Tach cutting in and out

[DirtyWood]

Quick 4 Stand-Alone Transmission Control with Remote Display

The Quick 4 controller makes your 4L60E, 4L80E, 4R70W, E4OD, or 4R100 transmission work in a wide variety of vehicles, including ones not originally equipped with electronic control. It also allows customization of the transmission's behavior with an intuitive, user-friendly UI. The compact...

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I'm on the fence about going this route myself.

 

[rreegg]

I replaced the TCM already also sorry I forgot to mention that in the original post it was about five years ago now but the truck has only been driven maybe 5,000 miles in that time the connection appears to be tight on the firewall.
That is the only computer I know of on this truck.

Somehow missed this before suggesting TCM before. Are there codes from the trans by chance or a way to isolate/test things?

For sourcing other members have purchased on eBay, some say maybe Oreilly (call for availability even if online says no stock) and rock auto has a refurb for sale.

The obvious non-helpful answer here is find a zf5

 

[Olds64]

You said you tried a junkyard instrument cluster that had the same symptoms. Is that truck still in the salvage yard? You could remove the TCM and try to replace the one you have before buying an aftermarket unit.

 

[Black dawg]

Really need to verify that power from the tcm relay to the tcm is solid. After that, grounds to the tcm.

what I have seen several times, the relay gets water and corrosion in it from not being upright in the holder that it belongs.

 

[BeastMaster]

The problem is likely the tach sensor. You replaced the throttle position sensor and vehicle spéed sensor. Did you replace the tach sensor?

These things, simple as they are, do go bad due to internal leakage/corrosion . I had similar problems as you.

Erratic Tachometer - Ford Truck Enthusiasts Forums

Pre-Power Stroke Diesel (7.3L IDI & 6.9L) - Erratic Tachometer - I have a 1993 F-250 w/ 7.3 liter factory turbo. I just purchased the truck this week and I've been trying to clean out some electrical gremlins. My current project is the fix the erratic Tachometer, the tach works in the sense that...

www.ford-trucks.com

Measure your sensor's resistance with an ohmmeter.

It should read about 2000 to 3000 ohms.

Connect your ohmmeter across the sensor and wiggle them at the seal into the nut where it screws into the engine to sense the passing gear teeth.

Internally, it's a length of fine wire wound around a magnetic pole. Thermal cycling cracks the seal around the big wires. Corrosive gases get in and corrode where the fine coil wires crimp onto the much heavier lead wires. Or at least that is how mine failed.

Good luck. It was a quick fix for me once I knew what I had to do.

Edit: Mea Culpa! The post below noted changing tach sensor and wiring inspection had already been done. My bad.

I need to be more attentive.

 

[rreegg]

Post #4 op says replaced tach sensor. Seemingly all the low hanging fruit has been replaced?

 

[asmith]

That said we all know parts these days are not great and many are bad out of the box. He should probably at least double check to make sure his new sensor is good, if he hasnt already.

 

[RaleighHaas]

First post for me, Oilburners folks have helped a ton on my 1989 "revive"

I have a 89 with a manual and tracked down an issue with a bouncing tach this week. I have replaced the tach sensor before (2x actually, one aftermarket one had the wrong thread pitch, so I found a NOS), when I drug the truck off a farm 2 yrs ago there was no movement on the gauge. Put the NOS in and it worked great, till recently. Last week it would sporadically start bouncing, but more noticeably at idle. If i pressed the clutch in it would almost always go away. I figured it was a connection issue since it could be replicated, and banging on the dash would bring it back, until a couple days ago when it went radio silent. I cleaned the tach sensor on the IP housing (end is magnetic, have read that metal can accumulate, hopefully not), and cleaned connector above IP. No improvement when I drove it the next day. Next check was the gauge and that was the issue. Not the gauge itself, but the where the pins on the back of the gauge go into the instrument cluster. The spring connections where the male conductive ends of the gauge are held in by the cluster, one or more had lost tension (age, the suspension similar to a fork lift, improper repair? idk) but carefully bending the inner parts of those tabs back out to where they grab onto the stud connections of the gauge fixed my issue.

Could be a long shot, but maybe the module uses a common ground with the gauge? Worth a shot before you start buying parts. Attached a pic of the tabs after I bent them cleaned them up a touch. Also, pic of the truck