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I'm having a fuel pressure issue. The fuel pump fuse is good and the relay is good. I figured the pump failed, so I installed a new Walbro 255 lph pump and a new fuel filter and still no pressure. When the car died it went out while at around 50mph. It started back up afterward but would only run for a few seconds up until the point that it wouldn't start. Any thoughts or ideas are appreciated.
First see if you have any DTC's accessing through DIC. What's the status now ??...a "cranking no start" ??...do you have spark ??...do you hear the pump prime for 2 seconds when you turn the key on ??...have you checked G401 (pump ground) which is behind left rear tire on the frame rail ??...do you have a fuel pressure gauge ??...if you spray some Brake Kleen into a vacuum line (PCV or brake booster) will the car try to start now ??...we can start here and if need be we can run through checking the fuel pump circuit which might have some electrical issues !!
No DTC's were set when the problem occurred. The fuel pump isn't priming. I can try some brake cleaner into the engine through the brake booster line tomorrow.
2020 Corvette of the Year Finalist (performance mods)
C5 of Year Winner (performance mods) 2019
try using a piece of wire and jumping the fuel pump relay, this should turn the pump on full time... if it does then either the relay is bad or the pins in the fuse box are loose... if nothing happens then you have another issue
As Nuetron had mentioned about jumping pins 87 and 30 just be SUPER careful you don’t jump 85 and 86....triple check your pin locations !!...
you can fry your PCM !!...the control side of the relay will have to be checked if jumping the load side works !!
Thanks a lot guys. The pic helps mucho too. Like I said I'll check these areas tomorrow along with the ground location on the frame rail behind the driver side rear tire. Is it on top of the frame rail? The thing I'm kind of concerned with is a few months back the fuse box under hood was dead in the center due to an ignition wire under the column. Maybe from a column lock bypass
Alright, so I found the ground wire to be loose. I cleaned and tightened it. No result. I jumped pins 87 and 30 where the fuel pump relay goes and I hear an actuator or something under the hood on the driver side, but the fuel pump isn't priming. I'll try the brake cleaner tomorrow, but I'm fairly confident the engine will start that way. Any ideas?
Ok, so G401 was loose ??...I don't know what you're hearing on the drivers side ?????...so you don't hear the pump running in the back ??...if not first see if you have 12 volts at pin 87 with key ON which is your load side feed...the power for pin 87 comes from the fuel pump fuse (fuse #13)...see if you have power at each test point on top of that fuse with a 12v test light or multi meter with black lead connected to a good ground...if GOOD now take a 12 volt test light if you have one and connect it to battery positive...now probe pin 30...if that wire is good to the fuel pump the light will light through the fuel pump windings to ground... If that is good now you will have to go down to the fuel pump and remove the connector....now take your test light if you have one and connect it to 12 volts somewhere....probe the black wire of the connector and if the ground (G401) is good the 12 volt test light will light brightly !!....not a real complicated circuit !!
I'll bring tools home tomorrow. I have a strange feeling that the problem lies elsewhere though. Missing the car like crazy, so I may just end up having it towed to the dealer.
It’s either the fuel pump or wiring...yes, it can be something else but like we say in the diagnostic field you just have to get in “the right funnel” ...not difficult to diagnose...all you need basically is a fuel pressure gauge and a 12 volt test light !!...why do you think the problem lies elsewhere ??...I would just jump 12 volts right to the pump and see if it works !!
Let me start by saying you guys are amazing! I have 12V at pin 87 and at pin 30! I put a jumper wire in at 87 and 30 and the car runs! The jumper gets hot so I pull it out fast. I feel I have a bad relay even though I replaced it with a vaucraft POS!!!!!!
If the new relay doesn’t fix it you still have to check the control side of the relay circuit...pins 85 and 86 !!..,pin 86 is powered from your fuel pump relay control... with a 12 volt test light the light will light for 2 seconds and go out..,with a multimeter you will see 12 volts there continuously !!....pin 85 is grounded through G105...G105 is on the left side of the engine block and the ground strap is under the brake booster !!..,you can swap the pump relay with the horn relay...horn relay sits caddy corner from the pump relay !!
I have 12V constantly at pin 86, I had around 9V at pin 85. I removed the ground strap under the brake booster and cleaned it then resecured it. Now I have no power at 85. If I can figure out why that could be the root cause.
It’s good you have 12 volts at 86...if you used a 12v test light it would have lit for 2 seconds and gone out when you turned the key on !!...pin 85 is GROUND...you should NOT have 9 volts there...it should have 0 if good...you cleaned the ground strap under the booster and it shows 0...you fixed the problem...see if the car runs now !!!....YOU HAD A BAD GROUND !!!....if you have a 12v test light connect it to battery POSITIVE and probe pin 85...it will light brightly if ground is good !!
No it cranks and dies shorty thereafter. It will run the jumper wire in. Do you think it could be air trapped in the system? What if I cracked the shrader valve?
How did you connect your multi meter ??...with the red lead hooked to battery positve and the black lead hooked to pin 85 you should have 12 volts on your meter...is that how you checked it ??...if that how you checked it and saw 9 volts you have high resistance on pin 85 (the ground circuit)...did you install another relay...like I had said you can swap it with the horn relay...does that new pump you installed have any special harness that needed to be installed ??
No special harness with the new pump. I tried the horn relay and it acts the same as the new relay and the original. Just checked everything again. 12V at pin 86 but only 1.5V at 85. What would cause this?
C5 Fuel pressure problem
