Fuel Pressure Issue?
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If you have a data logger I bet the STFT are high negatives at cruising. I'm sure your long terms are not any better but we don't know until u data log it. A good long term should be +5 or -5 nothing higher or lower.
Last edited by 996tt550hp; Mar 6, 2016 at 09:28 PM.
I think we're onto something with the regulator but you never know. We even did a replacement throttlebody. I mean we went down the entire list. With injectors this size he'd be safe just driving in to see how the drivability is. He wouldn't hit full throttle long if at all. The kicker is that the regulator is brand-new but he could've definitely got a bum one or even mis-labeled one. Short terms are back-and-forth which is why its tricky to figure out. Trust me some tuning champions are involved. I really hope this is it.
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Hey guys. Karl, I feel so bad for everything you've gone through with this car.
Car is definitely over correcting and going crazy trying to get it right. WOT is great as is idol because the car compensates. I think changing that regulator again is a good move. Or we can recalibrate. But I think it's too much and hard on the pump in your set up. Really hope this is going to be it buddy. Otherwise still an issue with air of some sort. Here for you as usual.
Car is definitely over correcting and going crazy trying to get it right. WOT is great as is idol because the car compensates. I think changing that regulator again is a good move. Or we can recalibrate. But I think it's too much and hard on the pump in your set up. Really hope this is going to be it buddy. Otherwise still an issue with air of some sort. Here for you as usual.
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To check if it's a 5BAR is easy since he has a gauge - pull the vac hose off. This will remove the correction for vacuum and yu will see what the FPR was set for as a BASE. the fuel pressure is SUPPOSED to move as load varies. Under vac the engine is attempting to SUCK fuel from the injector, under boost it's trying to BLOW it back up the pipe. The FPR adjusts for this 1:1 so that the injector sprays the same amount of fuel per fixed opening time under vac or boost so you have one less variable to chase.
Hope that makes sense of what you are or should be seeing with the FPR. So far as I know the ECU in the 996 doesn't control the fuel pump other than on and off so the FPR is what varies.
Hope that makes sense of what you are or should be seeing with the FPR. So far as I know the ECU in the 996 doesn't control the fuel pump other than on and off so the FPR is what varies.
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[QUOTE=996tt550hp;4482627]I think sambo is right. My 5bar did the same crap and Tony at epl did a great job in adjusting it. Even Tony said he doesn't like 5bars just upgrade Injectors and I have never been happier.
But if your running a 5bar and 1000cc there's your issue.
I'm not running a 5 bar. It's a 3.8bar and I replaced it two months ago.
But if your running a 5bar and 1000cc there's your issue.
I'm not running a 5 bar. It's a 3.8bar and I replaced it two months ago.
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Not a stock ECU...Cobb tune.
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Whoa! I'd pull the vac hose to check static base pressure to verify what FPR is in there but I sure would be VERY careful driving it that way. It could go pretty lean without the FPR pushing pressure up and you might hit the limit of the ECU's ability to compensate which would be "bad"...
He says it runs fine WOT so if the fuel trims are okay there and the tune isn't weird then the fueling is correct there. Maybe the FPR is sticking somehow? It's a mechanical device with an internal diaphragm and a plunger. Actually a ruptured diaphragm is a possibility and would push fuel into the vac hose but probably run WAY worse than it does now. I dunno', the ECU ran fine in another car but not with this tune right? Tune not matching the hardware seems likely. A bum FPR could do it, sounds like everything else has been checked. The readings don't seem too bad though, checking base pressure to make sure it's accurate seems like a good first move next.
He says it runs fine WOT so if the fuel trims are okay there and the tune isn't weird then the fueling is correct there. Maybe the FPR is sticking somehow? It's a mechanical device with an internal diaphragm and a plunger. Actually a ruptured diaphragm is a possibility and would push fuel into the vac hose but probably run WAY worse than it does now. I dunno', the ECU ran fine in another car but not with this tune right? Tune not matching the hardware seems likely. A bum FPR could do it, sounds like everything else has been checked. The readings don't seem too bad though, checking base pressure to make sure it's accurate seems like a good first move next.
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Good at WOT or not? No mention of black smoke anywhere in this thread. A 5bar on big injectors is a mistake if not calibrated for that obviously. Hence the suggestion to remove the vac line which provides a compensation signal and check BASE pressure to confirm the regulator, you could even use a mityvac to check FPR response. IF this is purely a fuel system issue this will be a first step.
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Guys,
Just want to thank all of you for helping out. I really appreciate it. Hopefully I eventually find the issue(s). It's been such a headache I can actually say I've been hating this car for the past 8 months.
Just want to thank all of you for helping out. I really appreciate it. Hopefully I eventually find the issue(s). It's been such a headache I can actually say I've been hating this car for the past 8 months.
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Have you checked the fuel lines at the pump within the fuel tank? Some of them have been known to split, causing unstable fuel pressures.
Potentially your ECU is compensating by increasing fuel trims which would cause deviations and instability given the the leak. You really need to see what the ECU is doing by checking out the ST/LT fuel trims in the different load ranges.
What happens if you were to reset the ECU? Does the car behave different initially?
Potentially your ECU is compensating by increasing fuel trims which would cause deviations and instability given the the leak. You really need to see what the ECU is doing by checking out the ST/LT fuel trims in the different load ranges.
What happens if you were to reset the ECU? Does the car behave different initially?
Yeah plug the line so it's not a leak. I am really hoping the FPR you put in is wonky. Good thought on teh in-tank line. We checked that too. When those go 99% of the time she will barely idle.
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Initial cold start is very rough and rich for the first 30 seconds or so. After that she idles perfectly smooth.
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If the vac hose is pulled from the FPR it will show base pressure. It should NOT deviate or move around. It's not going to receive either vac or boost signal so at idle it will run rich and under boost it will run LEAN. I personally wouldn't intentionally drive it this way but by looking at the pressure reading you can see if your FPR is a 5BAR or not.
If it's stumbling down low and too rich but fine up top it sounds like a tune issue
If it's stumbling down low and too rich but fine up top it sounds like a tune issue
Karl, see what it reads with the vacuum line disconnected (and plugged) at idle. Then drive around normal with and log. We will compare this and then see what to do next. For now it is getting 3.8bar under vacuum and 5bar on boost. I have never watched to see how erratic a stock 3.8 is on a analog gauge when under just cracking throttle and also am pretty sure it should be at about 35-40psi unver vacuum. It's really tricky because it could be either a bad FPR, crushed new one modded to act like a 5bar which is still different, or a factory 5bar. Who knows for sure now.
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Meaning a stand alone ecu.
I have rough cold starts too in cold weather because of my injector size. Take a video of the cold start.
Last edited by 996tt550hp; Mar 8, 2016 at 08:07 AM.