when first started cold. As it warms up it get much much worse.

Can you think of anything that would cause this? I'm suppose to go to a course with the car next weekend, which I've been preparing for the past couple months, however, if I can't get this sorted soon I'm going to have to cancel.

Really appreciate your time; Thanks.

BTW, I changed to the "test" version of nistune and all day I did not have a single crash.

[skylinegtrhr]

Try Yours MAF's on some other car with Z32 MAF which is running OK so You will then definitely rule out bad MAF's and off course check MAF wiring for continuity and shortening.

[drew6]

Still trying to sort this problem...

When the engine is "cold" it seems to run half decent now. (With the stock R33 parts and ECU). However, when the ECU reads the coolant temp as 50-60 degrees is when the idle hunting and AFR starts going out of wack. Faulty temperature sensor maybe?

[Matt]

It means that its running too lean. When the engine is cold the ECU adds more fuel. Increase you k constant further to add more fuel until your AFRs are better when rich

[eddyk-fab]

hello.... i have an s13 with a stroked ca18det...i am facing the exact problem... and it is not tune related as i started the motor with a factory ecu and sensors... everything was working fine until one night .. out of nowhere as the car was idling .. boom it started to jerk its idle and afr rounded up around 10/11 at idle.. i have changed every single sensor on the vehicle.. including 3 differnet ecus... and i even started the car on the greddy e manage ultimate just to save a data log file of the engines running condition.. nothing was wrong ...

did you solve the issue ??? is it intake or exhaust relatedd ?? thanks in advance for the reply

Eddy - Kunimitsu Motorsports

[cozmosland]

was there ever a solution to this?

[Matt]

Not that I can see. The last message was different vehicle but same issue on this thread. If its a problem with factory ECU then this really should be in the mechanical issue section rather than Type 2