Cat 3306B Power Loss/Stalling

[Cory W]

Hello! I've got a 1989 Ford L9000 dump truck with a Cat 3306B engine in it. While I was running up through the gears the other day, the engine just stopped pulling. It didn't quit outright, but wouldn't accelerate no matter the throttle position. I pulled over and parked, and the engine then slowly dropped below idle and died. I shut off the key switch, turned it back to run, and it fired right back up. No hesitation, ran great! It has done this a couple of times since, but always fires right up after stalling. I have changed both fuel filters, cleaned the fuel tank, and replaced the fuel pickup hose to the tank. I have a transfer pump on order, I have not checked delivery fuel pressure yet. The issue seems to happen at or above 3/4 throttle. Just strange how it will instantly fire back up. Any ideas? Thanks for any help!

 

[d9gdon]

Electrical shutoff switch failing? Check the wiring harness connections.

 

[Truck Shop]

When this happens is it producing black smoke or zero smoke?

 

[Cory W]

The shutoff solenoid seems good, I hear a solid click from it when I turn the key on and off. I cleaned the terminals on the solenoid itself and made sure it has good power and ground. Is it possible for one to partially fail? Once parked in neutral, engine speed slowly drops until it stalls, unlike shutting the key off. I see no smoke once it starts losing power.

 

[Truck Shop]

How many hrs/miles on engine?

 

[Cory W]

Not sure on hours, but it has around 165,000 miles on it. Runs strong other than this issue.

 

[d9gdon]

Is that shutoff solenoid powered through a relay that could be bad?

 

[Cory W]

Yeah it probably is controlled with a relay, I'll trace the wiring once I have it back in the shop. It's kind of annoying, I have a Ford L-series shop manual, but it doesn't make any mention of the Cat 3306 engine.

 

[funwithfuel]

Is the tether chain still on your fuel cap? If not, I'd remove the suction line and standpipe. I'll bet there's trash in there.

 

[Cory W]

So I did drain the tank and clean it thoroughly, kind of convenient that the filler neck is arm-sized lol. I also replaced the fuel suction line, but wasn't able to remove the pickup tube with the tank mounted on the truck. Cap tether is still present. Kind of wish I would've pulled the tank when it was empty and checked that pickup tube now.

 

[d9gdon]

I just don't see it restarting and back to normal so quickly if it was a fuel restriction.

 

[Cory W]

That's what has seemed odd to me too, it fires right back up and runs fine until the next time you get past that certain point in the throttle. Engine load also plays a role. I'm interested to see what it does once I replace the transfer pump, it's a plunger style one driven off the injection pump camshaft. I'll also be able to inspect the steel fuel lines at the same time.

 

[funwithfuel]

So as the fuel draw increases, it pulls whatever is in the pipe up to the elbow where it piles up and restricts flow. Once shut down occurs, junk relaxes and fuel takes its place.

 

[funwithfuel]

That's what has seemed odd to me too, it fires right back up and runs fine until the next time you get past that certain point in the throttle. Engine load also plays a role. I'm interested to see what it does once I replace the transfer pump, it's a plunger style one driven off the injection pump camshaft. I'll also be able to inspect the steel fuel lines at the same time.

Is it the kind you just pump furiously to prime and let it be, or is it the one you gotta lock down when it primes up. Those o-rings do get dry and leak air. The other thing to be watchful of is hidden racor fuel water separators or fuel pro . Those things will also suck air, but usually leave a fuel/dirt residue behind.

 

[Cory W]

I see what you're saying about the pickup tube, I will definitely investigate that. It does have a priming pump, it screws down and locks. Would it be able to suck air screwed down? It does have a water separator, it's factory though. I replaced the o-ring that seals the bowl on it this spring. Thank you for your help, I appreciate it.

 

[funwithfuel]

Worst case scenario, if you don't find any obstructions, you can pinch or plug your return line. Apply 3-5 psi of air pressure to your tank with the vent plugged. This will force fuel throughout the system. Any external leaks that show up are sources of air intrusion. You must be careful when pressurising your tank. It's not designed for positive pressure. It will oil-can or knock rust off and leak, so be extremely cautious.

 

[Cory W]

Great idea about pressurizing the tank, I will give that a try (carefully).

 

[Cory W]

Can anybody tell me whether the injection pump on this 3306 is a sleeve or scroll metering type? Engine serial number is 63Z14319. Thank you!

 

[d9gdon]

If it's like this one, it's a scroll type pump. I think they call it new or improved scroll type pump. The old scroll type pumps from the 60s and 70s were much narrower.

Another look at it from one on Ebay:

 

[Cory W]

Okay, update time. So I got the truck in the shop this morning. First thing I did was pressurize the tank, regulated at 6 PSI. Everything held pressure, soap tested all connections and the bowl on the primary filter, no leaks I can see. I just got done testing delivery fuel pressure to the pump, has a solid 30 PSI at idle, which I believe is within spec. I'm going to pull the supply line off of the primary filter housing and place it in a bucket, then apply pressure to the tank and see what I have for flow from the tank. I was kind of hoping I'd see low delivery pressure. I have a new lift pump coming tomorrow, I think I'll go ahead and install that anyways. Any more ideas? Thank you everyone for the help so far!