Praise the saints!
crapatalk it sucks for free
crapatalk it sucks for free
Fuel pressure drops then stalls
- Thread starter Tommy
- Start date
well that's just asking for a yeast infection.
Shayp29
Greenie N00B Member
My car exhibited the exact symptoms of your car (warms up to about 145 then the fuel pressure drops low and car dies). Trying to troubleshoot this down, I was unable to get the pump going by jumpering the “circuit” relay per the book. However, if I jumper the “f/pump 2” relay, the car runs absolutely perfect. Does anyone have any insight to what could be the problem? I’ve swapped relays with no joy. The wires ring out all good from the pump harness to fuse box. Thanks for your help!
You try bypassing and jumping the fuel pump resistor thats on the driver frame rail below the intake? It looks like an HID ballast. That being bad will exhibit the same symptoms
Shayp29
Greenie N00B Member
Thank you for the recommendation. I will give that a try! I did remove the fuel pump resistor earlier today to measure the resistance, and it is within spec.
the other weirdness, for the “f/pump 2” relay control pins, I measure 12v across with KOEO, which should fire the relay. However, when I insert the relay, it doesn’t fire, and there isn’t a voltage drop across the control pins. With the relay removed, it fires perfectly when I hook it to a 12v source and measures around 75.8 ohms, with good continuity on the “load” side. I’ve also checked good continuity from the “negative” side of the relay through the ECM harness.
Last edited:
cobra20sc
Greenie N00B Member
Thought I would share my experience with this issue on my 08 MS3 that I just fixed. With the help of this post and the MS3 factory manual I was able to quickly pinpoint the issue to a broken wire. Admittedly I had lots of doubts that this could be the issue since I've never had a problem like this even living here with the salty northeast winters.
Symptom as described in this thread, car starts up fine, idles well, and when warmed up, fuel pressure drops from ~500psi to 0 and car stalls and won't immediately restart. After letting it cooled down, it will start again but will repeat the issue after warming up.
Troubleshooting:
Measured resistance of FP resistor, it was 0.6 ohms out of spec. Jumpered FP resistor out to see what happens. No change.
After car was warmed up and stalled, I measured:
* "supply" voltage for the FP main relay and it was below the spec of 8volts. This was about 11volts when the car was cold.
* "supply" voltage for the FP speed control relay was 12.5 as expected.
* Continuity between Battery + to FP speed control relay "supply" => good
* Continuity between battery + to FP resistor supply (red wire) at harness => good
* Continuity between FP resistor connector return line (green/orange) and FP relay "supply," no good.
Conclusion, look for a break in the line between FP resistor and FP main relay "supply."
Issue: Wire (green/orange) from the FP resistor literally broke apart in my hand at the joint with the red wires one of which goes to the FP main relay supply (See pic, circled in red). Corrosion (green) at the connection was seen. To get to this, you have to disconnect the harness from the ECU at the fuse box and then "split" it so you can access the wires underneath.
Solution: I resoldered the wires together and all is good!
I noted some of the posts above identified an issue with a different wire in these loops and it's quite possible that the same symptom of fuel pressure dropping when car is warmed up can have breaks in different wires. This just happened to be mine. To find it, just refer to wiring diagram when troubleshooting.
Hope someone finds this useful.
-Chris
Symptom as described in this thread, car starts up fine, idles well, and when warmed up, fuel pressure drops from ~500psi to 0 and car stalls and won't immediately restart. After letting it cooled down, it will start again but will repeat the issue after warming up.
Troubleshooting:
Measured resistance of FP resistor, it was 0.6 ohms out of spec. Jumpered FP resistor out to see what happens. No change.
After car was warmed up and stalled, I measured:
* "supply" voltage for the FP main relay and it was below the spec of 8volts. This was about 11volts when the car was cold.
* "supply" voltage for the FP speed control relay was 12.5 as expected.
* Continuity between Battery + to FP speed control relay "supply" => good
* Continuity between battery + to FP resistor supply (red wire) at harness => good
* Continuity between FP resistor connector return line (green/orange) and FP relay "supply," no good.
Conclusion, look for a break in the line between FP resistor and FP main relay "supply."
Issue: Wire (green/orange) from the FP resistor literally broke apart in my hand at the joint with the red wires one of which goes to the FP main relay supply (See pic, circled in red). Corrosion (green) at the connection was seen. To get to this, you have to disconnect the harness from the ECU at the fuse box and then "split" it so you can access the wires underneath.
Solution: I resoldered the wires together and all is good!
I noted some of the posts above identified an issue with a different wire in these loops and it's quite possible that the same symptom of fuel pressure dropping when car is warmed up can have breaks in different wires. This just happened to be mine. To find it, just refer to wiring diagram when troubleshooting.
Hope someone finds this useful.
-Chris
Attachments
Nice info, any pics of the fix?
cobra20sc
Greenie N00B Member
Not really. My soldering skills are embarrassing, lol. Attached is a pic of the wires pre-fix. Picture a professional soldering job and heat shrinked!
Attachments
New2MeSpeed3
Greenie N00B Member
From the Work manual. If you happen to be testing resistors at the junkyard.
Verify that the continuity between the fuel pump resister terminal A and B is within the specification.
• If not within the specification, replace the fuel resistor.
Fuel pump resistor continuity.
0.304-0.336 ohms (20 °C {68 °F})
Verify that the continuity between the fuel pump resister terminal A and B is within the specification.
• If not within the specification, replace the fuel resistor.
Fuel pump resistor continuity.
0.304-0.336 ohms (20 °C {68 °F})
