Have an '89 Ranger with the 2.9L auto tranny. When it is cold it will run just fine going down the road. I can hit 55-65mph, when it warms up it loses at least half its power and I can't get over about 35mph but it still revs between 3K-4K. If you floor it, it downshifts but will not speed up at all. When it is cold everything seems to work fine. It has had new plugs and distributor cap in the last year. I thought it was tranny related until I noticed it seems to run fine when it is cold, now I am thinking more engine related.

The engine does knock and tap and use some oil but there is no black cloud at any time and it makes noise all the time. So I am wondering if there is a common trouble area on these engines that could contribute to this problem. I have never noticed the tranny slipping and the fluid looks/smells fine and has been changed in the last 20K miles.

Any ideas would be great.

 

How many miles on this truck? Could be a number off things.

 

It has around 130K

 

What grade oil are you using? It may be worth drain out a half quart or so of oil, and top it off with Marvel's Mystery Oil to try and get those lifters working again. I am thinking that the coolant temperature sensor has failed. The 2.9 has two coolant temperature sensors, one for the gauge and another for the computer. They are not interchangeable. The gauge sensor has 1 wire going to it, while the computer sensor has two.

AutoZone.com | Vehicle Selection - Year (It will make you select your vehicle and engine but should bring you right to the part once that is done)

 

IT gets 10w30 of whatever the cheapest oil is I find. I did figure some lifters have crapped out, might try some marvel to clean stuff up thanks for the idea. The gauge still seems to function so maybe that other one is bad, thanks for the link.

 

On my truck, the gauge sending unit failed, but the computer one still worked just fine. That threw me off for a little bit until I learned that it has two sensors.

Have you tried renting an OBD-I reader from Autozone to see if you have any codes? Some codes may be stored without actually triggering a CEL. (My 87 ranger doesn't even have a CEL!)

 

No I haven't, I'll pick one up when I get the oil and parts.

 

Well got the sensor and threw it in and no change. AZ doesn't rent out OBDI scanners anymore so I am still waiting on getting them pulled if I ever take it to town.

The thing that drives me crazy is when this happens I will be going 55-65mph and start to lose power so when it gets down to say 35mph I let off the gas and then floor it, I have been flooring it the whole time to that point anyway. The tranny will downshift and rev to 4Krpm but it will lose speed it will not speed up even when it downshifts. I'd almost suspect a torque converter but I don't know why it would work for 5 minutes when it is cold before it goes bad. I'd also suspect plugged cats but I don't know why it would run ok at all if they were bad. I did notice this last time that it smelled like it was running rich after I tried to floor it and nothing happened.

I think my next test will be checking the fuel pressure and change the fuel filter.

 

I just did some looking around, Advanced Auto and Orielly's (if there is any around you ) have rent-a-tool programs and free code checks.

Did you take off the battery cables for 10 minutes after changing the sensor out to reset the computer?