Engine Performance Problem

[Guest McRen]

Hi,

Recently my car has been misfiring at 5000 RPM, I own an R33 GTS-T.

I replaced the spark plugs using 1.05 mm gap. The car continued to misfire. I regapped the spark plugs to 0.8 mm and the misfire has gone.

The only problem now is when the engine hits 5000 RPM. Usually at this point you can feel a big power increase but there is none (the performance doesn't change). When the car hits around 6000 RPM you can feel more power but feels like it is hesitating...

The car is running standard computer and boost.

Any ideas?

[Craved]

Mc Ren,

have you got a boost guage on the car -- besides standard.

if so what is happening with boost at that point?

[SKYL9]

The power gain your talking about would be the solenoid thingo that changes the boost from 7psi to 10psi just b4 it hits 5k wouldn’t it?

[Airzone]

Correct me if I'm wrong, but the variable valve timing will change your timing as you accelerate... I notice this in mine, and it's probably the power increase you're noticing in yours.

About 5000 rpm is where the stock boost solenoid kicks in... If you're not getting that extra boost then you might want to look at the solenoid (it's near your power steering fluid bottle). Check the air lines for cracks too.

[Guest McRen]

I looked at the boost guage and the car is coming onto full boost. Something feels restricted or maybe the car has retarded for some reason? Resetting the ECU gives a slight performance gain, but this is really weird.

On a few occasions the car has been fine reving out to 7000 RPM, but mostly is loosing power at 5000+ RPM.

I think I'm going to replace the injectors, fuel filter and clean the air flow meter...

[crooser]

i have an almost identical problem which occurs at 4500 and dissappears at 6000. between 6 and 7k rpm the power comes back on hard.

boost solenoid is plugged up.

AFM has been cleaned.

tested with another factory ecu

played with base timing

on the few times i have tested, if the car is hot and decent heatsoak has occured (eg stopped for 10min gettin fuel), it revs through without a problem. after another 10mins of normal driving though when things have cooled down a bit, problem is back again. the AFM might be reading too much (cool) air and overfueling to compensate.

If you get a chance McRen, please test this in your car.

cheers

[nismoman18]

flat spots, sumtimes a bad batch of fuel, dirty fuel filter can cause this. My mate's car had flat spots when he filled up with mobil fuel, he went back and complained got a refund from them!

[Kdawgboostin33]

Had the same sort of problem. With only basic mods FMIC and exhaust car was not even hittin full boost, Car was just runnin way too rich. Changed the computer and it was fine

[Guest RedLineGTR]

or ya can get the stock ecu retuned by soem places to fix up the A/F ratios etc....cheap uprade and a good fix er up

[Guest McRen]

Originally posted by crooser

i have an almost identical problem which occurs at 4500 and dissappears at 6000. between 6 and 7k rpm the power comes back on hard.

boost solenoid is plugged up.  

AFM has been cleaned.

tested with another factory ecu

played with base timing

on the few times i have tested, if the car is hot and decent heatsoak has occured (eg stopped for 10min gettin fuel), it revs through without a problem. after another 10mins of normal driving though when things have cooled down a bit, problem is back again. the AFM might be reading too much (cool) air and overfueling to compensate.

If you get a chance McRen, please test this in your car.

cheers

Crooser,

It’s good to hear I'm not alone on this one, not that I'm wishing other people had a similar problem. I'm not 100% sure what heat soak is, I'll assume from what you’ve said this happens when the car has been turned off for 10mins after it was up to its normal temperature previously.

I'll try this today and let you know what happens. Now that I think about this I remember stopping at a newsagency for 10 mins or so and that was one of the occasions the car revved out properly afterwards.

Here are the things I've tried to rectify the problem.

* Changed spark plugs to 1.05mm

* Re-gapped spark plugs to 0.8mm

* Cleaned air flow meter (this was already clean, but I sprayed it with solvent anyway).

I'm going to change the fuel filter. I'll keep you posted tomorrow.

[Guest McRen]

I forgot to mention that I put half a bottle of injector clearner through the car. I just filled the car up full again after work today and the car feels like its starting to rev out more then it did before.

After 5000RPM it would hesitate. Now it still does a little after 5000RPM but not as much.

So I think its probably the injectors that need cleaning...

I think I'll put a whole bottle in next time I fill the car.

Does anyone know if you have to put injector cleaner in when the tank is empty?

[Napalm]

Originally posted by McRen

Hi,

Recently my car has been misfiring at 5000 RPM, I own an Datsun 120Y.

I replaced the spark plugs using 1.05 mm gap. The car continued to misfire. I regapped the spark plugs to 0.8 mm and the misfire has gone.

The only problem now is when the engine hits 5000 RPM. Usually at this point you can feel a big power increase but there is none (the performance doesn't change). When the car hits around 6000 RPM you can feel more power but feels like it is hesitating...

The car is running standard computer and boost.

Any ideas?

The points may have closed over.

You should also check the distributor cap for cracks.

[dan_the_man]

Read the instructions on the side of the injector cleaning bottle... I think u have to pour it in as ur filling, like a bit b4 u start to fill then fill then stop then add some more then fill

[no_gtr_yet]

McRen

check your timing or get your mechanic to check it out, poor timing and crap Tasmanian fuel = detonation

Cheers Alex.