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Fuel pressure loss.

98EdBomber

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NO Check engine Light. No stored codes. I do my own work on this vehicle.

192K miles. Replaced fuel pump maybe 6 years ago FYI. Cant remember brand I think Airtex or whatever. Had this truck since it was new. Looking to sell and need to fix this long crank issue first.

98 4.0 sohc losing fuel pressure after sitting for hours. Long crank when cold sitting over night. Have to cycle key few times to build pressure. Starts right up after warm. Im assuming I either have a fuel pressure regulator problem or a leaky injector.

I pulled all 3 plugs on the driver side and they looked a little carboned but not wet.

How do I isolate this issue without pulling the injectors? Can I bypass the fuel flow to the regulator (pump) assuming its in the gas tank and if I then have fuel pressure maintained I can assume the fuel injectors are not the problem?

Is there only one feed from tank to fuel rail since it is "returnless" or does this engine have a return line as well. If no return line then how could i isolate the injectors to see if fuel pressure is maintained?

Fuel pressure stays at 30 when running in idle. So I think the actual pump is fine.

I smelled the oil on the dipstick and i really cant say it smells like fuel.

The leak is slow. Its possible an injector is dripping slowly?

Is there a way to pinch off the return line or does this not have one? I want to isolate the injectors and see if they are leaking.

Or is there another easier way without an expensive scan tool.
 


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donalds

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The pump has a built in check valve
You can use it that way or replace the pump itself
Buy a bosch
Rare case it is a injector

If you do have a returnless fuel system your fuel pressure should be around 65-70
 




Mr. Alligator

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Except that you need to cycle the key/pump to get the truck to cold start, what makes you sure you have a fuel pressure leak? I assume you can not smell fuel. As @donalds points out, your idle fuel pressure seems low....

I would still suspect the fuel pump. Some of those pumps seem to be VERY unreliable or short lived. Try Bosch fuel pump. One of the harder aspects about maintaining these vehicles is cheap (Chinese) parts. You just can’t be sure you have solved the issue just because the part has been replaced.

Good luck with this.
 




98EdBomber

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I hooked up a fuel gauge last night about 10pm. It read 30psi when idling. Before i started it pressure was like 33 i think. Now I just went and checked it and its at 10 psi.

I thought that meant there was fuel leakage? Shouldnt the check valve hold more pressure than that? And when I turn the key off the pressure very slowlyy drops. Maybe its just a weak pump? I dont think pressure for this truck should be 65psi. If so id like to know where to find that info. From what Ive read it should be 30-45psi.

And how do i know if it has a returnless?
 




98EdBomber

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For V6 Explorers/Mountaineers from 1999 thru 2003 with the returnless fuel system (fuel pressure regulator mounted in fuel tank) a fuel pressure damper is mounted on the fuel rail.

1608820105240.png


This is what I have on my fuel rail. Passenger side towards the front of the engine on the end of the fuel rail. I think some late model '98's had returnelss added. Which makes it super confusing but I think I have returnless and if thats the case 30psi at idle is no bueno.
 




imp

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For V6 Explorers/Mountaineers from 1999 thru 2003 with the returnless fuel system (fuel pressure regulator mounted in fuel tank) a fuel pressure damper is mounted on the fuel rail.

View attachment 325935

This is what I have on my fuel rail. Passenger side towards the front of the engine on the end of the fuel rail. I think some late model '98's had returnelss added. Which makes it super confusing but I think I have returnless and if thats the case 30psi at idle is no bueno.
Has a rubber diaphragm in it acted upon by vacuum. Flow is thus controlled to maintain desired PRESSURE. A diaphragm LEAK will bleed fuel into the engine, wasting it, and causing rich mixture. The diaphragm may be tested using one's HEAD: draw a stiff vacuum with mouth & tongue then maintaining it, place tip of tongue over opening in tube, thus holding in the vacuum. If it bleeds away, diaphragm is leaking.
 




98EdBomber

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Yeah easy right? Try getting to that thing without taking the upper manifold off. LOL I was able to get a hose in there barely with my fat fingers and hooked a vacuum gauge to it and it held all day. So I can rule that out.
 




Mr. Alligator

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What is the status of fuel filter?

Still looks like you are chasing unusual gremlins, with an elephant in the room .... cheap Airtex or whatever fuel pump. Don’t buy these.

Even with zero fuel pressure in the line, a good fuel pump would very quickly attain adequate pressure. And I think you would immediately be aware of a odors from a significant fuel leak upstream of the fuel injectors. Does not seem like a substantially leaky fuel injector would resolve itself by cycling the key. Just my two cents, from afar.

