surging engine, dies, starts, dies again - help please!

[AKMooseMan]

Hi all – once again, I find myself in need of assistance from the cyber-diesel community!

The problem I’m experiencing is fuel delivery, and I’m hoping it’s simply the lift pump, but suspect it may be a little more drastic. Following is a description of what I have, what the problem is, and what I’ve done to-date. As I’m beginning to test the limits of my normally very understanding wife, any suggestions would be greatly appreciated

The Truck - 1984 GMC 3+3 4x4 converted to diesel 4 years ago, 1991 “J” 6.2, 18:1 compression, DB2 injection pump, and Banks Turbo. Two fuel filters, OEM (located on the back of the intake manifold - what a pain to get to for changing!) and a Racor R60S. The racor filter is primary (fuel enters it first) and the OEM is secondary. Mechanical lift pump.

The Problem – From a normal running condition, the engine will begin to surge in gear, in neutral you can see (and hear!) the RPM jumping by a good 1000 – 1500 RPM. It will do this a few times, and then the engine will die. Let it set for 3-5 minutes and it will start back – sometimes with only a few cranks and other times with a lot of cranking. After starting it may run for 3-10 minutes and then surge and die again, or it may die right away.

What I’ve done so far – This is the second time I’ve had this problem. The first time was about 6 months ago (and it was about 50 degrees warmer as well). I had a small fuel leak in one of the fuel lines, and I hadn’t changed filters in quite a while. I replaced the leaking fuel line, and also changed the R60S fuel filter (no sign of water in fuel). I did not change the OEM filter at that time. After making those changes, everything ran great…till two weeks ago.

The exact same symptoms started again two weeks ago. After limping home, I changed both fuel filters and looked for, but didn’t find, any fuel leaks (thinking possible air in fuel lines?). After changing the filters and dealing with an air lock in the lines (changed both filters at same time…oops!), all ran well for a week.

Last week the exact symptoms started again! I managed to get home, but haven’t moved it since.

When I changed the filter this last time, I did notice some particles in the filter bowl that suggested possible corrosion in the fuel tanks. There wasn’t a lot – just enough to notice it. I don’t think that the new fuel filter would have clogged that quickly…but it’s possible. I’m also not sure what I have in the fuel tanks at the inlet – there may be a filter (i.e. bag on end of pickup), but not sure – they were originally gas tanks before the conversion to diesel.

What I’m looking to do next – I suspect I have corrosion in the tanks, but do not like the prospect of dropping the tanks (no way truck would fit in garage…it’s ranging from 10-20 degrees at our place this time of year). I guess it’s also possible that the mechanical lift pump is failing...my next steps are to install an electric lift pump and see the results. If the results are the same, the next step is to drop one tank, inspect, clean…hopefully not replace, but we’ll see! After dealing with the one tank, I’ll disable the dual tank switch and run off the one tank until the problem is resolved.

I did just read the “finding air” sticky…I will give that a try as well – wouldn’t it be nice if that was all it was

As always...THANKS All!
(Oh yea...Happy Holidays!!!)

[john8662]

Sounds like a textbook air problem to me, for any number of reasons.

#1 duty, get yourself a clear line installed on the return side of the injection pump. Time to watch for bubbles while running. When the engine starts to surge, you'll see the bubbles.

Also, an air leak will show it's face while sitting overnight too. When you shut down the engine (running normally) fuel should say in the clear tube, overnight, for weeks even, longer if things are good.

If it's drained overnight, you for sure have a leak somewhere.

Could be a line on top of the tank, line connections to the tank switch module, etc, etc.

How are you priming the fuel filters? It's possible that they're not primed, especially the secondary.

Which secondary fuel filter do you have, a Big Metal Square one, or a round spin-on filter (back of intake).?

If you're getting prime, the bad lift pump scenario is becoming less.

J

[AKMooseMan]

Thanks for the reply. I tried to get the clear hose, but no luck today. I'll hit our local brewing supply store - I know they have clear hose

I'm not sure it'll run long enough, but that's the first thing I'll try next.

As far as which secondary - it's the big square one on back of intake.

I am getting the filters primed ok, but I had read where the mechanical injection pump can just about handle the lift pump duties as well...so was thinking...or more like hoping probably...oh well :-)

I'll be tracking down the air leak over the next few days hopefully - thanks again for the input!!

Sounds like a textbook air problem to me, for any number of reasons.

#1 duty, get yourself a clear line installed on the return side of the injection pump. Time to watch for bubbles while running. When the engine starts to surge, you'll see the bubbles....

...Which secondary fuel filter do you have, a Big Metal Square one, or a round spin-on filter (back of intake).?

If you're getting prime, the bad lift pump scenario is becoming less.

J

[neo]

Not trying to hijack, but I too am struggling with a similar issue. This is on a brand fresh engine, just rebuilt. Using the 6.5 round filter on the bakc of the intake. I get air in the return at the top of the IP where I placed clear tubing (can get from McMaster-Carr for next to nothing.) When running, there is a continuous stream of tiny little bubbles flowing out of the fitting, occasionally big ones. Thing is it idles pretty well, but under load makes what seems to me like a typical "injector misfire" noise, like a clacking. I believe the system is bled, and when I run the LP straight out of a jar of clean, clear fluid, I still get bubbles. This eliminates the LP back to the tank. So, CAN the LP leak air while running into the system at teh flared fitting where the steel pipe (to the filter and IP) attaches? Can air get into the ssytem in other areas (like around the filter or the input to the IP) while the engine is running, and the system should be under pressure?
Thanks.
NEO

[JohnC]

You shouldn't be able to get air in while the lift pump is running; the lines should be under pressure.

[neo]

Thanks John, That is pretty much what I thought too. Is it possible the flared fitting on the discharge side (pressurized) of the lift pump could be allowing a small trickle of air - these are very tiny bubbles for the most part - in when the pump is pumping? That is about the only connection I can think that could have air.
The engine sounds pretty good at idle, but has that sound like an injector not firing when asking it for power. Thanks again.
NEO

[JohnC]

It would have to be on the suction side. Is it a mechanical pump or an electric one? The mechanical pump could be leaking internally. The electric ones should have o-rings on the fittings.

[neo]

It is the original style of mechanical pump. So it can leak a little on the inside diaphram to let air in on the suction stroke, but not enough to let fuel into the crankcase? If I place some clear tubing between it and the filter, I should see bubbles should I not? The flared fitting I did myself, so it was my strongest suspect, I just could not understand how it could leak on that side since it should be under pressure all the time. Thanks for the help John!

[JohnC]

There should be a weep hole in the pump to prevent fuel from going into the crankcase, but, yes, it could leak on the suction stroke but not on the pressure stroke.