strange tach behavior when cold
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Senior User
Joined: Jan 2002
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From: Monument, CO
strange tach behavior when cold
Anyone seen this problem before?
My son's 89 BII (2.9L, 5 speed, EFI) gives an artificially high tach reading when it's cold. After driving for 10-15 minutes, the tach drops down to a normal reading without any actual change in the engine speed. We didn't notice this problem in the summer when we bought the vehicle, but it's been occurring since around November when the temperatures started getting very cold at night.
When the truck is cold, the tach reading at idle is around 1700 rpm, and at 35 mph in 4th gear the tach reads around 3000. When it's warm, the tach reads about 700 at idle and 3000 rpm in 4th gear is around 60 mph (3.45 gears if I remember correctly).
I'm assuming that this is a symptom of a larger problem that should be addressed. Any thoughts or suggestions would be appreciated.
Rich
My son's 89 BII (2.9L, 5 speed, EFI) gives an artificially high tach reading when it's cold. After driving for 10-15 minutes, the tach drops down to a normal reading without any actual change in the engine speed. We didn't notice this problem in the summer when we bought the vehicle, but it's been occurring since around November when the temperatures started getting very cold at night.
When the truck is cold, the tach reading at idle is around 1700 rpm, and at 35 mph in 4th gear the tach reads around 3000. When it's warm, the tach reads about 700 at idle and 3000 rpm in 4th gear is around 60 mph (3.45 gears if I remember correctly).
I'm assuming that this is a symptom of a larger problem that should be addressed. Any thoughts or suggestions would be appreciated.
Rich
New User
Joined: Jan 2002
Posts: 10
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strange tach behavior when cold
I have had the exact same problem on my 89 Bronco2 (auto, 2.9) ever since I got it 4 years ago. Though anoying, it doesn't seem to affect anything else. (But if you ever solve it, let me know).
-Marc
-Marc
Posting Guru
Joined: Aug 2000
Posts: 1,984
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strange tach behavior when cold
Guys, the tach takes it's signal from either the TFI module on the distributor, or the negative post on the coil. Try taking the connectors off, spraying with a little electronic cleaner, and re-connecting. Might help, might not, worth a try.....
Post Fiend
Joined: Jan 2002
Posts: 5,859
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From: USA
strange tach behavior when cold
Had an 87 Bronco2 xlt years ago,this was an indication the tfi module
was getting ready to die. and leave me stranded.I began to carry an
extra one with me all the time.
Rich
Ford Trucks Built Tough!
not with rocks
Watch out Mr Mayor of Truckville
was getting ready to die. and leave me stranded.I began to carry an
extra one with me all the time.
Rich
Ford Trucks Built Tough!
not with rocks
Watch out Mr Mayor of Truckville
