Intermittent power loss

[homelessduck]

Every once in a while my truck loses power temporarily. It seems to happen when my tank is below half and when I switch between tanks. This makes me think it's an air in fuel issue. I know the fuel pickup tube falls off, but I can keep driving it.. So it can't be that ..

My first thought was my wmo mix, then I had the same issue on diesel. I then thought lift pump so I replaced it ( not an airtex).

1994 idit 243k miles

Any help is greatly appreciated, as always .

 

[Devon Harley]

My guess would be fuel filter than the pick up in the tanks being clogged up from WMO. My next guess would be the shower being broke off too.

 

[homelessduck]

The wmo I run has a viscosity very close to diesel. I've had the power loss issue while running my front tank which is only diesel, so it leads me to believe it is an issue forward of the fsv (?).

I just put a new filter in. I'm down to 1/4 tank now and it still runs so I can't see how it would be the pickup.

It seems to " clear out" if I throttle through the power loss.

Fuel filter light doesn't come on. It's triggered by insufficient pressure, correct?
Hmm..

 

[homelessduck]

I forgot to add .. It does the SAME exact thing when I switch tanks. Just a brief power loss. Almost like it sucks a little air ..

Edit: Apparently I did mention that .. long day.

 

[hesutton]

Might be the FSV itself if it always happens when switching tanks. It'd be nice to know what the fuel pressure is doing when this happens. Have to crawl around under the truck a bit and have a good look at the FSV and the fuel lines.

Air intrusion tends to cause a surge rather than a bog/loss in power. My guess is an intermittant fuel supply loss rather than air leak.

Heath

 

[homelessduck]

I just drove 30 miles without any issues. No power loss when I switched tanks after warming it up. Then on my way home it started acting up. This time it wouldn't idle. I had to hold it over 1k. It would rev out fine in neutral but would not idle. I held it between 1-2k for a few minutes, gave it a few wot's and it started idling again. Still had poor power on the way home. I floored it from 20mph to see what would happen. It had zero power and struggled to take off.

Am I correct to assume that it isn't a fuel pressure issue if the filter light isn't coming on? I'm going to check the fuel pressure in a minute but I don't have a way to monitor it while driving.

 

[homelessduck]

Fuel pressure is ~2psi at idle, ~4-5psi over 2k rpm's.

I JUST replaced the lift pump and fuel filter.

 

[justinray]

Fuel pressure is ~2psi at idle, ~4-5psi over 2k rpm's.

I JUST replaced the lift pump and fuel filter.

New doesn't mean good, and that's insufficient pressure.

 

[homelessduck]

New doesn't mean good, and that's insufficient pressure.

I realize that. It was more of a " I really don't want to change out the lift pump unless all signs point to it" rather than " It's new so it must be good " . I would have to do it in the parking lot again, and it's currently snowing ... I've been driving it and it has cleared up. I'm thinking the pickup must be getting clogged.

Can you remove the rear tank pickup without dropping the tank? I have a 2" body lift.

 

[justinray]

I realize that. It was more of a " I really don't want to change out the lift pump unless all signs point to it" rather than " It's new so it must be good " . I would have to do it in the parking lot again, and it's currently snowing ... I've been driving it and it has cleared up. I'm thinking the pickup must be getting clogged.

Can you remove the rear tank pickup without dropping the tank? I have a 2" body lift.

If you can, it's tricky, you have 2 tanks correct? Drive solely on one for a week, if it doesn't do it, switch tanks, if it does it on tank #2, then it is likely your pick up being clogged, and vice versa, if it does it on both tanks, it could be a number of things, measure the pressure prefilter and post filter, that will either eliminate or blame the filter, if that's not it, it's either the lift pump or the FSV, the only realy way to test to see which is to disconnect the line that feeds the lift pump and run it into a 5gal bucket of CLEAN diesel, start truck and check pressure, good=FSV is bad, Bad=lift pump is bad.

 

[homelessduck]

Yes, two tanks. It happens 95% more so on the rear tank. The pressure at the schrader is post filter, correct? How can you check pressure pre filter? I'm not sure where I would connect the gauge.

I'll try to troubleshoot it tomorrow. I'll probably drop the rear tank as well, even though it's FULL of fuel.

 

[justinray]

You would need some sort of fitting to fit the line from lift pump to filter to test the pressure pre filter.

 

[justinray]

Wait, how long ago did you replace the lift pump?

 

[homelessduck]

Last Saturday is when I did the lift pump. It was acting the same before I replaced it, which is what lead to it being replaced.

 

[justinray]

Oh, ok. Was gonna say you may have put the arm on the wrong side of the cam.