Good luck, and please let us know how this is resolved.
 




C420sailor

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We need to devise a way to pressurize the system from the fuel filter connectors forward. This may be my new pet project...

Low pressure air/nitrogen?
 




98EdBomber

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Id say Im due for a filter. I changed it years ago but cant remember what the mileage was.

But Id still like to figure out what proper fuel pressure is for this system and what is acceptable pressure drop after key off.

If its normal to bleed all the way down over night then i may not have a fuel problem. It pressurizes to around 30 psi when i turn key on. No visible exterior leaks and definitely dont smell fuel. Battery checks out good as well. New plugs and wires and coil pack couple years back as part of 150K preventative maintenance. Went with Autolites and bosch wires.

My concern with the injectors is if they had small drips internally and thats where the pressure was going. Ruling out the regulator/damper the only thing left is the check valve in the chinesium pump. Ill most likely switch to the bosch regardless after running the tank down some. But if its a failing pump Ill risk being stranded. Of course its just my luck to have this issue with a full tank.
 




CDW6212R

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The pressure for a pre -99+ Ford is 32-42psi or so, it has two levels. Check it when off and turning the key to on a couple of times. That should get it above 32psi, 30psi is too low actually when running. Pull the FPR vacuum line, the pressure should go up a good bit, 35-42psi etc. There have been many ranges posted, so most are a range of accuracy. The FPR should add a decent amount extra, say 5psi over idle vacuum pressure.

Check the FPR diaphragm as suggested, that rules out one possibility. The injectors can be leaking excessively, but it's rare. The pump is a likely cause, which is why most people do that without much trouble shooting, and it's big job.

Do change the fuel filter, and pour out the old fuel from the inlet side to look at the gas. It shouldn't be too filthy, if it is, that can restrict flow a bunch, or it can mean rust in the tank(steel tanks not the old plastic ones).

FYI, the Bosch fuel pump was still around $45 on eBay in the Fall, I got one last Winter at that price too.
 




98EdBomber

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Yea Ive changed the fuel pump already maybe 6 years ago. I dont put a ton of miles on it so i want to say its only been maybe 30k miles since. Not too bad of a job if you take your time and have the right tools.

FPR holds vacuum with a gauge so im confident that is okay.

Whats left is the fuel filter, pump and injectors.

Im close to 200k miles im guessing the injectors need some love so I went ahead and bought a seal kit. Ive done the intake gasket oring years ago to fix the common erratic idle problem so familiar with that whole ordeal.

There is also a crankcase breather box down there with an oring that may leak. Ill change that oring and the pcv valve. Thats gotta have 50k on it.

One thing I didnt anticipate was with this much mileage and time how many seals have gone bad. Just had the washer fluid go out. The oil filter oring to block. I did the exhaust manifold gaskets as well. Pretty much any gasket i could think of LOL. When time and mileage add up so many things start to go wrong its crazy. But Ive been knocking them out one by one and so far so good. Thanks for the advice and have a Happy Holidays.
 




CDW6212R

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The injectors aren't bad to do after removing the intake(upper) etc, but what is pricing for just the o-rings? The top and bottom o-rings are reliable for the first 10-20 years, like you pointed out at this age any rubber part or seal is at its limits.

The injectors typically cost about $10 each as rebuilt units on eBay, from what I used to see. I have bought two sets of those before, one for my older 91 Lincoln, and about 7-8 years ago for my 98 Mercury. They evidently are not hard to rebuild, so there are many sources to buy them from at fair pricing. At that cost, I liked paying that for the injectors all ready to go.
 




98EdBomber

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The injectors aren't bad to do after removing the intake(upper) etc, but what is pricing for just the o-rings? The top and bottom o-rings are reliable for the first 10-20 years, like you pointed out at this age any rubber part or seal is at its limits.

The injectors typically cost about $10 each as rebuilt units on eBay, from what I used to see. I have bought two sets of those before, one for my older 91 Lincoln, and about 7-8 years ago for my 98 Mercury. They evidently are not hard to rebuild, so there are many sources to buy them from at fair pricing. At that cost, I liked paying that for the injectors all ready to go.
Well I finally got them all out and hooked them up to a 9v to clean them out. One of them is definitely leaking. So I have to find a replacement. Could be the fuel pump still as well but at least i know i have a leaky injector. Noticed loss of mpg as well and vibrating idle. Im wondering if I should just order a single one or get that refurb set.

