low fuel pressure

[90f250]

im sure its been gone over and gone over but id like some input on a few things... first off, its a 90 7.3 idi non turbo engine...with a turbo set up from a 93-94 idi ( I assume) .. I just sold my bronco and bought this truck so everything that has "been done" to this truck is the previous owner or before...I have some knowledge of the idi from a previous truck that had a 6.9 so im not completely dumb on the situation... ok here it is, im getting low fuel pressure and what I believe is because of getting air in the fuel lines.. the previous owner installed a small fuel pressure gauge on the filter housing, and when I bought the truck it read between 3-4 lbs pressure.. I drove the truck 2 1/2 hours home down the interstate runnin 70-75 the entire time with no problems, I shut the truck off when I got home and about an hour later I went to start it and it cranked and cranked for awhile. it started and ran for about 30 seconds and died. the fuel pressure gauge said 0..nothin..so I went to town and bought a new lift pump, installed it, had to jump start the thing but it ran and drove for about 45 minutes till I shut it off again meanwhile the gauge remained at 0 the entire time, it left me stranded at work the next day so I had it pulled home and I went to the part store again, bought an electric fuel pump..the green electric over the counter holley I believe, installed it and fuel pressure jumped to 7...that was fine with me, drove the truck again and made sure to get on it a bit...got home and looked at the gauge...2..still running and staying on 2..wth is what im thinking...all my caps and return lines looked dry but just in case I wiggled them..got diesel out of everyone of them...ordered the kit, installed it, and back to 7 psi running ...ok I said, drove around the block and got on it again, looked at gauge...back to 2 psi.. and so everyone knows the pressure drops to 0 psi in less than 1 minute from shutting it off so clearly there is a lot of drainback or air intrusion somewhere...AND since the front tank gauge doesn't work I figure ill save my self the hassle that ive had before with selector valves and do away with it and the front tank and just run a new rubber fuel line from the tank to the electric fuel pump and also do away with the (probly junk) airtex lift pump as well...so basically...im asking if im going the right direction or just overkill or what? ANY input is welcomed

 

[79jasper]

Have you changed the filter?
Fuel level?
Did you leave the mechanical pump hooked up when you installed the electric?

These engines don't require much pressure. And what you saw with the mechanical pump is about normal, IIRC.

Also any black smoke when you get on it?


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[90f250]

yes sorry I bounced around there... I installed a new filter yes, also a full tank again( it did get down to 1/8 before I refueled) , mechanical pump is still hooked up at the moment and yes there is some black smoke until the turbo spools, after that it doesn't smoke ..I had planned on turning the pump up a flat or two but at the same time I want to make sure it is getting enough fuel to turn it up without draining the lines

 

[icanfixall]

Welcome to the forum. Please don't run the electric pump thru the mechanical pump. The pressure from the electric pump will burst the diaphragm in the mechanical pump and flood the oil pan with diesel. That ruins the bearings fast. Is the drivers side of the injection pump wet looking. The bottom of the plunger arm is a seal that has leaked on some pumps. Takes plenty of work to replace it too. Also the hard line at the filter from the mechanical pump has a seal in it called an olive. Its in the brass nut. thats a 3/8 size. Also on each end of the feed line from the filter to the injection pump has a 5/16 olive in it. they are easy to find in any injection pump repair shop. Try calling Conestoga diesel in Pa because its close to you. Mel or suzi are the people to talk with. Great family owned business and great to deal with.

 

[90f250]

i actually ran the electric pump up top in between the lift pump and the filter housing ( i was in an ice and snow covered parking lot so i didnt really feel like layin on my back) ... i will look at that injection pump when i get home, im at the hospital right now with my newborn almost ready to be released! patiently waiting to go home, lol but thank you for the info, i have the next 2 days off work so ill have some time as long as the wife doesnt need anything while im trying to get it all fixed...

 

[79jasper]

Those pumps should be mounted close to the tank.


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[90f250]

Well from what i can tell is the pump is not leaking anywhere..hiwever my turbo.is.seeping some oil and apparently it has for awhile but that's a different subject, I'm starting to think someone half a$$ed this turbo set up or possibly the whole trucj, lol.. I'm also concluding that either I'm getting air in the lines or that the lines arw getting clogged somewhere. Because after a short drive without getting on it , it stikk drops fuel pressure and stays very low to nothing at all .. tomorrow I'm getting rid of. front tank and fsv and re running the fuel line (if i really think it needs done..not sure what kind of.line is under there right now ..and tuesday my manual pump block off plate comes in so that will be eliminated then and no longer a problem, however i do think icanfixall is on to something with the "olives" because it seems that i am leaking fuel out of the fitting coming into the filter housing. i know i go bacj and forth a lot, i do apologize, i don't mean to do it but for some reason its like second nature to me when i try to explain something so I'm sorry if anyone gets confused

 

[90f250]

Fixed!! Some previous owner had installed a electric pump on the frame rail..needless to say it no longer worked and was leakin diesel..i changedd the pump with mine, turned up the ip 1 1/2 flats and. put a mechanical pump block off in place of the llift pump..and i kept the front tank in instead of pulling it out...truck runs 10x better and starts up fast!

 

[90f250]

Welcome to the forum. Please don't run the electric pump thru the mechanical pump. The pressure from the electric pump will burst the diaphragm in the mechanical pump and flood the oil pan with diesel. That ruins the bearings fast. Is the drivers side of the injection pump wet looking. The bottom of the plunger arm is a seal that has leaked on some pumps. Takes plenty of work to replace it too. Also the hard line at the filter from the mechanical pump has a seal in it called an olive. Its in the brass nut. thats a 3/8 size. Also on each end of the feed line from the filter to the injection pump has a 5/16 olive in it. they are easy to find in any injection pump repair shop. Try calling Conestoga diesel in Pa because its close to you. Mel or suzi are the people to talk with. Great family owned business and great to deal with.

upon another look (during daylight) i can see that plunger arm your talking about, and yes its wet and definitely leaking...how do i go about fixing that? do i need to pull the pump to do so?

 

[79jasper]

Easiest to just replace it or have it rebuilt.


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[90f250]

YAY!!(sarcasm).... just what i wanted to hear

 

[icanfixall]

The pump will need to come off the engine. Then you remove the retainer from the arm pin. then remove the arm. Now remove the cap with the seal in it and take that to any good injection pump rebuild shop. Have them replace it with the very special drivers. It has a depth set point to that needs to be within 10 thousands of being correct... So I was told when I had mine replaced.
Sure happy you found the problem and it was just an oversight on your part. Funny how others "repair" things that don't need repairing. I wonder how many mechanical lift pump diaphragms were ruptured by running both electric and manual lift pumps...

 

[90f250]

Well i appreciate the tech there..i most likely won't be doing this due to funds, ill probly just deal with it, once its fiired up it runs great