Truck runs fine most of the time, from time to time it will just choke and choke i can revive it by pressing the gas sometimes but when it is really bad it just stalls and turns off. I can bring it back by turning off the ignition and turning it back on and punching it, it will soon then stall again. this was happening on a 4month old fuel pump (entire assembly not just the pump replaced) so i eventually had him replace the entire assembly. ran great out of the gate but today it did it to me again...wondering what else it could be?? i need to go back the mechanic with some more knowlege because i need this fixed i rely on my vehicle very much. the day when i finally was able to show up to the mechanic shop with the tuck choking, he plugged a gauge into it and the pressure was all over the place, mostly below 10psi, mechanic says it should be at 35 or close. this is a 4.2L V6 non 4X4.

 

Yes, it should be in the 32-40psi range. I'm wondering if the relay has a burned contact and the pump is not getting the proper voltage to run at a constant speed. I would also check all body to chassis grounds just to be safe.

Oh yeah, welcome to the forum.

 

thank you for the welcoming words. Electrical is definitely a good place to look next. is this relay identified in the users manual? if so which one is it? also how can i find out where the chassis grounds are located? is that in the users manual? thank you for your reply, i really appreciate it.

 

ok found a 20amp fuse in position 10 under the hood that is for the "Fuel Pump" i may sound like an idiot asking but is this the one you are referring to? it looks to be fine (not blown) could this still be the culprit?

thank you and i look forward to your thoughts.

 

Ok, i replaced the relay and the fuse for the fuel pump and it ran fine for a week...at the end of the week i stopped for a beer on the way home (at the gas station) i was inside for about 5 minutes at the longest, i came out started the truck and boom the same problem, choking, i had to punch the gas to keep her going...then i can feel the fuel pressure kick back in and the truck runs again, then it chokes again...took it back to the mechanic he is suggesting the fuel regulator now, I'm really starting to get frustrated, i need this fixed and I don't know what to do. any suggestions?

 

Any trouble codes detected yet ? A failing IAC valve will cause the same rough running/stalling/hard starting problems. Wouldn't affect fuel pressure though. Wouldn't be the first time that there might be a short in the harness under the truck.

There should be a code showing now for low signal or voltage in the fuel pump circuit. A corroded harness connection or a break in one of the wires would be the places to look for that. A shorting situation would also cause weak or non-existent power to the pump, but would also blow the fuse.

Dave

 

thanks for the reply dave

just had the mechanic clear the codes for troubleshooting. truck has run fine the last couple of days, i will be driving it today i will see how she does. when you say there may be a short in the harness under the truck what do you mean? what harness and where is it located under the truck. sorry, I'm not a car guy so i don't know what I'm doing.

thanks again.

 

got the codes read and they are P0171 (fuel trim bank one) and P0174 (fuel trim bank two) guy at autozone suggested cleaning the MAF sensor, did that no issues in the last couple days. any thoughts?

 

P0171 and P0174 are mostly related to vacuum leak. Let's for now keep them separate. As suggested, clean MAF sensor with a spray can labeled as mass air flow sensor cleaner, if you have not done it before.

1) Year and mileage?
2) Any occasional problem will wear out owner. Don't give up.
3) Last time you replaced fuel filter?
4) Get a loaner fuel pressure gauge from AutoZone. Look for a fuel pressure port under the manifold. If you stand on the left side of the truck, you can actually see the port.Connect the fuel pressure gauge and measure pressure with key ON engine not running. Since pump runs one second only each time key ON, you need to do this 2 or 3 times to reach max fuel pressure. Record the pressure. Wait 10-20 minutes and see if the pressure drops.

Why did the mechanic not replace the pump when he found fuel pressure was only 10 psi? I just cannot comprehend his inaction.

 

2x on the fuel filter -- maybe the fuel pump has all it can do to get liquid through it.

Also, how about the regulator? (I'm assuming that this is a 2 line system). It could be opening up at too low of a pressure.

If it's really 10 psi, that's just not right.

Good Luck,

hj

 

Thank you guys for the replies. here is the latest. I posted the codes as soon as i got them in a panic without fully updating the saga. this is a 2000 F150 V6 4.2l with 175,000 miles. all my previous posts include the first part of the story here is what has happened since the second new fuel pump was installed (under warranty). truck still crapped out on me (same exact symptoms) so i took it back to the same mechanic and told him to fix it no matter what it cost, just track down the problem and get it done. He replaced the fuel pump again (this is the third one now) with a different make and model than the first two. he also replaced the fuel regulator and traced and checked all electrical and fuel line connections. ran ok but it still didn't quite feel right to me. a couple days after i felt it beginning to choke on me again...problem always seems to start small and get worse increasingly....the day i felt it slightly choke was the day i got the codes read. I have now cleaned the MAF sensor with MAF cleaner and to be honest the truck feels really good, better than when i got it back from the mechanic. For one it has not stuttered or choked once...also i can feel that when i step on the pedal that fuel is being delivered to the engine...would a clean MAF really make a big difference or is this all in my head? I have not had a chance to get the codes read again since the MAF sensor cleaning, i will this week and post the results. as for the question on the fuel filter, i have changed it out 3 times this year (1st time truck wouldn't start {new filter fixed that issue}, 2nd time when the first fuel pump when on {truck wouldn't start unless i turned the key to the on position and then off and then all the way to start the engine}, than the 3rd time was when the second fuel pump went in {just as a part of the troubleshooting} ) any more coments, suggestions would be great. thank you for all of the help. I am contemplating changing the Oxygen sensors as it has never been done and i am reading online that the MAF and o2 sensors have a lot to do with fuel delivery.

thanks,

JB

 

FYI:
MAF went bad on my 97 V6. Sensor reading was zero air flow. But I drove the pickup for days without a driveability problem. Had I not checked codes, I would driven the pickup continuously. (Something's wrong with my service engine soon light. If anyone knows how to check SES light, please advise.)

When oxygen sensor gets old, it will become sluggish. Afaik, there is no code for being sluggish. Air/fuel ratio may not be adjusted by computer quickly. But it will not make engine choke or stop.

Once oxygen sensor gets really sluggish and gets stuck (either lean side or rich side), you will see a code. If you don't have a O2 sensor code, I doubt O2 sensor is the cause of your problem.