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Question for the crossfire crowd…. IMO this car takes too long to start on a cold start, probably spins for 10-15 seconds before it fires over. Thinking it might be fuel pressure related I made up a fuel line with a schrader valve to run between the throttle bodies to verify fuel pressure. With engine running at all rpm’s I get a steady 13 PSI on the gauge and the car runs fine with no driveability issues. However, when I turn the key on (no start) for the 2 second fuel pump prime I get 13 PSI but it immediately bleeds off to Zero PSI. The FSM is somewhat vague in description of fuel pressure after the key-on only process. I’ve read conflicting threads here where some state there is a check valve in the tank that prevents bleed off. I see where that is the case for TPI engines but not crossfire. For those of you with 84 experience checking fuel pressure is this bleed off normal?
One of the images in the FSM shows a constant bleed port in the rear throttle body which in my opinion would always allow fuel to drain back to the tank unimpeded. Appreciate any and all comments suggestions.
The pressure bleeds down, it's a safety feature to prevent your engine from fill up with gas. The fuel pump check valve is there to keep a volume of fuel in the line.
That makes sense! Appreciate the reply.
On further inspection it seems as if the fuel pump check valve should hold pressure for at least a minute. See “Cold Start” troubleshooting in the FSM.
Step 4. Connect a radiator test pump to the line and ap- ply 103 kPa (15 psi) pressure. If the pressure will hold for 60 seconds, the check valve is ok. This tells me the pump needs to hold pressure to assist in starting. On the 85 and above there is a troubleshooting matrix that specifies checks for this so I’m pretty sure the CFI needs the pressurized line as well. Would be nice to hear from someone who has actually performed this test and their results.
Tom
Well, a little bit of a follow up should anyone else stumble across this question. I pulled the rubber feed line off of the pump at the tank. Hooked up a fuel pressure Guage and turned the ignition switch to run. I instantly got 15 PSI and it held that pressure for a good 15 minutes before I released the pressure from the Guage. So clearly there is a check valve in the pump assembly that prevents drain back to the tank. The pressure loss at the throttle bodies is a function of the bleed port in the front TB. I also timed my start with a stopwatch and it took about 5 seconds of cranking to start. I’m guessing that’s about the best your gonna get out of this system.
comments welcome …
Tom
No, it just cleared out on its own. I did a 500 hundred mile trip and the issue went way on its own. Not sure why but I’m happy it’s running smoothly now.
Well, a little bit of a follow up should anyone else stumble across this question. I pulled the rubber feed line off of the pump at the tank. Hooked up a fuel pressure Guage and turned the ignition switch to run. I instantly got 15 PSI and it held that pressure for a good 15 minutes before I released the pressure from the Guage. So clearly there is a check valve in the pump assembly that prevents drain back to the tank. The pressure loss at the throttle bodies is a function of the bleed port in the front TB. I also timed my start with a stopwatch and it took about 5 seconds of cranking to start. I’m guessing that’s about the best your gonna get out of this system.
comments welcome …
Tom
Hey Tom, wanted to ask a question about this. So... it IS normal then that fuel pressure between the throttle bodies (I have a gauge) should drop off within seconds? When the car is shut off, the fuel pressure immediately drops... like, within 3 seconds. Is this what you're seeing too?
84 Fuel Pressure Bleed Off
