Tachometer has stopped working Safari Sahara Diesel

[clayhubler]

Hello all,

Trying to get this coach ready for the season. My tach isn't working on my 1994 Safari Sahara. It has the cummins 5.9 b series engine with an allison 6 speed tranny. There are no other symptoms that I know of, shifts are still at appropriate times, no loss of power, ect...

It was working and then stopped, but it wasn't abrupt. It stopped, then worked off and on for maybe a day, then has stopped completely.

I have checked the connections at the back of the gauge cluster inside the dash, all looks good. I don't know for sure where the tach attaches on my engine. I have done some research and I am thinking it might be the crankshaft position sensor. I located what I thought was the sensor and checked the plug harness, everything looks good there. I pulled the sensor and took it to napa to see if they had a replacement. All the sensors I have found online are for the dodge trucks, and they have three prong connectors. Mine has two prongs. Napa couldn't find one with two prongs either, and so they got my engine serial number and contacted cummins. According to napa, cummins claims my engine doesn't have a crank position sensor???

I'm not totally confident with this assessment from napa. I tried a diesel repair shop over the phone, and they gave me some businesses to try, but they are closed for the weekend.

I'm curious if anybody else has had this problem and also if they know what else I could check. I'm still leaning toward this being a crankshaft sensor issue, but it sounds like the sensors are around $80, so I don't really want to just replace it if that isn't what is causing the tachometer issue.

Any advice is greatly appreciated,
Thanks

[clayhubler]

Thanks to everybody who offered advice on this problem. I am happy to report that the issue is now resolved and everything is functioning properly.

The root cause of the tachometer failure was that I had simply hooked the tach wire to the wrong terminal on the alternator. Initially, after the reinstall of the alt, this didn't raise a red flag because the tach had already quit on me before the alt swap. I now know that this must have been when the first alt went bad.

I got a tip on another forum about looking into the battery isolator that set me on the right path. I became convinced that the bad isolator had killed my new alternator. But after testing the isolator with my multimeter, it proved good. After further investigation I realized that the terminal on the isolator that should run to the (+) on the chassis battery was in fact run to the (-).

This could only have happened when I changed the chassis batteries about a week ago, another fact that I left out of the conversation because I didn't think it was relevant.

So, to make a long story short, I initially hooked up the tach wire wrong, then later when I hooked it up correctly, it still didn't work because the alt was not functioning properly at that time because of the battery swap.

Thanks again to all who helped me out with this matter.
BTW, on my alternator, the correct terminal was marked (R)

[clayhubler]

Here are photos of the alternator model number and the terminals. It also has a ground terminal that is out of frame.


Click For Full-Size Image.


Click For Full-Size Image.
I ran a wire directly to the tach gauge from the R terminal and didn't get anything. Wondering if this tach is not wired internally to support the tach funtion?
Thank you to rv.net member 1492 for the photo posting help.

[MountainAir05]

wolfe10 wrote:
So, tell us what terminals the alternator has OR its model number.

All will have: B+ for positive alternator output to battery or battery isolator.

Ground-- some ground through metal to metal contact, some have a separate ground lug and wire.

Some will have a "sense wire" from chassis battery side of the battery isolator to the alternator sense terminal (small gauge wire).

Some will have an excitor wire which is hot only when ignition is on.

Some will have a tach out terminal.

When I work this system many years ago it was the stator tap but I have no current working knowledge. Neighbor is gone for a while so can not talk to him and he has my old books.

[wolfe10]

So, tell us what terminals the alternator has OR its model number.

All will have: B+ for positive alternator output to battery or battery isolator.

Ground-- some ground through metal to metal contact, some have a separate ground lug and wire.

Some will have a "sense wire" from chassis battery side of the battery isolator to the alternator sense terminal (small gauge wire).

Some will have an excitor wire which is hot only when ignition is on.

Some will have a tach out terminal.

[clayhubler]

Here is so me info I should have included in the post from the beginning, but at the time I didnt think it was related.

The tach quit before I replaced the alternator on a trip last year. When I replaced the alternator, there is a wire that was hooked to the old one, but is not hooked up now. The guy that I got the alternator from was from a diesel electric repair shop, and he really seemed like he knew what he was doing. I had already tried several autoparts stores, and they hadn't come up with anything. This guy saw the alternator and recognized it immediately.

I asked about the wire, and he told me that it wasn't needed because the new alternator didn't need to be energized like the old one had, and thats what the wire was for. However, he said it could be hooked up with no harm anyways, so that's what I did. Keep in mind at this time the tach was already not working, so I didn't believe the two problems were related. After the swap, I continued my drive home with now issues, the wire still hooked up. When we got home the next day, I could hear a tick, tick, tick at the back of the coach. After some investigation, I realized it was the hour meter still counting off, even when the engine was off. Knowing that the alternator swap was the only thing that had changed since the correct operation of the hourmeter, I disconnected the aforementioned wire and the meter stopped ticking off.

The wire remains disconnected. I do not know if the hourmeter runs when engine is running or not, but I am not as concerned with that at the moment.

Sounds like Mountainair05 may be right, but I don't know if I have a leece neville or not.

I am pretty sure now that the tach and the alternator are involved with each other, an allison transmission specialist told me as much when I questioned him about the sensor that I suspected was the crankshaft position sensor, but was in fact the engine speed sensor. He said the tranny has nothing to do with the tach, so I am back to the alternator, but even if I hook up the wire again, the tach doesn't work. This alternator looked identical to the old one, with terminals in the same locations and everything.

[clayhubler]

sorry, double post

[clayhubler]

So I went to a DSU Peterbilt service center on the way home today. They couldn't find the part. The sensor is actually mounted at the rear of the transmission, just forward of the bell housing, so the guy told me he thought I should go to an allison service center, and also that it was probably an engine speed sensor, not a crankshaft position sensor. I don't really know the difference, but I'll be going by the allison shop on thursday.

[wolfe10]

The good news is that Safari/Magnum used "off the shelf" components.

[clayhubler]

My safari has a magnum chassis. I don't now of any magnum service centers. I will know more after visiting the Cummins shop.

[polar76]

You may have to go to Freightliner, it was considered a chassi part installed after the delivery...

[clayhubler]

here it is on the engine

here is what it looks like


sorry, anybody tell me how to post pics on here??

[clayhubler]

I've pulled out the sensor again. Going to take it to the cummins dealer on monday to see if they can help me out. Thanks polar76, this is encouraging.

[1981k20]

Excellent, thank you for the ideas. Will check it out tomorrow and advise

[polar76]

My 97 Country Coach did that last year. Mine is and 8.3L but may be the same problem.
I took my sensor off the flywheel housing (2 wires) took it to Freightliner and they knew immediately what it was. about a $50-60 dollar part and back in operation.