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Old 07-19-2017, 01:49 AM   #1
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1987 bluebird cat3208

I'm new here. I have a converted 1987 Bluebird 40ft with a cat3208 in the back. Everything ran great when I parked it 7 months ago. I have started and moved it every other week since. This past weekend was the first time driving it at speed. My problem is now it will not rev past 2200 rpms. At this lower rev it will not shift into high gear therefore I'm stuck at 35mph on flat ground. Off the line and up to that speed everything seems normal but just won't go past 2200 rpm. At that speed if I shift into neutral it won't rev up at all. Please ask any questions that might get us to the issue.
Thank you

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Old 07-19-2017, 07:26 AM   #2
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Engine is entirely mechanical, sounds like a throttle linkage problem, do you know if it has an air throttle?
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Old 07-19-2017, 08:31 AM   #3
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Year: 1991
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does it smoke at all? maybe the diesel fuel got old and clogged the fuel filters?
-Christopher
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Old 07-19-2017, 09:19 AM   #4
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It does have an air throttle. No air leak. Possibly a crack in the diaphragm allowing air to blow by at the top end of the throttle?

No smoke. Replaced the fuel filter and blew the line out with air to rule out blockage. No change.
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Old 07-19-2017, 01:11 PM   #5
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You need to see if the fuel lever on the engine is being pushed all the way to it's stop when the throttle pedal is floored
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Old 07-27-2017, 11:25 PM   #6
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Latest update:
replaced the air line to the throttle, replaced fuel filter. Was able to confirm that the throttle is opening entirely which leads us to the transmission, Allison mt643. seems to be riding on the governor and will not shift into 4th gear. All shifts prior are smooth and on point. Any ideas on what could cause something to stop working in their over a 6 month nap?
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Old 07-30-2017, 01:42 PM   #7
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Still working on this. I have checked enough things to now believe it might be something with the air modulator. It sounds to me like maybe the trans is not locking up in 3rd therefore won't get to 4th. Does anyone out there have info on how to check, adjust, replace whatever could have gone bad during a 6 month nap?
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Old 08-01-2017, 11:25 PM   #8
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Talked to an Allison transmission guru old timer. He says my cat 3208 must run 2800-3000 RPMs to hit the shift points. I'm not getting near that so I'm back to trying to figure out why. Everything runs so smooth I just don't get it. Under load I'm only getting 2300-2400 in 3rd gear = 35mph on flat ground. Maybe a fuel pump? Can anyone tell me where to find the fuel pump?

Better yet anyone know anyone in Reno, NV. that wants to make some money? I can't even find a shop here that will let me pay them to fix this?????

Any help is greatly appreciated.
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Old 08-01-2017, 11:35 PM   #9
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My first thought was fuel filters, but you say they have been replaced. There may be more than one ... or two. These are probably the number one culprit of low power/loss of top speed. They should be replaced at least every other oil change. They will also probably need replaced after a period of storage and using the old fuel.

My next thought is to absolutely ensure the throttle is moving *ALL THE WAY* to its limit. Not just most-of-the-way.

I can't say for sure, but I don't believe the 3208 Cat engine uses a "fuel pump" as most cars do. It has a mechanical injection pump (and maybe a "lift pump" on the engine). It starts, runs, and idles fine and even does OK up to 35 or so which leads me to think something else may be going on. (Maybe a Cat guru can correct me if I'm wrong?)

Is it possible air is getting sucked into the system? Old fuel lines could allow that to happen. They're OK at idle and low speeds; start pulling a lot of fuel through them and they might let in a little air? I dunno; I'm grasping for straws at this point. It'll probably end up being something difficult to pinpoint but fairly easy to fix.
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Old 08-01-2017, 11:51 PM   #10
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Focusing on the (only) fuel filter I find. This was my very first instinct as to the culprit. I changed the filter, a large spin on like your typical oil filter. Not fully understanding this system, I fired the bus up and she ran great, no change to the top speed limit. So after chasing the ghost for a week and a half I spun the filter off again and realized it was only half full of fuel. So I poured some diesel into the filter to fill it up, re-installed filter, backed off the needle valve at the injector pump and pumped the primer until diesel spewed tightened the valve back down and went for a drive. Still no change to the top speed, or the overall smooth running of the bus. Dropped the filter again to find it was about 2/3 full of fuel this time. Am I sucking air through bad fuel lines? Or is there somewhere else I'm missing? I feel like I get lost in each possibility trying to chase the problem and might be overlooking the simple things.
Again if anyone knows anyone local to me I'll pay for repair!
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Old 08-02-2017, 12:10 AM   #11
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Air in the system will almost always result in rough running. I'm not sure about the spin-on filters but the Volvo I drive has a clear plastic cover over a cartridge type filter. When freshly changed, this filter will have only a little fuel at the bottom; the top being 'empty'. This is normal. As the fuel filter fills and approaches time to be changed, the fuel level will be closer and closer to the top. When it's all the way to the top, and I notice power/performance issues, this is the first thing I check. "Fuel filter full to the top?" It's probably past due for a change. I would expect a spin-on filter to work much the same way.
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Old 08-02-2017, 12:13 AM   #12
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Your bus may only have one fuel filter. Years ago I drove a Ford that had low power issues and took it to the shop for fuel filters. They replaced the 2 on the engine but it did not cure the problem. Turns out there was another underneath, on the frame. Once changed, the problem was fixed. (Yes, this bus had 3 fuel filters).
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Old 08-02-2017, 09:59 AM   #13
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An in-tank filter maybe?
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Old 08-03-2017, 09:38 AM   #14
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you can adjust the throttle cable on your MT643 to shift earlier... the 643 should ghave a cable coming from the side of the transmission up to the throttle.. I dont knwo the CAT. so it might be on the pedal itself or might be on the throttle linkage at the high pressure pump on the engine.. (with an RE it SHOULD be on the throttle at the engine) when your throttle actuates it pulls out the cable in the transmission which firms up the shift quality and also raises the shift points..

if the cable is adjusted too tight it will prevent the throttle from actuating all the way at the engine causing less than full power... it can also be adjusted tight enough that the transmission wont shift when its suppose to.. if itd adjusted too loose then the transmission shifts to high gear too early and the shifts feel weak or "slidey" or "slippy" and not firm or solid..

-Christopher
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