I have an 85 6.9L thats having issues. It starts fine and drives poorly. At some point anywhere from 10ft to 1 mile it starts to bog. And I can can get no additional power out of my truck from that moment on. It seems to happen quicker if I step on the gas. If it happens at say 20mph I can hold that speed but can't command any more power. Sometimes I can drive it just fine at 65 with no issues for a few miles. But more common is driving it say 1000ft between stops. When I pull it over it will generally stall out. Once I start it again it seems OK. And the sagga continues. I was picturing a clogged fuel filter, but I changed that out and drained the water. Anyone have any ideas...Thanks a ton for any insight.

Scott

 

Hi Scott. Welcome to Ford Truck Enthusiasts. The Ford truck resource.

Stick around, one of the resident experts will be by shortly to help with your problem.

 

Have you done a:
.... pressure and flow test of the fuel pump at the Schrader valve on the filter (FSS- fuel shutoff solenoid disconnected). Remove the tire valve core and hook a hose and pressure guage on it should see 4-6 psi when cranking. Then do a fuel quantity test same place, should see 1/3 pint in 10 seconds of engine cranking, route fuel to a suitable container with a hose.

If there is a problem with the lift pump and you are changing it, ensure the new pump comes with instructions as to correct installation procedure if it is the newer model pump with the almost straight arm.

 

No I haven't yet tested the fuel pump. This seems to be such an intermitent problem. I can run the truck in my driveway and get it to respond at times at full throttle. Would it be likely that the fuel pump would be intermitently working properly and what signs would these tests give if the pump was working properly at that particular moment. When I changed out my fuel filter my pump filled up the new one without problem and started right up. What type of readings on the pressure test would suggest a faulty pump?

Also what other types of issues do you think might cause these symptoms?

A little more history on the issue is that it started and became worse over the corse of about 50 miles.

 

it sure sounds like you are having a fuel delivery issue. do the tests like pc stated and check for 6-7 lbs pressure and the 1/3 pint delivery into a container. you may also want to check for full throttle movement on the injection pump. perhaps the throttle cable is frayed internally and not moving.

 

I'll give the shrader valve test a try today. Don't think it has anything to do with the throttle cable as this problem seems to occur even when I manualy work the throttle. Could this be an injection issue?

 

Does it give a surge of fuel before it stalls on u? it sounds a lot like my troubles right now, I dont think its the fuel pump either, it can run for too long for that to be it, just curious, good luck.

 

No. I definetly wouldn't say it has a surge of full before it dies. It definately feels like its not getting fuel. Well more like it's getting fuel until something gets clogged somewhere and then from that moment on it boggs down. Even when it's bogged down it's still getting some fuel. If the pump was failing when the truck was going say 30 mph would the engine suck in fuel or does the engine completely rely on the fump for fuel. I'm really not familliar with the workings of the injecter pump. Is there something on the other side of the fuel filter or fuel pump that could be getting clogged intermitently. Remember as soon as I shut it down, It starts back up just fine until it gets "clogged again" sometimes this occurs right away and other times I can travel a few miles before it happens again. It seems to happen quicker if I stomp on the gas!

Remember there are times when it runs fine so at least at these moments my fuel pump is working properly. I suppose the fuel pump could have an intermitent problem but it may not show on a pressure test!

Anyone have any other ideas related to the IP.

 

It is possible you have something in the fuel tank that is blocking the pickup tube.
When you turn the engine off it falls off of the pickup tube.
Start the engine again and it gets sucked back across the pickup tube again.

Have you run any fuel system cleaner in it?
I would also use a bottle of Diesel Kleen fuel treatment in it right now. Double or triple dose it for the first time.

 

You can go to a marine store and get a thing of Bio-guard. That may help out in a short period of time. You may have algae growing in your tank. It grows in the water that gets in tanks. It is like black grape jelly. It floats or sloshes around and gets picked up by the fuel pick-up. If you're sitting in the driveway overnight and then you start your truck and it runs fine, that's because the stuff is still sitting on the bottom of the tank, settled. When you start driving it can start moving around and get sucked onto the fuel pick-up. If you want an immediate, sure and quick fix you can drop the tank and dump out the fuel into a five gallon bucket and let it sit for a couple of days and then you can syphon off the fuel and keep the trash in the bottom to clean parts or the bottom of your engine and undercarriage. I would use a double-dose of the the Bio-guard and then put some more in next week if you don't drop your tank and dump it out. Make sure you're dumping out your water separator a lot, too. It is very common for someone to dump a quart or more of water into their truck tank by mistake by putting fuel from a gas can into the truck and not realizing that there is a bunch of water sitting in the bottom of it, probably even with algae gowing in it already. That is common. Light gets in through the gas can sides(plastic) or the caps on a metal tank and the algae grows in the gas can. Then you unknowingly dump it into your truck tank. I usually try to filter the gas that I put in from a can through a shop rag or a piece of cheesescloth. It pours fast enough through the shoprag and the cotton attracts any water or algae that you may have in the can and alerts you to the fact that there is water in the fuel. Of course the water will be setting in the bottom of the can and so ALWAYS leave the last two inches of fuel in the can and then use it for parts cleaning later. It is also a good idea to move your diesel cans slowly and pour it carefully and then any water or crap will sit in the bottom of the can and be left at the end. If you use your cans a lot for diesel it's a good idea to let them dry out completely from time to time for a day or so. Or you can empty them and put some gas(like a quart) in the can and slosh it around and then dump it out into your lawnmower through a shop rag. Then the gas can will dry out quickly because of the gas that was in it and the quart of fuel that you put in your lawnmower will work fine. Sorry about the long post. This all comes from personal experience and it does help to know about this problem.

 

One other check is to hook a hose to the return line from the IP cover, drain it into a white container and check for black specs. You could remove the 90* fitting from the top of the IP return line, remove and inspect the check valve for black pieces. Sounds familiear to the Governor Flex ring disintegrating, inturn blocking the return of fuel. This shuts down the IP due to an over pressure. May be time for a new IP, how old is the one on there now.

 

Yea it diffinatly acts like a flex ring failure. On mine which did the same thing, I could drive it for a couple miles then it would quit. I let it sit 5 minutes it would start run a mile and quit. it would idle great but as soon as I tried to drive it it would quit. Sound like a trip to the injection shop is in order. If you want to change it yourself (its easier than it looks) just put up a post and someone will walk you through it.good luck