Just south of Seattle my 671 with Spicer 4sp began "missing" about every four or five minutes yesterday after 3000 mi of faultless operation the past week.
It acts just like it has passed a small bit of water in the fuel which has happened a couple of times over the years but always stopped after once or twice.
I added fresh fuel thinking that would help but, if, anything it got worse.
My next move is to change fuel filters but fuel filter clogs usually just reduce power and don't cause "missing".
One thought is that there is an electrical problem in the fuel shut off circuit, maybe a wire grounding out when moving? I doesn't happen at rest and idle.
Doesn't seem to be any worse when pulling hard.
Injector??
Please feel free to diagnose!!
All ideas accepted!!
Air leak? Might want to pull the return line and run it into a container to see if you get air bubbles.
Good luck
Don 4107
Hi Gus, if you want to simplify things remove the control wire from the skinner (or whatever it's called) that way you can bypass all the wiring from front to back, especially the rear engine bay switch panel. WOuld be a weird short to "+" but could be. Let's hope it's that simple.
Zub,
Good idea. Power keeps the air valve closed, any momentary interruption of power could cause the air valve to open and shut off the fuel.
I hope it is just a loose wire somewhere in the engine compt, maybe at the rear engine control switch panel or on the shut off valve itself.
I can't do anything now because of weather but was hoping for a bunch of ideas to get my brain going!
Had similar problem a few years ago with my '04. Turns out the Racor water seperator drain plug threads were a bit buggered-up and allowing air to suck in, which caused the motor to "hiccup".
We were just leaving for the coast for our customary anniversary get-away when I decided to drain any water off the Racor. My wife said, "why'd ya have to screw with it ten seconds before we were ready to leave?!"
It was the weekend and the local truck supply house was closed. I couldn't find anything to thread into the Racor plastic bowl. I was getting desperate! I phoned a friend and asked if he could think of anything. He cleverly suggested an "expandable plug", the sort of things plumbers use to temporarily plug a pipe to check for air/liquid tightness.
I picked one up at the local hardware store, plugged-up the Racor and away we went. I actually ran that thing for a few months before finally purchasing a replacement Racor bowl.
Maybe, as Don 4107 suggested, it is an air leak somewhere.
Good Luck!
Bus Boy
Hi Gus. I hesitate to ask, but did you find the problem?
zubzub could have the answer, I had the same thing happen on one of my Kenworths. Bad electrical to the air valve, caused much excitement pulling up out of Leavenworth one night. Hope it's simple, Gord
I had a similar situation with my 8V92, and I finally found that it was a 12 volt accessory connected at a point where the device's start-up draw affected the input voltage to the ECM, causing what I called a hiccup.
If you know an electronic geek as a friend, have them monitor the 12 volt input to the ECM and see if there is a short voltage drop.
Another idea is to turn off every accessory, or perhaps you can remember what was turned on just before the problem began.
My problem I found purely by chance, because I turned the small inverter on while I was in slow idle, which are conditions that I have very seldom.
Hope this does not gives you something else to be frustrated by.
Your ecm is probably ok.
John 4104 as simple as it gets!
If by ECM we are talking about Gus's brain, I'm guessing it's fine. It's one of the older models, hardwired and time tested. :D :D :D
I was not saying the ECM was bad, only a momentary flicker in voltage (12VDC) to the ECM could, as it did in my case, cause a hiccup in the running of the engine.
The voltage flicker could be being caused by something totally unrelated.
I'm just joking around PCC, Gus has a 4104 with no ECM.
My ignorance is showing - And I thought I was being helpful !!! ???
Well, actually you have all been helpful. Please keep it up because the more ideas the better.
I haven't gotten into the problem yet because of steady rain and my granddaughter's graduation festivities. Since we will be here a while I will wait until the whirlwind calms down a bit before getting into it.
Supply fuel air leaks are a real possibility because it is a mechanical suction system but I'm going to attack the electrical part first.
I'm now even suspecting the engine run toggle switch on the panel because I've had three of those original switches fail in the past two years.
I don't really understand how the fuel return line could cause this problem but I'm willing to learn??
