TxDiesel007

Guys

i need some help here. I just replaced an overflow valve on my truck this afternoon. I had an old one on and my FP was at 12 psi for a little while and it would rise to about 20-25 psi when i would get on it. All of a sudden on saturday my truck just remained steady at 10 psi, and it never rose again, i felt like the truck lost some power. The pressure would go down a bit to about 8 psi, and i have seen it drop as of late as far down as 4 psi, and it rises gradually back to about 10 psi as a max.

I just let the truck have it again right now on the highway and again i felt a power loss, and i also felt that it was not gettin the pressure that it should be. I tried opening the needle valve again, to see if it was too closed, that did nothing but steady out the isolator (as it is i had minimal vibrations on the gauge itself). I ruled out the idea of a bad overflow valve, i cannot have two bad overflow valves in a row, not even im that unlucky..

My game plan is simple, im gonna clean out the prefilter screen and change out the actual fuel filter and do my best to clean out everything.

I have pinched the lines on the pump and i got no reaction from the gauge. When the truck is running, that short bout six inch hose that runs from the filter to a line has absolutely no pressure, i can pinch the fuel return line and the other fuel line as well and neither of them seem to produce pressure on the gauge.

All symptoms point to the lift pump correct? HOw much of a bear is this thing to change out? Surely where its located it cannot be much fun, or anything else. Guys i need some advice, where is it cheapest? procedure with pics prefereable? or any advice.

PS, the isolator is good, and i see no kinks in any lines...

HELP!!!

Thanks guys

Rick

Dr. Evil

Temporarily bypass the isolator and run fuel into the cab to see if it makes any difference.

TxDiesel007

EDIT

Well i went outside again and decided to pinch the fuel lines again and see what it does...

http://dodgeram.info/tsb/1996/14-07-96.htm

Using this instruction in my reference manual i pinched the return line on the thing to see what it does. LOW AND BEHOLD, i did this three times in three locations. The FP drops to zero! it has absolutely no pressure whatsoever to it, the truck dont stall nor sputter but it makes me wonder how it gets fuel up there.. Im truley stumped now..

Dr,

why would the isolator make any difference? My thoughts is this thing was supposed to minimize pulsations..

Rick

Dr. Evil

It shouldnt make a difference Im not necessarily saying it will - but Im curious...

It wont hurt anything if you do this.

But, yeah kinda sounds like the LP.

halerazor

i have an isspro fuel gauge that i bought from piers a couple years ago that does the same thing. mine usually stays right at 15 psi, until my fuel filter starts getting dirty then it drops down to 0. did yours come with that isolator(rubber diaphram) if so that thing is worthless. like i said i've had mine for a year now and it's pretty much just for looks now.

TxDiesel007

I bought the one from Diesel Manor

It was suggested that i buy an isolator so i run a steel line from the banjo bolt to the isolator, and from the isolator itself i run the oil pressure tubing to the inside of the cab, im not lookin forward to undoing all of that if i have to. That i know its not a rubber diaphragm. I bought a seperate isolator.

Rick

Dr. Evil

What are u talking about? Doesnt your isolator have a rubber diaphram inside?? .

TxDiesel007

This is the isolator i have, mine jsut has two little clamps rather than one large one across it (where u screw it down)

http://www.dieselmanor.com/dm_products/DM-CGI2240.asp

and this is the gauge

http://www.dieselmanor.com/isspro/r5..._fuelpress.asp

rubber diaphragm? im not gettin you I know u remove one part of it to fill it with a 1/2 1/2 mixture of antifreeze and water, and i know that the steel hose connects to it, from the isolator i run the oil pressure tubing into the cab.

Far as i know this stupid thing is supposed to minimize pulsations, as it does, i have it set up that way and the valve is barely open, now i opened it a lil more and nothing changed, so i closed it back to where it was at..

On the drive home i watched this thing like a hawk, it would fluctuate from a max of 12 to a minimum of 10, which is better than the four psi i saw yesterday and the day before, But im gonna call my shop, get a lift pump in order, a fuel filter and a strainer kit as well.

But im still open to more opinions, i want to know if its the pump or not..

My big thing that tells me it probably is, is simply the fact that when i pinched the fuel return line my pressure shot down to zero, even after the new overflow valve...

