Incorrect fuel pressure Key on and Engine Running

[Fless]

I would think that Alldata would have that. Found this, though (#3 on diagram):

 

[Matthew Jeschke]

I'm almost CERTAIN this replacement pump is no good too *sigh*. RockAuto hasn't processed my warranty yet... but I want to find out if I can get my money back. There's a couple more tests I can do but pretty sure my line isn't blocked. If it was I'd assume it would pressurize much more inconsistently and getting even 55PSI would be tricky. I think they're not building the pumps to spec... Likely they shifted production to China, India, or some other place other than western world where we care about quality and they're lumping defects in with good pumps.

 

[Matthew Jeschke]

I would think that Alldata would have that. Found this, though (#3 on diagram):

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Thanks! I ended up testing and found out there's no electrical issues in my fuel pump circuit. I maybe dense... I cannot figure out a great way to search AllData (at least the old version). I search for connector numbers and nothing comes up. Then I went to connectors by number and it didn't list C152. Thanks for finding that!

 

[Fless]

Be careful; that diagram doesn't look right if your PCM connectors are like mine. I have two long ones, not 4 shorter ones. YMMV

 

[Matthew Jeschke]

I'm looking at the fuel pressure spec for the Flex Fuel L59 engine in my Chilton's manual. It seems I'm getting the KOEO pressure the Flex Fuel system has. My system is a gasoline system with injectors are from the flex fuel system (poor man's high flow injector upgrade). I had assumed the injectors (when closed) would have no affect on pressure. Am I wrong?

 

[strutaeng]

There is a connector, C152A (also C152? connector on wiring diagram but not listed in FSM)... I cannot locate it? Anybody know where it is?


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I believe these are inside the fuse box. Pop the the little tab and the fuse panel swings up/out.

I have a return style setup. My Key On Ignition off pressure is 48PSI. 7 below spec which is 55 to 62 PSI.

I noticed, fiddling with my Corvette that the gauge will PEAK in the 55 to 62 PSI and settle down a bit lower, possibly even touch below that range. I'd venture you're pump is in great shape if you get 54 PSI during that test. Mine falls to 40PSI when engine is rev'd.

I have a new pump from Delphi (warranty replacement). Original pump I'm quite sure was bad regardless of pressure because the line set bled off quickly after engine & pump were shut off. It'd bleed down to like 35 PSI in a matter of minutes. This new one hold pressure in the lines even as much at 15 minutes later non has bled down.

Delphi tech support has me checking circuitry. They said to do voltage drop tests. I'm going to do that now. One across the whole line for starters then break into the positive side then negative side if necessary. Current draw, patching my amp meter in in place of relay was 5AMPS. I think maybe supposed to be 6 AMPS but battery charge was low. Lots of stuff I'm checking... Will update here as I go through whole process. I should have tested the voltage drops when I had the tank dropped. Now I have to drop it again *sigh* all be it only part of the way to access top of pump.

Interesting. Yeah, definitely should not be dropping pressure that much. To determine if it's an injector or the checkball, temporarily plug the return fuel line at the rail. I did this once with a vacuum cap and hose clamp. Prime the system and the pump will deliver maximum pressure (80 psi on mine IIRC). If an injector is leaking, it will drop pressure. If pressure doesn't drop, then you know it's not injectors and most likely the pump checkball.

BTW, my engine is actually an L59 with flex fuel injectors. Although it's running on an LM7 tune.

 

[Matthew Jeschke]

Good idea

 

[strutaeng]

Good idea

Or just pop the fuel rails, prime the system and let it sit for a bit. If one is leaking down, it will be pretty obvious. Put some shop towels down in case there's fuel coming out of them.

 

[Matthew Jeschke]

My old ones leaked... Yeah leaking injectors is on my list of things to check. I figured I'd pull up the rail and put shop towel under the injectors to see if there's any drips.

I was smelling the oil to see if there was any gas smell in it from leaking injectors. I'd imagine after shutdown the gas would leak out and eventually down into the crank case. I don't smell anything but maybe it's not enough gas.

I wish I'd built a fuel injector test setup out of an old rail but didn't think about it till after my project was done. I should probably still do that.

 

[Matthew Jeschke]

Or just pop the fuel rails, prime the system and let it sit for a bit. If one is leaking down, it will be pretty obvious. Put some shop towels down in case there's fuel coming out of them.

So I did what you said. I found a way to disconnect and cap the return line. I put on a test gauge.

It got up to 80psi priming the pump w/ return blocked off.
The Pressure bled down quickly but I couldn't see any leaks in the line set.

I then put the return back on, and took off the rail (raised it above the intake). I put paper towels under each injector.

Not a single drip of fuel under any of the injectors.
Now pump only primes to KOEO around 45PSI.

I'm studying this...

It seems the drop in pressure from 85 would be correct. It should have a backup relief valve in the pump itself.