My personal ECM is probably the weakest part of the whole system!!
Keep the ideas coming and I'll be sure to post the outcome once I get into it.
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Gus,
I had a bad toggle switch for the main that made lose power and recover. It seemed to be happen most on acceleration, but that could be that it was just more obvious then. I think I decided it was the switch because I remembered one of the contactors wiggled the last time I had looked under the dash.
I was told by a local electrician that we should be using switched rated for DC. He said those that are only AC rated will pit and fail more quickly. This may not be the problem this time, but keep it in mind that next time you change a switch. We actually want some of the stuff we turn on to stay that way for a while.
Dallas,
I don't think it is filters unless it is an air leak at the primary filter on the suction side.
I've had clogged filters before and they didn't cause momentary power loss, they caused a slow, steady loss of power. I really don't want to get into the fuel mess until I eliminate electrical.
I suspect the switch because I've had a few fail in recent years.
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Quote from: Now Just Dallas on June 01, 2010, 05:21:40 PM
Gus, that's my point....
IT could be a bad gasket on the fuel filter, either primary or secondary. Ask BK how we know this! :D Except his died on a two lane road with no shoulder about a half mile from home.
My choice in looking for Detroit problems is always the fuel first, electrical second and air third.
Dallas is correct we had a filter problem in a very bad location in between 2 hills on a country 2 lane no shoulder and average rednecks speeds of 60-65 mph in a 45!
On top of that I was dressed up in my driving attire and not about to crawl under the bus before going to pick up my group! (was also the very first trip for "Suzy" my at that time newly acquired Garmin 7200. Which after I got out on the open empty interstate on my way to pick up my group, erroneously showed me running 93 mph while "making up for lost time!" I know it was erroneous as the bus was governed at 78 mph by the DDEC! ;))
;D BK ;D
Gus if you think it might be electrical and your shut down cylinder is similar to my 8V then just loosen the bolts on the shut down cylinder and move it to the side so it can't push on the shut down lever. If it still hiccups, look to the fuel system. To shut it down you will have to push the shutdown lever by hand.
The reason I suggested running the return line into a container and checking for air bubbles is any air leak on the suction side of the fuel pump, fuel lines and primary filter, will show as bubbles in the stream of fuel.
Good luck
Don 4107
Thanks again to all.
It will probably be at least a week before I can get to it but I promise to post the results.
The way the weather has been so far, it might be August before you will get to it! ;D
I was able to do some checking and found the primary fuel filter top bolt loose. This is the original stacked disc filter. I changed the gasket just before leaving home so I'm hoping this was the problem
I don't have the bus in a location that allows engine testing but this may be the problem. I really can't even spend much time in the engine compt without getting into trouble with neighbors, this is not like being at home on the farm!
I also checked the engine run switch by jiggling the panel and watching the voltmeter but it showed no movement.
After tightening the primary fuel filter can bolt things got better.
It gave a some trouble the first day on the road over Steven's Pass in WA but hasn't caused any problems since. It was only a problem in 4th and 3rd, mostly 3rd, but none in 2nd for about three miles over the top of the pass??
Maybe I got rid of all the air bubbles before I had to shift down to 2nd?
Anyway, thanks for all the ideas - hope this is the last of this problem.
New Subject:Right now I'm spending my fourth day in Livingston, MT waiting for new bolts for the rear air bags. I had all the parts but the bottom bolts turned out to be too short. Seems the early 4104s had different thickness bottom bag bases. I ran across the same thing with rear hub bolts!! Mine is a '54, the second year it was built.
The bad news is the RR air bags still leak down in about five hours vs 1.5 hrs before. This after $400 for replacing the bags and adding plates.
However, we were hundreds of miles from the repair shop when we discovered they still leaked! I'm not upset, it was a heck of a hard job for the guy who had never seen anything like it before.
I'm glad I didn't tackle this job myself after all the problems we had with bolts. When i do the left side I'll know all this ahead of time.
The good news is the new bags sure air up fast!!
The air leak can only be in a few places so all I have to do is get out the soapy water and find it!!