Let me start with a little background of the car. Got the car with a bad cat car would start would not go over 2 Grand RPM. Remove the cat ran straight manifold and drove 15 minutes logging HP tuners. Park the car for a couple minutes and car would not start again. Changed injectors with known good injectors from another SS. They were the factory injectors that I took out for the 60 pounds I put in for my zzp stage 3. Change the fuel filter because the car sat for 6 months. There was low fuel pressure. Relay will Prime with absolutely no pressure in fuel rail. If I wait till the pressure dies down it will Prime again. I check the voltage to the pump it's good. Check the pump it's good. Have not connected a fuel pump pressure gauge as I can visibly see from my other SS that works perfectly fine it is less pressure. Swap the ECM with two others one of which is out of my perfectly running SS. The fuel pump still does not want to Prime the way it should. Check continuity to all the wires everything checks out. Fuse is in the right place and good the relay is in the right place and good. I can jump the fuel pump and still only have about half fuel pressure. If I spray the car with ether it will fire up and idle perfectly fine. I can drive it perfectly fine until I get in the Boost where the low fuel pressure force it into limp mode after a few times. If I stay out of boost the car runs perfectly fine. Any suggestions? I've searched and searched Google the forums every form that's out there and come up with nothing.

 

the fuel pump is dead. when my pump was on its way out it had roughly 30-35psi, the car would idle ok, but get into the throttle and it would stumble. if i kept driving it the thing the pressure would end up lower and lower till it wouldnt run at all.

 

changed pump to a known good pump and same issue. And it would explain the low fuel pressure but can't see how it would make the relay not prime. And it don't stumble. After I get into boost a few times it goes to limp mode. Before that it drive like it's brand new.

 

Based on your first post I was wondering what injectors you are running now? You said you swapped in stock injectors in the place of your 60lb injectors. Are you still running the stock injectors and if you are did you change your ECM tune accordingly?

 

the car in question is stock. The injectors are out of the s3 ss. Factory ecm factory injectors.

 

Factory injectors or 60lb (stage 3 as you say) injectors?

 

factory. 33lb injectors. The car is stock. They got took out of my other car that ran fine. The car that ran fine I put a s3 "kit" on. If I stuck 60s in it I would have took my hp tuners and tuned for 60s.

 

so what is the actual fuel pressure? your first post says its low, but you havent hooked a gauge to it, are you judging fuel pressure by how far it sprays fuel from the schrader valve when you push it?

what codes is the car setting when it goes into "limp mode"? does the display say "engine power reduced" ?

 

yes in judging by the spray. Basing judgment on my other ss with exact same fuel system. Codes I cant remember all of them but it was a few o2 codes as it's running mani only a lean code and once had a bypass valve code. None deal with the priming issue or low pressure which I think are the same issue.

 

well, without actual diagnostics it tough to say whats going on. when you swapped fuel pumps did you change the pump itself, or the entire basket? the fuel regulator is part of the basket, maybe its sticking open.

 

changed the whole unit. I can go spray it with ether and drive it to limp mode but the relay works while it's driving. Not sure how that helps with the priming.as far as the pressure gauge I can't see myself searching for it to rent just for it to tell me I have low fuel pressure when I can visibly see it's lower. At this point I've changed the whole fuel system except the line and evap. Evap as far as I know has no control over fuel delivery. The lines I can see a clog having low pressure but can't see it causing the priming issue. I'm open to all ideas at this point. With a good treason as to why. Pump fired a car with the rod in the pan and hole in block first try every time. So just saying a bad pump won't work for me as it's a known good pump. If there is a reasoning behind it I will listen. If there is a regulator bypass I'll try that as well.

 

Update. Changned the fuel line. That is the entire fuel system check with multimeter and then changed for good measure. What other sensors control fuel pressure or effect fuel pressure? I want to say the fuel tank pressure sensor as it does on older cars but I read on the delta's it only controls the purge valve because we are returnless.

 

I'm no expert, but if your engine is starving when attempting to go into boost after a couple of times, the. I would look at your AFR reads and record the numbers. Lack of fuel + more air = lean.

The only other thing I can think of, is how's your MPG? Has it gotten worse especially when attempting to boost? Another idea could be spark plugs or gunk in the fuel rail.

I'm grasping at straws here but I'm just tossing ideas and seeing what sticks.

 

when I got it it had a clogged cat so it wouldn't drive. Took off the car and made 1 test run. After that wouldn't start. It will run if sprayed with ether and limp mode is from the low pressure. I'm sure the low pressure issue has something to do with the priming issue as when I relieve the pressure from the rail it will prime. The entire fuel system from tank to injectors and all wiring harnesses has been changed even though they passed the checks. At this point I'm guess a sensor that controls fp is to blame but everywhere I read says there is no more. I know return style systems use a fuel tank pressure sensor to regulate the fp but I read the returnless ftps doesn't effect it only emissions. I'm at a loss as I check what I know controls fuel. Even put the ecm from a running driving car in to see if that's it and it's not.

 

When you mentioned you changed out the fuel pump and system did you change out the fuel lines as well? I would double check your connections.

 

lines harnesses checked everything more times than high heffner seen ****. I'm lost at this point.

 

there is no sensor to control fuel pressure, there is a mechanical regulator in the basket that keeps the pressure at 58psi. when you turn the key on the system should prime for 2-3 seconds, after that you have to turn the key off for 10-15 seconds before turning it back on to prime again, it doesnt prime every time you turn the key on. the ecm controls the fuel pump repay, but its a simple on/off, it doesnt regulate voltage to control the pump speed or pressure.

low fuel pressure will not cause a limp mode. there is no fuel pressure sensor, the ecm doesnt know the fuel pressure so it cant put it in limp mode because of that.

at this point, you need to put a fuel pressure gauge on it and see what the actual fuel pressure is, both when its priming and when its running (run it on ether if you have to). seeing how you have changed the entire fuel system in the car and your still having the same problem, it leads me to think its not fuel system related, and judging off a fuel squirt isnt scientific enough to diagnose the car. put a pressure gauge on it and see what the fuel pressure actually is at.

 

I do know a lean condition will cause limp mode and 12.5 psi of sc air and not enough fuel will cause limp mode.

 

the ecm wont actually go into a limp or safety mode, if the fuel pressure is low or drops under boost it will create a dead lean condition that causes the car to fall on its face. the ecm isnt commanding the throttle to close or shut off spark because it detects fuel pressure is low, and thats because there is no fuel pressure sensor, and no other way for the ecm to know what the fuel pressure is.

 

see I'm told by ase cert techs that the low pressure is causing not enough fuel to get to the cylinders and causes the limp mode. This is actually the first time I've heard anything otherwise.

 

So according to hpt my fuel tank pressure stays at 1.47v. Pump on pump off running car on car off just stays there. Not sure if it's what's causing it though because it's a evap sensor

 

your tank pressure has nothing to do with fuel system pressure. your tank pressure will generally wont vary too much, but if its not moving at all you may have another issue with the evap system, but thats not causing a your running issues.