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Discussion Starter · #1 ·
Hi, usual start to a forum, new to this (i will try stick to the main points and go further I detail if I can pick up some advice on here) decided to use this forum because my problem has been looked at by 2 specialists now and the problem continues.
I have a r33 gtst 1995 spec 2 with 55k miles on the clock. It's currently on stage 2 1.2bar 440whp with stock internals (next step is forged).
It has a strange intermittent problem which comes and goes when you drive it, it's obvious when you drive but difficult to explain so here it goes.
Between around 1000rpm and 2500rpm it's smooth no issues, above 2500rpm which I guess it begins getting into boost the engine begins to splutter, as if its misfiring. From this rev range all the way up to around 7000rpm the engine continues this strange on/off splutter, but the full power is also there. The turbo sounds like it's in anti lag and spooled right up. And the engine causes massive pops and bangs (which is fun sometimes) but not when your following miss Betty down the street doing 30mph. Worst part of this is the engine drones so bad you can't hardly have a conversation between 50mph and 70mph.
Then the strangest thing, the next day I take the car out, the issue Is not there, car drives super smooth and it's considerably quiet (unless you give it the heinz).

A guy I spoke to who's an vehicle technician but not a rb25 specialist, did say it could be the air temperature ie hot day - runs bad. Cold day - runs well. If this is the case, is there a temperature sensor linked to the link g4 ecu that could be providing weird information.

Really hoping someone may have some suggestions?
Thanks,
Lewis :).
 

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before we go down the diag rabbit hole, which i hate when i cant physically put my hands on the car. i have some questions before we start talking tunes and all that.
first question is does it do this when the car isnt in gear? in other words will the problem happen when just simply rev the engine or only with a load?

have we done the basic visual inspection? checking if there is anything broken, torn, burnt, corroded, lose ect.

what did the specialist say? were they able to replicate the complaint? if so, what diagnostic test did the specialist do? like reading live data from O2s , MAF ect. ( yes it can be done just alot more involved than an OBD2 cars) i am not going to assume anything, so i have to ask did they pull plugs and check for sooting , proper gap, ect. did they perform a injector balance test? stuff like that.
 

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Discussion Starter · #3 ·
Ok firstly thankyou for taking the time to read my issue and reply.
I could have made the first post 10times longer but just wanted to pick up someone with some ideas so stuck to the bassics.

I dont want to name the garages, because I'm friendly with them both, and the second garage is an actual rb specialist, where as the first garage, although a tuning specialist, rb engines may have been out of their knowledge, I say this because of the following...
The second garage when they performed the leak down test, and compression test believe that garage number 1 put 1.4bar through which has caused piston 5 to show a 10psi drop (which I know isn't too bad) than the rest which all showed 165psi throughout. So we think the first garage has possibly cracked the ringland on piston 5 (which as we know is a common issue). Probaly quickly worth mentioning, that thd second garage got 440whp from the engine with 1.2bar, where as the 1st garage got 440 with 1.4 bar.

Now answering your questions.
The engine does not do the intermittent issues when revving up, only in gear.

The second garage (rb specialist) performed all the test you have mentioned and what he said was the injectors are fowling up, and when you drive the car like a lunatic, it can clear. (Trust me I've tried this and I couldn't get it to clear).

Finally the engine does have a little bit of altered wiring done, more to avoid the ignition module which sits on the top plastic cover at the back of the engine (something that was done to get it to stage 2 I believe).

Hope that answers some more questions.
 

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i understand not naming names. i was just trying to see where were at on diag. that's good.

normally when i do leak down tests i do higher psi than that. youre doing to get a low percentage of blow by so thats normal. it sounds like the engine is good mechanical working order.

if we are leaning towards fowled injectors, i have a recommend cleaning you can fairly easy. i have been using this technique since i first started as an automotive technician in 05. the tool kit is called non dismantle fuel injector cleaning kit. here in the land of bald eagles and big macs the kit runs about $85-$160 . basically what it is, is a satellite gas tank. its a small cylinder that you put a cleaner into and pressurize with air. then dial it to the right fuel pressure. pull out the fuel pump relay, plumb it in to the fuel line going to the fuel rail. start the car and let it run until the cylinder empties. customer cars id always recommend 2 runs with cleaner. while i was technician this method had about 85-90% success rate for me.

there is another method you can use. and the kit is alot cheaper but more involved. basically you would dismantle the fuel rail and clean the injectors individually. using the tool to activate the injector and a aerosol cleaner to do the cleaning. i have done this when i bought used injectors. works out well

id also take a quick second to use a good MAF cleaner and clean the MAF. be careful not to damage the wire in the body. spray it and let it dry. avoid using compressed air to dry it as it can damage the wire in the body.

not knowing everything that was tested. those are a couple of suggestions that could possibly help.
 

