| Author |
Message |
Dennis_johnson (Dennis_johnson)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 24, 2006 - 10:15 am: | |
On my last trip in the bus on three occassions, I went to start the bus and nothing hapened when I pushed the start button. Each time I played with the shift lever taking it in and out of neutral and kept trying. After several tries it would start. I know that I had the lever in neutral because there is a definite click when it goes in. I know there is some kind of safety switch or relay to keep the bus from starting when it is in gear. MY thinking is that there is an intermittent problem with this switch. I can see the switch on the transmission. One wire goes to the starter solenoid. The other is a bit hard to follow but I am guessing that it might go to the start relay in the rear electrical panel.
The only other observation about the problem is that it has occurred always the first thing in the morning and not onother starts even though I typically start the bus 6 or 8 times during a day while traveling.
My question is does it sound like problem would be the switch on the transmission? If so it looks like it would be just a matter of removing and replacing. Or are there other things that should be checked out.
The bus is an MCI 7. The bus was converted 5 years ago from standard transmission to HT740 Allison. So my bus manual does not give any information about this transmission.
Thanks.
Dennis |
Stan
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 24, 2006 - 11:25 am: | |
Whoever did the conversion to the 740 should have provided updated wiring diagrams. At the very least, a piece of paper stating what wiring had been removed, added or altered. Without this information it is almost impossible to troubleshoot the circuit.
You can randomly change parts until you find the fault or else create a wiring diagram. Your possibilities start with the On-Off switch and end at the starter with all the protective circuits in between. If you study your original wiring diagram, you can get a good idea of the sequence in which to measure voltage while someone holds the start button down.
If the neutral switch was simply added in place of the wire from the start relay to the starter solenoid, then it is easy to check for voltage at the relay. However the neutral switch should be in the coil circuit of the start relay along with all the other protection circuits.
Finding an intermittent is harder than finding a total failure but it is easier to find an intermittent in your own shop than looking for a total failure on the side of the road. |
John MC9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 24, 2006 - 6:43 pm: | |
Re:
"nothing hapened when I pushed the start button. Each time I
played with the shift lever taking it in and out of neutral
and kept trying. After several tries it would start. "
Try that same starting procedure without playing with the
shift lever. Does it start after -X- many tries? If so, the
push button may need replacing.
If not, short the connection for the neutral safety at the trans,
and see if it starts every time. If so, there's your problem.
(make sure it's in neutral, tho, ehh?)
Check the simple things first. |
Rob King
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 24, 2006 - 10:12 pm: | |
Hi Dennis
Just because the shifter is in the neutral position doesn't necessarily mean the trans is in the exact neutral position. Over time the shifter cable can come out of adjustment relative to the shifter and trans shift arm so that the shifter says it is in neutral and the trans is just slightly out of neutral, enough so that it won't tell the starter that the trans is in neutral. Unless you have the patience of a saint and are mechanically inclined enough to be willing to take the shifter assembly apart and adjust the cable length then rassemble multiple times, it might be best for a knowledgable mechanic to do the adjusting. This is not meant to talk negatively about you as I don't know what your tolerances are. I spent the better part of two weeks (3-4 hours per day) readjusting my cable after I disassemblied everything to move it into the raised drivers platform just to get rid of this intermittent start problem. I know it is possible to adjust and it isn't hard work just tedious and time consuming. I got it but boy several times I was so frustrated, that I just got up and left the bus for a little time to let my frustration "cool off".
If you need more specific info relative to your problem and decide you want to tackle it, I can help, just let me know.
Rob
91 LeMirageXL
Missouri |
Earl-8-Ky
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 24, 2006 - 10:19 pm: | |
I have an MC8 that I had the same problem. The shift cable was out of adjustment. Take the end off the leaver at the transmission and put the lever in the nutural position. Then try to start the engine. If it starts put the shift leaver in the nutural position and then adjust the fitting on the cable so it will go into the hole on the leaver on the transmission. |
Chuck Lott (Chuckmc8)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 25, 2006 - 6:23 am: | |
Dennis,
The factory neutral relay completes the circuit by establishing the 'ground' (neg) to the relay when the trans is in neutral, thereby causing the relay to energize and allow the start circuit to power the front/rear start button(s).
(the neutral saftey switch just breaks the ground)
I know you don't have the factory setup, but info may prove helpful anyway.
Another thing the neutral relay does: it allows the 'fast idle' circuit to be activated only when the trans is in neutral. For saftey, it should also be included in the neutral saftey circuit.
I hope this helps |
Dennis_johnson (Dennis_johnson)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 25, 2006 - 8:03 am: | |
Thanks for the responses. It sounds like just changing the neutral switch would be premature at this point. I will look into it more based on this information, but may end up taking to a shop. I am not much of a mechanic, but trying to do the easy things myself. |
John MC9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 25, 2006 - 8:35 am: | |
Shops charge by the hour... around here, it's $100 per.