IT would be a shame to have done all that work, for my FP gauge to be a dud, if all else fails soon if i replace the LP, fuel fliter and strainer and pressure still dont go up, im just gonna chunk that isolator and run the tube directly from the hose to the oil pressure tubing, to the gauge itself, and see what it does.. what do u guys think?


still confused

Rick

halerazor

the reason you fill one side with antifreeze or water is because it has a rubber diaphram inside of it. the fuel pushes on one side and expands the diaphram which puts pressure on the antifreeze side then that goes to your gauge and gives you your reading

Dr. Evil

There is some isolator info here:

http://www.cumminsdatabase.com/read.php?id=84

scroll down a bit

v8440

The prefilter is very easy to check. Crawl under the truck with a ratchet, extension, and a 17mm socket. It does not have to be a deep socket, but it can be. The bottom of the prefilter/heater housing has a hex cast into the bottom of it. Put the socket on that and unscrew it, being careful to dodge the 1/2 cup or so of fuel that will come out. You should be able to clean it out if you don't have another one handy. If that's ok, your gauge is ok, and your lift pump is ok, then the next thing to do is drop the tank or lift the bed, and check the pickup screen. The mesh of that screen is VERY fine, or it was on my '98. It was also about 95% clogged up. I ripped that crap out and hoseclamped some windowscreen onto the bottom of the pickup to substitute for the original mesh. I don't think a mesh that fine has any business being so early in the fuel system-that's what the prefilter is for. I haven't had a problem since.

TxDiesel007

Guys

more questions, after using the search function on here, i have determined that i will follow what v8440 stated above. I have already bought a new Fuel filter, as well as a pre filter kit on order.

what is a bypass valve? and i know that the return lines are 3/8 and 5/16, but how much of each do I need? Also how hard is it to drop the tank?

My truck has lost some power, i can tell, but It kinda stumps me cause it will start fairly easily, one or two cranks now and it starts just fine, My fuel mileage is about 14 mpg at best, city or highway, i used 1/2 a tank in 208 miles...

Should i still suspect that stupid lift pump? It seems to me its the culprit, due to the ZERO fuel pressure when i pinch off the return line with vice grips..... Im seein that the prefilter, and fuel filter will not make much of a difference im thinkin, the tank filter might, but with fuel sloshing around, shouldnt it sort of self clean?

I feel im correct in assuming that if i had an air leak then my truck would be hard to start, BUT since its not, there has to be a fuel restriction somewhere, OR the lift pump is bad,

PS i have good smoke on a takeoff in second gear and at WOT, as well as when i get on it, But i have to get on it 1/23 to 1/2 pedal to get the smoke and some boost, with the 16.5 degree timing is this normal?

anymore thoughts?

Rick

infidel

I'm trying to figure out how pinching the return line would drop the pressure to zero, it would have no effect even if the lift pump was bad.
Sure you are pinching the right line?

My feeling is your fp is probably alright, it's just the isolator causing your poor readings.

v8440

Well, the screen in the tank will not self-clean. Fuel moves predominantly through it in one direction as the truck uses fuel. When I say the mesh is fine, I mean it's FINE. The dealer doesn't sell the screen separately from the rest of the pickup, even though the screen is easily removable from the rest of the pickup. Hence, my window screen fix.

As far as pressure when pinching the return line off, I dunno about that. You could try replacing the lift pump-that might well do it.

The definitive breakdown of the 12v fuel system was written by a member on another board. It has pictures and everything. His article taught me what I needed to know to tackle my fuel system problems. Here it is:

http://dieselram.com/ubb/ultimatebb....;f=45;t=000007


I believe you will find that article VERY helpful.


