tach goes to zero and all the sudden...Boom

mywhite89

Registered User
My buddy has an 89 5-speed. Intermittently, while driving his tach read-out will go to zero, then the car will run crappy then make a backfire type of sound through the exhaust. Any ideas? Car has over $170,000 miles, original harmonic balancer and crank sensor as far as he knows.<---if neither of these apply to the current problem, please stay on the subject:) He's a, "If it aint broke don't fix it" kind of guy with this car.
 
mywhite89 said:
My buddy has an 89 5-speed. Intermittently, while driving his tach read-out will go to zero, then the car will run crappy then make a backfire type of sound through the exhaust. Any ideas? Car has over $170,000 miles, original harmonic balancer and crank sensor as far as he knows.<---if neither of these apply to the current problem, please stay on the subject:) He's a, "If it aint broke don't fix it" kind of guy with this car.
Is there a CEL too? The CEL Decoder will tell you a few things. Also, if you have a manual, you could start with the cam or crank sensor checkout procedures and then move on to the DIS if that doesn't work. Heat can make the DIS go bad if there isn't proper heat displacement. You may want to try removing it, cleaning it and putting on a fresh coat of Heat Sink Compound between the DIS and the mounting point.
 
sensors, sensors

he replaced both the DIS and cam sensor 5 years ago.

I would have guessed DIS, but I will let him borrow my cam sensor and see if that fixes the problem. I will let you all know, just so I can 3rd that notion:D

chris
 
Ben ther done that

My car has the same problem, If you have a napa near you they can check the DIS. Change the heat sink compound under the DIS $2 bucks for the tube at radio shack. 5 min job. Look for lose wires. I found a small connector coming out of the harness from the crank sensor broken and it was repaired badly check battery connections and the battery. My car skipped after the crank sensor was changed so start at the top. The DIS then the cam sensor good luck the ford dealer says ( SCs are to hard to work on ) previous post, I would let you use my code reader if you lived closer:) I have a good friend that lives in Fort Wayne, Bill Ross good luck
 
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Zero Tach

Ok so my buddy has been driving his mustang and just parked the sc for a while. He's back to working on the SC again. We put heat sink under the DIS, installed a new air temp sensor. Previously when we scanned for codes, no codes came up that normally indicate a DIS failure. Like the 1,2,3 cylinder failure or whatever it is.

After doing the air temp and heat sink, the same problem occured a fews later(today). He said he had to wait 10 minutes and then it started back up. He previously stated this problem occured after hot starts, well not anymore!:) This was on a cold start.

I forgot about the advise to get a cam sensor. Glad I remembered to look back on here.

We will replace the cam sensor tonight and check all grounds. I'll let you guys know what we find.
 
Correct me if I am wrong, when a cam sensor goes the computer is lost as far as what cylinder should be fired upon. At this point you have a 1 in 6 chance of it firing on the correct cylinder upon cranking it over.
 
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Cam sensor controls when the injector fires. If you unplug the cam sensor and try to start it and shut it off around five times or so and it fixes the problem then it is the cam sensor more than likely.

These problems you are having directly relate to mine being a DIS problem. Unless you have a different or new DIS to try then just putting heat sink underneath the DIS module will not fix it by itself.
 
the problem

Ok tonight we put a cam sensor in. Drove it around and shut it off several times. No problems so far. It's very itermittent. He drives it to work every day and might have the thing mess up once maybe twice a week.

We'll see if he has any more trouble, if so, i'll have him try my DIS.

I'll keep ya all posted.

chris
 
Dis

Yeah, everything with these cars is intermittent, except the head gaskets!

The only thing that kept me from throwing my DIS on his car was that we never pulled any codes that seemed related to it.

Unless, i remember we got some code -spout failure or something??

edit:book in front of me. I think it was code 49: spout signal defaulted to 10 degrees BTDC
 
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The cam sensor in my '90 SC goes bad every year like clockwork.
Just put a new one in last week. (Replaced last year at this time).
I actually carry a spare one around in the car just in case.

I only replaced the cam sensor once in my '89 SC, go figure .
 
Well, so far so good. I believe the cam sensor has fixed the problem

TBirdDriver: I would check your wiring harness to the cam sensor for the 90, make sure its not burnt or anything, causing shortened life of your cam sensor. I had a multi-function switch that I had to replace every year until I finally bought a new harness, the old one was burnt and must have been shorting the switch out. Good to go!

Chris
 
Thank you Chris.
It might be the harness.
The wiring harness I used on the '90 came from the '89.
When I transferred it, it had 265,000 miles on the harness. I have since put another 100,000 miles on it, so that harness now has over 365,000 miles of use on it.
 
TBirdDriver said:
Thank you Chris.
It might be the harness.
The wiring harness I used on the '90 came from the '89.
When I transferred it, it had 265,000 miles on the harness. I have since put another 100,000 miles on it, so that harness now has over 365,000 miles of use on it.

Whew, enough said!:eek: The question you should be asking yourself is, "Where do I start?" :D

chris
 
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