I Think I Know Whats Wrong, Help Me Confirm It Please
 

well this problem has been getting progressively worse for the last 2 weeks ever since I got a tank of my buddy's "awesome biodiesel" now this isint a first time bio has been ran through my truck, normally I run b20 blend that I buy locally and on occasion I make my own and blend 50/50, never the less my truck has really started to lack in power above 1800 rpm for extended periods of throttle input... if I stomp on it out of the hole it is fine through 1st and builds 36# boost but when it shifts to second I loose boost down to 7-8# and when it kicks into 3rd I have nothing and the truck is running like shit with absolutely no power and it starts to slow down... lift off and wait a few seconds and then I can make 15# boost for about 3-4 seconds I give up"give: I have changed fuel filters 3 times in the last 1000 miles with no difference, if you open the water drain it seems to pump out a decent stream, the lift pump was replaced at 92k and I have 100k on it now (bought it with 95k on it) I don't have a adapter to check the fuel pressure but I am going to make one tomorrow to see because I am 80% sure the lift pump is dying a slow painful death.... what is a normal pressure for a 12v at full load? a friend said 15psi but that seems like alot for a mechanical pump

am I missing something incredibly stupid or am I on the right track? :sigh: I mis my 7.3 IDI:se:

hmmmm... could be the lift pump. have you cleaned the pre-filter too? mine got clogged up and i lost a ton of top end power.

http://dodgeram.org/tech/dsl/filter/pre-filt_clean.htm

your lift pump pressure should be at least 17 psi at idle and at least 25 psi at 2500 rpm.

take a read here too:

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

Incorrect Johnny....lift pump pressure at the inlet of the injector pump should be minimum 23-35 psi or so for a healthy lift pump. I highly doubt that the lift pump is the problem here. These are mechanical lift pumps and they do not wear out like the electric ones used on the 24V trucks.

As Johnny said, have you cleaned the prefilter? Also, it might be an idea to change the overflow valve if youve never done that.

I agree with regard to pump pressures along with the Doc. I run my pump with 45 psi of inlet pressure at idle, which drops off to 30 or so full throttle. I am going to enlarge all the fuel lines to keep pressure up better at power. Not many people talk about inlet pressures on 12 valves, but it's just another area of fine tuning that can return great numbers as well as ensure plenty of fuel for injection as well as lubricity if you're running garden hose injectors, DV's or high flow pumps.

But that's another post. Overlooking the pre-filter is a common practice as most don't even know it's there. It could definitely be a contributor, especially running bio which keeps cleaning the tank for a LONG time after switching to it. I completely removed my pre-filter, as well as the fuel heater pod. If this is the chosen path for anyone else, however, you can't just put the pump back on. Part of the bracket that makes up the pre-filter/fuel heater actually goes between the pump and block and is about 3/16" thick. You have to either cut this portion off the assembly and re-use it, or fab up a spacer in its place. If you put the pump back on without accounting for the lost space, bad things might happen bottoming out the plunger! Now maybe this isn't true, and the pump can absorb the difference, but I didn't want to find out...I err'd on the side of caution.

I have never had my pick-up module out of the tank, but maybe someone who has can attest to whether or not there is a screen on the draw straw or not...might be another suspect.

Are your EGT's falling off as the engine lays down, is there any smoke ie blue black grey etc?

Chris

well I went to the local cummins dealership today and paid the $10 for the screen and oring kit and the guy there said that it was most likely the screen being full and he recommended just taking the screen out and putting the bowl back on but I dunno about that:booo: as far as EGT's go they do indeed fall off some but if I keep it floored after about 15 seconds I get a light blue haze and the EGT's come up a little bit, the wind has been fierce blowing crap around so I figured I'd mess with it tomorrow, I'll post back

There are actually four "filters" in our fuel systems. I found this out this summer traking down the hard start demon. There is the main filter, the heater prescreen filter, a screen on the bottom of the pickup assembly in the tank and the secret screen i found inside the pick up assembly. I seperated the pickup assembly to check on the pick up tube condition and low and behold there was another screen on the pickup tube. So you may want to drop your tank and check the screens out due to the cleaning action of the bio.

I may be wrong here, but I thought in these older trucks Bio would break down the seals in the system. The material they are made out of aren't compatible with Bio.

I have had no issues with my truck while running bio neither has the guy who makes it and runs it in his '95.

You are running a mix arent you?

Yeah but it gets pretty close to B100 at times and Dave runs B100 in his as much as he can, course the cold weather will be changing that pretty quick.