funwithfuel
Senior Member
So when it's bogging down, is it still running because the running gear is turning via the clutch engagement. If you were to push in the clutch , would the engine recover or fall flat?
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Mobiltech
Senior Member
I would lean towards it either being a fuel shutoff problem or an internal governor problem. The governor flyweights on these can wear into the thrust washer and cause the rack to stick. Usually causes more erratic rpm problems though.
Most of the 3306 engines can be run with the shutoff removed and capped then just shutoff with the throttle linkage. You could try that to eliminate a shutoff problem.
The blocked fuel line idea could cause it too but I think you have covered that. Can you run it down the road with a fuel pressure gauge run into the cab?
Most of the 3306 engines can be run with the shutoff removed and capped then just shutoff with the throttle linkage. You could try that to eliminate a shutoff problem.
The blocked fuel line idea could cause it too but I think you have covered that. Can you run it down the road with a fuel pressure gauge run into the cab?
Truck Shop
Senior Member
My thought is if it's a fuel shut off solenoid-it wouldn't slowly die. Normally when the
solenoid take a dump-it's engine off right now. I've had those were I just cut the rod
off and screw it back in to get it to the shop.
solenoid take a dump-it's engine off right now. I've had those were I just cut the rod
off and screw it back in to get it to the shop.
Cory W
Active Member
First off, I want to say thanks to everyone again. Really helps being able to bounce ideas around. Yes the only reason the truck stays running is because it's coasting with the clutch engaged. If I push the clutch in, the engine will slowly die out. I think a bad fuel shutoff would cause a more instant shutdown too, but I'm planning on removing the solenoid and driving it. I will also run my fuel pressure gauge up where I can see it while driving. I'm currently working on swapping the fuel tanks around due to a pinhole leak I discovered during my pressure test (oops). With any luck I should be able to drive it today yet. I will report back with any news
d9gdon
Senior Member
Yes, either the switch is good or it's bad.
But if he has intermittent low voltage from bad relay, uninsulated wiring touching somewhere, poor connection at source (he said he checked termination studs), sudden high resistance...or intermittent loss of ground?
Is the engine or transmission moving around when it gets in a good pull and rubbing on the shutoff wiring? Is the engine ground strap connected to the frame and/or cab?
I think it would be best to remove the shutoff and road test.
Truck Shop
Senior Member
I have a new fuel shut off solenoid on the shelf, using a old heater motor
rheostat switch and digital meter it operated every time the voltage raised
to 9.9 to 10.1 volts. That's this one, I can't say it would be the same for all.
rheostat switch and digital meter it operated every time the voltage raised
to 9.9 to 10.1 volts. That's this one, I can't say it would be the same for all.
That's the way to do it.
Cory W
Active Member
So I didn't get to drive the truck today, swapping the tanks around and cleaning everything ate up more time than I would've liked. But everything is set for tomorrow; fuel pressure gauge plumbed in and truck starts and runs. I'm going to go for a baseline ride to verify the issue is still there (wishful thinking) and check fuel pressure. Then I'll remove the shutoff solenoid and see what it does. I know I'll lose oil with it open, any suggestions on how to close it up? Also, Mobiltech mentioned shutting it off with throttle linkage, pushing the linkage in the idle direction will kill it?
d9gdon
Senior Member
Just make a temporary blockoff plate out of some scrap steel. Use a long temporary stud in the back of the pump for ease of reinstallation of the plate and later the switch. Sometimes those switches are hard to get at.
Just put it in high gear and let out on the clutch to kill the engine without the shutoff switch.
Just put it in high gear and let out on the clutch to kill the engine without the shutoff switch.
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Cory W
Active Member
So I finally went for a ride this morning, problem is still present. Engine runs great under light to moderate load. Once I get up to seventh gear (8LL transmission) if I go beyond 3/4 throttle and put a load on the engine, it loses power. I can lightly throttle all the way up to the governor in 7th or 8th and be fine, so it's definitely load related. Just to be clear, the truck is empty, just moving itself. Tried removing the shutoff solenoid, no change. Fuel pressure at the secondary filter sits right around 30-35 PSI, no change in pressure once it loses power. I'm going to remove and inspect the steel lines to and from the lift pump, and change the lift pump while I'm there. I might even pull the filter bases off and inspect them as well. Looks like persistence is key on this one.
Cory W
Active Member
I also plan on replacing the diaphragm in the air/fuel ratio control once I get gaskets. I know it's most likely not related, but should really be fixed as well.
Mobiltech
Senior Member
Sounds a little strange but I think it’s heading towards a sticking rack or governor issue.
One other thing that crossed my mind is a possible intake air hose collapsing and acting like a positive air shutoff. Is there an air to air aftercooler on this?
Is there a hose before the turbo that could collapse?
I had a 3304 in a hoe years ago that under load would collapse the intake hose and kill the engine. It would start right back up and run okay until you loaded it heavy.
One other thing that crossed my mind is a possible intake air hose collapsing and acting like a positive air shutoff. Is there an air to air aftercooler on this?
Is there a hose before the turbo that could collapse?
I had a 3304 in a hoe years ago that under load would collapse the intake hose and kill the engine. It would start right back up and run okay until you loaded it heavy.
Cory W
Active Member
It does have an air to air after cooler. Good suggestion about the intake hose, I had to go and look! It's a plastic molded tube from the air cleaner to the turbo inlet, doesn't look like anything that could collapse under vacuum. I'm not very savvy on how the governor or fuel rack operates so forgive me if you would. The rack is always trying to add more fuel, and the governor pushes back against it to limit fuel depending on rpm/load?
Cory W
Active Member
I changed the fuel lift pump out this afternoon and cleaned/checked the steel hard lines going to and from the pump. Drove the truck, problem is still there. Looks like the new pump gave me a small bump up in pressure, sits around 38-40 PSI now. I've got parts on order to fix the AFRC, not holding my breath though. If that doesn't do anything, I might look into the governor/injection pump. I might also just drive the thing, I've used it all summer and it still runs great besides this problem. Oh well, happy Friday!
Mobiltech
Senior Member
The rack won’t do anything on its own. It stays wherever the governor weights put it. When you step on the throttle you are compressing a spring that is fighting against the flyweights to give the pump a higher rack position. The higher the engine rpm goes the more centrifugal force the weights generate until they overcome the governor spring pressure and push the rack back towards less fuel. There is a thrust washer and bearing between the weights and spring that can get worn and cause the weights to stick. When the thrust wears the engine starts to run like a wound up rubber band as the load comes on it just drops rpm until it stalls because the weights can’t react to keep a steady rpm.
If left too long it will run away at some point.
The governor can be disassembled on the truck to inspect the weights and washers but it is easier on the bench. The trick is to find someone who has had one apart then it’s not really a big deal.
Truck Shop
Senior Member
Isn't there a Cat tool group for this pump?
Mobiltech
Senior Member
Nothing special is required for the governor end of the pump. It runs in engine oil. A 7/16 socket gets most of it apart. Its knowing what to look for when you're in there that takes some experience.
The special tool is for plunger and barrel removal which you would want the pump removed for.
Truck Shop
Senior Member
I'm thinking 3406 I guess.
Cory W
Active Member
Thank you for that explanation Mobiltech, that helps me picture it a little better in my head. I don't like tearing into things without understanding how they operate first. I ordered a service manual for the 3306B yesterday, so that should be helpful as well. We'll get to the bottom of it eventually!
Coaldust
Senior Member
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I’m thinking it’s a governor issue, as well. The slight wear required in the flyweight assembly to cause that problem is so subtle, it’s difficult to detect unless a experienced Cat guy points it out.