Fuel Cut

[66yostagea]

I am still no closer to curing the intermittent engine semi failure and sometimes failure. It just dies after having a good hiccup. Being an auto it is a real sod in traffic. No steering and less brakes. If it was manual at least the momentum would keep it going till the problem rectifies itself.

99.999% of the time it is perfect and the problem seems to occur during gentle driving and trying to slowly accelerate. Boost gauge goes up to about 3 psi the drops to zero and the motor coughs and splutters and sometimes dies.

At the moment I am running the simple manual boost controller set for about 5/6 psi. Have checked all the boost/vacuum lines and IC lines. Am running the Greddy copy FF plenum and this problem only started after fitting the plenum.

The reason I ask about fuel cut is that can it be disengaged and if that hiccup I have is fuel cut will it cause any damage not to have it. I guess the ecu knows what it is doing.

The problem does not occur when the car is driven really hard.

Am waiting for a spare ecu and bov to get here from SA. So that is another area I will be looking at.

Has anyone got any ideas for me, please.

[M I K E]

my guess would be an air leak, whether that be boost or vac i'm not sure.

have you tried resetting the ecu? the old disconnect battery, pump brake pedal a few times and let sit for half an hour?

i'd also be looking at the mating surfaces of the plenum. i know that it's on the car now, but you can get a sheet of glass and sit the mounting surface on it to see if it is sealing everywhere.

still on the air leak side of things, grab a short length of hose and hold one end to your ear. move the other end around the engine bay and it will amplify any leaks you may not have noticed

[mattye]

The fuel cut is there for a reason dude. Should only be activated if something is not right.

Have a look at your old plenum and mainifold. Make sure there arn't any lines that may have been left off or you've missed.

Could be as simple as a vac leak.

Also maybe try adjusting your throtle body close point. make it stay farther open with no accelerator input. If its only happening at low speed it could be that the new throttle body is just not lewtting in enough air at idle.

[QWK32]

when you say fuel cut do you mean air flow cut? it wont be air flow cut, that only happens during higher loads under boost by maxing out the ecu's load limit. the only other fuel cut i know of is when you back off the ecu cuts fuel for a couple seconds to prevent over fueling on run down. both of which you cant alter or do anything about without aftermarket tune-ability like nistune or a chipped ecu.

does it boost fine and hold pressure? when it coughs and sputters is it when the auto changes gears?

Edited November 18, 2010 by QWK32

[rd-runr]

Sounds similar to the problem I have with S1 RS4.

Have you tried switching the mode button on to power? Does this solve the problem?

[Zorro]

fuel/boost cut can be solved with an intercept unit like the HKS FCD, but it doesnt sound like that is your problem! Did you move the TPS when mounting the throttle body on the new plenum? also air leaks could explain it.....

[mattye]

when you say fuel cut do you mean air flow cut? it wont be air flow cut, that only happens during higher loads under boost by maxing out the ecu's load limit. the only other fuel cut i know of is when you back off the ecu cuts fuel for a couple seconds to prevent over fueling on run down. both of which you cant alter or do anything about without aftermarket tune-ability like nistune or a chipped ecu.

Fuel cut on a RB works as a overboost defence. If the computer senses higher than standard boost pressure it retards the fuel flow. But this will obviously only happen when you have your foot down. A fuel cut defender alows you to raise or eliminate that limit.

Theres various on the market. EG. http://www.turbosmartonline.com/index.php?...l-cut-defenders

EDIT: Dude why don't you see if you can throw a Youtube Vid up. Might make it easier to troubleshoot.

Edited November 18, 2010 by mattye

[Tangles]

have you retuned the engine since fitting the plenumn?

my guess is the stock ecu maps arnt happy when slowing down off the gas - similar to blocking off the BOV on an auto, stalls.

[QWK32]

Fuel cut on a RB works as a overboost defence. If the computer senses higher than standard boost pressure it retards the fuel flow. But this will obviously only happen when you have your foot down. A fuel cut defender alows you to raise or eliminate that limit.

Theres various on the market. EG. http://www.turbosmartonline.com/index.php?...l-cut-defenders

EDIT: Dude why don't you see if you can throw a Youtube Vid up. Might make it easier to troubleshoot.

there is no way for a series 1 rb25 to detect boost pressure therefore no boost cut, the ecu only knows how much air is coming through the airflow meter, if a set amount of load is exceeded for the current rpm, the ecu cuts the engine. series 2 neo's have a map sensor that triggers at a set pressure (about 1 bar) when that is hit it is an engine cut the same as the airflow cut.

it would be very risky running one of those "fuel cut defenders" as once you clamp the afm output the current injector pulsewidth will not change even if the airflow does. anyway that is definitely not the problem hugh has.

hugh, how did you plumb you BOV return back in? is the return pipe aimed back at the turbo compressor? if its not it could be upsetting the afm when the auto shifts at lower rpm, you'll notice the BOV release a small amount on gear changes. could be enough to stall the air flow meter.

[mattye]

there is no way for a series 1 rb25 to detect boost pressure therefore no boost cut

Didn't know S1's didn't have it. But yes as I said deffs not the prob.

+1 for checking the bov plumb back too

[dirtyRS4]

Hugh pictures would help alot. Checking for a leak is too obvious, but sometimes well worth it. A twice over the vacuum hoses would be advisable. I would check the AFM. IIRC, didnt you have to relocate the battery and plumb back the factory bov in another area for installation of the FFP? Check that. Unlikely factory ecu IMO.

Duncan's car was a bit different because he ran a manual. Not much chance of eratic idle, hunting or stalling -but autos always. Have you done the constant voltage mod. Do you run a SAFC or SITC with the manual boost controller? Dunno about getn into fuel cut as a scenario atm. TPS, standard rail, old fuel pump and dirty fuel filter, cleaned AAC valve lately -the list goes on mate? Is it running rich, might be dumping fuel. Just want to get down to the simple things.

Is this your sons 25G? Pity if it is. This is why im going manual to avoid a few S1 auto issues. Time for a GTST box in the RWD G??

Edited November 19, 2010 by dirtyRS4

[66yostagea]

An interim THANK YOU to all. I will endeavour to get on top of this over the weekend. Must get it fixed asap.

[Duncan]

funnily enough my car also has an intermittent dying problem at the moment - definately electrical though, whole heap of melted plugs after that bloody voltage spike. unlikely to be any help to you though.

[dirtyRS4]

funnily enough my car also has an intermittent dying problem at the moment - definately electrical though, whole heap of melted plugs after that bloody voltage spike. unlikely to be any help to you though.

Voltage spike Duncan? Hugh i would only look into this if you had pulled something electrical apart. If so, serves you right old man for tinkering. lol

Edited November 20, 2010 by dirtyRS4

[66yostagea]

OK. Seeing as Mike replied first I took his first suggestion.

There is/was a definite air leak around where all the hoses are and possibly at the AAC/Cold start valve. Tightened the bolts,can only get to two of them, and tightened the hose clamps a bit more.

It seems to start a bit easier and maybe run better but will have to give it a week to see if that is the problem, because it only does it when it feels like it.

If it is fixed, firstly I will forgive Mike his past sins, and then take the plenum off and fix some bits I am not happy with.

You are never too old to tinkerLOL.