3FE power issues, quick diagnosis (1 Viewer)

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May 29, 2012
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Long story short. 1991 80 series, 3fe 196'000 miles. Winch bumper, sean rear swing out carrier, rear drawer system, rack, 3" lift. Stock gears.

Tuned it up 2 years ago. New plugs, wire, filter.

Several months ago it wouldnt pass smog. After two fails I bought a refurbished EGR and it barely passed. Guy said to replace O2 sensors and theyve been replaced.

So driving on highway no matter what gear, somewhere at about 3200 RPMs the engine loses power and has no umpf. At about 3900-4k rpms.the power picks up again. I noticed that in first when I floor it, the engine winds fine up to 3200 and then loses power but still climbs..but if I let off the pedal to like 75% the power comes back. So it seems that I lose power in that rpm range only at full throttle.

I have cleaned the afm and have no apparent vacuum leaks. I have also just ran fuel injector cleaner.

Any thoughts on something im missing? The Cats dont rattle so theyre not broken. Ive done several searches.but dont find any similar exact symptoms.
 
My guess is throttle position sensor. If you have a multimeter you can check yours as per the FSM specs and replace if necessary.
 
Check all your engine harness connectors.

It won't be cats, nothing about them is nothing to cause that much of a significant change.
 
What is a "refurbished EGR" and how does one get refurbished? Both the EGR and EGR vacuum modulator have diaphragms that deteriorate over time. Typically, a failed EGR system will lead to poor acceleration at lower RPMs and open up around 2400 or so. Your problem seems to be the exact opposite of that.
Certainly check the sensors mentioned previously according to the FSM, but I wouldn't rule out the EGR just yet.
Catalytic converters become clogged over time and can restrict flow, but this is typically noticeable over the entire RPM range.

There are 2 fuel filters that should be changed. The frame mounted filter below the distributor and there is a pick up filter in the tank on the fuel pump.

The fact that the truck is not passing emissions testing is pointing to O2 sensors, cats, and general maintenance.
You say you did a "tune up 2 years ago", which was plugs, wires, and filter. Please have a look at this thread regarding a full tune up.
https://forum.ih8mud.com/threads/general-3fe-tune-up-info.270758/#post-4204984
 

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