So far as dropping the tank, it's not hard if you do it the way I did. First, I jacked the left rear corner of the truck WAY up. Use a BIG jackstand to hold it. Then, I got two floorjacks, and one near each end of the tank. Mine was about 3/4 full; yours will be easier to deal with if you don't have as much fuel in it. There are two straps that hold the tank up. Each has a nut that goes up a threaded rod sticking down. You'll need a deepwell socket and an extension. I THINK the nut is 9/16, but I'm not sure. In any case, it's some common size, nothing weird. Undo the straps, and let the tank down some. You'll be able to wiggle the straps around and get them to come completely out of the truck before you completely drop the tank if you're patient. It's a ***** sometimes, but it's worth it to not have the straps in the way when the tank hits the ground. You may need a light to see up where the straps are hung in the truck. Once you see, how to remove them will be self-explanatory. Once you get them out of the way, lower the tank. Here's where it gets interesting-the return and supply hose are too short to allow the tank to hit the ground while still connected. You can argue with the quick disconnect fittings on the hoses until you turn blue, or you can simply do what I did, which is to take a knife and cut that dumb **** off. The fuel hoses there are plastic-any ordinary knife will render them harmless in short order. There is also an electrical connection, which is for your fuel gauge. Finally, outboard of the frame is the other end of the two hoses that go to the fuel filler neck. Ordinary hose clamps hold these on. Remove those, and leave the tank end of them connected-they'll flop up over the frame when you drop the tank. After all that is removed, you can drop the tank and pull it out from under the truck. You will now see why I said jack the truck WAY up-the tank is fairly tall, and doesn't want to come out under the frame of the truck. Once it's out, take a flathead screwdriver and a hammer, and stick the end of the screwdriver up against one of the many little lines in the plastic nut that holds the sending unit down. You'll see what I mean when you get the tank out...Start tapping it counterclockwise to loosen it. To get it off, you'll have to completely remove the fuel lines from the tank, as the part they connect to is aimed such that they will be sticking out directly over the plastic nut you're removing. Once you get the nut off, you can wriggle the sending unit out. Be careful that you don't damage the float arm while removing the sending unit. DANGER WILL ROBINSON DANGER!!! HAVE A BUCKET HANDY TO PUT IT IN, AND HAVE RAGS OR TOWELS BETWEEN THE TANK AND THAT BUCKET!

This contraption is capable of spilling incredible amounts of fuel, LONG after you think you've shaken and tilted it around enough to get rid of all of it. Trust me, have the bucket and rags handy. The screen is at the bottom of this thing, and removal is easy-press in the little plastic tabs with something like a screwdriver while pulling down on the housing of the screen.

What I did was simply cut the screen out with a knife, and I took some window screen and trial-fitted it there. I cut the screen with a pair of scissors as necessary to get it shaped the right way. I then took a hoseclamp made for securing clothes dryer hoses, and clamped the **** out of it. While you have this stuff apart, raise the hood and disconnect that end of the supply line. This is VERY easy to do once you know where it is. Get a small stool and stand just in front of the driver's side hood hinge. Reach down to the only fuel line from under the truck that you'll be able to reach from the top. You can disconnect this easily by hand once you see how it works. Then, bend it around to where it's trapped inboard of the starter. Put a bucket under it and blow air from the back of the line near the tank to the front. Then, blow back the other way, moving the bucket to the back of course. This will ensure you don't have a partial blockage in the line.

When putting all this back together, I swapped over to diesel rated hose to eliminate the "quick" release junk. I took my trusty knife and cut off the part of the original plastic line that was slipped over the ends of the steel line from the factory. See, the majority of the fuel line is actually steel-they put that plastic line at the very back end where the tank is. Make sure you get diesel-rated hose-you don't want to be doing this again because the hose deteriorated internally and plugged something up. I got 3/8 hose for both the supply and return, even though the return is smaller. I just double clamped it-you could be correct about it and get the right size for both. It is possible to kink or pinch these hoses when reinstalling the tank-see to it that this does not happen. Be sure to put enough hose on there to allow the tank to hit the ground without stretching the hose. DON'T FORGET TO RECONNECT THE FUEL GAUGE PLUG.

When you get all this done, you'll have a hell of a time priming the system, since the fuel line will now be empty, unless you do this: Take your compressed air nozzle, and put it down in the filler neck. Jam a rag around it to seal it. Take a 10 mm wrench and loosen up the bleeder screw on top of the fuel filter canister. Blow about 20 or 30 psi of air into the tank, letting off occasionally so that the tank doesn't get too much pressure in it. If you have a helper, have them watch the bleeder screw to tell you when fuel with no air bubbles is coming out. If not, just run back and forth. When only fuel comes out, close the bleeder screw and start the truck. You will now have a guaranteed good fuel supply to the lift pump.

TxDiesel007

Im pretty certain that im pinchin the right line

On the fuel pressure check bulletin i have as a link above, (keep in mind my truck is a 96) I have tracked the lines back, they go down to the tank, and i see no other lines that go back there, aside from vacuum lines and the small one from the fuel heater to fuel filter.

In either case, my next step is the isolator itself... since its a matter of just changin some connections. If that fails, well its time to replace my prefilter and fuel filter anyways, see what it does then, IF that fails, ill drop the tank, If that still fails, ill buy the pump and replace it... most of this will be done tomorrow.... im off from work...

Rick