Intermittent electrical problems are by far, the most difficult
to resolve, taking the most time..... (your $$$$$$).
Look for the easiest, most logical things first. Poor grounds
are common on old vehicles, switches wear out, and relays
get weak, pitted, etc..
Chuck pointed out, that the same relay controls the fast idle
via the neutral safety.. You didn't mention any problem with
the fast idle? That could narrow things down a bit...
It's all a process of elimination. You can save yourself some
big buck$, by doing it yourself.
Don't get overwhelmed by the initial complex appearance
of the electrical system... It's all really, very basic. Think "easy". |
Dennis_johnson (Dennis_johnson)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 25, 2006 - 1:27 pm: | |
I'm unfortunately aware that shops are expensive. I am now frustrated that I have been unable to recreate the problem at home to troubleshoot. On one of the occassions when it didn't start my wife was beside the coach and heard the relay in the rear panel which seems to indicate that the problem is not in the push button or other connection prior to that point. I think that mine is not the factory setup described above as the wire from the neutral switch to the started solenoid would indicate that it is not to break the ground. I no longer have a fast idle which was removed when i had a jake brake installed - I don't recall the specifics but it seems there was a very expensive part needed to retain the fast idle with the jake brake. I will keep looking at the system and hopefully be able to find the problem. |
Floyd Lillies (Flois)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 25, 2006 - 10:31 pm: | |
My MC9 has an intermittant starting problem as well ... hard to trouble shoot when on the road. Have had to start by shorting the starter solenoid many times. The fast idle has never been a problem. No loose wires on the starter switch and the solenoids "click" with the key. Once I was able to catch it when it wouldn't start and checked the fuel pressure switch which checked out OK. No amount of wiggling the 5-speed shifter in the neutral position has any effect. Will try some of the above suggestions again to see if by process of elimination I can get reliable starts again. Have learned a lot by reading this board. Thanks! |
Tim Strommen (Tim_strommen)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 25, 2006 - 11:08 pm: | |
When I bought my bus the first thing the Mechanic at the yard did was crawl under the back and manually move the air shifter into neutral. Apparently with the air shift solendoids losing air pressure they would "Give" and push the shift lever just out of neutral (and the transmission's neutral switch must have be dead-center in the neutral detent to allow a start).
Of course after a long non-use soak, the air system is out of pressure and it can't shift back into neutral. I've had to do the same under the bus dance at least three times since I've pickied it up. I plan on replacing the transmission shifter with an electronic variant but that will come later...
Cheers!
-Tim |
Tom Caffrey (Pvcces)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 25, 2006 - 11:44 pm: | |
Floyd, something that could help you. The starter solenoid does two jobs. It engages the starter drive gear with the flywheel and it closes a circuit that lets power reach the starter motor.
In a car, even if the gears don't mesh all the way, the starter will get power, turn slightly, and then engage the gears.
In heavy equipment, if the gears don't mesh, the armature never gets power. This will mean that everything down to the starter will work normally, but the starter does nothing.
Because they are designed this way, it is possible, with some wear of the main contacts or with a recent rebuild, for the adjustment that controls the contact timing to get out of adjustment.
When that happens, the armature will not get power and it will not turn the engine. The cap over the fork must be removed to reach the adjustment, and it takes an air wrench to adjust it while the starter is in the coach.
BTDT.
With the starter out, the drive gear should be about 1/8" from the end of the gear opening with the solenoid energized. Look in your service manual for the adjustment.
Good luck with your problem.
Tom Caffrey PD4106-2576
Suncatcher
Ketchikan, Alaska |
John MC9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 26, 2006 - 12:13 am: | |
Oh...uhhhh...
"I no longer have a fast idle which was removed when i had a
jake brake installed -"
What did they remove, to disable the fast idle? Is it related?
Maybe a trip back to the one that installed the Jake, can
resolve the problem for you! (and maybe for free). It didn't
have this problem prior to the Jake install, right? |
Tom Caffrey (Pvcces)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 26, 2006 - 9:50 pm: | |
John, I think that when his Jake was installed, the fast idle cylinder was removed and a Jake switch installed that senses a closed rack.
To save the fast idle, the combination switch and cylinder from Jake would need to be used, and they get a pretty good chunk of change for it.
For what it's worth.
Tom Caffrey PD4106-2576
Suncatcher
Ketchikan, Alaska |
John MC9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 27, 2006 - 9:40 am: | |
Tom -
Understood that! But if he's had the intermittent problem
since the Jake install, it makes me wonder if the rewiring of the
fast idle could have anything to do with the problem now.. |
Jack Conrad (Jackconrad)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 27, 2006 - 10:30 am: | |
From the factory, the fast idle is wired through the neutral switch and the parking brake switch so that the fast idle can only operate when the bus is in neutral and the parking brake is applied. Since this is not an OEM installation, YMMV. Jack |