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High Idle not steady after battery change
I can’t be sure that it is related, but the coach sat for a few weeks and the starting batteries died (they had a trickle charger but had just reached their limit (7+ years). I removed and replaced them and now the bus starts great, but now when I put it in high idle it is not doing a smooth idle. It will rev slightly then decrease then rev again. Doesn’t seem to be consistent, meaning it will sound “normal” for a bit then you can hear it lower or increase the RPMs. It seems to happen at least every 5 mins or so. It is not rhythmic – pretty random.
I have never had that issue in the 8 years we have had the bus so it is a new issue to me and given the battery replacement I can’t help but think it is somehow related. Could the computer (DDEC), which I assumes controls high idle speed, be having an issue after a power reset? Any other ideas of things to check into?
Thanks as always!
PS – On low idle it remains nice and constant. It is only happening when on high idle.
Mike Harper
2004 Marathon XLII -
7 Replies
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Just guessing this morning … are you absolutely 100% sure the new batteries were 100% wired correctly?
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I did the before pics and used to replace, but good idea Dick to do another thorough review. Will do that today.
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Look closely at grounds and all connectors.
I had a battery problem shortly after buying the coach. Had to pull all four chassis batteries and take them to the Interstate Distributor in Milwaukee to prove to them one of their five month old batteries was no good. During the process of putting them back in, my neighbor and I noticed one of the ring terminals on a small wire had been bent back and forth enough between the crimped wire and the ring that it was barely holding together. He repairs all kinds of machinery and said something like, “Replace that NOW. Those things are four hours of chasing rabbits through a rabbit hole down the road just waiting to bit you big time!” So often its little things.
With DC power, another problem area is poor grounds. If you’ve ever owned a trailer of any kind (especially a cheaply built one or one wire on Monday) you know what I mean.
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Maybe the alternator is pulling the engine down, i would also check the fuel,
you mention coach sat for a bit. I guess i would take it for a good run before
getting too involved.
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Thanks Dick. It sat for about 3 weeks, but agree, rather than idle I will take it out for a run this weekend and see if behavior changes.
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With our coaches having a 24/12 chassis electrical system I would check the voltages probably easier done at the terminals on the equalizer. They may be OK but if the 12 volt side is not exactly 1/2 of the 24 volt side that may contribute to the problem.
The only reason I mention this is because problems after a chassis battery change occur at a relatively high frequency due to errors in hooking the batteries back up. That includes not only the heavy cables, but the smaller wires with the ring terminals.
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Wanted to close out on this issue.
Turned out to probably be a flaky ground – negative. I ended up sanding all of the cable ends and replacing one cable that ran from Negative-Negative and it cleared up.
Thanks as always for the ideas.
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