Missing/flatspot/surging At Boost But At Low Rpm.

[WogsRus]

Hi Guys.

Well ok so my car seams to have never ending niggling problems, mainly related to me being so dam anal about being perfect.

The car has the mods as listed in my sig.

Central 20 maped ecu + SAFC II. The SAFC II was tuned with the Central 20 ecu to give optimal results, and pulled 217 rwkw at 14.9 spi.

Walbrow pump, FMIC, intake and filter. Basically all I needed to get the power I was after wich was anything over 200 rwKw.

Ok so here it goes. I have two main issues, SO PLEASE READ ON AND HELP ME.

1)I had the car tuned and so forth about 6 months ago or more, and ran like a charm, never had any issues perfect, finally. Then we had a massively hot summer day in Tas, yes these do happen, and the car had issues producing boost. My first thought was that i damaged the motor, so i checked the compression, and i got 155psi across all the cylinders. I did not do a leak down test however.

The car does not use any oil, or blow smoke, as such, the turbo seal is a little weeping when cold, but hay.

Every since that day i have been having cold start issues with the car. Basically the car will start to fire then bog down and miss, to 400 rpm and then cough and clear itself and idle fine at 1200 rpm. Any other time after that if i start the car it starts without caring on, BUT it still does not start properly.

On a normal skyline, when hot, if you crank it over the car will momentarily rev to 1200 pm and then settles to a steady idle. MINE DOES NOT.

The car will start at 500rpm and rise to 750 rpm and hole. SOMETIMES it does do the 1200rpm and drop, but only, say 1 out of 50 starts.

So far i have done the following:

-New plugs, All good.

-Checked compression, still all 155psi even.

-Checked for vacuum leaks, but vacuum appears to be as per before, still to do more searching. Found a hose loose on the intake side fixed that no difference. Still to follow up on full vacuum tests on the hosing and intercooler.

-AAC valve cleaned, and rechecked, and appears to work correctly. Tested with consults, appears to open and closes when tested through consults.

-Redline fuel injector cleaner, special stuff. New fuel filter, new fuel lines.

ALSO did the following test. I put a fuel pressure gauge in and tested the fuel leakage and so forth. Basically if left alone the fuel pressure eventually bleeds off to 14.5 psi, over the night, which is to spec, I need to find the correct page again to give details. So then I pressurized the system and blocked off supply and return. The reading was 40psi, after and hour still 40 psi, after 2 hours 39 psi, but this was at night 11:30pm to be exact. Then over night the pressure dropped of to 20psi or so. However I was told that the pressure loss is worked out over 30 minutes, so if there is no substantial pressure loss the system is ok. THIS IS TAKEN FORM A MECHANIC THAT WORKS ON FUEL DELIVERY SYSTEMS. CAN SOMONE CONFIRM. Also pressurised each the fuel rail with air and pulsed injectors to remove ANY FUEL form injectors. NO GOOD.

-Checked for blown head gasket by getting a snifter test, came back negative. I have no water in the oil, or oil in the water. I did have some frof in the water, but I traced that down to the fact that I had some washing detergent left over in the bucket used to refill the water, and this coursed the water to froff a little. All fine now, no more frof. Another thing I did, was to put some pressure into the radiator, not sure how much, but with a hand pump, so very little. I took the plugs of this morning, turned the fuel pump off, and run the engine with paper towels in the holes, no water visible from the strokes of the engine. I let the engine crank over for a while like that to ensure that there was noting in the cylinders, fuel or water. Put the plugs in, and the car still started like crap. So I don’t think a leaking injector or water in the block is the cause. No visible smoke in tail pipe, no overheating, no sweet smell from the exhaust.

-Put a new ECU temp sensor in, no good

-rechecked timing, and still as per before.

-cleaned air filter, no good, new air filter no good.

-Fuel pressure and flow correct

-Spark plugs all look even and nicely colored.

- Put in some temporary earths and nothing.

-Cleaned all the electronic connectors, put on contact cleaner, and some sand paper, ECU and engine side, still nothing.

-checked cold start, but not sure. Put some air through it, appeared to work ok???? Is there a better test for this other then disassembly?

-Reset the computer, drained all the fuel out of injectors, opened all the air bleed vents, and then restarted it the next morning, and it still did it.

-New CAS. No good.

I am beginning to think it's the ACC valve in some way, but no idea how.

PLEASE ANY ADVICE.

2) This issue is linked to the above.

When car comes onto boost at low rpm, say bellow 3500 @ 12 or above psi, the car stumbles, and farts around like it was hitting R&R witch the ecu does not have and was never a problem before the above occurred.

The car feels like something is holding it back, it literary feels like it stops momentarily, and then bang off it goes into wheel spin. This only happens under high boost and high TP%.

I did a consult run, no issues there, all sensors are ok. HOWEVER i noticed that when this anomaly happens, the cars O2 sensor drops out to zero, and then back again, then to zero and so forth. VERY WEIRD.

So i tried to add more fuel in with the SAFC II and nothing, no matter how much fuel i add or remove, it still does it. I have tried a new AFM and a CAS and no good.

The car still makes great power up top no issues but bogs down at low rpm. It is using about a 53 per 350 kms in town. I have no idea what it may be.

Could a cracked valve or something cause any of the above?

What about the PCV in the rocker cover?

Could a faulty AAC valve cause issues like this?

I need some help as all the mechanics down here in tas have basically no idea.

Can someone, anyone, give me some advice. I have searched 4 different forums for answers to no avail.

THANKS.

PLEASE HELP ME.

[govich]

Put it on a dyno. If that fuel usage is out of the ordinary for you, it might be oxygen sensor related, and yours is playing up, so check out what's happening. If the ECU is playing with mixtures to account for a 0 oxygen sensor reading, it won't really matter what you do on the SAFC..

Failing that, trial fitting another ECU might be a good idea.

Edited May 27, 2007 by govich

[WogsRus]

Oh i forgot to say, the Ox sensor is 1 year old, and if i unplug it it still does exactly the same. I have the old one i will try, but i think it's something else.

my ECU has been tested onother cars and found to be A OK.

[Strik3r]

a faulty AAC valve could be causing your idling problem. even if you've tested it, might be worth borrowing a working one to see if it causes problem. i'd also be trying yet another AFM and tripple check that is not the issue... i have a similar issue at the moment. car was not idling properly and is running lean through the power range. AFM appeared fine on CONSULT. we replaced the AAC as it was found to be sticking/jamming and that part fixed the cold start problem, but car was still a bit off. Swapped AFM out with a known working one and it started working properly. I'm buying a 2nd hand one tonight, and retune tomorrow morning. ill let you know if its all fixed up after that.

[WogsRus]

thanks mate.

The AFM i borrowed was of a good ruuning car.

[govich]

IMO you should try other ECUs in your car instead of your ECU in other cars so you can really eliminate them as the problem.

[BHDave]

for issue 2; Have you looked at the coils yet? Either the bodgy tape solution or clean the contacts? Or even trialing someone elses coils?

[WogsRus]

I got new spitfires in, and have tried my old ones, exactly the same, plus i would have figured coils come into play more at high rpm.

Yeah going to get another ecu to try soon.

ALSO.

Got a new working ACC valve, no go. New Tp sensor, no go. Have a set of 6 new injectors to try, but need more time. Also getting a 3rd AFM to try and some knock sensors.

[paulr33]

get a real ecu, all your problems go in the bin when you do

[WogsRus]

It's not ECU related, i have tried a PFC, had same issue, it's something either electronic in the car, or mechanical in teh engine. BUT what i don't know.

Putting a PFC made NOOOOO differance at all.