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r32 GTR having random hesitation issues

Malachi1364
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Malachi1364 Apprentice

Malachi1364

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r32 GTR having random hesitation issues

So i bought this r32 gtr about a month ago and am now starting to have some issues. (link to the car/mods)

So i replaced the Plugs with brand new NGK BKR7E plugs, New fuel filter, Cleaned both mafs (with maf cleaner), Reset base timing to 20deg, and checked the car for boost leaks. Now im having a problem. I randomly get hesitation between 2k-4k rpm, Kinda like a bad MAF sensor would give, but then it will all of a sudden go away and drive fine. And will reappear sometimes 3 minutes later, sometimes 20. Never has a problem over 5k rpm or in boost. Just seems like part throttle low RPM. So today i pulled my plugs back out and checked my coils to make sure they were good (.9 ohms on every splitfire coil). Every single one of my plugs is showing a lean condition (plug tip is white). When I changed the old plugs out there were dark black and smelled like gas (obviously i was running rich). I have only driven this car maybe 20 miles since ive done the routine maintenance after I got it.  So my question is this. What could have happened to make the car all of a sudden run lean? Checked the ECu codes and had nothing (code 55). Could one of my MAF sensors be messing up after i cleaned it and not throwing a code? FPR take a shit on me? Faulty fuel filter? (yes its installed correctly).

I bought a Haltech with the CAN wideband controller and 3 bar map sensor. I wanted to wait until this winter (in the USA thats 3 months from now) before i went to install it. But my dyno tuning shop wont tune a car that has any issues prior to installing the Haltech so i dont think i will pass inspection.

I should have just left well enough alone when i got the car as it ran good but was running rich (but thats better than lean!)

Also the boost leak test found I have a small pinhole leak above 12psi on the intake manifold which will be fixed this winter. I cant imagine that would be an issue. And did a compression check on the engine just now and it read 155, 165, 165, 165, 165, 155.

Any thoughts would be appreciated!

blind_elk Grand Master

blind_elk

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Unless the engine is seriously modified, a "7" heat range plug is just WRONG. (Those plugs are recommended for various NA low performance engines). The recommended plug for a GT-R is a PFR6A-11 (although most people tend to use something like BCPR6E). So you need a "6" heat range, and seeing as you have relatively new Splitfire coils, open the gap back out to over 1mm (40 thou).

I'll theorise that if one MAF was misbehaving, then you would have different "leanness" indicated in 1 / 2 / 3 compared to 4 / 5 / 6. The old plugs are probably black because they weren't getting up to temperature (usually a result of short trips).

Malachi1364 Apprentice

Malachi1364

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Being a "7" heat range wouldnt cause me to run lean if anything i would think it wouldnt spark the fuel and make me run rich.

Today at work thinking i may have figured out the problem. I took the fuel pump out of the fuel tank to see if it was upgraded and the power/ground wire plug clip is broken off so It doesnt clip back into its spot. Im thinking as im driving the voltage is changing to the fuel pump causing me to have the wrong fuel pressure and therefore a lean condition across all the cylinders evenly.

Im going to order a fuel pump rewire kit and figure out a way to fix that plug. Also going to buy an AFPR w/ a gauge so i can make sure my fuel pressure is good.

If i am totally wrong with this guess let me know. From my past experiences when your MAF or 02 sensors goes back it causes a rich condition, not lean.

SEN_R32 Apprentice

SEN_R32

Posted
Posted

How did you go with diagnosing this issue?

I have the exact same hesitation issue as you are describing on partial throttle 3-4k rpm. My car is stock apart from turbo back exhaust and I've removed the boost restrictor.

So far I've got my hands on another pair of AFMs and its much better than before it hasn't fully fixed the issue.
I tried my AFM's on another car and it was having a hard time idling (my car doesnt have idling issues) so I was confident it was definitely AFMs causing the issue.

swapping AFMs:
The Good: Car accelerates a lot better, pulls harder.
The Bad: Hesitation is still there but I cannot replicate it all the time.

I'm gonna tackle fuel filter, fuel pump maybe (I'm assuming its still the OE unit) and CAS timing.

Malachi1364 Apprentice

Malachi1364

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Well im not 100% certain exactly what fixed it because I changed a bunch of things over the weekend. I had a small leak at my intake plenum to cylinder 4 throttle body so i replaced all the gaskets with brand new TOMEI metal ones. Then i rewired my fuel pump with a relay and constant 12v source straight from the battery. Also i installed my Haltech Platinum Pro ECU so it eliminated both MAFS and both 02 sensors for a 3Bar Map sensor and Wideband 02. Doesnt seem to have any hesitation issues anymore but i have not reved it up much because i need to get it to the dyno to get tuned.

I do believe it was the fuel pump wiring though. The rewire honestly took me an hour max and with how old the wiring is on these cars id recommend doing it even if you arent having problems.

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