hpx maf

[Matt]

Post your setup (injectors, engine etc) and current tune file and will have a look

[mastermechanic5]

My setup is an RB25DET S2, 660cc side feed injectors, HPX n1 maf, aftermarket intake manifold with q45 throttle body, z32 ecu. I attached my .bin file. I spent some more time messing with it today. It seems like my wideband might not be working properly, so I ignored it and just went by how the car was running. It runs half decent with those settings when its cold, than once the car warms up the idle starts surging and no adjustments will clear up the surge. Thank you Matt.

[Matt]

Many changes at the same time make it more difficult to get a good base line

- Bigger injectors require a flatter fuel map
- K constant appears very high. I had about 250 for this value with a tune I was doing

Try recalibrating your wideband sensor in open air and then see if you can get it going again so you can get logs

I use gas from a cigarette lighter near the sensor end (not lighting it but to remove oxygen) to check the sensor functions

[mastermechanic5]

The only changes I was making were my MAF and my exhaust manifold, but my old .bin file looks like it may have gotten corrupted so I decided to start fresh. I did a open air calibration on my wide band and checked it with butane and it seems to be functioning properly. I made several logs, On my first one you can see a little after 2 minutes my AFR all of a sudden goes from very lean to rich. I'm fairly sure that I was having the exact same problem before I changed the maf but that was 6 months ago and I don't have any logs to compare. I've had ongoing problems for awhile now, It was dyno tuned and running well and than I started having problems with hard starts, constantly changing AFRs, stalling, rough idle and hesitation. It has fresh gas, and I've checked the timing and ignition,plugs, timing belt,vacuum leaks, compression and leak down and everything seems alright. I'm just really stumped what could be the cause of my issues. Thanks again Matt.

[Matt]

Can you post an updated tune with this or is the last one sufficient for playback?

[mastermechanic5]

The tune file I posted was the one I used for the log, I may have changed the k constant slightly. I tried installing a stock rb25 maf and the car runs great, so the hpx maf must be my problem.

[Matt]

I spent some more time messing with it today. It seems like my wideband might not be working properly, so I ignored it and just went by how the car was running. It runs half decent with those settings when its cold, than once the car warms up the idle starts surging and no adjustments will clear up the surge.

Try tuning off the O2 sensor and see if it doesnt change the way it runs after 50degC. I noticed this when using Z32 on my RB25. Once disabling I could get K constant in the right place. The fuel trims from the O2 sensor were messing it around

How is the HPX installed? Is it in 3" tubing, pre or post turbo? Try doing it pre turbo. Ensure a straight pipe with no close curves near the sensor (it will affect straight air passing through it)

[Matt]

Looking at tune file. K constant seems very high (1900 vs 172 standard RB25 setup). This does not seem right

The vehicle should be running similar K constant to the Z32 300ZX but a bit to compensate for the larger injectors.

[mastermechanic5]

I did try disabling the o2 feedback last time I had the hpx maf installed and I don't think it seemed to affect the afr much but I will reinstall the hpx and try again. I realize that my k constant was extremely high, however the car would not start or run cold with any lower of a k constant. I thought maybe my enrichment tables need to be adjusted?



Here is a picture of my maf pipe, would the 45 deg bend before the maf be enough to cause problems? Unfortunately there is really no room for straight tubing on my setup this was as good as I could get it.



Here is my rb25 maf installed in the car, I also had a Q45 maf installed in this way without issues.

[Matt]

I havent tried the HPX on the blow through side of things, only suck through. It shouldnt require K where you have it set at the moment.

If you put that pipe on the intake, does it work differently?

Also the curve is right before the sensor so may cause some turbulence (imaging the airflow akin to a waterslide where the majority of airflow is on the edge, and by the time it reaches the sensor which is located in the tube centre, the amount of airflow does not reflect what is actually in the tube).

I would move the bung towards the end of the straight part so there is a greater distance in there. Unfortuantely my intercooler piping is too narrow, so could not test blow through setup.

We used straight piping with the air flow cleaner in front. This guaranteed perfect airflow through the sensor. MPS machining also offer honeycomb air straighteners to locate in front of these sensors which might assist the issue (alongside moving the bung towards the end)

[mastermechanic5]

I will try installing the pipe directly to the the throttle body drawing from the atmosphere and see if it makes a difference.

I will also order an air straightener and try that as well as moving the bung further back in the pipe.

I don't have much room in front of my turbo so a draw though application might be difficult.

I could install the maf bung in the tubing before the intercooler, there is a longer length of straight tubing. However the tubing is 2.5" rather than 3" and I would have to relocate or recirculate my blow off valve.