Weston Posted June 18, 2011 Share Posted June 18, 2011 Okay. RB25. BONE stock, stock fuel, stock turbo, stock ecu, stock maf. STOCK! The only thing I have upgraded is a FMIC and a Walbro 255 pump. That is all. No AFPR either. Here is what is happening. I go to floor it. Try to burn tires whatever. As SOON as I get just past half throttle I hit what feels like a fuel cut problem! AFR's go from low 11's all the way to lean. Past 18's. I let out of the throttle and then its back to normal driving. The car runs absolutely perfect when driving normal. But as soon as I go past 1/2 throttle I fuel cut. Not a missfire, it completely cuts out. Just out, gone, nothing. Imagine as soon as you go past half throttle, some air gets sucked into the fuel line, the more air, the longer and harder the fuel cut is. The less, and well the less. Sometimes its so minute that I can keep it to the floor and it does fine, after the lean burp, other times its so bad I have to wait a bit for the fuel to come back.. I have tried 3 MAF's, 2 FPR's, 3 Fuel Pumps, wiring the pump straight to the battery, making sure battery terminals were tight, new plugs, no boost leaks, right about 19 vacuum at idle. The car idles flawless, drives flawless, but once I try to go full throttle, it poops out! I have no idea what to check next. Some people have said I have a dirty injector. No. If I have one bad injector i would have almost a missfire, not fuel cut. PLEASE HELP!!! Quote Link to comment Share on other sites More sharing options...
1972 240z Posted June 19, 2011 Share Posted June 19, 2011 I had the same problem, i dont have a A/R gauge so i dont know what it was doing but my problem was the coils getting weak but i think that would make it run rich not lean? It something to think about. Got new coils and it ran perfect. Quote Link to comment Share on other sites More sharing options...
rsicard Posted June 19, 2011 Share Posted June 19, 2011 Its either lack of fuel or lack of ignition. Temporarily plumb in a fuel pressure gauge into the regulated pressure portion of the EFI system. If when it cuts out there may be a small temporary rise in fuel pressure if there is a commanded cut from the ECU. If there is a significant fuel pressure drop then fix same. The most suspect sensors in the EFI system would be the TPS or MAP. MAF, CLT, O2, IAT won't cause this symptom. The only other possibility is the ignition system or wiring for it or wiring for the EFI system. Quote Link to comment Share on other sites More sharing options...
stony Posted June 19, 2011 Share Posted June 19, 2011 (edited) Or the ECU is getting a false boost signal? OR its getting an accurate boost signal? due you have a boost Gage? maybe actuator is sticking?other possibility is clogged fuel filter. I had a similar issue with mine and it turned out to be the wrong fuel filter for the system. Edited June 19, 2011 by stony Quote Link to comment Share on other sites More sharing options...
ovenfood Posted June 19, 2011 Share Posted June 19, 2011 I don't know what it could be but would your computer be receiving a signal from the knock sensor? I am unsure if this would affect it but just thought I would mention it... Quote Link to comment Share on other sites More sharing options...
jakeoster Posted June 19, 2011 Share Posted June 19, 2011 (edited) With the walbro, make sure you have an adjustable FPR on there and it's adjusted correctly. I read that you've been through two, so you must already know that. You could try getting some fuel injector cleaner and mixing it in with your fuel then driving it around. Can't hurt. Edited June 19, 2011 by jakeoster Quote Link to comment Share on other sites More sharing options...
RB26powered74zcar Posted June 19, 2011 Share Posted June 19, 2011 What is your fuel system consist of? (tank, filters, lines?) Sounds like you have trash in your tank/filter... Quote Link to comment Share on other sites More sharing options...
motoman Posted June 19, 2011 Share Posted June 19, 2011 (edited) From what i have read the stock fpr cant regulate the pressure from the walbro 255. I would try putting on a AFPR. That may be a problem later on. I think this engine is in a s13 if i remember correctly so the fuel setup shouldn't be a problem. I would agree with rs speed on the tps, that would be my first place to check. Edited June 21, 2011 by motoman Quote Link to comment Share on other sites More sharing options...
RS Speed Posted June 20, 2011 Share Posted June 20, 2011 A leak or tear in an intercooler pipe coupler wouldn't effect your idle vacuum so I would go through them and see if you have any boost leaks. I would also check TPS voltage for smooth operation from ~.45v to ~4.5v Quote Link to comment Share on other sites More sharing options...
rayaapp2 Posted June 20, 2011 Share Posted June 20, 2011 (edited) Instead of guessing I will offer diagnosis. This will require you get your hands on some real tools if you dont have them already. Connect a digital multi meter or DMM securely to your + and - posts on your Fuel pump. Your looking for voltage drop here. Secure everything and take it for a test drive while you monitor your Voltage across the pump. IF nothing suspicious posps up then its time to try the next aproach. Fuel Pressure gauge. Harbor freight sells them darn cheap, and I believe most local Autoparts stores have a rental available. GEt one. Connect it and run the gauge up to the windsheild under the wiper arm. Test drive again and watch your fuel pressure. Report back what these things are doing. Personally I have not heard good things about the Walbro 255 pumps. I chose the Bosch 044 unit. -disregaurd lack of ignition. Lack of spark results in raw fuel = rich condition at O2. -Dont worry about what the stock FPR regulator can or cannot handle at the moment. Outflowing the stock FPR cap will result in a rich condition not lean, and the early pre OBDII global systems are not fast enough to cause a lean swing that would result in the data you have presented. -Knock sensors do not CUT fuel usually. They affect Ignition Map Timing and possibly a few other minor things., but not usually Fuel Cut. -A boost leak would likely result in a rich condition as well. Metered air allowed to escape under boost = less air and same amount of fuel. "What is your fuel system consist of? (tank, filters, lines?)" Name off used parts too like if you used a 1975 fuel tank or whatever! My money is on pressure falling out, but at least you will be able to dis-include the wiring for the fuel pump for further diagnosis. Sorry computer is on dope this week, and I did not mean to come off as an ass or mis-spell everything. My computer just takes a million years to catch up with my typing. Edited June 20, 2011 by rayaapp2 Quote Link to comment Share on other sites More sharing options...
240zdan Posted June 25, 2011 Share Posted June 25, 2011 From what i have read the stock fpr cant regulate the pressure from the walbro 255. I would try putting on a AFPR. That may be a problem later on. I think this engine is in a s13 if i remember correctly so the fuel setup shouldn't be a problem. I would agree with rs speed on the tps, that would be my first place to check. i ran a stock regulator for a while with a walbro and stock ecu/turbos and had no problems. it ran a bit rich thats all. still revved out though Quote Link to comment Share on other sites More sharing options...
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