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DDEC IV Tach
I have not succesfully got my ecm to talk to the tach. K1 on ecm 505 wire to tach. Ground good–power to tach good. No workey. Continuity good 505 wire. How can I see if tach is any good? This is a complete coach rebuild with unknown tach. No W terminal on Alternator to use a pulse tach from it.???????98 XLE with ddec IV pre emission engine.Runs good. I have exhausted my brain. By way wire # s on tach does not agree with prevo elect schematic. wires were still connected to tach when I started. Bob
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9 Replies
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Robert. You can check if your tach wire is pulsing with a cheap computer test light. It won’t tell you much about the signal other than if it is pulsing. (Blinking light)If it is it is probably the gauge.
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Harbor Freight sku 30779 or similar
Jeff and Lindsay
91 Marathon XL -
oops wrong number 98709
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next site I will visit.. Thanks!
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G0t tester! nice the way it changes colors for hot/red and Green= ground. No response on K1 pin either way on DDEC IV????engine ideling. Bob
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Robert,
Yes I like that tester and use mine a lot for simple stuff. I like that it tells you if your on ground or positive without having to switch leads around.
If you can find the magnetic pick up on the bell housing that might be a logical place to start testing. Then try to trace it up to the DDEC. However, it seems like you would have issues with the bus running if your DDEC didn’t have a tachometer signal. Hopefully someone more familiar with the chassis wiring will help you trace the tach signal? Jeff P.S. I assume you had the tester power leads on chassis and not the house side.
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Yes. I don’t have a house side–home builder— pole to pole or gen set. Going to see if ecm was configured with tach output. 2000 freightlinner is what the engine and trans came out of. Life is a day to day challange.. I guess when we get everything figured out=we aren’t here anymore. I must be good for awhile..Bob Thanks for the info!
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If your engine was from a truck, there are SEVERAL parameters that will not be compatible with Prevost. DDEC was the only ECM from the major engine manufacturers for which the inputs and outputs could be configured/programmed to do several different functions. In the French Canadian ultimate wisedom, Prevost had to be different and reassigned about a dozen parameters and I/O pins on the ECM to do a different function other than the way the DDEC standard Over the Road Truck Vocation setup was on a stock Series 60. When I was the engineer at Vogue, we put all three engines in our Vogue 5 coaches, and I tried to stay with the standard Vocation programming as much as possible so only a few things had to be changed by the Detroit dealer if an engine ECM was changed.
I have run into this MANY times when an engine ECM failure occurs. You MUST go back to Prevost with the original VIN and engine serial number (Detroit calls it Unit Number) to get the correct configuration to make things work properly. I can tell you right now, the cruise control, jake brake, tach and several other items will not work or work properly until you have the ECM set up with the original Prevost program, and keep all the wiring as per the Prevost wiring diagrams tell you it should be.
Hope this helps.
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that is what is happenig. I had just realized (suspected) that was the only answer. It is running good just was trying to get all of the Dash tools working(mainly tach) Have oil pressure gauge Water temp etc. Tach would have been nice but not a necessity. Volt meter works also.I have freightlinner wiring schematic and have discovered several wire # differances. Thanks again for lifting the fog! I have a magnetic pick up tach I can install. No W. on alternator. Bob
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