Engine/Transmission (1994 - 1998) Lift pump on a 12 valve??

[tp0d]

Sounds like the shop foreman has a lot of his own hardset opinions. Dont like ppl that think only inside the box. (sounds a bit like my old man lol)



Do the overflow yourself and save some dough. If your truck has less than 200-250k I`d say your lift pump is fine. The plate is very easy to do also. That #6 will probably munch your clutch if its stock.



I`m interested in what theyre charging you, just to keep in the back of my head. If you feel like it, plz post the ending numbers. .



good luck



-j

 

[MLee]

John G.

In all these post I have not seen anyone suggest that you change you fuel pressure pick up point to the fuel line going into your P7100, via a banjo bolt with taped threads. As a one time member[no longer able to post here] always recommended to get fuel pressure here. But of course you need a snubber to control the pulsataing of the needle, or a sending unit.

Marv.

 

[Joe G.]

John G.



I think if you can't do your own work you should find someone else to do it. Those guys just don't know what they are doing. The last thing in the fuel system that will probably fail is the lift pump. The fuel hoses are a common failure. So is the overflow valve. I think I would put a temporary machanical pressure gauge on to check to see if your gauge is reading properly. I don't think a P7100 equiped engine will even run on 2 PSI. The service manual says that it should be at least 25 PSI. Anything below 18 PSI is considered to be a sign that something is going wrong. This is how my fuel pressure gauge is hooked up:



<IMG SRC"https://www.turbodieselregister.com/user_gallery/sizeimage.php?&photoid=13568&width=2">

 

[biggy238]

Joe that's interesting because my new lift pump, overflow valve, and fuel filter only like to produce about 20psi at idle and 18 on the highway.

 

[Joe G.]

Check your service manual. The overflow valve is supposed to regulate fuel pressure. If it's weak you won't get the proper pressure. Mine idles at about 22 PSI. In some instances it will peg my 40 PSI guage. Normal highway driving is in the low 30s. A slight air leak will also lower fuel pressure. That will only get worse.

 

[JohnG]

fuel press

Thanks guys. . There's 115,000 miles on my truck. . I am getting the feeling that these folks might be taking some liberties as I have admitted to being somewhat of a novice. . BUT, I did learn some very good stuff from their 'Pump guy'. . , IE: The overflow valve(s). . There were 3 in succession w/ pn#'s ending in 086, 093, and lastly 101. It is the 093 that I received from Precision Diesel, for about $42, and the 'pump guy' said that it's been superceded and that's why I got it so cheap. . The 086 had a steel ball pressed into the top to hold in the little spring that holds the check ball, the 093 has a tapped hole w/ a small bolt in it, and the 101, the CURRENT, latest, version looks like the 093, but the bottom hole is made smaller as an orifice to reduce the amount of fuel it will let pass, thereby helping reduce loss of pressure as the spring weakens, (as they all will do eventually do to the throbbing of the lift pump). .

Prelim costs are not completely out of line w/ what I expected

$225 for the #6 BD plate + inst 1-2 hrs

$130 for 3000GSK + inst 2-3 hrs

($170 for lift pump?) + 1 hr) ?



When I get more news later in the day about the cause of my low fuel pressure reading, I will post. . JG

 

[JohnG]

fuel press

Correction. . The throbing is from the P7100 pump outflow to the outflow valve. . and also check my 1st 2 pn's, but I think I got them right. . defenitely the 101 is the current model. . JG

 

[JohnG]

HMMM. . Just realized that with my fuel pressure guage take off point at the (out side?) of the fuel filter, changing the outflow valve won't affect the incoming pressure. . ? Yes. ?? No. . ? So I still might have a bad lift pump? I'm thinking maybe more likely a piece of crud in the isolator, or a bad guage ?? I can't bring myself to believe that I have bad fuel lines as, if the lift pump were putting out 20-25 lbs, but the gauge reads 2 psi. . all that fuel would be coming out all over the place, right?. . (and again, the truck seems to still run fine). . We'll see. . they're starting to work on it right now. . Later. . JG

 

[Joe G.]

First of all you paid way too much for the overflow valve. Do a search on this forum for the valve and who sells it.



Second, the fuel pressure in the fuel supply system is regulated by the overflow valve. The throbbing is from the lift pump.



Third, the lift pump is VERY seldom the problem on a P7100 system. Your original one is probably ok. It's easy to take apart and check out. If no springs are broken. If the piston valve is not skinned up. If the three check valves are ok. Then the pump is good. It's really a simple mechanical gadget.



I've posted the following a few times.



The list of fuel system low pressure problems that can cause a leak and/or low fuel pressure in order of probability is:



Fuel supply and return hoses

Overflow valve spring less than 1/2" long

Fuel heater

Fitting on top of fuel heater

Pre-filter and fuel heater gaskets

Fitting on input to fuel filter

Curved hose between pre-filter and lift pump

Sticking fuel solenoid

Lift pump O-rings

Lift pump



You may have a faulty gauge so you need to check the fuel pressure with a another gauge. Best to use a mechanical gauge for that. Too bad you are not closer to where I live.

