M35A3 leaking fuel near filter

[Hoefler]

I need help to solve fuel leak issue. Beneath the fuel filter-and to the side there is a jumble of piping that terminates to an electrical sensor (two wire). Fuel is dripping-slow drip off the bottom of this sensor. There is a lot of fittings: Senso is at end, pipes to a 45 degree pipe elbow, which pipes to a short nipple which pipes to a dual compressuin or flared fitting which connects to long straight nipple. Hard to tell which fitting is leaking. Question-what is this sensors function, why are there so many fittings between it and first long nipple. If I simply take apart and silicone tape the threads, will I need to bleed fuel systyem?
Has anybody else had a leak here?
Thanks in advance.
Pete
I could supply a photo if needs more clarity.

 

[flyxpl]

I am unsure what all the wires do . The fuel line towards the front of the truck coming into the filter housing from the pump feeds the filter fuel. The line towards the rear go into the rear of the head/valve cover area and feeds the fuel rail / injectors . If you open this up you will drain the fuel filter and fuel lines ,maybe even the fuel rail . You will for sure be putting air in the system . I have a high mileage dump/plow truck with the cat 3116 in it . After changing out filters because of old fuel and algae I am haveing a hard time getting it going. Even with the old fuel and algae in the primary filter it ran good . You may be ok since you will not introduce air from the tank up to the pump .
If you have not already checked it , make sure the filter is on tight .

 

[glcaines]

Make sure the fuel filter is on tight, but be careful not to overtighten or you'll never get it loose again. I would actually recommend removing the fuel fiter and replace it with a new filter rather than tightening the old filter. You need to thoroughly clean and dry the whole external surface of the filter mount / water separator. Have someone else crank and start the engine while you watch. If the surface is clean and dry, shine a light on it and maybe even use a mirror to see where the fuel is coming from. You may find that replacing the filter solves your problem.

 

[Hoefler]

The area beneath the fuel filter looks a little wet as well. I did see a couple drops come off the end of the electrical switch. Maybe the drips are spraying back onto lower assembly where filter goes on. I will start with new filter though.
Its a Sparta M36 truck-have driven her about 350 miles now-so figure something had to leak!
There is a petcock on the filter support base-is this to be opened to drain water out?

 

[flyxpl]

Yes, the red petcock lever is for draining water . Until you get it all cleaned up it will be hard to tell where it is coming from .

 

[glcaines]

If the engine is running, the fuel should squirt out the petcock under good pressure. Sometimes you need to rod out the petcock with a piece of wire if it is crudded up and hasn't been opened in a while. You will need a good quality oil filter strap wrench to get the filter loose. Have you cleaned the check valve located on the top of the fuel tank where the fuel line exits? They are notoriously crudded up and will cause fuel starvation problems or make the engine hard to start if it lets fuel drain back down in the tank. If you take out the check valve, make sure you hold the fitting securely when breaking the joint loose as it is very easy to bend or break the fitting on top of the tank.

 

[Hoefler]

Have not got into fuel system yet. Did the transmission with good results.
Have read where the fuel systems on thes trucks can be pretty gummed up. Though It starts great and runs well, I will clean up and service the fuel system. I actually like taking stuff apart "carefully" and cleaning it.
I appreciate the heads up on the check valve. I may take pictures and post them.
Pete

 

[jaymcb]

does anyone have actual pictures of the fuel filter changes? The NAPA filter I got doesn't look to be even close to the same size as the original.

A picture of the 'check valve' cleaning would be appreciated too, because the TM is less than clear, and it isn't like you can call AAA to have it towed if you render the truck FUBAR....

 

[CobraCDR]

I agree on cleaning things up to pinpoint just what is actually the source of the leak. You will want to drain off a little fuel on a regular basis to check for water (if you follow the -10, it covers that as part of the PMCS). It doesn't sound like anything major at this point, clean it up a run down just where the problem is.

 

[glcaines]

does anyone have actual pictures of the fuel filter changes? The NAPA filter I got doesn't look to be even close to the same size as the original. QUOTE]

I used a filter from CAT, P/N 7E9763. The cost wasn't that bad. If the fuel filter from NAPA is not the same physical size, I would suspect that it is the incorrect filter.

