I have a 90 f150 with a 5.0. The truck ran great until the other day. I went to start it and it just cranked, didn't try to spit, sputter, or anything. I switched to the rear tank and it started right up (yes the front tank had fuel). After about 5 minutes I switched it back over to the front tank and it ran fine for another couple weeks. Now the other night I was driving home and the engine started stumbling. I switched it over to the rear tank and a few seconds later the stumbling stopped. I am pretty sure that it is the front fuel pump but wanted to know if there is anything else I should look at first (Relays, Valves, Etc.). Any help would be greatly appreciated!!! Also, I don't know if it's related but the day it wouldn't start it was really humid, and the other night when it was stumbling it was raining pretty hard. Is there anything that moisture could get into that would cause this behavior?

 

Takle fuel pressure to verify condition. Your descripion does point to the pump, just good to confirm before money is spent.

 

Yes, with very bad condition ignition wire's would behave this way with moisture.

 

Will a fuel pressure check show a consistently low pressure if the problem is sporadic? What pressure is the cut-off line between a good/bad pump? Thanks again!

Slip: The ignition wires are pretty old as well as the plugs and are in need of replacement. I would think that bad plugs/wires would cause the same problem regardless of which tank was sending the fuel, which is not the case. Maybe I'm wrong on this?

 

Negative on the consistencey of pump pressure. Readings of 30-40 is range of operation. As you questioned, problem needs to be ocuring for pressure test to be valid.

 

My truck does the same thing, and here's what the deal with mine is. The front tank pickup pump is bad, but my truck has the inline fuel pump as well. So when the tank is very full, the truck will run off the front tank, but when the level drops and the inline pump cant keep up, it sputters and tries the stall. It's bad to put that much strain on the inline pump so I just never use the front tank. If your tank is full when it runs fine, I believe you have the same problem

 

Problem solved, I think... I ran a fuel pressure test and it was a solid 40 psi and the flow rate was great. Took the truck out for a test drive and got it good and warm and it died as I pulled into my driveway. Turns out it was the TFI Module (I know, completely unrelated to the fuel pump). I read on a mustang forum that you can gently tap it if its bad and the engine will shut off (it did). I purchased an Accel Permance TFI for $80 and installed it and the truck would not rev past 3k rpms. A trip to the local Ford garage and $166 later for a Motorcraft TFI and the truck works great (so far). Guess you really do get what you pay for. As a side note I was told by both the Ford garage as well as they guy that sold me the Accel TFI to use di-electric grease between the TFI and the distributor. I decided to go to RadioShack and purchase a tube of Thermal Grease (made for mounting heat sinks to processors in computers) for $10. It was 99% Pure Silver, and should transfer more heat to the distributor than the di-electric grease.

BigGreyBox: Thanks for the input! I found out while researching for fuel pump prices that 89 was the last year for the three pump set up in our trucks. In 1990 they went to one pump per tank, and no in-line pump. Mine is a 90 but my friends is an 89. If his starts having these symptoms I will now know what to look for!

 

It's a good thing really that you only have two, one less part to go bad ha. But glad you got it going. I read that they actually recalled a lot of these on lots of fords because it was too close to the motor and the heat would kill it, so they started mounting them on the fender

 

Hello, I am new to the forum. I am having a similar problem with my 93 F150 302. I filled both tanks this morning and started on the front (gauge doesn't work) drove about 45 miles and the truck started acting like it was running out of fuel switch to rear tank stumbled a little and smoothed out and ran fine. As I returned home I messed with the switch some and it would run for a little bit on the front tank then repeat. Seems like fuel pump to me but I would like to check fuel pressure to be sure. Is there a special gauge to test this or does and normal tire pressure gauge work?

 

When was the last time you changed the Fuel filter?