 

[JohnG]

Joe. . I got the overflow valve from a search on TDR. . From Precision Diesel Injection at the price I read in TDR. . and I got the superceded valve from them. . for about $45 total. . I sent it back. It would prob have worked just fine for a long time, but what the heck. . I don't mind paying $75 for the 'newer' valve from my shop guys... . Just a drop in the bucket compared to the rest of the $$$ I'll be spending there. Should hear what's what by the end of business today. . JG

 

[Joe G.]

Big money saving tip. Find the problem before you fix it. Just throwing parts at it until the problem goes away costs big bucks and if you didn't guess right the problem is not fixed. Most of the time on a 12 valve the problem is pretty cheap to fix once you find it.

 

[JohnG]

I agree with you, but the overflow valve seems like one of those things that get worse over time anyway and prob never been changed, and it wasn't that much money for the piece of mind.

NEWS... Just talked to the shop and while the overflow valve was poor, (and now replaced), the problem was a bad isolator !! 25 lbs in and 2 psi out! (Maybe they installed it backwards?? I'll call Hewitt tomorrow). Don't need a lift pump. Kinda glad I stayed on them about that. I have read some pro's and con's about using an isolator, but they said they've never used them and I have a sneaky suspicion they had diesel fuel in the line to the guage anyhow. . (humph). . anyway, they just removed it and all's well. I wouldn't mind hearing some more tips on that one. I'm thinking I may need a 'snubber' or orifice, or some such to dampen the pulses to the guage? We'll see what it does tomorrow.

They've got the #6 plate in and are starting on the 3000GSK. Truck should be finished tomorrow.

Also re-reading last few days reminded me about the banjo fitting and I seem to recall buying that part (over 6 mo's ago), w/ the special? bolt and it should have been in the box I gave then w/ all the other stuff, but they didn't use it, instead hooking into the top of the fuel filter (There's an outlet there already?) I only glanced at the hook-up. Any more info on why to use the banjo? Thanks for all the help guys. . specially Joe G. . JG

 

[Joe G.]

The banjo bolt is better. It's out of the way and won't be accidently damaged. The threads in the fuel filter output are not standard so you have to have a special fitting. If you manage to damage it then you have to find the proper fitting to use. The plug that is supposed to be in that fitting is used to bleed the fuel filter. If you have a pressure gauge installed there then it's in the way when you want to do that. I drilled and tapped the banjo bolt to 1/8" NPT. You need to install something to protect the pressure gauge. I tried a snubber. Not enough. Then I added a needle valve before the snubber. The needle valve is closed to start with. Then open it just enough that the gauge barely works. That's the place to leave it. The pressure spikes from the lift pump will kill a mechanical gauge or sensor for an electrical gauge in a short time. My set up is: drilled and tapped banjo bolt, needle valve, snubber, grease gun hose, T fitting, 10 PSI marine alarm sensor on one leg of the T, sensor for the pressure gauge on the other leg of the T, and a Westach 40 PSI electronic pressure gauge. This has been working fine over 200K miles. The marine alarm switch was added sometime after the original gauge installation. I have one on my lube oil too. If either fuel or oil pressure 10 PSI or lower it turns on a big red light on my dash. I know it works because everytime I start it the red light is on until both pressures are up.

 

[Joe G.]

Oh, I forgot. The stock '95 overflow valve is easy to fix if nothing is broken. What happens is that the spring gets tired and too short. You can stretch it back to specs (a little over 1/2" - . 550") if you are careful. Overstretching it wrecks the spring. My overflow valve is the original. My fuel pressure is about 20 PSI or a little more at idle. It runs in the low 30s most of the time. In some situations, it will peg the needle in my 40 PSI gauge. If the overflow valve dies again I will get a new one. Until it does I will keep using mine with the stretched spring.

 

[JohnG]

Thanks. . That's what I needed to know. That's a great set-up with the idiot light. (You got 2 lights, or one bulb run by both oil and fuel?). I just sent you an email on another topic, but could you tell me where to get the marine alarm sensor, and the snubber? Thanks. John G

 

[biggy238]

I hate to hijack but this is along the line of the thread. When I replaced my filter this last time i've lost a few psi. Thottling before the transmission locks up can pull it down to 16psi. I'm going to check for air leaks when i'm well again, but I would like to see a picture of the hose that runs, I think, from the lift pump to the fuel heater. It's a larger diameter hose that makes a right angle. I don't like the shape mine is in. It looks like it is folded enough to be restrictive. If anyone has a picture I would appreciate it. If I don't find a resolution for my pressure problems, i'm going aftermarket with a system.

 

[Joe G.]

Is this the hose you mean?



#ad

 

[Cooker]

It looks like it is folded enough to be restrictive. If anyone has a picture I would appreciate it.

The hose has a 90 degree bend in it, obviously. I replaced mine recently with the part from the Cummins dealer which has a premolded 90 degree bend in it so as to not restric flow. It is not just a straight hose bent to a 90, which would restrict the flow some IMHO.

 

[biggy238]

Yes Joe, Thank you.

The hose has a 90 degree bend in it, obviously.

I'll take that as being meant in a constructive manner.

It's a larger diameter hose that makes a right angle.

Ah yes, I thought I was quite aware the it was 90*- obviously. :-laf



How restrictive it would be in it's natural state on the other hand, I needed some insight toward.

 

[Joe G.]

Kyle,



The hardest air leak to find I have found in my fuel system was the fuel heater. It actually is very easy to test. Take it out and see how the truck runs.