Has anyone had any experience with a turbo that runs great, but doesn’t start well? There is an interlink between oil pressure and the fuel pump. It takes 30 seconds of cranking to develop enough oil pressure to activate the fuel pump. After starting its fine. Any suggestions? Thanks…
Providing info about the year, type of Pontiac, and mileage could help.
Most oil senders only require a few PSI of pressure to activate and I would be very surprised if oil pressure is the problem. If that were the case the oil light should be coming on at idle, the engine knocking, etc.
My guess is that you have a failing fuel pump with a problem in the check-valve that maintains residual fuel pressure when the engine is off. The extended cranking could be caused by the pump displacing air that is in the lines.
It’s possible that the oil sender itself could be faulty and to rule this out it should be a simple matter to jump across the sender terminals and bypass any potential “low oil pressure” problem. For test purposes only of course.
1985 Sunbird Turbo 1.8 engine - new fuel pump was added - no affect. Oil pressure gage indicates high pressure when running and car runs as fast as a scared rabbit after its started (no knocking or engine noise). Car did sit garaged for 10 years.
Boat anchor syndrome here. You might want to abandon ship soon. I think that there is a nice car just waiting to be bought. Glad to notice just now that it sat for ten years and it may be worthwhile to use thicker oil and make sure you are using the recommended stuff.
is the fuel pump regulated by the rise in oil pressure? i thought when you turned the key on, with the engine off, that the fuel pump automatically comes on in modern cars??? NO?
Haha… I guess I’m just trying to relive the 80’s? I’m guessing that seals and perhaps oil pump may be faulty - which would appear logical, purpose of the question was to see if there were any inherent issues with this motor.
Plus - this was Grandma’s car, you’ve got to keep your grandma’s turbo charged Pontiac!!?
Apparently the fuel pump cue’s off the oil pressure and doesn’t come on until the motor has achieved a certain amount of oil pressure (during cranking).
Usually when the oil pressure switch is used to shut the fuel pump off when the engine stops, there is a secondary circuit that passes battery voltage to the fuel pump on cranking. The problem you have experienced shows up when that circuit is faulty. Hope you have that system.
I shouldn’t speculate, but I’m pretty sure that when the key is in the crank position, the fuel pump is commanded on, regardless of the oil pressure.
I think you should beg/steal/borrow a fuel pressure gauge and see what your cranking fuel pressure is.
You have a defective fuel pump relay circuit.
When you turn the key on the pump is supposed to run for about 3-5 seconds to pressurize the system. The pump turns off and when the engine starts the oil pressure switch closes and powers the fuel pump. The problem could be a open wire in that circuit, a defective relay or even the PCM.
I have the wiring diagrams and the diagnostic flow charts to check out the circuit.
According to my mechanic, he says that the for 1985, because the engine oil also runs the turbo (same oil passes through both) that this is a safety - that unless there is sufficient oil pressure during cranking, the safety won’t allow the fuel pump to activate. He says the cure is a new oil pump and seals.
I bought an official 1985 Sunbird Service Manual. Is that flow chart in that manual? If not I’d really appreciate the diagrams and diagnostic flow chart. Thanks.
It should be. Look under powertrain management. The charts are “engine cranks but will not run”, CHARTS A-3,A-4,A-5,A-6. These charts have wiring diagrams with them. This is what it should look like.