305 TBI Camaro won't start unless primed

[kutison]

My "new" 89 Camaro won't start....sigh....


When cranking the engine while starting, the injectors won't spray.
However, if I pour a bit of gas into the throttle and crank it over, the pistons fire, and it gets the injectors spraying.

I replaced the fuel pump, (it was burnt out) and the fuel pump relay.
The fuel pump still won't work through the relay, I have it bypassed at the moment.
All of the fuses are good.

When cranking I can hear the fuel pump running, (only because it is hotwired)
but even then the fuel still isn't spraying out of the injectors. unless I put gas in the throttle to get it going...


Tell me how I can fix this and you'll get 5 cool points!

[Genopsyde]

you definitely have a unique problem here. Lets go with the basics first then go from there. In these cars, if the oil pressure sensor does not detect any oil pressure, it will shut the fuel pump down. It will prime when you turn the ignition on, but it won't run while cranking. Next, if the ecm connection to the ignition control module (base of the distributor) isn't connected the injectors will not fire. With that said, if the Oil pressure sensor is faulty it will shut your fuel pump down. I tested this by checking the wire that runs from the sensor plug to the fuel pump relay( i think it may have been gray in color) with a volt meter. as for the ecm plug, that's just a matter of making sure the plug is properly in place and not corroded.

[kutison]

ok, well I just spent about 15 minutes checking all of my wiring around my distributer and to was all secured pretty well. Except for my tachometer, which i fixed.

And am I correct in assuming that the oil sensor relays pressure information to the oil gauge?.
if that is true then the oil sensor is working, because the gauge is working.
I am getting a reading of 35-40 PSI which is a bit high right?

As a side note it is idling rough once running. It will idle between 450 and 650 RPM. according to my newly working tach.
If I jump the RPMs up to about 3500 and take my foot of the gas quickly, it will stall and die.

When the fuel pump primes it should stop making noise right? because once the car is running, i can still hear the pump

[Genopsyde]

i had an issue earlier this year where my oil pressure gauge was reading fine, but the sensor was still faulty and shutting my fuel pump down, hence me checking for voltage directly at the sensors wiring while someone else would crank it over. I'm starting to think that this isn't your problem tho. I'm gonna wait for morley or wrightz28 to see this and see what they think before I make any more suggestions.

[Morley]

Originally Posted by kutison

When the fuel pump primes it should stop making noise right? because once the car is running, i can still hear the pump

When the car is running, the pump should be running too, otherwise the engine would shut down.
The oil pressure switch is not going to prevent the pump from running. In the schematics it is wired in parallel with the relay, so either the ECM will turn the pump on via the relay OR when the oil pressure switch closes it will send voltage directly to the pump, bypassing the relay.

Remove your ignition module and take it to an auto parts store and have it tested. If it is bad replace only with an AC Delco unit.

[Genopsyde]

a faulty oil pressure switch will prevent the fuel pump from running after it primes. I have experienced this first hand. I may not be wording it perfectly on how it functions, but that's really not the point.

[wrightz28]

Originally Posted by Morley

Remove your ignition module and take it to an auto parts store and have it tested. If it is bad replace only with an AC Delco unit.

This is what I was thinking as the injector pulse referense passes through it.

[Morley]

Originally Posted by Genopsyde

a faulty oil pressure switch will prevent the fuel pump from running after it primes. I have experienced this first hand. I may not be wording it perfectly on how it functions, but that's really not the point.

Then your car is wired wrong or something else is wrong (relay not working correctly) I know my car will start & run with the oil pressure switch disconnected. The ECM actuates the relay and keeps the car running. If this method fails the oil pressure switch is a backup for it.

[Genopsyde]

well my car is still factory wired. it even shows this in the wiring diagram. maybe it's the later models that have this (89-92). it was either on this forum, or TGO that I learned of this, so i'm definitely not pulling it out of my ass.

the way I remember reading it is, that it's a failsafe thing where if you lose oil pressure the ecm will stop the fuel flow to prevent damaging the engine. in my situation this past spring, I would turn the ignition on, and I would hear the fuel pump prime, the carb bowls would fill and the car would start and run, but the fuel pressure gauge read 0 and the car would stall out after the bowls emptied. I dropped the tank and put a new fuel pump in and it still did the same thing. Then i remembered what I read about the oil pressure sensor. I looked up which wire ran from the sensor to the fuel pump/relay then tested that wire with a volt meter while someone else cranked the car over. it had no voltage. I replaced the sensor and tested the same wire again, it had voltage, I now had fuel pressure and the car runs fine now.

[kutison]

Ah man, this means im going to have to do some actual work now?.....crap....

[Morley]

Originally Posted by kutison

Ah man, this means im going to have to do some actual work now?.....crap....

If your relay won't prime when wired correctly you could have a bad ECM, which could also be why the injectors won't fire when attempting to start the car.
First thing to check are the injector fuses then check the grounds at the back of the engine.

[kutison]

Sorry about the delay guys, Ive had some other problems come up that i have to take care of first.

most notabley I had a radiator line split down the line and empty a good portion of my radiatior on my air filter and parking lot.

it will be a couple of days before I can check all of this stuff. It's friggen freezing at time with like 50 mph winds. I can only work a couple of minutes at a time.

on a positive note, my local junk yards are having a 50% off sell this weekend
so I may get a lot of various, non critical crap replaced.

[wrightz28]

Originally Posted by Morley

If your relay won't prime when wired correctly you could have a bad ECM, which could also be why the injectors won't fire when attempting to start the car.
First thing to check are the injector fuses then check the grounds at the back of the engine.

Don't forget the ECM fuse by the battery, it's a 20A inline.

[Morley]

Originally Posted by wrightz28

Don't forget the ECM fuse by the battery, it's a 20A inline.

The pump shouldn't run at all with that fuse blown, it is also the pump fuse.

[kutison]

Remember that the pump is not working, I have it wired through an accessory line

The fuses are good

I'm going to check the ICM followed by the ECM if the problem isn't fixed