Will not start...Starter makes a thunk but will not spin engine at all

Topic: Will not start...Starter makes a thunk but will not spin engine at all (Read 643 times) previous topic - next topic

Will not start...Starter makes a thunk but will not spin engine at all

September 05, 2017, 03:29:16 pm

This morning we fired up the coach, left our campsite, drove down to the dump station. I leveled the coach, turned it off and went outside to dump.

Now, the coach will not start from the dash or the rear start panel in the engine compartment.

I put the key in, turn to the run position. When I turn the key or press the start button in the rear I get a "THUNK" but the engine does not spin even the slightest.

Anyone have any ideas? I'm not really sure what to think.

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #1 – September 05, 2017, 03:33:51 pm

I would start by re-seating my battery ground.

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #2 – September 05, 2017, 03:42:28 pm

Battery connections are probably the culprit. Pull and clean the terminals. Your dash warning lights probably dim or go out when you get the thunk noise.

Pierce

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #3 – September 05, 2017, 03:49:21 pm

Agreed-- battery connections most likely suspect.

But, any other symptoms-- Allison shift pad illuminate/stay illuminated when you try to start? Dash HVAC fan on when key on? When try to start? What does voltmeter gauge in dash do?

Does Boost Switch make any difference?

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #4 – September 05, 2017, 04:22:25 pm

Quote from: Pierce & Gaylie Stewart – September 05, 2017, 03:42:28 pm

Battery connections are probably the culprit. Pull and clean the terminals. Your dash warning lights probably dim or go out when you get the thunk noise.

Pierce

3 Lights light up for 1/10 of a second. They are Check Engine, Engine Shutdown and something else. The come on then go off faster than you can read them when i turn the key to start. This is kind of alarming. Is this what you were refering to?

Since it started easy the first time I was thinking starter or solenoid.

I was trying to start it with the generator running and the boost switch on.

I'm battling two problems. First, I can't get under the coach on the starter side to check the cables to the starter or to bridge the lugs on the starter.

I have to drive 1 mile up a hill in the toad to post to the internet or use the phone.

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #5 – September 05, 2017, 04:24:55 pm

Quote from: wolfe10 – September 05, 2017, 03:49:21 pm

Agreed-- battery connections most likely suspect.

But, any other symptoms-- Allison shift pad illuminate/stay illuminated when you try to start? Dash HVAC fan on when key on? When try to start? What does voltmeter gauge in dash do?

Does Boost Switch make any difference?

Boost switch is on, makes no difference. Neither does starting Generator.

Dash HVAC fan does come on when I turn the key on. Key pad says N N when I turn key on.

Will check what happens to volt gauge and Allison keypad and be right back.

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #6 – September 05, 2017, 04:38:02 pm

Allison key pad stays illuminated any time the key is on. Doesn't dim or go out when turning key to start.

Dash volt meter is just above 12V. Dips just a little when I turn the key. Not much.

Battery terminals appear to be clean and tight. No sign of corrosion. I haven't removed them or cleaned them yet.

Anything else to check?

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #7 – September 05, 2017, 04:49:50 pm

When was the last time the starter batteries were replaced? From what I understand, the boost switch means diddly if one of the starter batteries are bad. Though, odd your gen started. Less voltage to start the gen?

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #8 – September 05, 2017, 04:52:01 pm

Even with the boost switch on, all juice goes through the start battery. Even though the connections look good re-seat them to either start the engine or eliminate them as the culprit. If it still doesn't start, I'd look and see if the start battery went south.

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #9 – September 05, 2017, 04:57:45 pm

Sounds like it may be time to have someone turn the key to the start position as someone small (I know you said you can't get under there but you may be able to reach it from the top side) taps on the starter solenoid. This may jar either the solenoid or the starter loose. I like a 4# hammer for this task. Now don't beat the crap out of it just a couple of love taps.

Pamela & Mike

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #10 – September 05, 2017, 05:01:09 pm

Does your generator start? Oops I see yes. Make sure it's running when you hit your boost. Done that.

Can you get your towed close to your engine batteries ? With the generator running, hook your booster cables between the towed & coach.

If you have said booster cables & they reach, connect them end to end & connect plus terminals together, negative SHOULD connect via the chassis.

Using said jumper cables jump around the boost relay.

But it does sound mechanical, rather than electrical

Where are you?

Lotsa Luck !

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #11 – September 05, 2017, 05:28:24 pm

If start batteries are in question, EASY TO TEST:

Check voltage at start battery.

Have Amanda turn the ignition to ON.
Then have her try to start it.

What are voltages in all three conditions?

If big voltage drop when trying to start, batteries bad.
If not big voltage drop, then something downstream (such as start solenoid) are not working.

If the latter, pull out the wiring diagram on your coach. As I recall, check connections and solenoid behind the driver's side rear wheel.

Do this check at both the battery posts themselves AND at the cables (that will tell you if you have a poor connection).

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #12 – September 05, 2017, 05:56:19 pm

Thank you, everyone!!!!!!! The coach is running!!!!

I disconnected, cleaned, and reinstalled both the positive and negative battery cables. The coach immediately started right up. This makes absolutely no sense what so ever, however, it was a great lesson to learn. Even though the cables looked perfectly clean and seemed to be tight, this one change is all that was needed to start the coach. Even trying to jump start it with our toad was unable to get our coach started.

I will never again doubt the recommendation to clean and reinstall the battery cables.

Thank you to everyone who replied and helped me out.

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #13 – September 05, 2017, 06:24:29 pm

Douglas I experienced the same issue. Start and drive all day shut off; next morning nothing. I would take off the battery cable, clean them and start up. When I got home same thing happen all over again.
This time I completely removed both cables, and that was when I found the clamp portion of positive cable cracked clear though.
Replace both cables problem solved.

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #14 – September 05, 2017, 06:30:33 pm

On the isolator panel are two solenoids. One of the two is the Aux Start Solenoid, which flows battery current to starter on the big terminals. The small terminal is from the ignition key. With key on, a temporary touch with any small diameter wire to the small terminal could start engine. The other end of the temporary wire could be touching any battery source, like the battery side of the Aux Start Solenoid, or on either side of the other solenoid, which is the Boost Solenoid. Use a meter to determine if battery voltage is on the big terminal of choice.

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #15 – September 05, 2017, 09:05:21 pm

Three hours at the dump station, that's why I do not turn off the engine when I am dumping tanks or refueling. Been there done that earned the T-shirt.

Roland

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #16 – September 05, 2017, 09:10:39 pm

X2 Roland.

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #17 – September 05, 2017, 09:27:00 pm

Douglas--Glad you are back up and running. We will remember to check the connections.

Three hours at a dump site is better than three hours at a Wal-Mart diesel island, right?

Floor it, Brother.

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #18 – September 05, 2017, 09:57:10 pm

While you are down there clean the connectors on the cables and the batteries and then spray with battery goop or apply some grease. If they are just a metal to metal connection they will corrode once again.

Speedbird 1.

Re: Will not start...Starter makes a thunk but will not spin engine at all

Reply #19 – September 05, 2017, 10:06:17 pm

Quote from: bbeane – September 05, 2017, 09:10:39 pm

X2 Roland.

Times three...... also never shut down in "questionable" areas.......

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