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Tom
Tom, ASE Certified Technician
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Experience:  ASE Certified Master Technician
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95 isuzu rodeo has hesitation acceleration and wandering idle.

Resolved Question:

95 isuzu rodeo has hesitation acceleration and wandering idle.
Submitted: 4 years ago.
Category: Car
Expert:  Tom replied 4 years ago.
Most common are cracked intake manifold gaskets.Spray the intake manifold and see if the idle raises if so thats the issue this is very common let me know what you find.
Customer: replied 4 years ago.

After injectors were replaced, the mechanic sprayed in that area and found no leaks.

 

i did the same and found no change in rpm.

 

Another mechanic did a smoke test and found

small leak from the pcv grommet and it was replaced with new one.

Expert:  Tom replied 4 years ago.
Has the o2 sensor replaced?
Customer: replied 4 years ago.
no
Expert:  Tom replied 4 years ago.
Ok this will cause this code .If timing is fine you need to check the o2 sensor next and repalce it and also make sure the catalytic converter is not clogged.Has o2 sensor cause this exact issue .These are the next steps.Positive feedback and bonuses greatly appreciated.Last could be a faulty ECM.
Customer: replied 4 years ago.

Only code 12 stored.

Timing is 8-10BTDC.

Converter was checked at 2 muffler shops, not clogged.

Would not a defective o2 sensor show a code?

Expert:  Tom replied 4 years ago.
Yes it will give the code 12 and sometimes code 44 . This is either an o2 sensor issue or ECU issue . If compression is good start here next. Hoped this helped . Positive feedback and bonuses greatly appreciated.
Customer: replied 4 years ago.

One mechanic had checked compression but i think it was done on one cylinder.

 

I will check all 6.

 

Doesn't this engine require 4 o2 sensors.

Expert:  Tom replied 4 years ago.
Ok check compression and yes there are 4 sensors so test them before just repalcing them .
Customer: replied 4 years ago.

how should i test the o2 sensors?

 

 

Expert:  Tom replied 4 years ago.
With your meter or scanner.
Customer: replied 4 years ago.

I'll check the o2's tomorrow.

Thanks for your help.

Expert:  Tom replied 4 years ago.
anytime .Dont forget to click the green accept button so I can get credit for my help.You can add to the question for no further charge if you still need help.Positive feedback and bonuses greatly appreciated.
Customer: replied 4 years ago.

Sorry I have not replied to you sooner, did not mean to leave you hanging but I had family health issues that take priority.

Last time we talked you suggested checking the o2 sensor.

Results:

1) Original o2 sensor heater element showed no resistance; and real-time o2 output

measured at ECM was .020-.080v instead of .200-.900v, crossover was approx

1x /sec @750, 2x /sec @2000 rpm. Amplitude low but frequency good.

2) Checked circuit integrity of o2 heater and signal: good

3) Replaced o2 sensor with oem Denso.

4) New o2 sensor heater element measured 3.5-15ohms; and real-time o2 output

measured at ECM was initially .340V for 30 seconds then dropped to .020-.030V at

750rpm; .060V @2000rpm @45mph cruising at level, and .200-.720V @ 2000rpm cruising uphill.

5) Performed back pressure test utilizing the o2 sensor hole. There is only one o2 sensor

and it is located pre-catalytic converter.

Result was: 0.5psi @750rpm, 1.0psi @2500rpm, and 1.5psi with sudden throttle.

6) Final result: car performs with same symptoms of hesitation at partial throttle at any speed but not as bad. Car hesitates and stumbles then seems to clear up then strong acceleration.

Expert:  Tom replied 4 years ago.
OK this can be caused by a faulty ECU or the catalytic convertor is damaged and is the cause .I would have this checked again.Hope all is well with your family as thats what counts in this world.I would check these next .
Customer: replied 4 years ago.

1) Why is the o2 reading so low at idle, ex: .060v instead of .2-.8v.

2) I tested backpressure .5@ idle and 1.5@ sudden throttle. Isnt under 2.0

acceptable?

 

Expert:  Tom replied 4 years ago.
No that's why this is either a catalytic converter issue or ECU issue . These are what will cause this and need to be checked next. Hoped this helped. Positive feedback and bonuses greatly appreciated.
Customer: replied 4 years ago.
how do i check a faulty ECU?
Expert:  Tom replied 4 years ago.
Unfortunately it would need to be sent out and tested for about 75 to 100 dollars to test the printed circuit board inside.
Customer: replied 4 years ago.

I will take my car to where i bought the last convertor and have them check it tomorrow

morning and ill let you know what they found.

Thanks.

 

Expert:  Tom replied 4 years ago.
No problem . Don't forget to click the green accept button so I can get credit for my help. You can still add to the question for no further charge . Hoped this helped. Positive feedback and bonuses greatly appreciated.
Customer: replied 4 years ago.

I took the car in yesterday morning to check the condition of the converter and muffler.

1) They put it on the lift and found the converter and muffler to be good.

Isuzu spec states if 1 3/4-2.0psi @2000rpm backpressure that converter is plugged.

I'm getting .8-1.0 psi @2000rpm.

2) They noticed the connector to the MAP sensor had a broken locking tab and used

a tie wrap to secure the wires to the sensor mount. I took it for a test drive and 95%

of the hesitation problem was gone. Pulling away from a stop at low rpms it ran

strong. They suggested I check the integrity of the connector and wires.

3) Drove to a gas station to fill-up and on the way there were no problems. After restart

it went back to hesitation problems.

 

Expert:  Tom replied 4 years ago.
Ok if those map sensor wires are damamged theres a good chance its loosing its signal and its possible the map sensor is also shorting out.These need to be checked next.Hoped this helped.Positive feedback and bonuses greatly appreciated.
Customer: replied 4 years ago.

I subscribe to Mitchell1 and Alldata and I am presently downloading wiring diagrams

so that I can check the wiring harness this weekend.

 

I have not rated you yet because i thought as soon as i did it closes this thread and it

helps me by reviewing your answers.

 

 

 

Expert:  Tom replied 4 years ago.
No once you click accept you can continue for no further charge and I will continue with you .
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