 

[flyxpl]

I used a wix filter . It looked identical,

 

[Hoefler]

New filter on-still wet at base. Had her clean and dry. New problem now-she starts up well. Drive 1/2 mile down the roda and engines barely runs. Pumping throttle (seems to work better than floored) barely keeps engine running. Lots of smoke when this happens. Sit on side of road until she slowly comes back to higher RPM. Limp back and she stumbles and falls flat but not dead-sit and try to idel then proceed back. When back at shop, I let her run at 1,000 RPM-no load and she eventually comes back. Its acting like a plugged fuel filter-but cant be its new.
Do I have air in line? How do I get purged? Have not gone into tank for check valve yet. All was fine before I changed filter. Any advise will be greatly appreciated.
Thanks,
Pete

 

[glcaines]

It is almost undoubtedly one of the check valves, most likely the one on top of the tank. Was the smoke white that was coming out of the exhaust? White smoke means lack of fuel. Black smoke means too much fuel. I would advise pulling the check valve and cleaning it thoroughly. Be very careful disconnecting the fuel line from the top of the tank. It is very easy to bend or break off the fitting on top of the tank unless you securely hold it while loosening the fuel line. Mine was extremely tight and I had to use a breaker bar to get enough torque on the wrench.. I cleaned mine in gasoline and blew it out with compressed air. It was full of crud. This would also be a good time to drain and clean the fuel tank. This is not a very difficult job to do and is a very common problem with A3s.

 

[Hoefler]

Gary,
It was white smoke. Dont understand why changing out tthe fuel filter would result in the check valve acting up. Maybe the flow was different past the check valve as the fuel filter was being filled up? I will take the check valve out today and clean. I will have to run the tank volume down some-she is over half full. Thank you for your help-I will follow up with result.
Pete

 

[flyxpl]

Pete, I am going through the same thing with my GMC plow truck with a cat 3116 in it . After changing out a filter because of algae in the system I had a hard time getting it to start . I finally got it started and took it for a drive . It ran great . The next day I go for a drive and it starts to starve for fuel within one mile for home . It struggled just to get home . Not sure how the A3 isset up , but the cat 3116 is supoesed to have a check valve on the return line up on the pump , you might also need to check that .Being that the filter is on upside down we may just have air traped in the filter .
Joe

 

[Hoefler]

Joe,
I am going to take a look at the check valve in the fuel tank. I dont understand what has happened.
I changed the filter to a new filter. She ran great for about 100 miles-but still had leak. Took filter off and drained dry-then cleaned the boss till supper dry. Did notice the black rubber gasket does not fit on crimped end of Cat filter very well-it looked like a loose fit. Anyway-got her back together (still wet at higher RPM) but now she is fussy and bellows whitish smoke-let her idle for a while and she is a tiger again for awhile. It seems like fuel starve. I will follow up with what I find in the tank.
Pete

 

[glcaines]

Gary,
It was white smoke. Dont understand why changing out tthe fuel filter would result in the check valve acting up. Maybe the flow was different past the check valve as the fuel filter was being filled up? I will take the check valve out today and clean. I will have to run the tank volume down some-she is over half full. Thank you for your help-I will follow up with result.
Pete

I actually experienced the same thing as you. I came to the conclusion that this was caused by a temporary increase in fuel flow. The fuel filter on an A3 is mounted upside down, preventing pre-filling the filter. This is probably a good thing as it keeps people from pre-filling the filter with unfiltered fuel. However, when the engine is turned over, a much larger flow of fuel occurs temporarily while the filter is re-filled with fuel, potentially carrying trash up and clogging the check valve. During normal operation, the fuel flow is miniscule in comparison. Mind you, this is just a theory based on the fact that I can't think of anything else. Could also be just coincidence.

 

[CanonNinja]

i had the exact same thing happen to my truck. Ive blown every filter now on my truck, but I also had all original yellow cat filters on. My fuel filter was trashed after a long drive, probably the firs time it was really driven since the guy i bought the truck from was the first owner after GL. The check valve was nasty as **** too, film funk was so think it looked like wet paper towel blocking it.


that was a fun road-side fix.

 

[Hoefler]

Gary,
You where right. I took the infeed fuel line off of tank. I unscrewed all of the small screws and pulled it from the tank. The large opening gave me a good view into the inside of tank. She was clean. When I took of the 90 degree elbow at top to reveal the check valve the first thing I noticed was lack of fuel dripping from fuel line to engine. Hmm...Looked in side of the fitting (picture sort of shows it) and saw translucent gunk. I used a small screw driver to push the check valve open-it popped open after a little force. She was bound by the gunk. Once I saw this, I remembered that I had put a pint of fuel cleaner-conditioner into the tank a week ago before the issue started. It was getting cold out so I thought it would be a good idea the make sure there was no moisture in the tank. TGhinking that the cleaner stuff loosened up the gunk and it got caught in the check valve.
I have cleaned the valve and gave her a shot of WD40. TGhe rubber O-ring looked to be in good shape. The valve is now sliding up and down freely. Put it back together and did a short 3 mile test run. Its running fine now-good enough to try a 5 miler then a 10 miler to make certain. I still have the drip at the fuel filter. I think it might actually be coming from the piping that holds the fuel shut of mechanism. Leak is not bad-just drips here and there but its driving me banana's. She is an otherwise dry truck.
Every A3 should have the check valve clean. All one really has to do is take the upper elbow off-10 minute job.
Thanks to everybody for your help.
Pete

 

[CanonNinja]

yup, thats pretty much how mine looked. had to do exactly the same thing too, screw driver to pop it open and scrape the gunk out.