i've been haveing problems with my car starting lately. it cranks for a good time before it starts. i've noticed that the oil pressure starts out at 0 when i turn the key to the on position, and while cranking, it build up slowly, and finally starts everytime it reaches 30psi. now, on my other camaro, as soon as i turn the key to the on position, the pressure goes up, if it isn't up already. my problem camaro is a 91 rs 305tbi, and my other camaro that starts good is a 89rs 2.8. is there a difference in why my 91's pressure doesn't build up right away? is this what is causeing my car to not start right? i've changed the fuel filter already, fuel pump relay, cleaned out the carb, put the better gas in with fuel injection cleaner. i don't know what else to do? like i said, everytime the oil pressure reached 30psi, it starts right up. oh, this also started about an hour after i got my oil changed last week. it seems like it has something to do with that, but i'm not sure. please, someone give me an idea. i'm trying to diagnose this the best i can, and give the right info. thank you.

 

The fuel pump is connected to an oil pressure sensor to avoid engine damage. For example, if you changed your oil and didn't put enough in.

First of all, I would check your oil level to make sure there is enough oil in there.

After that, check the sensors to make sure they are hooked up properly.

Alex

 

Sounds like a fuel pump relay...

The relay works the pump while the key is in start, and an oil pressure switch takes over when the key is in run. Your symptom would be consistent with no relay, but proper OP switch operation.

"The simplest explanation that fits all the facts is usually the right one"
—Occam, ~2500 years ago (FI was real crude back then)

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"So many Mustangs, so little time..."
ICON Motorsports

 

i've done the fuel pump relay already. i just checked my oil level tonight, and it's ok. ALEXJH, where are those sensors you're talking about? do you think the fuel pump itself could be bad? i wish i knew more about cars. this is really frustrating. thank you guys for your response. Shawn.

 

There is a splitter on the back of the motor that ties one to the gauge and one to the fuel pump cutoff. It could be bad or just clogged up in which case take some carb cleaner and spray it out.

 

The Oil Pressure switch is backup power for the Fuel Pump when the "normal" circuit fails. (don't beleive me? unplug it and start your car......) The switch will turn on the power for the FP when pressure reaches some predetermined level.

Sit in your car, with the window rolled down, and turn the key to the "on" position, the FP should run for 2 seconds. (you may also hear the relay click) If the pump runs, the indicates the FP circuit is functioning properly, if you don't hear the pump, your problem is in the FP circuit controlled by the relay. (wiring diagrams are a "must" at this point) If the pump does run, start the car and check fuel pressure, should be fun on a TBI, no real provisions to make it easy like on TPI. If fuel pressure is ok, with the engine running, (not sure what correct value is for TBI, sure someone in here knows though) Turn off the engine and watch the pressure, if it bleeds off quickly, you need to replace the pump. If it holds pressure, well, someone else will have to take it from here, I am not that familiar with TBI.

 

Ploegi is right, the car will still start if the fuel pump relay is bad or not plugged in. At least a TPI will, mine does. If you're sure the relay is good, maybe there's a problem with the wiring. Turn the key to the run position (don't crank) and see if you hear the fuel pump buzz. That should settle it as to if your relay is working.
It may be something completely different, like check compression, ignition system, vacuum leaks, and sensors, like CTS.

 

Where is the fuel pump relay on a TPI car? Thanks!

 

It might differ from year to year, but in my 89, it is on the driver side firewall along with the MAF and MAF burnoff relays.

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1989 IROC-Z 5.7L
NOS 150HP kit
ProBuilt 700R4, PI Vigilante 2800 stall lockup
Baer Brakes 12" Sport System

 

Here are the specifics on the OP switch and fuel pump relay.

The FP relay has the primary responsability for turning on the Fuel Pump. (Hence the deceptive name) However, if the FPR is dead the OP switch at ~5 PSI will open the FP circuit.

If you have to crank a lot, l would bet your FPR is dead, or you fried your ECM. Either one would work.


Clayton


BTW the OP at startup is 0 PSI, therefore it would be happy to let you crank your motor w/o oil. If it would shut it off or not afterwards, l dont know, but as far as cranking, it would let you.

 

Your 89rs 2.8 must have a bad sender/guage if it shows oil pressure with the key on and not running. Don't compare anything to that.


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82 camaro--original steering wheel, brake/gas pedals, seats--everything else modified
82camaro