high rpm while cruising down highway

[puty72]

first off my truck is an 89 ranger 2.9 auto. my tach works because i have an aftermarket one but anyways while cruising down the highway at 55mph my truck screams at between 3500 and 4000 rpms. I was wondering what could cause this.

 

[IMenriched]

first off my truck is an 89 ranger 2.9 auto. my tach works because i have an aftermarket one but anyways while cruising down the highway at 55mph my truck screams at between 3500 and 4000 rpms. I was wondering what could cause this.

It could be a faulty fan clutch for the water pump....sometimes they get stuck on high & make it sound like the engine is really rapping up. But seeing that you do have a tach.

If the engine is really running that hard then the transmission is not shifting into higher gears. Could be a simple shift modulator....see if the vacuum line is any good going to it.

any codes tripped?

 

[AllanD]

presuming 3.73 gears you should be doing only ~2100rpm in 3rd gear @55mph
with an A4LD.

3rd is 1:1.

unless you have BOTH 4.56 gears and are running on temp spares....
I'd guess there's something wrong with that tach.

AD

 

[puty72]

my check engine light has been on since i got the truck and i didnt have this probally till recently. ill have to get the codes broguht up and ill check the transmission modulator

 

[AllanD]

Check engine light? on an '89?

Somethin' ain't right here...

AD

 

[fastpakr]

Allan, when were they added? I had thought '88 or '89 was the first year.

 

[LittleHorse]

pretty sure my '89 has a CEL. They weren't advanced yet to the point that transmission codes registered though so if the transmission is the issue the codes aren't going to tell you anything.

Have you counted the shifts? Start from a stop and see how many gears you get to. Doesn't sound like you're getting through all of them.

 

[loneranger48]

i agree with little horse my 88 has a check engine light.

 

[Psychopete]

My '88 had a functioning check engine light too. Used to pulls codes using the CEL instead of a meter...

Pete

Edit:
Pull codes if you have a lit up check engine light - EEC-IV diagnostics in the technical library...