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Author Topic: Lack of power troubleshooting guidance needed  (Read 901 times)
Kitt
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« on: April 14, 2014, 07:28:16 AM »

(cross post from another board in case there's a different audience here...)

Hi all-

I'm having a lack of power issue in our '77 Eagle 05 with an 8v71 and HT740.

Here's some more background, and I hope it is either relevant in pointing out an issue or helping rule out something that isn't:

Last summer I removed the high idle solenoid and put in a Jake buffer switch (the old Jake switch never worked right and just sensed the throttle position). Changed the oil, oil filter, air filter, and fuel filters. I replaced all of the fuel lines from just before the primary filter all the way through to the heads and added a priming pump. In the photo the line from the tank goes to an AN fitting AN-10 hose and loops around to the top of a (3/8?) brass tee. That connects down to a Detroit check valve, another tee, and the out another AN fitting and AN-8 hose to the inlet of the primary fuel filter. The tees connect to an Airtex E8153 pump for priming. That pump is a 10-14psi pump, and met the specs of what I could find as being ok to use and not damage the engine fuel pump. The primary filter connects to the inlet of the engine pump with AN-8 hose and fittings. Out of the engine pump, to the secondary filter, and to the engine are all AN-6 fittings and hose.

This first started on a return trip camping last fall. The drive out was uneventful and had no issues. Three days later, about an hour into the 1.5 hour return drive I felt the power drop and had trouble accelerating. Fluid levels were normal, plenty of fuel, no white or black exhaust. When accelerating I felt a vibration after shifting into third gear and a more when in fourth gear.  I drove it the rest of the way home at 30-40 mph.

Long winter, didn't do much with the bus... This weekend I went over the connections and checked that nothing was leaking, oil and coolant levels were good (and hadn't changed since the last trip).

Today I took the bus out for a quick trip to get fuel (it had about 100 gallons in it) and see if the problem was still there. Engine starts normally, no issues. Sounds normal. Driving when cold is ok but seems like it doesn't have as much power as I recall, but nothing really obvious and I hadn't driven in a while. After about twenty minutes of driving I started to experience a lack of power - when accelerating I start to feel a slight vibration after shifting into third gear and a little more when in fourth gear. A few times when starting from a full stop there wasn't much power at all (barely started moving) and then after two or three seconds I would feel more power and accelerate. Back home, I used a temp gun on the exhaust manifold and all cylinders seemed to be within 20 degrees of each other (I checked just after I shut the engine off, if that makes a difference). I checked the primary filter for water/sediment (the Baldwin filter has a drain) and got out what would have been a half-inch or so of really dirty water and then just fuel.

I usually point at the things that changed (buffer switch, fuel lines) when a problem crops up, but the initial run last year was good, so I'm wondering if something unrelated happened and is causing this problem.

I don't have a pressure gauge to test the output of the fuel pump and see if that is working ok. The vibration/shuddering makes me think of fuel starvation. The AN fuel lines should be sufficient for the pressure and volume needed, and I would hope the brass tees and check valve aren't too much of a restriction to cause a problem.

I find it interesting that the problem gets worse when he engine gets warmed up.

Any thoughts on where to start, or probable causes? I was going to try again tomorrow and drive with the priming pump on and see if that helped at all - good idea or bad?

I appreciate everyone's suggestions or comments.
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1977 Eagle model 05
8v71, Allison HT740D
bevans6
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« Reply #1 on: April 14, 2014, 10:44:59 AM »

I think the first thing I would do is check the fuel pressure.  Running the pump shouldn't make any difference.  I pull through my priming pump with it off no problem.  You should have around 15 psi at idle up to around 50 - 60 psi at speed.  I would also change the filters and inspect the air filter, all the usual suspects.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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gumpy
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« Reply #2 on: April 14, 2014, 10:54:29 AM »

A couple things...

First, I may be wrong, but I was under the impression that the check valve was supposed to be mounted horizontally, with the writing up. 

Second, 1/2 inch of water in the filter seems excessive. I think I'd address that first and get the water out of the tank and change the filters.

Third, you said it starts shuddering when in 3rd gear. If you stop then, will the engine rev normally, or does it seem like the engine is starving when
sitting in neutral?

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Craig Shepard
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TomC
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« Reply #3 on: April 14, 2014, 11:34:19 AM »

Check the transfer pump and pressure output. Sounds like the pump is heating up and loosing pressure because of being worn. A transfer pump is relatively cheap. Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #4 on: April 14, 2014, 01:47:24 PM »

Is the transmission oil level ok ?

dave
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1990 mci 102c  6v92 ta ht740  kit,living room slide . home base huntsville ontario canada
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« Reply #5 on: April 14, 2014, 03:19:11 PM »

1/2" of water with the sediment being dirty? Yeah, change the fuels filter(s).

If you can put a stick or rod down the filler neck, there is a water test paste you can put on the bottom of the stick (again, if it will hit the bottom of the tank) and check for the presence of moisture in your tank. Most fuel stations will keep some on hand to check their underground tanks, just ask and I'm sure they will part with a dab or two. I can't remember what the paste is called but it starts green and turns bright purple if there is any moisture in your tank.

The rocking motion of travelling may stir up any built up moisture in your tank.
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Jim A.
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luvrbus
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« Reply #6 on: April 14, 2014, 04:07:28 PM »

The 05 Eagle should have a plug in both tanks to drain the water
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Kitt
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« Reply #7 on: April 14, 2014, 08:20:45 PM »

Thanks for the suggestions so far. I'll go get a pressure gauge to see what's going on with the pump, check the filters, double check the transmission fluid level, and look for the fuel tank drains. We're supposed to get snow tomorrow so it might be a couple of days before I get out to try things.
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1977 Eagle model 05
8v71, Allison HT740D
luvrbus
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« Reply #8 on: April 15, 2014, 04:56:31 AM »

The pickup tube has a screen on the end in the tank use air and blow through the pickup line before draining and the crap will drain out most of the time 

Check the return line also if the fuel gets hot they lose power in a hurry but yours seems to be water and crap
« Last Edit: April 15, 2014, 05:53:09 AM by luvrbus » Logged

Live each day like it was your last,one day it will be
Kitt
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« Reply #9 on: April 29, 2014, 04:32:38 AM »

Hi all. An update on where I ended up... I drained a bit from the bottom of the tanks and got some dirty junk (a little water and some fuel/dirt/junk mix) out. Added some "Clear-Diesel" and "Bio Kleen" to the tanks (half to each side). Ran my electric priming pump for a while to circulate the fuel a little, then changed the primary and secondary filters. The secondary filter was clean, but the primary filter pleats were covered in sludge when I cut it open to look.

The transmission fluid level was good, btw. The air filter was still pretty clean too (only changed it just last fall and didn't drive much).

I took the bus out for an hour drive (each way) to get new tires and it seemed to drive fine.

Assuming that was the whole problem, I got an experience in diesel that has sat around for a few months. I can see the advantage in having a Davco fuel filter and being able to see the element inside. In the future I'll be making sure I add something to the tanks to keep this from happening.

Thanks for the recommendations, everyone.
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1977 Eagle model 05
8v71, Allison HT740D
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