CH302K
Registered User
I have a 1993 7.3 non turbo.The tach is at 0 at idle and pulses when the blinker is on. Any bodyelse have this problem or knows how to fix it?
Thanks
Thanks
LAZY TACH
- Thread starter CH302K
- Start date
icanfixall
Official GMM hand model
My guess is you have a ground problem. Sorry I can't be more help. Others are much better in this electrical area.
SparkandFire
We're drinking beer
Some time back I spent an entire saturday trying to fix the exact problem you are having. Above 1200 RPM my tach works great... at idle it goes to zero. I pulled the dash apart and cleaned all the contacts with a small copper wire brush and contact cleaner. Pulled all the grounds off I could find and wire brushed the wire eyes and the chassis, put copper anti corrosion compound on all the engine compartment grounds, contact cleaned the connector for the tach sensor, etc....
Still does the exact, same, thing....
Although I did completely clean the inside of the gauge cluster and replace a bunch of failed lamps, so it wasn't a total loss.....
Still does the exact, same, thing....
Although I did completely clean the inside of the gauge cluster and replace a bunch of failed lamps, so it wasn't a total loss.....
iverger
Full Access Member
Good chance the tach sensor needs to be replaced. I was experiencing the same thing on my 89 (makes for an unhappy E4OD). I believe it is a dealer only item, for a new one at least.
It sits on the pump housing and pretty simple to change.
It sits on the pump housing and pretty simple to change.
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The tach circuit is very sensitive to voltage fluxuations. Any loss of ground or B+ will result in lower readings. The ability of the sensor to generate a signal is likewise sensitive. The normal troubleshooting is to buy a new sensor and see if that fixes it, and go from there.
Ataylor
Full Access Member
I replaced the sensor on my 1987 and all problems were cured. I think it cost around $80, but I could be off. Really easy job to replace.
Devon Harley
Full Access Member
56 last week at the local stealership for my 89
SparkandFire
We're drinking beer
Times like this are when it's nice to have a small fleet of spare trucks to pull parts from, I swapped the working sensor over from "Smokey the Black" my '85 truck and still had no working tach...
The sensor is what's called a "variable reluctance sensor" which produces voltage in the range of 5-100 millivolts linear to RPM. With voltage that small, and old wiring and connections and such, it's easy to loose a millivolt or two.
The sensor is what's called a "variable reluctance sensor" which produces voltage in the range of 5-100 millivolts linear to RPM. With voltage that small, and old wiring and connections and such, it's easy to loose a millivolt or two.
