RB26 VERY unstable idle/won't take load

[drew6]

Hey guys,

I'm having some issues that I'm really scratching my head over; to be honest I'm completely baffled. I've messaged Matt at Nistune and he didn't have much insight in to my issue either. Here are the facts:

- R32 GTS4 w/ R33 RB26 swap done in Japan. I've rebuilt the engine and have had it out a few times since I've owned it. Never had any issues like this before.

- About 50km before I pulled the engine last time (unexpected clutch issue) I swapped in new turbos and Z32 MAFs. I am using Nistune - Had no major issues with the car during that period, except, the K constant was not spot on so my fuel was a little rich.

- I put the engine back in with the same configuration/tune and now it barley idles. The AFRs are all over the place at idle (9.8 - ~15) and it is idle hunting from 1200-1400 rpm this gets much worse when it is warmed up. I again started a new tune and adjusted for the Z32 MAFs with no luck. Extremely unstable idle and will not take any load. (IE: pulling it out of the garage in 1st causes it to stall constantly)

- I swapped out my Z32 MAFs for the stock MAFs and put the R33 ECU back in. Now the car is idling really high ~1600rpm with some slight idle hunting and again the AFRs are all over the place - Mostly on the rich side ~10-~14. This does not surprise me though as I swapped to a Z32 due to these MAFs going really crazy with it was humid/wet out. Again, the problem gets much worse when warm.

- Using the stock MAFs with the Nistune has very similar results has when using the Z32 mafs. However, with this setup the cold idle is more stable.

- My O2 sensors are disabled. (As when you set the K constant in Nistune you have to do this) However, I was running a simulated narrowband from my wideband unit.

- I've replaced my temp sensore and checked the IAT sensor. Both are good.

- CAS does not have any issues.

- Checked for intake leaks. Replaced some questionable clamps.

- My "middle harness connector" is currently unplugged as the connector was damaged when I bought the car. This is what connects the IAC, cold idle valves and knock sensors to the main harness. I never had a problem running the car like this with the exception of the car stalling when going from high load to idle.

- Forcing the car in to limp mode (by unplugging the MAFs) the car runs super stable at 1000rpm, with he exception of the super rich limp mode aft (~9.8-10). I am able to move the car around my garage/driveway like this.


Now for the really strange parts:

1) My number one cylinder stopped firing randomly while using my Nistune ECU. Not sure why, I tried swapping coils and plugs and no change. I then tried my stock ECU and it worked perfect. When I plugged in my Nistune ECU it worked perfect again. I have never had this happen before and it has not happened since. WTF.

2) One of my Z32 MAF plugs just went bad. I can't even fathom why.. It always worked until now. I swapped plugs on the MAFs and it is definitively one of the plugs not the MAFs. I checked the wiring - all good. The pins are tight and appear to be making connection. It makes no sense. I swapped back to the stock MAFs and plugs and they send signals without issues. WTF.

This is where I am with it. I am at my wits end and if I can't get this sorted very soon I'm ripping out all the stock **** and running a megasquirt with a new harness.

Any thoughts? I really don't want to rip it all out if I dont have to.

[Dakota_gsx]

You could look at the Igniter, or even the coil harness. Picking up a new coil harness never hurt no body. Around the $150 mark and its one thing you can confidently cross off the list of possible causes.


Or buy a Vipec and get rid of the MAF's

[judasentinel]

Drew, what about the TPS? Idle hunting is a typical symptom of the TPS setting being out of whack. I am sure you know how to check it for errors. Do you know if your ECU is throwing ANY codes at all?

Error codes are codes for singal loss, and do not confirm physical damage to the components. Even if all your parts are working fine and yet the wiring is messed up, the ECU will mess up the AFRs and might even throw a code or two.

It seems that there is something not OK with the Nistune settings. And because of what you had to mechanically adjust in the engine bay, even when you put the stock ECU and MAFs back on, the settings are out of whack. May I suggest something?

This is what I would do: Forget the Nistune-installed ECU for now, completely, along with Z32 MAFs. Just put the stock ECU and MAFs on and go to town with adjusting stuff - start with TPS and adjust its voltage according to the manual. Then adjust the IACV for stock settings and bring your idle down. The IACV could be clogged or messed up. Check for boost/air leaks. Once you get it running in stock conditions, should you swap out the ECU and MAFs.

Otherwise, you are playing with two sets of parallel variables with more than one value to input and unless you hit a fluke, you will likely end up wasting a lot of time figuring out the most ideal combo. Just go completely stock (or as much as you can) with ECU, TPS settings, IACV, MAF, CAS positioning, and check for leaks. You will find something that's not ok I am sure. And as Dakota suggested, also look into the ignitor - just confirm each cylinder/plug is firing.

Do tell what you find.

[Skym]

When swap in R32 GTR ECU you are meant to run R32 GTR o2 sensors. When swap in R33 ECU you are meant to run R33 GTR o2 sensors.

When o2 sensors go they make ECU run engine rich longer due to o2 sensors being slow to respond, pops flames from exhaust, etc. Try unplugging stock o2 sensors with R33 ECU and see if problem solves itself.