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R32 Gtst Coughing Under Boost And Revving Up On Its Own

Aidan32

By Aidan32,
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Aidan32 Rookie

Aidan32

Posted
Posted

Okay had a quick look over the forum and google searched and can't really find anyone else with this same problem,

Last night I picked up my very first Nissan,

It's a r32 GTST type M

Car apparently hadn't run in 3 years

Had a quick check over the car when inspecting. Compression is a bit lower than normal but even across all 6, when we were cranking it over when first inspecting I could hear a few cylinders fire so it gave me hope and I got the car and bought it home,

So the first thing I did was plugs, pulled them out and inspected, cleaned them up and slapped them back in, checked if it was getting fuel, just pulled the line off and cranked and kept cranking until the fresh fuel I chucked in started coming through. Tried starting car and it was very very close to starting, rechecked plugs and when watching for spark noticed it was weak and arcing between the threads of plugs,

Found some brand new ford falcon plugs in garage that were same thread so just chucked them in to test it, bam the car fired up straight away, was stoked that it started up after just a few little basic checks,

BUT as you'd expect the car was running smooth exactly, would barley idle, was running richer than bill gates, fuel was pouring out the exhaust, and if you accelerated it would just sit hunting around 2500rpm, even when foot flat,

straight away I thought it would be afm, but the car has a brand new genuine Nissan afm installed just before I bought the car, came with receipt for it,

Later on a friend came over and plugged his laptop in and used some program that reads all the sensors readings, start the car up, CAS was a little out, but when warmed up was sitting on 15 (got told this is where it should be)

TPS sensor was a little bit out so we set that, still no change,

Then we noticed afm wasn't getting a reading at all, checked it was all plugged in, checked the wires around close to turbo and stuff, looked all okay, checked inside around ecu as previous owner had been messing around with something and left trim off, found a single

Black wire with a male and female end which wasn't plugged in, plugged them together and started it up and BAM the car idles and revs up fine, but it had a misfire. Went and bought the standard plugs for the car and then it idled perfectly :) was super happy ,

After all this the computer said we had code 55 from memory ,which said (no sensor faults)

So all was good,

But then I went to go take it for a drive, started it up, was fine, tapped the accelerator pedal and all of a sudden it revved up on its own to 7500rpm and then dropped back down to idle , I reversed out and went up street putting around, was running smooth just driving normal, got it up to temp and went to go boost it, as it goes to come on boost it goes no where and coughs and splutters and blows out black smoke, and then when I back off after trying and press clutch in it all of a sudden revs up to 7500 again all buy itself, stock boost guage reads it is boosting but you don't feel it because it sits coughs and spluttering.

And that's where I'm up to, I know a lot of you guys will jump and say coil packs, but I don't wanna jump to conclusions, because of the fact it revs all buy itself that high,

I still need to gap the plugs, got told to gap between 0.6-0.8

At the moment I think they are at 1.1

Need to change fuel filter

Dump all fluids and filters and put all new fresh ones in

Need to check for any leaks (vacuum and turbo piping)

If anyone's got any other ideas I could check let me know please, thank you

Aidan32 Rookie

Aidan32

Posted
  • Author
Posted

I'd start by putting the correct plugs in there for sure. At least one boost leak is probable. As for the free-revving, not entirely sure.

It has the correct spark plugs in it now, no change

Went over and pulled off and reinstalled all turbo pipes, shouldn't be any leakage

GH05T Grand Master

GH05T

Posted
Posted (edited)

my fuel pump died on me slowly, caused missfiring.
new pump and filters can solve so many little issues.

7500rpm sounds like something just got stuck. throttle body cleaner would be my first purchase, clean the idle controll valve ect

also after tapping the pedal and getting 7500rpm, your damn keen to put it into reverse. could have been interesting.

Edited by GH05T
Aidan32 Rookie

Aidan32

Posted
  • Author
Posted

my fuel pump died on me slowly, caused missfiring.

new pump and filters can solve so many little issues.

7500rpm sounds like something just got stuck. throttle body cleaner would be my first purchase, clean the idle controll valve ect

also after tapping the pedal and getting 7500rpm, your damn keen to put it into reverse. could have been interesting.

Yeah a friend of mine told me to clean the idle control valve and shit aswell so I'll make sure I do that,

And the way I saw it, if it starts reving buy it's self I just clutch in and it won't go anywhere lol

Ben C34 Grand Master

Ben C34

Posted
Posted

Revving like that isnt caused by the IAC. Its more than likely the throttle got stuck. Which seriously needs to be addressed before you go much further.

And looking for leaks isnt the same as pressure testing for leaks. I strongly recommend you pressure test to find leaks. You will be surprised.

Aidan32 Rookie

Aidan32

Posted
  • Author
Posted

Revving like that isnt caused by the IAC. Its more than likely the throttle got stuck. Which seriously needs to be addressed before you go much further.And looking for leaks isnt the same as pressure testing for leaks. I strongly recommend you pressure test to find leaks. You will be surprised.

Throttle cable deffinatly dosnt get stuck, I've already checked that,

And okay I'll do a pressure check

scotty nm35 Grand Master

scotty nm35

Posted
Posted

Well I was going off something online, how are you meant to check them, they should be good anyway, cause it doesn't misfire at all

I was going to say with your tongue, but I don't want someone to actually try it on my suggestion. :P

If it's revving to 7.5k there is a large air leak somewhere after the throttle, and the car is running way too rich. Sounds like it may have been modified at some point. I would be replacing the AFM with a known good one and perhaps checking the injectors aren't highflowed.

Aidan32 Rookie

Aidan32

Posted
  • Author
Posted

I was going to say with your tongue, but I don't want someone to actually try it on my suggestion. :P

If it's revving to 7.5k there is a large air leak somewhere after the throttle, and the car is running way too rich. Sounds like it may have been modified at some point. I would be replacing the AFM with a known good one and perhaps checking the injectors aren't highflowed.

If you read the information I've supplied,

AFM has been replaced with a genuine BRAND NEW nissan one

And is reading correctly (checked with plugging in consult cable)

There's no air leaks ANYWHERE

And it just revs up buy it self only sometimes when I start it and touch throttle now,

Sometimes is rich when I first start it but clears up quickly and runs fine

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