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Discussion Starter · #5 ·
Ah great think I will try the second method.

So last week I took the injectors out of the car, I separated the manifold plenum, there was 4 bolts pointing down, I think these are done this way to test my existence.

I then thoroughly cleaned the injectors by blowing them through with air (I forgot to mention these were flow tested a few weeks ago with the rb garage and shown to be working well) I then put everything back together and thoroughly cleaned everything while doing so.

Took the car out for a test drive Friday night, the car drove perfectly no issues.

Then Saturday morning, when leaving for the show the car was booked into, 5 minutes into the drive, started playing up again so ended up going back.

Which leads me to believe maybe the air temperature does play a small part of truth, because it was around 10 degrees Celsius Friday night, and 20 on Saturday.

Do you reccomend a certain brand to clean the injectors even more thoroughly.
Also, what I can clean the maf with not to damage the wires (ipa 70% I'd probaly use).

Thanks
 

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to be honest im not 100% that these will solve your problem. you may have pump failing or a CAS failing or something that has been overlooked.

for the MAF i was referring to element inside the barrel of the MAF. the piece that protrudes into the airstream . and that you can find a specific MAF cleaner at your parts stores. just take the MAF off and spreay the cleaner into the MAF body and let it dry. i dont know brands because i assume brands are going to be different between the US and you guys.

i have see guy use non chlorinated brake to clean the injectors. i havnt personally do that but they claim that it works well. the few times i have used this one i used choke and carb cleaner because i couldnt find an aerosol of the injector cleaner i liked. i had success with that.

this is the kit i have for the second option
 

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Discussion Starter · #7 ·
Ok fantastic I will try this and let you know how I get on.

I did go to have a look at it last night, it doesn't have a maf after the air intake, it has a sort of maf that's been welded into the j pipe, I tested it and there is around 5v going to this, I'm going to clean this up and clean up the wires as it has electrical tape around it.

I think its all about eliminating different issues to try to solve the problem, which for me would be;

Cleaning the maf (sorting the wires out)
Using the car on a cooler day/then on a hotter day.
Cleaning the injectors again, maybe sending them off to be flow tested again.
Testing the petrol pressure.

Thankyou for your help,
Lewis.
 

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Discussion Starter · #9 ·
Hi just an update.
Fitted a new link air temperature sensor, took the car out, no problems, cleaned the old sensor, took the car out, no problems. I thought I had solved the problem. Ofcourse I hadent.

Most times the problem begins after going down a hill when the cars in gear and I'm bassicaly either engine braking or on hardly any throttle, this hasn't caused the car to begin its issues every time, but more times than not now I think about it, it begins after going down a hill.

Again, this evening, I took the car out, the car was fantastic. Came back down and as soon as I began accelerating after the bottom of the hill it began to play up.

So now I'm moving onto just another idea, and please give me your advice, It must be something to do with the fuel pressure? 'I'm just slightly steering away from the injectors because they have been flow tested so in theory should be working good' Maybe the link ecu is sort of putting the car into limp mode because the fueling isn't right?

The car must have a upgraded fuel pump because surely it cannot produce the hp on a stock pump?

What if the problem is either the fuel pump? And/or a regulator, regulating the fuel back to the tank?

Only issue I can see with a regulator is I think it needs setting up correctly? Or is there possibly a 'go to' setting?

Appreciate any further help as always.

Thanks,
Lewis.
 

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I am surprised that the fuel pressure has not been checked by one of the garages? Is it still running the std FPR or is there an aftermarket one? If std I would just get a decent one with a gauge and set up as per manual and see if that helps, another thing I am surprised at is that nobody has fitted or used a wideband lambda set up as this alone would tell you if there is a fuelling issue or not, and even if it was a coil pack problem it could give an indication if you know what to look for.
 
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