Possible Maf problem, need help diagnosing

[aN4rk1]

Hey,
I have a 91 R32 GT-R and Iam having a weird issue with it. The car pulls pretty hard under low RPM. Anywhere from 0-3500ish, its perfect. After that, it has trouble getting to 5000. At first I thought it was a boost leak but I had someone look at it and said there was no visible leaks and everything seems to be alright. He said it might be the mafs. After driving it himself, he this its starving for air at high RPM's and think its the mafs. I took it out for a spin after and i have major trouble getting upto and over 140, in high rpm range. On the 401 I had trouble getting to 120 in 5th.

Any recommendations on what it could be other then the mafs?

IF it is the mafs (kinda hoping it is, semi-easy fix) I want to upgrade to the Z32 ones. Is there any special modifications or adapters I need to do make the Z32 mafs work?

thanks

[Smilez]

z32 maf require ecu re-map. the voltage map for the z32 is completely different than the stock ones. you'll need nistune or aftermarket ecu like power fc or vipec.

[Skym]

MAF is a load sensor that is used by stock ECU to help select load cells on fuel, ignition map. MAF's hotwire inside round part of MAF can get dirty and MAF malfunctions. Or get bad solders on circuit board inside square part of MAF that can make ECU select the wrong part of fuel or ignition map and engine probably won't accelerate properly. When MAF fails, ECU makes engine idle at 1500rpm when warm and get MAF error code on ECU.

So 1st thing is to buy CRC MAF cleaner and clean the hotwires in MAF x2, as shown (how to) in this videoclip -

http://www.youtube.com/watch?v=vPT8rL0noYg

Do not use carb cleaner.

Then check and resolder MAF if necessary (need to buy high temp black silicon sealant to reseal MAF housing).

Z32MAF x2 + Z32MAF plug / tail x2 (plug / tail should be available from Tomei, etc)

Then need Nistune for stock ECU (to change MAF voltage to load translation table).

Another cause could be faulty knock sensor, as there's a fuel cut rev limiter at 5000rpm (safety rev limiter) that should engage if knock sensor is faulty.

[aN4rk1]

Thanks for the info guys. Will check out and report back.

[sarazinj]

i used intake medic
seemed to work ok

[aN4rk1]

Ok so engine does not idle at 1500, it idles at 1000 easy. Getting MAF cleaner tmr and also going to see if cleaning my airfilters will help as well. There is no fuel cut at 5000 so iam thinking its a just a bad maf. I did find good prices on mafs so i got some too (cant hurt to have spare)

i used intake medic
seemed to work ok

Never heard of this. Where can I get more info?

[Skym]

Watchout for the Z32 MAF copies if you decide to upgrade later on. They are usually easy to spot due to no Nissan logo, etc on MAF housing.

[sarazinj]

well i bought it from part source, a light spray, let it drip, another light spray and then let it dry, it worked great and didnt harm anything, if your ever cleaning your throttle body i suggest a seafoam soaked rag, jesus does that stuff clean well

[aN4rk1]

Ok first tired cleaning and soldering the mafs. No go.
Then REPLACED the mafs....again no go.
Iam stuck here.....Huge hesitation after 5000.....Talked to someone about knock sensor, they dont think thats it.
Any other suggestions?

Also, the time that this happened I just did a timing belt and water pump change and this seemed to happen RIGHT after? We make sure the timing was correct, we checked, rechecked and checked again when putting it back together. Could we have screwed something up?

[GTRADDICT]

Weak coils? Letting go on boost...

Check for codes

[aN4rk1]

Weak coils? Letting go on boost...

I hope not...that cant be good....although it would, give me an excuse to buy the yellow jackets

Check for codes

Yea I have yet to do this...will do this later today.

Anyone else with ideas?

[bellis_GTR]

Is your filters+MAFS bolted down to the frame? or something steady? Because my friend with a s13 had a rb20 in it and he has his filter+MAF just sitting there. He said randomly it would cut after 4000rpm and just jerk. So I remembered someone on here having the problem and they said just to make sure the MAF isnt moving around, because it cant read the right amount of air. And I think it puts the ecu in limp mode. Check that and see if it works.

[aN4rk1]

Mine is def not bolted down. I dont think yours is either, if its a stock setup its not. I wouldnt know how to bolt it down without drilling into it or something but ill keep that it mind. Will check the ecu soon. Maybe do a ECU reset (cutoff battery for more then 30 secs and then retry). More ideas are always welcome

[MarusGTR]

Weak coils? Letting go on boost...

Check for codes

Or the plugs, bad tips getting snuffed by boost. Should get a misfire code for bad spark, right?

Edit: Stock boost plateaus near 5500RPM...

[TW]

doesnt sound like a maf issue to me.. sounds more like plugs/coils to me. did you test your coils? check for fouled plugs? gap plugs properly?