Confused GM High Pressure Fuel
This car had confused us all, it had an extended crank, rough idle and fuel rail pressure doesn't go over 100 psi unless u hold rpm at 3000 then it goes to about 300 psi until you let off then back below 100 psi. When you turn car off pressure slowly rises to 1000 psi on rail, and then car starts right up. We changed pressure sensor on rail with no luck, tried a used high pressure pump no luck. The low side pressure is between 55-70 psi.
Although low side pressure has very large swings in the if you slightly vary rpm just right pressure swings very fast and its hard to read gauge from 40 - 80 psi and high pressure pump makes strange noise.
It seems the high side pressure is the same as low side pressure if allowed to idle byself. In the SI I read if the high pressure fuel pump isn't being controlled (unplugged) then it should produce max pressure. Is this correct because I disconnected the high pressure pump regulator and pressure still stayed about 100 psi.
I'm so confused. Now I didn't see the car fixed the the other tech who was actually working on the car as I was just trying to help, said he put a throttle body on it and that fixed problem. I don't understand how the throttle body could cause this can anyone explain what happened to this car? Wish I could have gotten some more data but like I said this wasn't my car so I'm just an observer trying to understand
- why the tech even tried throttle body,
- how the throttle body caused this,
- will this car be back?
Ask the tech who fixed it for more details, ask him the questions you listed here, ask him what all he did,
It seems as though he is messing with you. Is the atmosphere so bad there that you cannot have a productive discussion about it? If so, and you cannot effect great improvement, move on. Collaboration is a very important tool.
here is my reply it was a dumb ass question, any tech that would ask this is incompetent, as for your comment marlin, FO, I believe the tech that fixed it did not tell him all the details, , ur a fkn priock
He doesn't speak English very well so little hard to have technica discussio and I didn't get to see car before left.
Hmm, that is a problem. If he is inclined to interact, it seems that you should be able to have some useful discussion. He writes his testing and results, doesn't he?
His testing is used parts from junk yard. When that dont work he ask me to take look.
Ugh. Seems like a place where I wouldn't work. I don't know what to tell you, but I still don't think that your story is accurate. I respect you for trying, though.
Would never think a TBI will fix this problem… I've had stuck/leaking injectors cause this.
Ask the tech why he thinks the throttle body was the cause of the issue and why it fixed it. True repairs needs to be diagnosed, repaired and rechecked, otherwise it's a costly guessing game. I'd be looking at the fuel pump cam or HP fuel pump itself. You need to have good service information to repair modern automobiles.
I suspected this also, and have seen quite few injectors amd pumps leaking, but there was no fuel in gas, and all the waveforms for power and control side looked good.
1,000 psi not sure if that's a BCM priming or a regulator closed key off or how exactly it primes on that one .. Sounds unrelated to those regulator codes ,P0089 is one of them Chevy wire chafe codes .100psi no where near normal surprised it runs, should be up around 300-2100 psi running with PCM 12v PWM the High pump control valve ,not sure about the used pump story . Yes the high psi pump is…
Yeah thats what I read so when I unplugged the pump it should have maxed out but didn't so how could it be anything but pump, sensor, or restriction.
Pretty sure you will have a comeback unless the Tech lied to you. Fuel Pressure codes are not related to TB operation. Take Care
Your high pressure should not rise when KOEO, it's mechanical. Low pressure will rise with key cycle. Electrical issue? Sensors switch? How is throttle body related to circuits?
High pressure does rise during koeo if engine is warmed up- Charles law or Boyle's, can't remember the exact differences except one pressure/temp and the other has to do with fixed volume whereas pressure rises as temperature rises.
Sweet, would love to see a study on that. I have dealt with temp versus psi in my job for years, but would love to see 100psi at idle go up to 1000 psi at KOEO. I may have a new fuel pump design in mind.
Try it. It just takes a scan tool, a vehicle, and some time.
Remember though, that is fixed volume. Your getting into laws of thermodynamics, you can't get something for nothing or even break even. Look up gas law theory for detailed explanation.
I was thinking this same thing, temperature and pressure directly proportional, but all the way to 1000 psi i found hard to believe
I bet he forgot to install the cam follower for the pump. And then quickly installed it and said the TB fixed. Just my opinion.
No I checked that, it was in there looked good and came out easy, that was one my first guesses too
What did it look like any signs the 3 cam lobes were wiped
Well, I only looked at the one the fuel pump rides on, and I couldn't see any wear on it, although I was using mirror and flashlight, I told him to take valve cover off so we could have better look but I dont think he ever did that. Maybe I dont understand this cam, why do you say 3 lobes?
Now I'm confused The 3 lobes on the camshaft that drive the GDI pump .
I think most people here agree the throttle body didn't fix this car and he will shortly see a come back, if I do see it come back I will update, thanks to all the people that helped keep sanity on this one, cuz there's no way I was thinking throttle body.