b4000 wont pass 3700 rpm

[ranger_impersonator]

has anyone ever encountered this problem? my 98 mazda b4000 4x4 auto trans WILL NOT go past 3700 rpm, full throttle, or easing up to it, it just wont go past it. it hits 3700 rpm and acts like it hits a speed governor, the rpms decrease but the engine still runs, if i keep my foot in the gas, the rpms will just keep dropping. if i let go of the gas it goes back to being normal. the truck seems real under powered too. i can rev it to redline in neutral and park too. any input would be very appreciate, i dont even know where to start looking, no codes no warning lights.

 

[adsm08]

That kinda sounds like the fuel pump can't keep up.

I would start by running a loaded fuel pressure test. Pressure should hold steady or go up as the throttle angle increases. Go rig up a fuel pressure gauge so that you can see it (this will probably involve zip ties around a wiper blade) and go for a drive. If the pressure starts to drop when you hit WOT, you need a new pump and filter.

 

[Lil-Pony]

He could have a cat thats begining to clog

 

[ranger_impersonator]

I will have to check the fuel pressure thank you. Is there any way to check the cat?

 

[Lil-Pony]

unbolt the cat and see if there is any improvement in the rpm band

 

[stmitch]

Sounds like the truck is in 'limp' mode. The same thing happened to mine once. The Vehicle Speed Sensor was bad. Took 10 minutes to put a new one in, and it was good as new.
Does the speedometer work?

 

[ranger_impersonator]

The speedo works just fine. It only does it sometimes I've noticed. But it has no consistency

 

[alwaysFlOoReD]

I seem to remember reading something about a rpm limiter when in park or neutral. I don't know if that would apply in your case or how the computer would think it's in that gear while traveling down the road. I'm just adding this thought in case it may have bearing.
Good luck,

richard

 

[adsm08]

There is a P/N rev limiter that should factor in here, but it sounds to me like he is seeing this while driving. The rev limiter doesn't apply in gear.

 

[Lil-Pony]

yah, in a auto 98 the trans is ecm controlled right? anyway even if the ecm saw the trans as being in P/N all the time, you should be able to start the truck in drive, which i dont recommend.
to check for this situation disconnect the start wire that leads to the starting solenoid and test for voltage on that wire while the trans is in drive and the your cranking the key. MAKE SURE TO DISCONNECT THIS WIRE when you test for voltage if not we will call you bad names when you come back and tell use your truck shot though the garage

 

[Earl43P]

I seem to remember reading something about a rpm limiter when in park or neutral. I don't know if that would apply in your case or how the computer would think it's in that gear while traveling down the road. I'm just adding this thought in case it may have bearing.
Good luck,

richard

It does and I have experienced it on a 99 Explorer.

The transmission has an advanced neutral safety switch called the DTRS (digital trans range sensor). In P or N the 3500 rpm limit is applied. If the DTRS is out of adjustment (or bad as was mine) it can think it's in Neutral when you have selected Drive.

A simple test is verify the reverse lights work. If not, suspect DTRS adjustment will fix it. It's as simple as loosening the 10mm mount bolts and lining it up so the reverse lights work (There are alignment marks on the DTRS but they are hard to see).

The DTRS is mounted to the input spindle of the transmission linkage, visible by looking up under the driver side. Another test is when it does it, shift down to 2nd and floor it.

If you end up replacing it, do not over-tighten the big spindle nut. It will be hard to move the lever into gears if you do (ask me how I know).

I'm surprised it hasn't lit up your Check Engine Light.

 

[ranger_impersonator]

It is already a little hard selecting gears come to think of it

 

[ranger_impersonator]

ok now i noticed it is taking too long to shift out of first gear.... maybe related, or unrelated? anyone have any idea what that may be from? its the 5r55e 4x4 trans