Can anyone tell me the procedure to troubleshoot a dead tach on my 85 300tdt. Its been out for quite some time, but thought it might be nice to fix it. Anyone know where to start. I think the 85 year is different from the others, not sure though. Thanks, Brian

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85 300TDT 456,000 orig. miles

Replace the diode/cap on the diagnostic connector and odds are it'll work fine.



Joe

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Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.
Raleigh NC
919-881-0364

on my 83 tdt the tach has a magnetic pick up . if that get real dirty / greasy then it wont work
the pick up is a round pointer located at the front of the block in the middle off to the right as you stand in front of the car it is round. clean that
next is a black round cyclinder located on the fender right side. it looks like a 35 mm film canister. take the cap off, pull the piece out of the cap place a cig butt in the cap and put it back together. that should work .
it puts preasure on the solder which causes it to work .

that is all.
john m

I'm sorry but where is the diode cap located on an 85?? thanks

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85 300TDT 456,000 orig. miles

I think the tach setup is different on an 85

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85 300TDT 456,000 orig. miles

Round diagnostic connector on the l/f fender well. Behind the headlamp in front of the upper shock bolt and upper a-arm bolt. Threaded cap about 1.5" tall when removed, has a little plastic leash on it.




Joe

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Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.
Raleigh NC
919-881-0364

I found the unit, Is there a way to test it or should I gamble and just replace it? I unscrewed the cap, but how do you remove it? Thanks

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85 300TDT 456,000 orig. miles

Thank you Madsen and original poster. I followed Madsen's simple to understand directions, and in minutes fixed my tach that has been going on the blink.

There is a 'cigarette butt' trick that can be done to fix that tach unit (the thing that looks liek a garbage can at the left front fender). Essentially, you jam something between the lid of the the unit and the actual connections inside the unit. Makes the connections actually work, which then allows the tach to work.

I didnt bother with that, just got a new one from fastlane and havent had any problems in 2 yrs/50k.

Another option could be a dirty/bad connection in the insrument cluster. Pop it out and check.

JMH

P.S. The cigarette butt trick was one of the first things that got discussed at length when I started watchin this board, at almost its beginnings. Look way back in the archives and youll find lots of info on it.

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)

Is the part called a diagnostic connector?

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85 300TDT 456,000 orig. miles

Diode



Joe

__________________
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.
Raleigh NC
919-881-0364

The first thing I fixed on my 83 was that very piece. Sitting in a rest stop in TN at 3am, tired of seeing my tach come alive then die, come alive then die. I think I used a piece of cardboard. Always inteneded to try and solder it or something, but have just left well enough alone since then.



It is called a diagnostic connector, but I can't recall why.

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One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K

Can I smoke it first?