So I've got an odd situation.

Twice now I've had the Fuel Filter Plugged light come on at WOT in 2nd gear and go out about 30 seconds after changing into 4th or 5th.

Mind you I can't get it to do it all the time even on the same day.

First time it happened I'd been follow a slow vehicle (doing about 50 kph) for about 5 km's in 4th gear. Finally get to a clear point when I can overtake and change down to second and accelerate past. By the time i've got up to 4th again the FFP light is on, don't know exactly when it came on but it was definitely at WOT. Engine is still running fine and light goes off about 30 seconds later. Tried a couple of times on the rest of the trip home but could not get it to come on again.

Second time it happened (was about 4 weeks later) had been idling along a dirt track in second gear for about 2 minutes. After turning onto the main road and accelerating at WOT the light comes on again. Stays on until I get into 5th then goes out about 10 seconds later. Once again engine is running fine and I can't get it to do it again.

Seems to be after running a low revs for a time and then using WOT.

Fuel filter has less than 500km on it. Both were on the same fuel as I had not added any fuel during this time. Both were on the same tank (rear) as I don't normally use the front tank except as a backup.

Engine is 7.3 N/A from a 1993 F350 with ZF5 speed.

Any ideas.

TIA

 

<p>i would check fuel pressure at WOT. your lift pump may be failing</p>

 

x2 on the lift pump.

Also, I don't know if the sensor is on the pre-filtered or post-filtered side of the fuel filter. If it's post-filter I would think a partially clogged filter could cause these symptoms as well.

 

Thanks.

I'm guessing i'd need to check the pressure at the inlet to the fuel filter?

Any idea what pressure and fuel flow (GPH) it should be?

I'll swap over the lift pump any way, have a new one sitting here as a spare.

Cheers
Ross

 

<p>1/3 pint (or 157 mililiter) fuel in 10 seconds crank time, and 7 PSI at the outlet of the filter to the injector pump.</p>

 

Replace both the filter and the pump; They are both cheap enough that you might as well do it right now. Lift pumps aren't long-life items, and they get weak over time if they don't fail.

 

I doubt that it's the filter as it was replaced between the two occurences and it's less than 500kms old.

I don't know how much they are in the USA but they are about $70 each plus freight here.

I can get 7.3 psd oil filters here for $32 each but the 7.3 idi filters are $45 each so I use psd oil filters.

 

OK, then it's the fuel pump. Easy fix!

I use PSD filters myself, but in my case it's simply cause they are bigger. And under $20 for me.

 

So finally got around to looking into this.

It turns out that there were actually two problems.

First was a faulty fuel line coupling, this is a 90 swivel type where the line goes into the fuel selector. It's weeping fuel so is causing air intrusion, I bypassed it and the occasional slight surge I was getting as well is gone but the FFP light was still coming on.

I then bypassed the fuel selector and prepump filter all together.

Problem solved.

I pulled the prepump filter which is a reusable washable type cleaned it up put it back in and now no FFP light at WOT.

So now I know that the FFP will tell me when both the pre-pump filter and main filter is blocked.

Thanks all for those who helped with suggestions.

Still need to replace the coupling but have to wait for replacement to arrive, so just running on the rear tank only for the time being.

 

There's a pre-pump filter? Where?

 

Older trucks have one on the firewall, below the brake booster. It's a silver can looking thing, more a water separator than filter. Every one I've seen in person was bypassed.

 

Ok. So remember my whole truck is basically custom built, see the build thread.

I have:

Fuel tanks -> Pre-filters -> Fuel selector -> Electric Fuel Pump -> Main filter -> IP

The pre-filters are 30 micron Aeroflow billet filters, one for each tank, these are washable so I can clean them where ever. I don't have the problem of trying to source them in the middle of nowhere.





Given that it was both tanks with a problem I'd say last time I fueled up both tanks there was some dirt in the fuel.

Both pre-filters had dirt in them the rear one about twice as much as the front.

The filters are there to protect the Fuel selector and the Fuel Pump