R32 GTR misfire

[Doug345]

Hi All,

I have been having a misfire with my '94 R32 GTR for a while now and I am starting to get frustrated with it. I have tried a bunch of different things to no avail.

Basically, I have a misfire that doesn't happen all the time, only randomly - I cannot peg it to any certain situation. It's not like it happens only when the air is humid or exceptionally hot, or dry or cool. It does not only happen when the car is cold or only at running temp. When it does happen, it usually happens between 2k and 3k rpm. At other times that range will be good and it will have a problem around the 5.5k to 6k range. Sometimes there is no problem at all. When it does happens, the misfire can happen sitting in neutral, or under load on the road.

The things I have tried so far are:

Changed fuel pump
Changed fuel sender unit (the contacts were corroded and falling apart)
Changed fuel filter
Changed air filter sponge (HKS mushroom type that were pretty eaten away)
Changed and gapped plugs (BCPR7ES gapped at 08.mm)
Cleaned MAF sensors
Changed coil pack harness
Installed decat pipe (I read somewhere this might help but it didn't and I wanted it anyway )
Adjusted CAS with timing light to make sure timing was at 20 degrees BTDC

I think that's it...if I have forgotten anything I'll let you guys know.

What I plan on doing next:

My injector seals are good but since the car is over 20yrs old, I bought an OEM kit because my next step is to clean the injectors and replacing the seals seems like the smart way to go.

If this doesn't work, I was planning on buying a new igniter and see if that solves it.

I've read about taking apart the MAFs and resoldering the pins so that's an option too.

The last thing I want to do is change the coilpacks. I currently have splitfire coilpacks installed that were on the car when I bought it so I'm leaning to that not being the problem. What is the best way to test these?

Could boost leak be a factor? I haven't done a test for this yet but i run a stock setup (with restrictor removed) and in neutral I get about a 0.9bar reading from an aftermarket Apexi gauge, but under load, it usually peaks a little above 0.7bar.

Has anybody else had this problem? Can anyone point me in the right direction...like I said, I've tried alot of things and it's starting to frustrate me. I also bought a nismo adjustable FPR but I doubt this is the problem so I haven't yet installed it. Any input and help would be much appreciated. Thanks

[Skym]

Most of the missfires I have had have been coilpack related. The grey tracking marks on the side under mounting bracket gives it away at which is leaking. The other is airleak behind MAF causing stuttering, similar to coilpack missfiring.

Coilpacks can be tested via a multimeter (consult manual), but I had them tested on a coilpack testing machine that has input, output gauges and can see the actual spark from the coilpack (measures the input voltage, output voltage). It picked up 2x faulty coilpacks which is normal.

At 3000rpm sounds like boost cut / fuel cut (intake air leak between airflter, MAF's, especially if the airfilters clamp onto adaptors). But at around 5000rpm sounds like the safety rev limiter (fuel cut) and engages when there's a speedo input problem (Okm/h from dash) or a knock sensor failure.

Missfiring can be cause by ignition module, but would happen after 10 minutes of driving. Let it cool and it will do it again within 10 minutes of driving. Not always the case, but how it happens.

But I would check your sparkplugs, as they might not be gapped correctly (factory is 1.1.mm, needs to be at least 0.8mm) or not the right heatrange. Incorrect gap, heatrange on sparkplugs is usually the cause of a coilpack failure. Other is age (change them out every 100,000km under normal road use, earlier if used for racetrack, dragracing, etc).

When you open up the exhaust the cylinder temps rise due to rise in boost level, leaner A/F ratio, so you go one heat range colder with sparkplugs. Factory should be PFR6A-11 for stock RB26 (same as RB25DET) and you fit PFR7A-11 with 0.8 mm gap with basic intake, exhaust mods.

[Doug345]

Thanks for the reply Skym. Sorry it took so long to get back to this..

So there is a possibility that my problem is air leakage behind the MAF sensors? And I'm guessing that could be anywhere from directly behind the sensors all the way to the plenum? At the higher range I never get a 0km/h reading from the dash. How can I check to see if I have a knock sensor failure?

I cleaned my injectors and put on new seals. Had no gas leaks and the problem still persisted. Haven't had a chance to check the coil packs for those grey marks you mentioned but I will be doing that soon.

[bobbo]

I'd be willing to bet it's your ignitor failing. I had the same problem... assuming you've eliminated the coil packs.

[Skym]

Thanks for the reply Skym. Sorry it took so long to get back to this..

You're welcome.

So there is a possibility that my problem is air leakage behind the MAF sensors?

Could be, would need to eliminate it as a cause.

Intake airleak infront of MAF = fuel cut / boost cut kicks in earlier than it should on ECU as the MAF or MAF's max out earlier than they should.

You get this with airfilters that use a metal adaptor that bolts onto the MAF, then airfilter fits over the metal adaptor and clamps onto the metal adaptor via using a intake hose clamp. If tighten the intake hose clamp it usually solves the problem. That's why airfilters like Apexi for example bolt directly onto the MAF's with a gasket inbetween airfilter, MAF itself.

Intake airleak just behind MAF's (rubber intake pipes that the MAF's fit inside of) = stuttering as the MAF gets 2x airsources instead of one. Because the MAF gets more air, the MAF sends the wrong voltage for the rpm to the ECU and the ECU picks the wrong cell on fuel, ignition map, hence the stuttering (similar sound to a coilpack missfire).

I think the stuttering sound is from the engine running richer than it should + wrong ignition timing in all the cylinders. It's similar to what happens when a faulty coilpack fails to ignite the fuel properly or at all in one cylinder.

And I'm guessing that could be anywhere from directly behind the sensors all the way to the plenum?

Intake airleak before or just after the MAF's (rubber pipes that the MAF's fit into). The rubber intake pipes have ribs and it can crack inbetween the ribs (common).

At the higher range I never get a 0km/h reading from the dash.

Okm/h reading is into the ECU itself from the dash (where the engine ECU gets the speed input from), you would need to use Consult (Nissan's handheld diagnostic computer) or Conzult + Consult cable to see if the ECU is receiving input from the speedo. Sometimes the wires on ECU plug fall out and cause problems, especially if someone has pulled on the loom when removing the engine ECU in the past. Sometimes the ECU is not seated correctly into the ECU plug before they bolt it down and warps the plug causing missfiring, etc.

How can I check to see if I have a knock sensor failure?

Usually shows up as a knock sensor error code on the stock ECU. That would require getting hold of Conzult + Consult cable or Nistune tuning software, PLMS Consult cable. The knock sensors are hard to get to as are located under the intake plenum, should be one front, one rear on the engine. So a bit difficult to use a multimeter on the sensor plug (correct sensor voltages are in the GTR workshop manual).

I cleaned my injectors and put on new seals. Had no gas leaks and the problem still persisted. Haven't had a chance to check the coil packs for those grey marks you mentioned but I will be doing that soon.

The are quite obvious (grey tracking marks from the coilpack leaking) against the stock black coloured coilpacks.

[KojiKP2]

Skym, thank you for all this info. I've been keeping an eye on this thread as I have some issues too. After your post, I'm going to have to look at my air filters/mafs/tubing.

[Skym]

Skym, thank you for all this info. I've been keeping an eye on this thread as I have some issues too. After your post, I'm going to have to look at my air filters/mafs/tubing.

You're welcome.