Newbie Help Please

[low_boost]

hey guys and girls im new to skylines and have just broughts my self 2 and im having problems with 1 its just a r33 gtst rb25 manual have changes plugs,coils fuel pump and throtle postion sensor and the problem im having is when u go flat to the floor it gets to 4500rpm and sorta hesitates and kinda back fires but if ya back of a lil bit it will rev out can any body give me some tips please thanks

Edited July 14, 2011 by low_boost

[GTR260]

Afm?

[low_boost]

yeh not to sure havnt got a spare 1 of those to try

[SiR_RB]

usual rb25 flat spot. turn boost down below 10psi

[low_boost]

its runin stock boost and factory hi low switch still only mods are front mount and decat pipe and 3 inch exhaust but also not really get any more than 3psi

[JonnoHR31]

what plugs and what gap?

[75coupe]

its runin stock boost and factory hi low switch still only mods are front mount and decat pipe and 3 inch exhaust but also not really get any more than 3psi

r33s have a factory hi low switch????

air leak

afm

search, its a common problem...

[SargeRX8]

r33s have a factory hi low switch????

air leak

afm

search, its a common problem...

I think he means the 5psi boost to 4500rpm then 7psi to red line.

Anyhow it sounds to me like a misfire of some sort. Could even be lean popping. Does the car start and idle fine? If you hold RPM at say 5k in neutral does it pop? Does it hold fine? It could be many things. Gap your plugs to .8mm and wrap up your coil packs in tape(I don't know if this affects S1 coils but I don't see why it doesn't).

Inspect your old plugs. See if it looks rich or lean.

[low_boost]

ok plus are irridue bre6s gaped at .8 all ready if u drive long in first flat to floor its sorta hesitates then picks bak till round 4500to5000 the just pops the if ya back off to like 3/4 throttle it ill rev rite out on idel its perfect same as starting plus are a light brown colour but on gear changes when u find its happy spot and wants to go it ill shoot flames out the exhaust it kinda sounds like the timing isnt advancing its up in the revs

[low_boost]

and its only breakin down under load

[The Dan]

It seems as though all the generic answers have been applied.

You changed the fuel pump but have you changed the fuel filter?

Do a fuel flow test on the return line at 3000rpm to see if the pump is doing what it should. If the pump is not doing what it should (at minimum 2.5L/min but better to have 3L/min or more)then run the earth mod to improve the power circuit. If flow does not improve then run fresh power to the pump as the old wiring could be cactus. Recently had a car that did this with a new filter and brand new Nismo pump. New wire and all sweet now.

If the fuel system is up to the task then check the ignition. Gapping plugs down is a bandaid fix but going to 0.8mm is ok. If you have checked every possible avenue and still can't find the problem, try gapping them down to 0.6 or 0.4 but only as a test. If the missfire goes, improve your ignition system. It may not be the coils either, many of these old things have terrible wiring looms.

It would be rare to be an airflow meter problem. I've fixed hundreds and hundreds of these things and it's almost NEVER the AFM. I don't even know why so many people suggest it. Maybe if it was an old rusted out R32....maybe

I would say that if you still can't find the problem after doing all that, then take it to a specialist as the problem is likely to be complex. No amount of throwing parts at it is going to make it get any better. It's only going to make your wallet lighter

[low_boost]

thanks just put in a bosh o44 out of other r33 have thought of earths of wirering maby even fuel presure reg ??

[The Dan]

thanks just put in a bosh o44 out of other r33 have thought of earths of wirering maby even fuel presure reg ??

Absolutely not. The reg is usually the last place to look. I know you said you replaced the pump now for the second time but what about the fuel filter?

[SargeRX8]

Could it be that your CAS is fizzled? Have you checked to make sure the cars timing is fine? After hearing that you are shooting flames, it COULD be that you are hitting R&R which would explain the flat feeling til red line, but does not explain the splutter before 4500rpm. Your car will pull timing and dump fuel there to prevent any possible damage to the motor. Check its timing at 650rpm should be 15deg. There are too many things it could be man, you need to eliminate problem by problem with doing, as above, little temp fixes to see what gets rid of what. Tape up your coils. Check the wiring for your coils is still relatively supple.

Too many issues. Your pre 4500rpm issues sounds like the symptoms of my old failing fuel pump. Be careful, if your pump is failing you could detonate your engine on a lean fuel mix.

thanks just put in a bosh o44 out of other r33 have thought of earths of wirering maby even fuel presure reg ??

Just read this. If you are doing as you say you are, shooting flames, you shouldn't be worried about the fuel flow I don't think. You've got enough fuel to get you moving and enough fuel to catch fire and explode in your exhaust. I think its an ignition issue.

Edited July 14, 2011 by SargeRX8

[low_boost]

fuel filter is new as well all fuel lines have been blown out yeh have been thinkin bout the CAS but dont know enouf info on these things atm but coil wireing didnt look to bad or to be britle at all

[The Dan]

It still sounds like you have a fuel problem. Peak torque is at approx 4500 in relatively stock form. The highest demand for fuel is at that point. You need to do a flow test before you test anything else. The problem is more likely to be mechanical rather than electrical but start there. When you have done the flow test and can tell me you have 3L/min or more, then You can move on to the next most likely cause

[SargeRX8]

It still sounds like you have a fuel problem. Peak torque is at approx 4500 in relatively stock form. The highest demand for fuel is at that point. You need to do a flow test before you test anything else. The problem is more likely to be mechanical rather than electrical but start there. When you have done the flow test and can tell me you have 3L/min or more, then You can move on to the next most likely cause

What is the best approach to this? Just run the return line into say a 5L bucket, mark it at 3L then start the car for a minute?

[low_boost]

ok will try that over weekend

[GTSBoy]

<snip>Peak torque is at approx 4500 in relatively stock form. The highest demand for fuel is at that point.<snip>

Now that's just untrue. Peak air intake per cylinder fill cycle may be highest at that point, peak fuel consumption per cylinder cycle may be highest at that point, but max fuel consumption will always be around max power. That much should be obvious.

If something makes say, 200kW at peak torque but is making 250kW at peak power, then there is at least 25% more fuel being burnt at peak power than at peak torque (to just pick some random but indicative numbers out of the air). Otherwise the engine would be massively more thermodynamically efficient at peak power than at peak torque, and we know that's not the case.

But otherwise, I agree that something is quite possibly suss with the fuel system and I reckon you should pop it on a dyno with a gas analyser and fuel pressure gauge on it rather than try to track down, on the road, something wierd that seems to not be all the usual suspects.

[The Dan]

What is the best approach to this? Just run the return line into say a 5L bucket, mark it at 3L then start the car for a minute?

We would normally do a 1L container, put the return line after the reg into the top, start the engine, start the stopwatch, and either run til the 1L is full and calculate over 1 minute or run it for 15 seconds and multiply by 4

Now that's just untrue. Peak air intake per cylinder fill cycle may be highest at that point, peak fuel consumption per cylinder cycle may be highest at that point, but max fuel consumption will always be around max power. That much should be obvious.

If something makes say, 200kW at peak torque but is making 250kW at peak power, then there is at least 25% more fuel being burnt at peak power than at peak torque (to just pick some random but indicative numbers out of the air). Otherwise the engine would be massively more thermodynamically efficient at peak power than at peak torque, and we know that's not the case.

But otherwise, I agree that something is quite possibly suss with the fuel system and I reckon you should pop it on a dyno with a gas analyser and fuel pressure gauge on it rather than try to track down, on the road, something wierd that seems to not be all the usual suspects.

Wrong