Tach Trouble

[dpuckett]

I have a recently (ok, not THAT recently- back in late January) acqired 92 D350 that I'd like to hook up one of my ISSPRO tachs into. Problem is, I hook it up and start the engine. I'll have 350-400rpm for 3-4sec, then it drops dead. Air gap on crank sensor is set to . 048-. 049" per directions in this very forum. I tried jumping the input and tach output wires (43 & 24) like one person here did recently, to no avail. He had good luck.



Could I need a new crank sensor? (cruise is inop; voltage reading is sporadic- 12. 5-13. 5; but it IS a factory gague) Or am I missing something painfully simple? Guess I could hook a voltmeter up to the wire under the dash, and see if the output is smooth as RPM increases. I would use the setup from the 91 (no plug in on it), but I am missing the magnets, cause I forgot to take them out of the old truck when it sold. but I'd like to just plug it in and go. Chris (dieselman359) said he had similar troubles when he plugged in teh tach on his 93, and fixed it with the install kit from ISSPRO; others ahve said it is a waste of money.



Daniel

 

[AKimmel]

I was the one that jumped the wires in the PCM. It worked for me, but I ended up buying a crank sensor, because my tach would work to about 2200 then die higher than that. As the motor got hot the rpm limit would drop to 1900 then it would die. My cruise, A/C, and alt. never had a problem, but I guess the tach needs a stonger signal. The new crank sensor fixed my problem, and I'm guessing it would yours. The harness is a waste, I bought it like people recommended, and my tach wouldn't work at all going through the filter (the only thing that makes the harness special), I ended up bypassing the filter, like I was told by the tech at isspro and it went to working.

 

[Greenleaf]

Perhaps the rason the filter didn't work out was that the crank sensor was kaput. That or the tach you installed didn't require the sensor? Some models do and some don't. The flat faced 2-1/16 inch unit does and the convexed do not. There are exceptions to this rule I'm sure.

 

[paccool]

I fought this for several years. Tried a couple of different tachs, none would work. I finally started tracing voltages and the short of this is there was a good pulse from the crank sensor but no signal from the PCM. Turned out the PCM was not putting out a signal for the tach. All other items the PCM controlled was working OK. I got a killer deal from another guy that had a 93 that he sold but still had a new PCM for it. I installed that and all the trouble went away. I was even able to get a OEM tach that was used in the 93's, had never been installed. All is working right now.



Sure sounds like the full range of problems has been encountered on this subject!

 

[AKimmel]

Perhaps the rason the filter didn't work out was that the crank sensor was kaput. That or the tach you installed didn't require the sensor? Some models do and some don't. The flat faced 2-1/16 inch unit does and the convexed do not. There are exceptions to this rule I'm sure.

My crank sensor was good, but I guess a little weak for the tach to work at higher RPM's. And I am using a 2 1/16 flat face isspro tach, R8503 I believe. When I got the sensor harness and it didn't work I called Don at isspro, he told me to bypass it with the other wire. He told me before, that the tach should work without the filter, but I ordered it anyway to see if it would solve my other problems, it didn't. The thing I can't figure out is when I check continuity through the filter, there is none. When I sent it back to isspro to be tested they said you won't get continuity through it, but then how will the tach get a signal?

 

[dpuckett]

I'll try to find a digital voltmeter and test the wire coming from the sensor as well as from the PCM, and get back here with the results. And not in the same way I have gotten back here with pics of the two TX trucks, either.



Daniel