Overdrive Problem

[pauls98eb]

Hi, first I want to say that I have spent literally hours looking for an answer to this problem. I have a 98 E.B. with a SOHC engine and automatic. The trans works perfect when the engine is cold, but when it warms up it keeps dropping out of overdrive and then re-engauging. The shifts also seem to occur too fast after it warms up, although they do remain positive. If I turn off the overdrive I can drive all day long with no issues. Please tell me that it's something as simple as this loose valvebody that I've been reading about. The truck has 99k. TIA Paul

 

[Brain]

Paul, it could be something as simple as adjusting the TPS (throttle position sensor). Are there any codes (check engine light)? It could also be a bad solenoid valve, but it would give you a code because it monitors itself....

 

[pauls98eb]

Hi Brian, thanks for the reply! No there are no codes. Paul

 

[Brain]

Did you check it with a scanner, or just looking at the CEL? Pending codes won't turn on the CEL...

 

[pauls98eb]

just looking at the CEL, also the OD light works normal- no flashing Paul

 

[Glacier991]

This is gonna sound dumb... have you cleaned the battery terminals lately? I'm suspicioning there may be some ECU (PCM) issues here and that is always a good place to start. Be interested to know the sensor readings as well...

 

[pauls98eb]

A friend checked for codes and said something about the front and rear axle speeds not matching? I don't understand that because I'm having the problem in 2 wheel drive. Again thank you for your help! Paul

 

[TPLYNCH]

Transmission shifting issues can be caused by alternator or engine temp problems. Have you noticed any electrical problems, fluctuating/flickering lights etc,? Is the engine running hot at all? Does it idle high when warm?

 

[raginraj]

A friend checked for codes and said something about the front and rear axle speeds not matching? I don't understand that because I'm having the problem in 2 wheel drive. Again thank you for your help! Paul

that could be your problem, or at least a part. i'm assuming your EB is a 4x4 and has ControlTrac (Auto, 4H, 4L). have u done the "brown wire mod" to disable the transfer case from electronically engaging? a speed mismatch on the front and rear axels is a condition that normally activates the transfer case because it thinks some wheel is slipping. your erratic transmission behavior could, in some part, be caused by the computer anticipating driving conditions that are different from what u're actually experiencing. from my experience, if u're in 4 wheel drive u should never get to the overdrive gear. if u do, it means u don't need the 4wd for the road conditions u are facing. the overdrive engaging/disengaging could be the computer mistakenly trying to compensate.

 

[pauls98eb]

TPLYNCH There are no electrical problems that I'm aware of, everything works perfect. The engine also runs as it should, however the shifting problem does seem to be temp related. Thanks for the reply! Paul

 

[pauls98eb]

RAGINRAJ- I'm not familiar with the brown wire mod, could you please elborate? Thanks Paul You're correct, the transfercase is auto,high,low. If I turn the OD off the only thing that I notice is that once the engine reaches normal operating temp. the trans seems to shift from 1rst to 2nd way too soon,before 15 mph. Paul

 

[pauls98eb]

Still trying to figure this out. It seems that it's not shifting from first to second but maybe it 4wd that I feel kicking in? If the computer sees slipping would it kick in 4wd and thtow it out of overdrive? If I do the brown wire mod would that hurt anything or would it eliminate my problem because it wouldn't be able to go into 4x4? Thanks again for your help! Paul

 

[TPLYNCH]

In auto, you are always starting with 35% of power to the front, that gets stepped down in 5% increments as the speed increases to 35mph. 4x4 shouldn't effect tranny shifting. Have you tried shifting manually, starting in 1, shifting to 2, then D?

 

[pauls98eb]

yes,I can manually shift all the gears.The shifts are firm and positive.I really can't believe that this trans is shot! Also this problem is definately temp related. Thanks as allways, Paul

 

[redfusion]

that could be your problem, or at least a part. i'm assuming your EB is a 4x4 and has ControlTrac (Auto, 4H, 4L). have u done the "brown wire mod" to disable the transfer case from electronically engaging? a speed mismatch on the front and rear axels is a condition that normally activates the transfer case because it thinks some wheel is slipping. your erratic transmission behavior could, in some part, be caused by the computer anticipating driving conditions that are different from what u're actually experiencing. from my experience, if u're in 4 wheel drive u should never get to the overdrive gear. if u do, it means u don't need the 4wd for the road conditions u are facing. the overdrive engaging/disengaging could be the computer mistakenly trying to compensate.

Time traveling here..I have the same problem as OP did, currently on my 98 sport (4wd/ControlTrac) and I believe the "speed mismatch" is what is causing my issues with the OD engaging then quickly disengaging at highway speeds (around 60mph is when it will start presenting itself.) I recently had a tire that was replaced with a brand new one (same tires all around) and I believe it is the tread depth that is causing the speed mismatch between the axles, engaging the transfer case causing it to hop out of OD. This issue never arose before the new tire, no codes were reported to me after a local trans guy hooked up his scanner and monitored the shifting.

I'm wondering if putting another new tire on the same axle will solve this problem, but I don't know how the speed sensors in the axles are compared (right to left, back to front, both, etc) which signal the computer to activate 4wd. Or, just do the BWM?