Diagnosing the DB2 pump

[shadpeters]

Thanks Jozseph, I am reading through that and its already given me a wealth of information that I did not have before, and I'm just getting into it.

Quick update: apparently I am to dumb to use the fancy fuel pressure gauge rental from o'reiley, or its broken. anyway, I tried using that gauge on my suburban (a known working vehicle with the same engine) and it read 0 psi as well, so clearly i was doing something wrong. So I went and bought one of those super simple vacuum/fuel pressure gagues. Here is what I found: when I attached the new pressure gauge to my suburban and cranked it over it immediately jumped up to 10 psi and stayed there. by contrast, when I hooked it up to the M1008 after a quick crank of a couple seconds like it did on the suburban it jumped up to about 4 psi, if I cranked it a few seconds longer it would jump up to 5, and the 6, kinda of in little bursts. It also would not hold preasure, within a couple of minutes it would bleed back to 0 psi. The measurments were all taken at the fuel filter outlet, and I ran the gauge up to do windshield so I could watch while cranking.

Also worth noting, there is a connection on passenger side wheel well, where steel fuel line transitions to rubber fuel line that runs to the lift pump, and it appears to have been leaking a bit. If I preaurized the system up to 4 or 5 psi on the gauge, I could walk over and watch a very slow drip on that line. I'm sure thats no good.

I also found earlier that if I ran a clear plastic hose from the fuel filter house outlet into a bucket, and observed the hose, there were tons of air bubbles in it. One Air pocket in the hose was probably 3 or 4 inches long, and there were bubbles all throughout the length of it.

The lift pump is so hiddent behind the cross over pipe for the turbo, and other cross members that I really can't get a good look at it, but it feels pretty dry and I don't see a bunch of fuel dripping down from that area or anything like I did when the lift pump went bad on the suburban, but I suppose it could be bad internally. I hate the idea of changeing the thing cause its so hard to get to. I think I'd rather go to an electronic lift pump than to try and get that old one off.

Seems to me that regardless of whatever other problems may be preasant, even if there is something wrong with the IP, that I have an issue with air getting into the system.

 

[AECS]

it sounds like a lift pump, HOWEVER now you mentioned a turbo... That should change everything. Do you still have the factory lift pump? most commonly it is removed to add the oil return from the turbo. An electric pump is usually put in line back by the tack to handle the duties of the remove mechanical pump... The plot thickens.

 

[richingalveston]

the banks manifold allows you to keep the stock lift pump. the only problem is it makes it even harder to change. probably have to remove the crossover to get to it. The oil return line can be ran to a fitting in the oil pan.

It is the lift pump, then possibly the filter base.
fix the lift pump first then get system primed good and then check for bubbles. get that leak fixed it will allow it to suck air.

that leak plus a partially clogged tank sock will cause similar problems to what you have.
so fix. leak. change pump and retry.

 

[Skinny]

Sounds like you should start at the fuel tank and work your way to the IP replacing everything along the way. It really is the only way to gain reliability in an old truck. All it takes is one old hose or bad clamp to wreak havoc.

 

[Thomas_G]

I put an Airtex 8135 electric pump on mine and it cured my hard/no start issues.

 

[Skinny]

I put an Airtex 8135 electric pump on mine and it cured my hard/no start issues.

Not really, it is just masking the root cause.

 

[shadpeters]

The Saga continues.....

So, here is what I found out today- I can actually get the truck to run, but I have to get it well primed first- this thing is definately sucking a ton of air. So, I had a big filter sitting around like what you would put between a tank and a transfer pump, I figured I would throw that on there just to eliminate one more variable so I bypassed the box filter completely. I also used an extra two foot section of hose between the lift pump and the filter that was clear so I could watch the fuel. This was the first time I have been able to get it running in over a month, so I was able to acutally observe the fuel while running, what I found was that once the initial few spurts bubbley airated fuel ran through the clear line there was not a bubble or air pocket to be seen anywhere coming up from the tank- so I don't believe its sucking air while running. However, as soon as I shut the truck off I can watch it start bleading backwards and sucking air somewhere. I also noticed today after I got it running that the front drivers side injector was a little wet after running. Also, there was a piece of clear line for the return on this injector, and I could watch the air bubble running through it was well. I took a video of it, this is right after shutting the truck off, and when I touch the line you can see bubbles running through it, and if you listen you can almost hear it sucking air as well. its looks like who ever put that section of line on just twisted some wire around it with pliers, so I'm gonna get some proper clamps and see if that helps.
https://www.youtube.com/watch?v=Usoxq0XXt4Q

I don't really know anything about the return side of the fuel system, but I think that might be where my problem is. I'm gonna have to read more through the manuals that jozseph posted a few days ago.

I also, I follow the lines from the tank clear up to the engine bay, and besides the one spot I noted the other day I found no other signs of wetness or leaking fuel, and the steel lines look really good, most of it doesn't even have surface rust. a couple spots had a little surface rust, but were over all in really good shape.

 

[richingalveston]

There is a check valve on the IP that is supposed to keep it from draining back if everything is air tight between the fuel pump and the IP. The valve is probably dirty but your filter base is definitely got problems. I would do the spin on mod and see what problems you have after that.

that is the return line and I believe it is normal to have bubles there. that is just the fuel that the injector did not need and it gets returned to the tank