I'm looking for some help with this truck I just bought. Its hard to start. Sometimes it will start and seem to run fine for about 5 minutes, then stall out. Restarting is difficult and I have to wait a while.

I cleaned the IAC, there is no check eng light lit while running. Any ideas?

I have read some other forum entries and am leaning towards the TPS and the Engine Temp Sensor,, but kind of hate to just throw parts.

 

How many fuel tanks does it have? Mine did that when an o-ring in the fuel tank selector valve was swollen.

 

It has 2 tanks...I wonder if its possible to bypass the valve to prove its faulty?

 

Not an easy way I know of, when this happens can you flip the switch to the other tank? Does it occur when you are on the front tank or rear tank?

 

I would say your fuel pump on the frame isn't working. Or at least one of your fuel pumps aren't working. Unfortunetaley, I would say it is your most expensive pump on the driverside frame. Switch that out along with your fuel filter and it should fix the issue. Before you do, check your fuel line pressure. I think it should be around like 65 psi.

 

While this is very possible, if it works after switching tanks, then that pump would not be the issue. Also, pumps normally work, or not, they don't work for 5 min. and then cut out. I'm not saying your wrong, as the problem is most likely fuel-related, but it could be a number of things. Troubleshooting is the only way to know for sure. I agree with checking your fuel pressure, but you would need to check the fuel pressure right after the engine dies.

 

To booba5185, the reason I say this is because there are three pumps in that truck, and I had a problem similar to his before. I found that the in tank pumps will get enough fuel and pressure to the injectors after turning the key enough times, thus starting the pumps (hence the humming noise you should hear before you start the truck). But once the truck is running, the pressure drops quickly and after about 5 minutes the truck does stall. That pump on the frame (from my understanding) keeps the fuel pressure up so the truck can continue to run.

 

The in tank pump supplies about 5 psi to move the diaphrams inside the selector valve, and then to the high volume pump to provide the higher psi to the motor. My truck had the exact same problem as well, but the high volume pump is fine. The o-ring inside the selector valve swelled up, choking the fuel supply. Like I said, either could be the problem, and both would be somewhat easy to replace.

 

So, it sounds like the first thing I need to do is get to Autozone and borrow a guage... I can get it started and watch the fuel pressure at the time of stall. If it drops to less then 65psi, think about the high pressure pump in the frame rail.

 

If it drops below 65 psi that doesn't mean that its the high pressure pump, it just confirmed our theory that it's fuel related. If that little o-ring is swelled up, it'll cause the fuel pressure to drop just the same.

 

Here's a site that shows you what the selector valve looks like, and where the o-ring is.
http://stangler.com/motorsports/arti...alve/index.htm
You can see it in the lower left (along the outer ring)here:


Right there ---------------------^
Another pic, with it circled. You don't have to remove all the stuff thats removed in this pic to get to it though.

 

I know this is going to sound stupid, but, I have only tried running the truck with the front tank selected, should I put gas in the rear tank and see if the problem goes away.

Or does the port that O ring seals get used by both tanks?

This brings another question. Depending on switch position/tank selected, the low pressure pump in the tank selected is the only pump that runs, (besides the high pressure) in other words, the deselected tanks low pressure pump will not run?

 

Correct on both accounts. Every time mine sputtered I'd switch to the rear and it'd run. I can't remember if it would KEEP running, but it would at least buy me another 5 min or so. I fixed the problem the day after it happened, and it was about 6 months ago. I do know for a FACT that it would at least get me going again.

Edit: I remember now, the rear tank would always work, but my selector valve was really screwed up. The rear tank would fill the front tank, so I couldn't leave it on the rear tank for long. That was the issue.

 

Allright, I took the selector valve out and removed the top and inspected it, I couldn't find anything wrong, I ran low pressure air through it and it switches fine depending on which port is under pressure. I found some of the lock clips missing from the fittings but I think they were the returns so most likely not a problem there.

One thing I noticed is the fuel seems soured, Im not sure how long it has been sitting.

Another thing I checked was: I have the low pressure lines off the selector valve and I turn the key on, I should get a stream of fuel from one of the lines dependent on tank selection? Is this true? I get no fuel from either.

To me it seems there should be nothing to keep the fuel from coming out.

If so then my problem is upstream at the low pressure pumps or in the electrical circuit.

Also when I turn the key on I hear a pump run but I'm fairly sure it is the high pressure pump.

PS, I thought I saw an electrical print somewhere online,Booba do you know where I can find one?

 

Yes, there should be some gas coming out of the line you have switched on (front or rear) when you turn the key on, but only for about 2 seconds or so max. The EEC (computer) truns it off after that, until the engine is running. What I did when it was only me working on the truck was unpluged the fuel lines from the front tank (left the rear plugged in), switched the switch in the cab to the front tank, then turn the key on to run (NOT START) for a few seconds, then looked for a puddle. If theres a puddle of gas, then the front lower pressure pump is most likely not your problem. Then do the same test, but with the front fuel lines still hooked up and the rear fuel lines unplugged. This was the easiest way I found out that my rear pump was bad (in my case it happened before the o-ring swelled up...yea I was sick of working on my fuel system). Just because it can't hurt, I would switch out the fuel filter (cheap, about $9 or so). If both your low pressure pumps work, then it's time to rent a fuel pressure gauge and wait for the the truck to stall again, because if it does end up being fuel related, it's most likely that high pressure pump that damiansalmond mentioned. Good news is that by all this test we know what it's NOT, so that way you don't throw money at it that you don't need to. Lemme go hunt for a schematic for ya.

Found one: