New car, need help, car runs rough+rich+misfire+wheel stud+grinding etc..........

[Adler]

Hello all, I recently purchased a 91 GTS-4 sedan in need of some work. First off, when coming off throttle and putting the clutch in, the revs drop so low that the car wants to die; also, it idles like **** at about 1100 + - and the idle is never very steady (dropping down to 500rpm or less).

Secondly, the car runs pig rich. I can smell it and it misfires/hesitates/backfires sometimes. It's equipped with an rb25 turbo + manifold, hks bov, 3" exhaust. He said the coilpacks are going and gave me a set of used CA18 coils which he also said some of them may be on their way out aswell........ what should I do here?

also a front wheel stud snapped, I believe from reading it is a 300zx front stud right? easy to replace?

after driving it for a bit last night, there was some liquid which looked to be oil, coming out of the apexi air filter. is this normal?

last, it grinds into forth at high RPM. people say that redline shockproof heavy will fix this issue. any experience?


Thanks all.

[rob_96]

honestly man i had same issue with my gts4

what u need to replace is

plugs
Maf
coil packs
wiring specialist ignition wiring harness
ignitor

this will fix ur misfires/hesitates/backfires

Whee stud

Take off brakes and rotor and hammer out the stud
order new stud and put in
Call right drive speak to Darryl great guy

u might have a lot of blow by, you need to compression test the engine or get a catch can


what boost you running and is the car tuned for bigger turbo ?

post some pics or a vid

[Skym]

Check that TPS is on idle contact and that there's no TPS failure error code on ECU. TPS (idle contact) + ECU kick rpm up to prevent engine rpm dropping too low, stalling when back off throttle.

Could be lazy o2 sensor which makes ECU make engine stay rich longer (popping from exhaust, etc). Or BOV venting to atmosphere which would explain the engine running rich (need to recirculate the air with a draw through MAF setup, which is basically the MAF placed before the turbo).

Replace with genuine coilpacks. There's 2x types, Series 1 with spring + piece on end of spring (also mounting bracket to suit the different height due to spring + piece on end of spring), Series 2 with just a spring (also mounting bracket to suit the different height due to spring).

Can buy Nismo wheel studs (longer) or factory. There's a thread with parts numbers on here somewhere (search the forums).

Could be blowby or front oilseal on turbo has failed and due to reversion (air reversing direction when turbo slows down due to BOV venting to atmosphere) the oil is reaching air filter.

Sounds like synchro's are worn (gearbox needs a refresh). Another option is find a good gearbox as a replacement (alot easier, cheaper). It's about 7 times the cost (compared to a replacement gearbox) to properly refresh the gearbox (shift forks, synchro's, bearings, seals, reprofiling teeth on cogs, etc). Some say they can do it cheaper, but I think that excludes fitting new shift forks, reprofiling teeth, etc (just bearings, synchro's, seals).

[Nismo_line]

Z32 studs will fit. i have used them

[Adler]

thanks for the very informative answers guys. I am gonna have a look at the intake in the daylight; have a feeling it's just blowby from the pcv valve and if so I guess I'll have to run a catch can? I can't see it being the turbo seal it pulls steady boost @ about 9 PSI (i think? gauge is in BAR) and the oil pressure stays steady from what I can tell.


car has new plugs & ignitor so next step is new coils & a MAF sensor clean. could also be going wonky from the oil on the maf?
I hear yellow-jackets are a good, cheaper alternative to OEM coilpacks. can anyone verify? also - the guy I bought it from said it was using the stock ECU to his knowledge. Does the RB25 turbo really make a big enough difference to need a tune?


ill post a vid soon

[Skym]

Failed turbo oil seal is fairly easy to spot, as there will be oil in bottom of 90 degree elbow / intake piping just after turbo and inside of intercooler will be caked in oil (cleaning out inside of intercooler and cleaning idle valves, BOV, etc would be a good idea after fitting a catch can or replacing turbo).

