1988 RX7 that sat a few weeks as we were getting the trans out due to an issue with the car being stuck in one gear and found the pilot bearing came apart. That replaced and the trans about to go back in, we thought it a great time to replace the fuel filter as she sits right next to the bellhousing on the drivers side. One she was buttoned up and everything put back together. My nephew then went to start her a day later and she'll fire up but then die, even though he knows well the starting procedure. No bleeder on the fuel rail, so he tested the fuel pressure right after the filter and got 35-40 psi, but after the initial start, it drops to 5 psi. I'm thinking air in the line, and we tried to bleed it best we can as this design is what it is.

Any ideas?

 

Should check if the pump is working when cranking the car.

 

Yeah, that's a grand idea and we tried that. Initially, and when the car is cranking, the pressure is at 35-40 psi, but soon drops to 5 psi after the engine starts. That tell you anything?

 

Dealing with fueling issues on my BMW and there was a problem where the DME would send the fuel signal to the fuel pump during cranking, but then wouldnt tell the pump that the car was actually RUNNING, and as soon as it lit the fuel pump would shut off. Not sure if theres any similarity. May be worth seeing if you lose power to the fuel pump once the car lights and you stop cranking.

 

welcome to the board.

do you have a copy of your FSM? if not, you can get one here: Foxed.ca

you can use it to try troubleshooting the fuel pump circuit while you wait for answers from other members.

my first guess would be take a look at the relay.

 

Thanks for the link, we're checking it out now. I think that's very sound advice; thanks!

 

Thanks for the idea, it is fuel related to be sure. Interesting if it's coincidence, but I'm thinking it was due to the battery being disconnected for a few weeks rather than the replacement of the filter right now as I recall those late 80's cars were just getting computer controlled and they seemed to be fussy post battery disconnect, especially in regards to the fuel air info.
We'll see.
At this point, all troubleshooting ideas are good ideas.
Thanks!

 

Is the air flow meter plugged in? There's a switch inside it that tells the circuit-opening relay under the dash that the engine is running and powers the fuel pump. This relay has a second input (from the ignition switch) so it runs the pump while cranking as well.

If the air flow meter is unplugged (or faulty (unlikely)) it will cause what you're describing. The ignition switch will still power the relay while cranking, but once you release it to the on position the relay loses power.

The other option I can think of is that the fuel pump is going bad and can't sustain pressure. Maybe it's fine when cranking since the engine uses very little fuel at <250 rpm, but once the car starts up it drains the rail faster than the pump can maintain pressure. That one's hard to diagnose other than just swapping out the pump

 

Thanks for your thoughts, they made me ponder... especially the one above, that one is very much worth checking out asap.

 

Just to add a little more detail. The 'switch' signal is AFM flapper door opening due to airflow. A vacuum leak upstream can cause the door to stay closed and cause the same symptom.
​With the key on, you can push the flapper door open and listen for the fuel pump turning on.
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