Mechanics

QUESTION HESITATION/LOW POWER AROUND 2K-2.5

1995 Isuzu Rodeo

Engine Performance problem
1995 Isuzu Rodeo Question 6 cyl Two Wheel Drive Automatic 160000 miles

I did start a post a few months ago, but I let it go as it seemed it went away after a completely new exhaust was put on.

Here is the issue:
Around 2-2.5k RPMs the engine seems to "choke/hesitate" while driving which in turn causes me to downshift to get past this pesky RPM range. It has harly no power during this range. To me it seems like it's getting a bad fuel ratio in some fashion. While in park I can step on the gas and it seems to rev up just fine past this range fine. Also at idle, it runs really rough at times. When the engine is cold, it seems to run better.

Sometimes, maybe like 10% of the time... the truck runs fine even when warm. After I put the Rodeo's new exhaust on back in Sept, it seemed to run great and I figured poor back pressure messed up the fuel mixture. However, it's come back with a passion! Maybe because of the cold weather in New YorK?

Also, if I put the truck in gear and hold the brake, it cannot even come close to breaking loose (pressing the gas hard) and spinning in the gravel drive-way... not sure if that matters as all my other vehicles could break loose more or less.

It's gotta be a bad sensor somewhere... I also replaced the vacuum lines recently too.

Related post:
http://www.2carpros.com/forum/viewtopic.php?p=610112#610112
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Kenyu73
December 17, 2009.



Hi kenyu73, Welcome to 2carpros and TY for the donation and selecting us as your auto repair site Feel free to ask questions at anytime and Merry Christmas and a Happy New Year 2010

Your possibilities here could be one of the following causing the problem of lacking acceleration, hesistating and surging-

Oxygen sensor
Catalytic converter
Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)

Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include: Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires

Rasmataz
Dec 17, 2009.
Thanks for the followup.

* I have brand new exhaust including converters.
* I used about 10 injector cleaners over the course of 1 month
* The vacuum lines are new
* Fuel Pressure Regulator is new
* used dry gas a few days ago
* Installed new IAC value

Before I replaced the exhaust, I went through and did a bunch of sensor swaps including: TPS, O2 and MAP. However, I didnt notice any change, but the rotten exhaust may have been the cause?

Anyhow, I'm trying to determine the best logicial steps to take so I dont waste money adding parts by guess alone.

What would you suggest?

Tiny
Kenyu73
Dec 18, 2009.
But the rotten exhaust may have been the cause?

A rich fuel mixture will often produce a " rotten egg" odor in the exhaust (the smell is hydrogen sulfide). Underlying problems may include an engine management system that is not going into closed loop (check the coolant and oxygen sensors, or for a thermostat stick in the open position), plugged PCV valve, or excessive fuel pressure (bad fuel regulator). High CO levels in the exhaust can also be caused by an inoperative air pump system.

Rasmataz
Dec 18, 2009.