I also need to replace the green orings on the fuel rail but cant find a part number for them?
 




CDW6212R

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See if the injectors are still about $10 each on eBay. That will include new o-rings and cleaning with testing. I'd replace them all if the sellers are still there and reliable.
 




98EdBomber

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See if the injectors are still about $10 each on eBay. That will include new o-rings and cleaning with testing. I'd replace them all if the sellers are still there and reliable.
Yeah for the cost and the amount of work it takes to get to them it is worth it. I can bench test the remanned ones to make sure they at least dont leak but will only know if they spray right until i fire it up. I found a seller that has some bosch ones for like 60. I know there are fakes out there so i made a careful buy. They have a warranty anyways. Hopefully I get lucky. Then if it still long cranks, its got to be the fuel pump.
 




crunchie_frog

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Sure sounds like the fuel pump. 6 yrs for a non OEM pump is pretty good from my experience, particularly if you did not remove the tank and give it a good, thorough cleaning when you replaced it last. Guess you will find out if you don't replace the pump, you could end up on the side of the road somewhere, let's hope not.
 




98EdBomber

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Sure sounds like the fuel pump. 6 yrs for a non OEM pump is pretty good from my experience, particularly if you did not remove the tank and give it a good, thorough cleaning when you replaced it last. Guess you will find out if you don't replace the pump, you could end up on the side of the road somewhere, let's hope not.
Well that is definitely my concern. Ill update soon when the injectors arrive.
 




98EdBomber

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Sure sounds like the fuel pump. 6 yrs for a non OEM pump is pretty good from my experience, particularly if you did not remove the tank and give it a good, thorough cleaning when you replaced it last. Guess you will find out if you don't replace the pump, you could end up on the side of the road somewhere, let's hope not.
Welp strike 1. LOL The ebay injectors were a dud. Engine stumbled like crazy on first start then thick white smoke started coming out of exhaust. Like THICK. Im like uh oh the head gasket?? But HOW? There was never any signs of leaking head gasket before the repair. Coolant level was completely full so i knew it wasnt that.

So I take off the upper and lower intake and low and behold. I happened to catch the intake valve in its closed position (Can they actually get stuck closed???) when i shut off the engine. And when I shined a light in the port it was completely full with fuel. Injector stuck wide open. Confirmed with a test after I removed them. I did the leak test before i installed them and they didnt leak. I dont know. They were originals bosch that matched my old ones. Not sure what I want to do now. If I buy refurbed ones they will be 20 year old injectors. So now Im back to square one.

For now Ive drained my oil. And had to get some towels to soak up the raw fuel in the intake port.

the exhaust was also dripping ALOT. Can that really be fuel??? If the injector was stuck wide open can it dump so much fuel that it gets sucked into the exhaust and drip out the pipes? Didnt make sense and why i thought it was coolant at first. But the coolant level didnt drop whatsoever. And drained oil was still fine although very thin which makes me think its because of all the raw fuel from the stuck injector.

Anyways...the saga continues
 


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Welp strike 1. LOL The ebay injectors were a dud. Engine stumbled like crazy on first start then thick white smoke started coming out of exhaust. Like THICK. Im like uh oh the head gasket?? But HOW? There was never any signs of leaking head gasket before the repair. Coolant level was completely full so i knew it wasnt that.

So I take off the upper and lower intake and low and behold. I happened to catch the intake valve in its closed position (Can they actually get stuck closed???) when i shut off the engine. And when I shined a light in the port it was completely full with fuel. Injector stuck wide open. Confirmed with a test after I removed them. I did the leak test before i installed them and they didnt leak. I dont know. They were originals bosch that matched my old ones. Not sure what I want to do now. If I buy refurbed ones they will be 20 year old injectors. So now Im back to square one.

For now Ive drained my oil. And had to get some towels to soak up the raw fuel in the intake port.

the exhaust was also dripping ALOT. Can that really be fuel??? If the injector was stuck wide open can it dump so much fuel that it gets sucked into the exhaust and drip out the pipes? Didnt make sense and why i thought it was coolant at first. But the coolant level didnt drop whatsoever. And drained oil was still fine although very thin which makes me think its because of all the raw fuel from the stuck injector.

Anyways...the saga continues
Wow, I hate that the work didn't solve anything. Who was the eBay seller, the user name? We should avoid that seller for sure, the point of the rebuilt injectors was to restore the reliability of them. I hope you contact them and see how they respond, they should be testing their results fully.
 




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