Fuel pressure issues and engine stall

[Juicer83]

I have been having hard starts when the engine is warm and recently the truck stalled and wouldn't restart. It was towed back to my house (thanks Geico) and I got a chance to hook up a fuel pressure guage. The prime before starting yielded 20psi and when running i got just under 30. When the FPR had the vacuum line removed it raised to 35. Then while the vacuum line was removed the Guage started being very erratic and eventually slowly fell to 0 and the truck stalled. Also I noticed when revving the engine with the vacuum line disconnected the fuel pressure would drop a hair. Just reaching out to those of you with more experience then me. Do these findings point to a bad fuel pump or FPR, or is there any more testing I should do? FYI 94 Mazda B4000 4x4.

 

[MrShorty]

If you can get a suitable tool/clamp/vice grips that won't cut the tubing, the next test I would perform would be to clamp off the return line (from the FPR back to the fuel tank). If the pressure still remain low, that will indicate that the fault is the fuel pump being unable to generate enough pressure. If the pressure jumps way up, then that indicates that the FPR is opening prematurely.

 

[Juicer83]

If you can get a suitable tool/clamp/vice grips that won't cut the tubing, the next test I would perform would be to clamp off the return line (from the FPR back to the fuel tank). If the pressure still remain low, that will indicate that the fault is the fuel pump being unable to generate enough pressure. If the pressure jumps way up, then that indicates that the FPR is opening prematurely.

I'm having issues deciphering which fuel line is in and whichave is out. Is the line that connects to the FPR in? It seems as if the fuel pump cuts off. I'm planning to test pressure before the fuel rail, should it be the same reading or higher. I'm wondering if I have a pinch before the rail causing the fuel pump to cut off.

 

[Juicer83]

If you can get a suitable tool/clamp/vice grips that won't cut the tubing, the next test I would perform would be to clamp off the return line (from the FPR back to the fuel tank). If the pressure still remain low, that will indicate that the fault is the fuel pump being unable to generate enough pressure. If the pressure jumps way up, then that indicates that the FPR is opening prematurely.

I pinched off the return line and no change in fuel pressure. I removed the bed to access the fuel pump I washed everything off an plan on testing the wire connections tomorrow. So far my symptoms are stall after 10 minuets of running, low fuel pressure prime, an below average fuel pressure at idle. Something is causing the low fuel pressure and the pump to stop working.

 

[trashtruck]

also check the reset switch under the rug, on the passenger side. this cuts off power to the fuel pump in case of an accident or rollover.

 

[Juicer83]

also check the reset switch under the rug, on the passenger side. this cuts off power to the fuel pump in case of an accident or rollover.

The inertia switch wasn't tripped. I'm wondering if it's the coolant temperature sensor, but I can't find anything online that says if it would trip the fuel pump to stop pumping .

 

[MrShorty]

The inertia switch wasn't tripped. I'm wondering if it's the coolant temperature sensor, but I can't find anything online that says if it would trip the fuel pump to stop pumping .

I am not aware of any connection between any of the temperature sensors and the fuel pump being turned on. The only sensor I am aware of that the PCM uses to turn the pump on is the CKP/profile ignition pickup (PIP). If the computer sees that the engine is rotating, then it will turn the pump on. If the pump is cutting off, it could conceivably be a fault in the "circuits" between the PCM and the ICM that tell the computer that the engine is rotating (though those faults seem to trigger PIP/CKP or similar codes), or there is a fault in the fuel pump circuit, or the pump itself is dying.

 

[Juicer83]

I am not aware of any connection between any of the temperature sensors and the fuel pump being turned on. The only sensor I am aware of that the PCM uses to turn the pump on is the CKP/profile ignition pickup (PIP). If the computer sees that the engine is rotating, then it will turn the pump on. If the pump is cutting off, it could conceivably be a fault in the "circuits" between the PCM and the ICM that tell the computer that the engine is rotating (though those faults seem to trigger PIP/CKP or similar codes), or there is a fault in the fuel pump circuit, or the pump itself is dying.

Thank you, I for some reason was oblivious to the absence of a check engine light with the key on engine off. Just replaced the bulb last night, will pull codes this afternoon.

 

[Juicer83]

Pulled code 336. Seems to be egr related. I may have found my problem as to why it seems like my fuel pump cuts out.. While inspecting my coolant temp sensor I noticed a bare wire , as I followed this wire down the front of the motor I found it ended at the Crank position sensor. I will start my repairs there and see if I have any more issues.

 

[Centaurious]

336 usually indicates a bad DPFE Sensor. Suggest the Airtex/Wells re-engineered unit, got mine at Autozone.

Please keep us informed as your repairs progress. It's a great resource for others and we like the stories, especially when they end well.

 

[trashtruck]

a bad crank sensor has little to do with power to the fuel pump. the sensor sends a signal to the icm which sends a signal to pcm which sends a signal to injectors and icm to advance timing. with a bad crank sensor, you're not losing power to the fuel pump, your losing power to the ignition system.

 

[Juicer83]

a bad crank sensor has little to do with power to the fuel pump. the sensor sends a signal to the icm which sends a signal to pcm which sends a signal to injectors and icm to advance timing. with a bad crank sensor, you're not losing power to the fuel pump, your losing power to the ignition system.

I went to the bone yard to pull a wire harness and noticed it the Cpk has 2 wires. The exposed wire I saw was part of the wrap. I drove it down the street and got a chance to pull another code 335. Although when I got home I noticed white smoke coming from the tail pipe. Very faint, I barely noticed it. Things not looking so bright right now.

 

[trashtruck]

codes 335and 336 are for the dpfe sensor. replace the sensor. cpk sensor has 3 wires, 2signal wires surrounded by a shield wire to cut down on electrical interference from the engine.

 

[Juicer83]

codes 335and 336 are for the dpfe sensor. replace the sensor. cpk sensor has 3 wires, 2signal wires surrounded by a shield wire to cut down on electrical interference from the engine.

Ok, the shield is completely gone for about 3 inches, I mistaken the shield wire for a ground.

 

[Juicer83]

I ran a compression test and all my cylinders have 170 except for #4 which has 150. I'm hoping it's valve related. I cleared the codes and ran the truck again and got 332 and 176. Right now the truck idles at 1k and I haven't found a vacuum leak yet. I'll do a leak down when I can get my hands on a compressor.