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Old 05-31-2005, 08:44 PM   #1
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I have a '98 36' Alpine Coach with approximately 70K miles on the 325 HP Cummins. This last week we were driving across New Mexico & Texas and I noticed my tachometer jumping about 500 - 600 RPM as we were driving down the road. One minute I would be running 2000 RPM and then it would jump to 2500 or 2600 RPM and then go back to 2000 RPM again. This occurred numerous times during this single day and it wasn't just the transmission down-shifting. Occasionally it would only jump a couple of hundred RPM. Previously, I often drove the coach at 1900 RPM and typically the 1900 RPM would correlate to 68 - 70 MPH. For the few days before I saw this erratic behavior, I noticed that I was losing MPH when maintaining the same 1900 RPM; I was down to about 62 MPH and starting to wonder if something was wrong. The only cause I could come up with for the reduced speed was possibly because I was driving in the mountains, but I didn't think that was the root cause for my loss of speed. Has anyone had anything similar to this happen before? If so, what was the outcome? What RPM do you typically drive at? Does anyone know what a good cruising RPM is for this engine?
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Old 05-31-2005, 08:44 PM   #2
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I have a '98 36' Alpine Coach with approximately 70K miles on the 325 HP Cummins. This last week we were driving across New Mexico & Texas and I noticed my tachometer jumping about 500 - 600 RPM as we were driving down the road. One minute I would be running 2000 RPM and then it would jump to 2500 or 2600 RPM and then go back to 2000 RPM again. This occurred numerous times during this single day and it wasn't just the transmission down-shifting. Occasionally it would only jump a couple of hundred RPM. Previously, I often drove the coach at 1900 RPM and typically the 1900 RPM would correlate to 68 - 70 MPH. For the few days before I saw this erratic behavior, I noticed that I was losing MPH when maintaining the same 1900 RPM; I was down to about 62 MPH and starting to wonder if something was wrong. The only cause I could come up with for the reduced speed was possibly because I was driving in the mountains, but I didn't think that was the root cause for my loss of speed. Has anyone had anything similar to this happen before? If so, what was the outcome? What RPM do you typically drive at? Does anyone know what a good cruising RPM is for this engine?
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Old 06-01-2005, 01:56 PM   #3
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Hello & Welcome Jedova:

I have not had any problems with my Tachometer so I can not help you with that question. But I run at about 60 mph at about 1600 rpm. I have a 2001 38ft FDDS Alpine with a Cummins 350 hp ISC engine. When I pulling hills/mountains I lose speed like everyone else put I attempt to maintain about 2000 rpm, which helps with engine cooling. If I do not down shift manually, the transmission will not down shift until it is about 1400 to 1500 rpm. I sometimes do not feel the 6-5 down shift and will not notice unless I look at the VMS 200, which indicates what gear I am in. My speed will be reduced but my rpm will still be close to 1600 until the transmission down shifts into 4th.

Is it possible that your transmission had down shifted then up shifted at the moment you were watching the Tachometer?

Can you tell if the engine rpm is actually increasing or is it just the tachometer?

You my want to have Allison look at the transmission to insure it is working properly, since the rpm is erratic.

I hope this answers some of your questions.

Dave
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Old 06-01-2005, 06:25 PM   #4
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Dave,

Thanks for the reply; your RPM to MPH ratio appears to be quite similar to mine. I'm certain that the transmission was not downshifting; we were running down the flat interstate when I noticed the fluctuating tachometer and I could tell the engine was not changing speeds.

Thanks for the suggestion,

Jeff
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Old 06-01-2005, 08:37 PM   #5
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Jeff,

I have a 2002 34 fdds W/ 350 ISC. I have had problems with both the speedo and tach. The speedo was replaced a couple of times before I got a good one. The factory is supposed to be sending me a replacement, but after many calls I still don't have it.

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Old 06-02-2005, 12:08 PM   #6
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by jedova:
I have a '98 36' Alpine Coach with approximately 70K miles on the 325 HP Cummins. This last week we were driving across New Mexico & Texas and I noticed my tachometer jumping about 500 - 600 RPM as we were driving down the road. One minute I would be running 2000 RPM and then it would jump to 2500 or 2600 RPM and then go back to 2000 RPM again. This occurred numerous times during this single day and it wasn't just the transmission down-shifting. Occasionally it would only jump a couple of hundred RPM. Previously, I often drove the coach at 1900 RPM and typically the 1900 RPM would correlate to 68 - 70 MPH. For the few days before I saw this erratic behavior, I noticed that I was losing MPH when maintaining the same 1900 RPM; I was down to about 62 MPH and starting to wonder if something was wrong. The only cause I could come up with for the reduced speed was possibly because I was driving in the mountains, but I didn't think that was the root cause for my loss of speed. Has anyone had anything similar to this happen before? If so, what was the outcome? What RPM do you typically drive at? Does anyone know what a good cruising RPM is for this engine? </div></BLOCKQUOTE>

I haven't had a problem with the tach, but my speedometer behaved just like that -- going down a level road at a constant speed the speedo will just flick to maximum, then back to normal. Of course when the speedo flicks up, the cruise control flicks off and the engine stumbles.
I have installed a VMS/PC monitor, so I have an independent readout from the engine/transmission data bus, and it shows the same "flick" of speed. Therefore, I believe the problem must be the speed sensor or perhaps a bad connection.
My coach is a 2001 FDDS with the Cummins 350, bought used just about a year ago. The problem is intermittent: on a recent trip across country we had 2000 trouble-free miles before this problem recurred.

Frank
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Old 06-04-2005, 07:19 PM   #7
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Thanks for the feedback. It sounds like there may be some quality issues with the speedometer and tachometer being built into these coaches. I think I will see about getting the sensor and/or connections checked out. My tachometer issue is intermittent since I have seen it vary while driving since I wrote this original topic; sometimes it acts normal and other times it seems to be off by a few hundred RPM.
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Old 06-04-2005, 07:50 PM   #8
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I had problems with tachometer at about 19k miles on my 01 36 fdds. It either wouldnt work at all, or it was errratic. I was told that they had some problems with them. I replaced it and it has been fine since
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Old 06-04-2005, 08:57 PM   #9
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Hello & Welcome NFOGGY:

Glad you found the Site. You live just down the road from me. Hope we can get together someday, and you my want to join us at a Rally with Alpine So Cal , and/or Alpine Coach Association (ACA). You'll meet a lot of great people who own Alpines and we can trade stories.

Dave
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