KA24DET MAFS need help

[NameOfUser]

Background Info- 1991 Dual cam KA, T28, Z32 MAFS, RS Enthalpy tune.


I've had this car for about 4 years now... every time it's pulled out of winter storage it runs like shit and needs something done to it. Pretty annoying but also expected.

The ECU has sent code 12 (MAFS) each and every time, even though
the MAFS has never actually been the issue. Last year it was the throttle position sensor that was causing issues (only to be realised after a new
mafs was installed). If I recall correctly, the year before that it was the crank position sensor.

Anyways, here we are today, with all these parts I listed having less than 10,000 miles on them. I find it hard to believe one of them needs to be replaced again already.

Now to the issue at hand. ECU sends code 12 once again. I clean mafs, get
corrosion out of the terminals (which really wasn't that bad). When the MAFS is connected, the car will start and immediately die. When it's unplugged, the car idles perfectly and sounds great. Just can't drive it because limp mode.

I also let it warm up for about 15 minutes unplugged, then it died instantly once I plugged it back in. I don't know anyone with a 300zx, unfortunately, or I'd try their MAFS on my car.

I realize there are an abundance of threads across the internet involving mafs issues on 240s. I'm just tired of the only comments being "I have this problem too", and that being the end of the thread.

Anyways, really hope someone can help me out and I can get the car going without giving up and sending it to a shop. Let me know if you need any more information.

Thanks for reading

[NukeKS14]

Check your grounds.

Are you getting any other codes? Do you have your maf set up as a draw through or blow through? I had a lot of trouble getting my KA-T to run correctly as a draw through, it worked a lot better as blow through.

Youre not running a Spectra maf are you? I tried a spectra unit while troubleshooting mine and it made my shit run stupid rich.

Check your connections between your maf pigtail and harness.
How did you wire that up? It should be soldered IMO.

[NameOfUser]

Nope, just code 12. I do have a draw through setup.. I've seen some videos on people converting to blow-thru, might have to look into that.
The Maf is OEM, off a Nissan 300zx. Is spectra just an aftermarket maf?
The Maf connector wiring was redone last year (at the shop that replaced the TPS), but I'm not sure how they did it or how far back on the harness they went.

Looks like I'll be checking grounds and maf connections this weekend. Hopefully I come back with good news.

Anyways, thanks for the reply. I appreciate the help

[NukeKS14]

Hope it helps. The problem youre gonna run into with blow through is the mafs was never designed to be pressurized so youre gonna have boost leak issues down the road
If youre going to stick w your setup id look into.something like this;

https://performancemrp.com/i-30497602-nissan-300zx-z32-mass-air-flow-housing.html

I gave up and converted to speed density. Price of admission on a standalone is steep but worth it.

[NameOfUser]

Yeah, a standalone is definitely my next step when I have the funds for it. This enthalpy tune is at least 4 years old now, it's probably about time lol

[NukeKS14]

I noticed ISR is selling N62 mafs. That's probably worth looking into if you find yours is indeed the problem.

Theyve got a portion in the FSM for testing the MAF and associated wiring too. Have you gotten into that? In the EC section.

[Kingtal0n]

To fix your issue
A. need a good maf sensor
B. Boost pressure test all the plumbing to ensure no boost leaks
C. position maf in optimal location (around no turbulent bends, and far from turbo inlet, and use an air filter)
D. Recirculate the bypass or use an HKS SSQV style bypass ONLY
E. Use the rom tune + wideband + Safc to get fueling correct

Using this method should be able to command any 450hp sr/ka

only need a wideband when passing 500rwhp with that maf.
maf is very reliable and ideal, just needs proper tuning.
Last week I tuned a 450rwhp with that maf running out of pump/injectors on an sr20det 28psi of boost
pic for fun
https://i.postimg.cc/hGYmK0vT/IMG-3096.jpg

[NameOfUser]

Hey, thanks for the good info talon. Howd you get into tuning if I may ask? I'm currently studying to be a computer programmer but I'd love to get into vehicle tuning.

And nuke, I'm going to have to do the wiring troubleshooting this weekend. My buddy is much better with wiring and electronics in general than I am. I'm pretty clueless and useless when it comes to checking grounds, continuity, etc.

I'll get back to you with the results. Should be getting into it Saturday morning.

Where can I find the FSM online? Iirc there was a website with them but it got shut down...

Thanks for the help guys!

[NukeKS14]

https://nicoclub.com/archives/nissan-240sx-factory-service-manuals.html

You want the 91-94 general fsm. Then go to the EC (engine control) section.

Diagnostics starts on pg 33, the mafs procedure is on page 96.

[NameOfUser]

Damn nuke you're comin through. appreciate that. I'll post again tomorrow with results

[NameOfUser]

It ended up just being a really bad vacuum leak

[NukeKS14]

:ddog:

Glad you got it fixed and thanks for following up. Most people just solve their problem and move on.

May be worth looking into your other vacuum lines if they're aged as well. Might as well fix it before it becomes a problem again down the road.

Kingtalon recommended a boost leak test and that is a great idea if it isn't how you located your vacuum leak already. A good spray bottle w/ some soapy water and an air compressor are a valuable troubleshooting tool.

[NameOfUser]

Haha yeah, I almost forgot to post back but I figured I better not be the type of guy I complained about in my initial post lmao. I'm definitely saving this thread for next time, you guys gave some great information. Thanks for helping me out, take care guys