Tachometer bouncing ( under load) ?

Slyclone

Slyclone

Well-known member
Messed around with the gauge cluster the other day and fixed the issue with the oil pressure gauge.

Just drove home and noticed all the sudden... 3000rpm and above the tach goes... Bounce..bounce...boooouncccceee all the way to 5-6-7k into the red!

What the **** is this all about? And it also seems like my speedo is like off. Or slow. Slowing down from 85-90mph the truck speed seems to stay "up" and slowly descends down. Wondering if I was even doing 85-90? Coming to a stop the thing was almost reading 40.. I don't really know what is going on. I know when you get a tach bounce during start/crank the ignition module is cooked. 3000rpm truck hovers there
Blip throttle or step on it and it goes wild.

Anyone know anything about this?
 
Slyclone

Slyclone

Well-known member
Re: Tachometer bouncing ( under load) ?

Is there anything like a RPM/SPEED sensor? In on or near the trans?
 
Slyclone

Slyclone

Well-known member
Re: Tachometer bouncing ( under load) ?

I just rebuilt this one..

Its not the ICM is it?

Like mention, I under stand that when they start to fail they bounce when you try to start as it does not send the reference signal.

 
Slyclone

Slyclone

Well-known member
Re: Tachometer bouncing ( under load) ?

Took me a few minutes to really get motivated, but I went out to the truck and popped the hood. I looked over the dist. real quick and that was it. I moved my intercooler lines( all rubber) and discovered that the coil wire was very loose not even clipped in So I was like hmmm.. Probably on to something. Looks like the intercooler lines are straining things. Then I inspected the wires that plug in and sure enough one wire has been strained and is exposed at the bottom part of connector ( worst type of break as its right there??!). Probably going to need some liquid band aide or liquid tape.. I'll see if what I found even fixed it and move forward.:tup:
 
Slyclone

Slyclone

Well-known member
Re: Tachometer bouncing ( under load) ?

So far, it seems like the coil wire worked its way off. The one connector is taking some wear as well on the bottom part of connector into coil pack its self. One of the 2 connectors. Its actually one from the main harness. I have a few of the other removable ones laying around ( white wire/red).

After I found that and put it back on the tach only bounced 1-2 times since and it was early on like it was setting its self back in. Put at least 200 miles on truck since and hasn't happened again.

Currently dealing with a driveshaft issue I am about to check into once again.
 
Jimmy

Jimmy

Banned
Re: Tachometer bouncing ( under load) ?

When it's overboosting the tach will act crazy like that.
 
Slyclone

Slyclone

Well-known member
Re: Tachometer bouncing ( under load) ?

I am not sure if its overboosting... My datalogs looked pretty solid about a month ago..

Here is what I found. you can see how I have the intercooler hoses routed. Directly under the back hose is the coil plug. That must rub or the hoses flex/move. Must take a lot of movement for it to work the coil wire loose. Also if you look closely you can see the RED/WHITE wire, gray terminal connector into coil pack, the wire has been worn. Like I said it appears to be worn at a very bad spot as its the furthest point down on the connection. If you look closer you can see the wear starting on the other wires from the slouching intercooler hoses.

Still has not bounced or jumped yet..



 
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