Engine won't rev above 3,000 RPM

[Mtn_ranger87]

1989 bronco 2 will not go above 3 grand while driving, but in neutral I will go to rev limiter. No codes, no check engine light, ran running code check, no issues. All sensors are fairly new, can't figure out why it won't go above 3 grand when it warms up and is in gear. Does smell like it's running rich as well. Advise would be much appreciated, thanks in advance

 

[RonD]

Welcome to TRS

Change fuel filter if you don't know when it was last changed

Reving in Park/Neutral requires very little gasoline
Under load is when you need max. fuel flow from pump and filter.

If fuel filter doesn't help then you should check fuel pressure, 35psi is average, run engine up to 2,500rpm, approx., and hold it there for 30seconds or so, fuel pressure should NOT start to drop.

FPR(fuel pressure regulator) is on the engine, it has the Return fuel line and a Vacuum line.
Remove this vacuum line and check it for gasoline, if found replace FPR
FPR diaphragm can leak, gasoline is sucked into the engine causing Rich running, and also lower fuel pressure with limited RPMs.

 

[Mtn_ranger87]

Welcome to TRS

Change fuel filter if you don't know when it was last changed

Reving in Park/Neutral requires very little gasoline
Under load is when you need max. fuel flow from pump and filter.

If fuel filter doesn't help then you should check fuel pressure, 35psi is average, run engine up to 2,500rpm, approx., and hold it there for 30seconds or so, fuel pressure should NOT start to drop.

FPR(fuel pressure regulator) is on the engine, it has the Return fuel line and a Vacuum line.
Remove this vacuum line and check it for gasoline, if found replace FPR
FPR diaphragm can leak, gasoline is sucked into the engine causing Rich running, and also lower fuel pressure with limited RPMs.

I have actually been a member for over tens years but didn't remember my username and the email I used to use is closed so i started a new one.

The FPR is fine doesn't smell of gas already checked that, even capped the vac line and tried driving it that didn't change anything. The FPR was changed about a year or so. Checked fuel pressure between 35 and 40 psi. Brand new fuel filter was installed just before the problem showed up. Changed filter again after the problem, no change. Swapped the module on the distributor as well. Just pulled plug on o2 sensor and drove around, did make it better but not by much.

 

[rusty ol ranger]

Wonder if the cat is plugged?

 

[Spott]

Are there any exhaust leaks between the engine and the O2 sensors?

If so, the leak can draw a little fresh air into the exhaust pipe, which will be detected by the O2 sensors, and the computer will mis-interpret that as an unbalanced fuel-air mix. It will try to correct that by increasing the amount of fuel delivered to each cylinder, however, no amount of additional fuel will stop the fresh air coming in that leak, so the computer keeps increasing the amount of fuel until it reaches its internal limits. (At this point I would expect it to set an error code, but sometimes unexpected things happen.)

Another possibility that might cause your engine to run too rich and lose power, would be clogged fuel injectors that continuously leak fuel, or that dribble a thick stream of fuel instead of spraying a fine mist (large drops of liquid fuel are much harder for the engine to ignite than a fine mist of fuel vapor). Have you tried running some fuel system cleaner through the gas tank recently? It might be worth applying two treatments in a row, in two tank fill-ups, if you haven't tried it before.

 

[rangerenthiusiast]

Does it have a bad vibration when you get up near 3 grand? I just bought a ’92 Ranger about a month ago. When I first got it, the truck would vibrate like a mofo anytime it dropped under 3K while under load (it was fine when sitting in the driveway). Also had a dead miss in cylinder 5. After some testing, I replaced the injectors and it ran like a totally different truck. Not saying it’s what’s going on with yours, just a thought.

 

[Mtn_ranger87]

Wonder if the cat is plugged?

Cat is gutted, muffler is not clogged either. Found no leaks in exhaust before o2 sensor where it could draw in air. Have used seafoam and Lucas treatments in fuel system as well.

 

[truckerdawg]

If you have the infamous lifter tick, that could be the culprit. Otherwise the ignition module possibly is weak with heat or the coil. Just a few more guesses added.

 

[rangerenthiusiast]

Cat is gutted, muffler is not clogged either. Found no leaks in exhaust before o2 sensor where it could draw in air. Have used seafoam and Lucas treatments in fuel system as well.

Not saying it’s the injectors or anything, but I ran two cans of Seafoam through mine and it did absolutely nothing.

 

[Mark01]

If you have the infamous lifter tick, that could be the culprit. Otherwise the ignition module possibly is weak with heat or the coil. Just a few more guesses added.

That’s what that tick is. Hmm [emoji848]


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