How to spend the whole day chasing a fuel delivery issue. (1 Viewer)

[TurboDennis]

So i have a truck (1997) that sat without an engine for a year and i finally found the time to put an engine in it (a good running engine that i tested myself).

With everything hooked up, it cranks but doesnt start at all. So i proceed to troubleshoot.

I know that the compression is excellent, so that's not the issue. Checked spark... - OK.

So i suspect fuel. Good.. - fuel system on these trucks is fairly easy to diagnose. Or so i thought.

1) CEL is on while cranking, so i assume the electronics are probably OK. Lots of fuel in the tank.
2) I remove the fuel return line at the junction where it connects to the main hard line that runs to the tank (near the fuel pump relay). Crank the engine, no fuel coming out.
3) In the order of likelihood i decide to completely take the controls/electronics out of equation. I disconnect the fuel pump relay and feed the connector 12v straight from the battery to run the fuel pump (completely bypassing all relays and their controls). Still almost no fuel coming out of the return hose near the fuel pump relay (just a few drops).
4) Next step is to open the feed line, to check if fuel is getting to the engine from the tank. I open the flare connection at the same junction as the return line i removed earlier (near the fuel pump relay). 12V to the pump, fuel gushing out of the the feed line. GREAT! The pump is working and fuel is getting to the engine
5) To isolate the problem area further, i remove the line from the fuel filter outlet (before it enters the fuel rail). Power the pump, fuel just dripping from the filter outlet. This pretty much narrows it down to the clogged filter. Which was odd, considering the filter was fine last time it was used.
6) Regardless, i remove the filter, and attach another used filter to the feed line that i know worked good. Power the pump, nothing changes (still just drops coming out). At this point im really starting to try and turn my brain "on". I come to the conclusion that perhaps the pump is putting out enough flow for the fuel to gush out of the fuel feed line, but no pressure, so it cant overcome the resistance of the filter. Didnt seem probable, but OK, worth a try since im running out of ideas.
7) So i proceed to remove the rear seats to access the fuel pump. Do the same thing on the parts truck (which ran great). Swap the fuel pump bracket assemblies. Hook everything up. Power the pump. Fuel dripping out of filter. WTF?!? At this point im officially out of ideas.

Anyone wants to take a stab at what the problem was? (I did figure it out later..)

 

[Railwelder93]

D light not working?

 

[BILT4ME]

Isn't there a check valve in the fuel line to maintain pressure at the fuel rail when off?

If it sat that long, I'll bet the check valve is stuck.

Find it, bang on it, make it submit.

 

[ppc]

Replace the filter with new. After sitting for a year the media is going to be plugged.

 

[Brimley]

So tell us already

 

[TurboDennis]

So tell us already

Some weird debris stuck in the short fuel hose, just before the banjo connection on the fuel filter inlet., which almost completely blocked the line.

Step #4 is where it all went wrong. I opened the fuel feed line at the junction near the fuel pump relay to check for fuel flow (just because it's much easier to access than further down the line, (where it actually enters the fuel filter)). There was flow, so i assumed the fuel was getting to the fuel filter. After removing the fuel filter later, i never checked the output at the actual fuel filter inlet, because of my assumption earlier.

 

[Brimley]

Some weird debris stuck in the short fuel hose, just before the banjo connection on the fuel filter inlet., which almost completely blocked the line.

Step #4 is where it all went wrong. I opened the fuel feed line at the junction near the fuel pump relay to check for fuel flow (just because it's much easier to access than further down the line, (where it actually enters the fuel filter)). There was flow, so i assumed the fuel was getting to the fuel filter. After removing the fuel filter later, i never checked the output at the actual fuel filter inlet, because of my assumption earlier.

I had one of those days too. It was the pump. It was working weakly so had flow, but would only idle.

 

[TurboDennis]

I had one of those days too. It was the pump. It was working weakly so had flow, but would only idle.

That's what i thought the problem was (in step #6), so i proceeded to remove the pump from both the truck i was working on, and the parts truck and swapping them... Which turned out to be a colossal waste of time (and could've been avoided). So the lesson here is that if you want to eliminate a possible cause during diagnosis, make sure you REALLY eliminate it before proceeding to increasingly more difficult steps.

 

[Rifleman]

Some weird debris stuck in the short fuel hose, just before the banjo connection on the fuel filter inlet

Don't be surprised if you look closer, that that weird debris doesn't turn out to be some kind of dead bug that decided that you're open fuel hose looked like a great place to set up a home.

When i overhauled my charcoal canister i found a dead family of earwigs that had set up home inside the vent hose on the bottom of my canister.

Plus I've also lived where mud dauber bees are common, and given a chance they'll plug up any small openings they find.

Because of little critters like these, i now make it a point to cap off, or plug any lines if it's going to be a few days before i reconnect them.

 

[shocktower]

The stock fuel pumps are really a lifetime warranted they never die the only thing is the sock could get dirty and never swap a used filter get a new one and make sure you have it in the right direction ( yes you can put them in backwards ) and make sure fuel is exiting, so does it now run ??