The truck starts up fine. then after a minute or so it starts to spit and sputter and back fire through the intake then dies.


What could cause this? Intake manifold gasket leak?

Will a clogged fuel filter cause this?

Any thoughts?

Thanks in advance.

5.4

 

I would start with the fuel filter....

I'm not familiar with the injector configuration on your engine. If there is a cold/start injector, it could be possible that you have a vacuum leak somewhere and the cold start injector is covering up that leak for a few moments when you start it.

Another may be an issue with the IAC motor...

Yet another may be the start/run circuit on the electric fuel pump... This overrides an oil pressure switch for making the electric fuel pump run when there is no oil pressure..

Still - cheaper and easier to do a maintenance on the fuel filter in my opinion.

 

How many miles are on the engine? Has it been scanned for codes? Was anything recently done to this engine?

A backfire through the intake generally (but not always) means that your ignition is firing while an intake valve is open. There can be many causes of this, some simple, some very expensive. A stuck or poorly sealing intake valve, timing chain, crankshaft position sensor or head gasket failure come to mind as a cause, but there are others.

Start with getting the truck scanned for error codes.

 

carbon build up or some other foreign material (spark plug parts, etc) is preventing the valves from closing......

 

Respectfully - if it were a valve issue, the engine would not start up and run fine for a moment, it would backfire immediately. Same holds true for ignition timing.
Lean conditions are well known for causing intake backfires and I think that's what the OP is up against..

 

Backfiring through the intake I thought was always timing. Bad coil packs? Bad connections to said coil packs? Is the CEL on?

 

My only CEL are transmission codes. I took it to a transmission shop and they said the codes would not make the engine do this.

 

There are 250,000 miles on the truck. The truck sat for a long time thats why I was thinking junk in the fuel filter

I "think" the last thing that was done was I got some gas.

 

Ok let me tell you what I have done.

When the engine starts to die i sprayed engine starter in the intake and it returns to idle. If you give it gas it sputters. Sounds like a lack of fuel? Its too cold and too much snow to replace the fuel filter right now.

What do you think?

 

I don't think you're going anywhere until you replace the fuel filter. What you've told me is a classic story of fuel starvation..

The fuel filter is the first thing to replace and from the sound of it, the most likely candidate.

 

UPDATE

Replaced fuel filter made a huge difference.

Next thing is to clean out the fuel tank.

Thanks for the help!!

 

Glad to hear it man...

If you have a bunch of crud in the tank, you may need to replace the pump and strainer sock in order to get all the way to 100%

 

Spoke too soon. still doing it. Looks like I am dropping the tank.

Are there any good instructions on dropping the tank?

 

Yeah, it sounds like you have a tank full of crud / water... Best thing I can advise is to get it as empty as possible by siphon first.. Then it's just a matter of getting a big floor jack under it and removing the straps and filler neck. When you drop it down a little ways you should be able to get at the wiring harness on top to disconnect.. That's when I take the fuel and vent lines off as well.. You will probably need the special disconnect tool for the fuel line. Not sure on your year truck as I never had to do it on my 99...

 

I love it when a plan comes together!