I am having fuel problems on my 90 vert. It is increasingly harder to start. I put a pressure gauge and I am not getting fuel pressure when I turn the key on. It comes up after I start turning the engine over to start it. Also, when I am looking at the gauge with the car idling the fuel pressure fluctuates rapidly between about 36-38 psi. When I rev the car the fuel pressure jumps up a couple of pounds and then goes way down to around 30psi. With the vacuum line disconnected I have around 43 psi. Is this the pump, relay or something else? I just went out and tried it and it doesn't even want to start. A week or so ago while driving it it acted like it was running out of gas and it died and wouldn't start. I came back for it a couple hours later and it started fine and drove all the way home. There are no codes.

 

Sounds like you aren't getting power to the pump thru the relay, but Are getting power back there thru the oil pressure switch (well - actually as a result of the ECM seeing oil pressure...I'm making an assumption here that the '90 is wired the same way as my '85). Either that or the relay is "intermittent", or the pump itself is flakey (or the wiring). Try unplugging the relay (on the firewall near the brake booster) and using a jumper wire across the terminals in the connector - hot to pump feed. Or direct from the Battery to pump feed. That should make the pump run, regardless. If not - pump or wiring (or fuse - it's in the circuit) is the trouble. If it Does run - replace the relay.

BTW - the relay is energized for a couple of seconds when the key is turned from Off to Run (not crank). Only for a couple of sconds. That "couple of seconds" timer will reset if you bump it to crank, or when you shut the key back off and wait 5-10 seconds. If it's quiet you can hear the timer "click" behind the passenger side of the dash when it resets...

If the vacuum line is off the fuel pressure regulator, the pressure Should be steady. Any fluctuation is the pump or the filter or a problem with the pressure regulator itself. With the vacuum line Connected, engine running, a drop in vacuum should cause an Increase in pressure. If it isn't doing that, the regulator is bad. I've seen regulators get crudded up and not seal well - do all sorts of crazy things with the pressures...

 

 

I've looked on the firewall for my fuel pump relay and I don't see it there. I looked in the same place that it is located on my 85 and there is no relay there? Anyone know where it is located on a 90 vert?

 

You were right the first time. The power to the fuel pump, from the oil pressure switch is fed directly from the switch. In order for the ECM to run the pump, it has to activate the relay, which is already in question.


The "pump or wiring (or fuse - it's in the circuit)" isn't the trouble. Once it is running, there is plenty of pressure and there are no complaints of drivability.


Correct. If the pressure is bleeding off because of the regulator, the check valve, or leaky injectors, the 2 second priming period may not be enough to bring the system up to pressure.

RACE ON!!!

 

 

 

Where is the relay located?

What would cause my fuel pressure to bounce between 38-40 psi? I can actually feel a thumping when I hold the pressure gauge in my hand.

Now the car doesn't even run so now that I have a hard failure it should be easier to find the culprit.

 

On the earlier models, it is on the firewall near the windshield wiper motor. You can check your FSM if the 1990 is different.


That is a very narrow range, but my first guess would be an engine miss that causes rapid fluctuations in the vacuum, causing the regulator to change the pressure.


Possibly. During an extended period of cranking, does the fuel pressure come up?

RACE ON!!!

 

No.


Another problem is at WOT the fuel pressure jumps to about 44psi and immediately drops to about 30 psi and stays there until I let the throttle go back down.

 

Quote:
Originally Posted by CFI-EFI


Possibly. During an extended period of cranking, does the fuel pressure come up?

RACE ON!!!


If the fuel pressure never comes up, how does the engine start, so you can observe the fuel pressure (which never came up) at WOT?

The purpose of the vacuum line to the regulator is to boost the fuel pressure when the engine is under heavier loads. The fuel pressure is generally about 10 psi greater at high manifold pressure that at idle. It may pay to spend a few hours studying the fuel system section of your FSM.

RACE ON!!!

 

When the thread was started the car ran but was experiencing problems. Now it does not start/run at all. What I was telling you was what I was able to determine BEFORE the car went into a no-start condition.