Lift pump pressure ???

[offroad-anarchy]

Found Bills old post on tearing down a fuel tank selector valve - https://www.oilburners.net/threads/fsv-tear-down.50770/

Doesn't show how to clean it from debris, if that might be where my partial blockage is. Will have to see when I get it off the truck

 

[offroad-anarchy]

try pinching the return line at the top of the filter head.

Not sure what that might do ???

edit: Think I found this... maybe so the return lines don't spray fuel all over me when I disconnect them

 

[offroad-anarchy]

Well, that was all fun and good yesterday

Pulled the front sender/fuel pickup and it was clean as a whistle. Not even a spec of crud to be found. Replaced the shower head (that was fine as far as I could tell), the gasket and lock ring.

Next I pulled the fuel selector valve after some rather long winded sessions of werewolfing 4 letter explicatives. It had a bit of crud down in each of the ports when I sampled with some q-tips, but it was working fine. I cleaned it all up with some citrus degreaser and screwed it back together. I blew out the line from the fsv to the lift pump and all the fuel came out clean as whistle there too.

Got it all back together and now I'm getting 3-6.5 psi after the filter when idling and no load revs. I guess that was worth the work, but...

...it didn't fix my no power above idle problem that has me down this rabbit hole in the first place. Perfect starting, smooth idle and just nothing when you stomp on it. Revs to 2800, but no black smoke no matter how hard I try to roll coal.

Looks like I have something up with my IP. Will save that for another search and thread when I get there. Will check back when I find what's up. Also here's some pics of the piece parts apart if anyone comes down this lane and wants to see what the insides look like.

Thanks again for all the help and suggestions.

 

[Clb]

Soooolongshot , have you checked the downpipe and muffler?

 

[mblaney]

Not sure what that might do ???

edit: Think I found this... maybe so the return lines don't spray fuel all over me when I disconnect them

I switched an an electric pump (Walbro) and found that it cycled a lot (pulse rate seemed high). I found that the filter head vent (return line) was bypassing a lot of fuel so I pinched it. You can greatly reduce the fuel flow though the return line, theoretically increasing your supply pressure.

In fact, I tried blocking the filter head return completely and didn't have any issues. In my case, the e-pump cycle went from maybe two per second to less than one every two seconds. I think the only point of the filter head return is to vent any air intrusion from the supply, so if your suction lines are good then it serves no purpose. As a compromise I just restricted this line.

Just try it with a pair of vice grips and see how your feed pressure responds.

 

[offroad-anarchy]

Thanks @Clb, but have a new exhaust. Pretty sure unless there's some sort of new rats nest burned up in there somewhere with me driving it daily, that's not the issue.

I've been tracking down the throttle assembly or possibly the metering valve in the IP as the source of my issue. If it's the metering valve not adjusting with throttle position, it would be the opposite of all the problems others I've seen have with the metering valve linkage getting locked at high volume and not starting well. Not sure how it could not meter up unless the pressure in the pump is too low, which would mean a new IP

Trying not to do anymore part swapping until I'm sure what's up.

In my travels I came across this link for the 7.3 IDI turbo diesel service manual. Wow, what a great find I thought some of you might like !!!

1993 FORD 7.3 L IDI TURBO DIESEL SERVICE MANUAL SUPPLEMENT : ... : Free Download, Borrow, and Streaming : Internet Archive

...

archive.org

Maybe that archive will have one for any of your specific trucks.

Cheers, Pete

 

[offroad-anarchy]

I switched an an electric pump (Walbro) and found that it cycled a lot (pulse rate seemed high). I found that the filter head vent (return line) was bypassing a lot of fuel so I pinched it. You can greatly reduce the fuel flow though the return line, theoretically increasing your supply pressure.

In fact, I tried blocking the filter head return completely and didn't have any issues. In my case, the e-pump cycle went from maybe two per second to less than one every two seconds. I think the only point of the filter head return is to vent any air intrusion from the supply, so if your suction lines are good then it serves no purpose. As a compromise I just restricted this line.

Just try it with a pair of vice grips and see how your feed pressure responds.

Oh, will go give that a try right now !!!

Thanks

EDIT: Update... Nope, that didn't change anything. Thanks though.

 

[Cubey]

I had an idi that didn't like pressure over around 3-3.5 psi. it lost all top end power at 5-6psi. pedal to the floor would barely get to 55. i had installed a holly red because the mechanical pump was weeping to the ground. it was on an Econoline and getting to the pump was harder due to how the engine is mounted. i had to add a dial style pressure regulator to reduce the pressure. it did the trick, had no problems at all after that. the regulator was before the stock fuel filter.

 

[offroad-anarchy]

Finally after doing all the fuel system checks and pressure tests, I finally came to the conclusion that the internals of the IP are bad. Pulled it this morning and found that the timing advance in the pump was locked up and wouldn't let the throttle open all the way much less let the timing advance.

Didn't notice that it wasn't rotating to the the stop until I got it out. Duh, never thought to look to see if it was hitting the stop !!! Funny how when you're a newbie it can be hard to understand all the little details to check. Explains why it starts and idles perfect just won't give it any juice

Hopefully have that rebuilt, a new valve cover gasket on the drivers side and get her all back together by next week.

Thanks again for all the suggestions and help on this one.

Cheers, Pete

 

[IDIBRONCO]

I'm glad that you got it figured out.

 

[offroad-anarchy]

Figured I'd finish this one out. Got the rebuilt IP in and timed last Thurs. Been noodling around with it for a couple days and a cold start this morning at about 40 deg F it hit on about third rotation with virtually zero smoke and runs like a top.

I now need to be a tender foot to keep from rolling coal in the lower rpm ranges, but it all seems to be zooming.

Again, thanks for all your help. Next is onto sort a couple small oil leaks.

Cheers, Pete