Isspro 4k rmp tach - malfunction

[JGrefenstette]

brandnew tach, just installed. the tach will not behaive at idle. it flutters untill it reaches 1500rpms then it locks in and is steady... untill it gets under 1500rpms, then it starts fluttering.

what in the world is going on?



1. is the actual tachometer malfunctioning?

2. is the truck giving a bad signal?

3. could the wireing have any effect? (it seams strange that it is bad only untill 1500rpms)



ANY help or experience EXTREAMLY apreciated



-jimmy

 

[MMeier]

Did you go over and recheck all your connections? Sounds like a loose ground or signal wire.

 

[JGrefenstette]

yea the best i could. i mean thats exactly what it seems like the issue is, but what i dont understand is why it works fine after 1500rpms. if it was a bad signal or ground connection wouldnt it not function right through all the rpms?

 

[bgilbert]

Alternator or crank pickup tach? My two Isspro 4k alt tachs have performed flawlessly.

 

[JGrefenstette]

ya know, thats a good question. i have no idea where the signals origin is. i simply wired the tach into the harness under the dash. i assume its from the crank sensor but i dont know.

does anyone else know where my signal is coming from on a 93' W250?

 

[dpuckett]

If you used the harness under the dash, it comes from the crank sensor. Make sure the gap is . 050", +/- . 001".



DP

 

[JGrefenstette]

well this morning i talked to a tech guy at isspro over the phone. he told me to swap out the white wire with the yellow. the instructions told me to use the white with my application, but he said to go ahead and try the yellow. i did, and its worked flawlessly eversince. its only been a day, but i think the problem is solved. he said the reason was that one of the 2 wires has a filter and the other does not. i dont understand totally what that means but it worked and thats what i was goin for.

thanks for the help guys.

 

[AKimmel]

I had the exact same problem, but mine wouldn't read at all below 1200 rpm. I tried switching wires like you did, but mine didn't work at all going through the filter. I replaced my crank sensor, with no difference. I finally bypassed the computer and ran it staight off the crank sensor, it works now, but cuts out above 2300 rpm. So I give up.

 

[JGrefenstette]

huh, thats just plain strange. i hope i have better luck than you do. sorry for you misfortune. have you called isspro about it? not that they could help you, it seems that youve done all you could, but i would, to atleast hear what they have to say about it.

 

[AKimmel]

I called them and even sent my tach back to them to be tested, but they said it checked good. Whats weird is since I'm reading the signal straight off the crank sensor, when my tach loses signal you would think other signal dependent things would quit also, but they don't. Probably if I replaced my computer and hooked the tach back up through it, it would probably work. But, I can't justify buying a computer for just a tach signal.

 

[JGrefenstette]

how did you wire it up? butt connectors? thats what i did. and one of the guys suggested i solder all the connections for a better chance that it wasnt bad wiring.

 

[AKimmel]

Soldered. .

 

[JGrefenstette]

whew..... well its sounds like you got your work cut out for ya.

 

[dpuckett]

AKImmel- ISSPRO makes a sensor kit for the older, non-computerized trucks that mounts to the oil pan and reads the harmonic balancer. Cost me about $25 3-4 years ago for my 91.



DP

 

[AKimmel]

I thought about doing that, but it involves glueing magnets to the balancer and I'm afraid it would interfere or possibly damage my factory crank sensor. I know the FSM says to use a non-magnetic feeler guage when setting the air gap, so I'm guessing magnets are not good for it.

 

[Moab4x4]

If cold my ISSpro 4k tach that I got around a year ago flutters sometimes. It settles down when warmed up.

When I first installed it it would frequently just die after about 2 months of use but would work if you tapped it. It had to be a connection but they were all tight. I slightly turned the brass post that you hook the signal wire to the tach with while trying to tighten the connection nut. Lo and behold the problem went away almost all of the time. It looks like the intermittent connection problem was inside the tach and the slight movement of the post tightened up some connection inside. I was lucky it didn't break something inside the tach when that post turned.

I too have soldered all possible connections. (old electronics tech habit)

Ken