From what I understand, MAF works via hot wire being cooled down by incoming air and ECU provides voltage to reheat it. More air = cooler the hotwire gets and more voltage is needed to reheat it (what ECU sees, 0-5V). If hotwire is dirty (coated with oil) it wouldn't be cooled as much, so should make engine run leaner (if my theory is correct). Also there's usually a intake temp sensor next to hotwire that takes intake temp into account, changes output voltage from MAF. CRC MAF cleaner is used to clean MAF.

I have heard of yellowjackets failing on high hp GTR's, OEM coilpacks seemed to solve the problem. But there could be many reasons why they failed (excessive dwell settings on ECU, spring length + mounting bracket thickness problem, just to name a few). Coilpacks just don't fail for no reason, there's always a cause. Usually incorrect sparkplugs (heatrange, gap) with stock coilpacks (stock coilpacks failed on my car due to wrong sparkplugs). Also age (should be changed every 100,000km as part of routine maintenance). These cars are 20+ years old, rarely maintained properly when modified, so coilpacks, etc would fail. Like any car, if maintained, tuned properly they have next to 0 problems.

The heatrange of sparkplugs differ when engine is running rich (stock is PFR5A) vs when running leaner (PRFR6A or PFR7A if running really lean) due to lower (rich) or higher (lean) cylinder temps. Reading the sparkplug tips is the best way to know what's going on inside cylinders and then adjust sparkplug heatrange to suit.

NGK show how to read the sparkplug tips -

http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp?mode=nml

Due to stock fuel map it runs leaner at lower, mid rpm's, then safe at near to peak hp. Lowering boost level helps alot (can use a auto RB25DET internal wastegate actuator, which is rated at around 5psi). Stock boost gauge is in x100 mmhg (look at corner of stock boost gauge). Max (+7 on boost gauge x 100 = 700mmhg) is around 13.5psi.

[Adler]

should mention it has an hks BOV with a manual boost controller. new vacuum lines. and a walbro pump. and 0.8 mm sparkplugs

[Skym]

The BOV sounds like a vent to atmosphere BOV. Also the bigger lph fuel pump wouldn't help, as the engine runs even richer (it goes into 10's at mid to high rpm on dyno chart, maybe richer on some cars).

From what you have said, ECU re tune (for bigger fuel pump, bigger turbo), good recirculation type of BOV (or fit stock BOV), change o2 sensor (gets fouled by engine running rich).

[Adler]

okay, i'll change the 02 sensor to be safe. what would be the most effective way to get it tuned for the turbo?

here is a video http://www.youtube.com/watch?v=C3UfMKklVfk

kinda short but it shows how it dies out

[Adler]

pulled the maf sensor, the mesh is broken..... is the maf no good? also theres not any oil in the intake, it looked like it was seeping through the cone filter but it must have gotten spilled on cause its dry behind the MAF sensor.

[DarkCaporaL]

That's just the mesh to prevent you/debris from hitting the sensor inside. If the sensor hasn't been touched it should be fine.

If the MAF was broken you wouldn't be able to rev past 2-3k rpm.

[Skym]

As far as I know, the gauze screens help to keep debris out, straighten airflow towards hotwire.

I would replace the MAF, inspect intercooler end tank for debris and check edges of turbo compressor wheel for damage.

[Adler]

I have used CA18 coilpacks, are they good to use as replacements until I can afford all new ones?

[Adler]

tested the current coilpacks and they all read .8 ohms so I guess they are okay .......

[Adler]

really stumped. we adjusted the tps sensor to .48 and replumed the original recirc blow off valve. runs a bit better but still stalls worse than before. the idle is up and down. sometimes I can't even get it to idle without pumping the gas pedal. car chokes when we pull the tps so thats not it. cleaned the maf and it ran a bit better but the only thing I can figure is that I need a new maf. seriously stumped now, gone through everything