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Help, s10 4.3 tbi hesitation problem

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Old 04-26-2010, 07:26 PM   #1
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Help, s10 4.3 tbi hesitation problem

Hello,
My 94 s10 pickup with a 4.3L TBI is having a bad hesitation problem. The engine runs good when its cold, but when it warms up it starts to run like crap. When i try and accelerate or pull out from a dead stop, the motor hesitates badly.

So far I have replaced,
Cap and rotor,
plugs,
wires,
coil,
ignition module,
Water temp sensor,
Map sensor,
fuel filter,
air filter,
egr valve,

Also I have checked the following,
Fuel Pressure, 12.5 psi after the filter
Ignition timing, 0 degrees BTDC w/ computer bypassed
Vacuum check on engine, steady 19 in hg
Compression check, High pressure 175 psi, low pressure 160 psi
Catylitic converter has been taken off and checked (looks clean and unobstructed to me.)

Any ideas???? I'm totally stumped
Old 04-26-2010, 07:58 PM   #2
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Re: Help, s10 4.3 tbi hesitation problem

Check for exhaust leaks before and shortly after the O2 sensor, check for proper O2 sensor operation, check the CTS also.
Old 04-27-2010, 01:40 PM   #3
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Re: Help, s10 4.3 tbi hesitation problem

UPDATE*
I checked my coolant tempature sensor today. It looks ok. With the engine warmed up, it has 4 volts of signal voltage to the sensor, and almost no voltage from the sensor to the pcm. Is that normal?

Also, I looked and it seems like I have a crack in my y-pipe not to far from my O-2 sensor. Might this be my culprite? How do I check my o2 sensor for proper operation?
Old 04-27-2010, 05:46 PM   #4
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Re: Help, s10 4.3 tbi hesitation problem

Hello i just got over this problem with my truck if i were you i would change the cts and cts pigtail that was the problem for me and also get that y pipe checked and and take the 02 sensor out and check to see if it is all carboned up and check for voltage changes at cold and operating temp it should change because the 02 kicks in at operating temp
Old 04-27-2010, 07:32 PM   #5
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Re: Help, s10 4.3 tbi hesitation problem

Another update: My y-pipe actually looks OK under closer inspection, and my oxygen sensor seems to be operating properly; the signal wire on it fluctuates voltage between 1.1 millivolts and .26 millivolts with the engine warmed up and running.
Old 04-27-2010, 07:40 PM   #6
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Re: Help, s10 4.3 tbi hesitation problem

Possible problem,
I was looking at my coolant temperature sensor and there are two wires to it. One is yellow and one is black. With the key on and with the engine being hot or cold, the yellow wire has 5 volts; but the black wire, with the key on and the engine hot or cold has 0 volts. With the engine warm, shouldnt the resistance in the CTS go down and allow some voltage to be detected on the black wire?
Old 04-27-2010, 11:34 PM   #7
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Re: Help, s10 4.3 tbi hesitation problem

Take and go to autozone and get yourself a cts pigtail they are 14 bucks and re wire it in and see if that fixes it like i said that was my problem so give it a try its not that much money
Old 04-28-2010, 12:47 PM   #8
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Re: Help, s10 4.3 tbi hesitation problem

After some research, i found out that the yellow wire to the Coolant sensor is the signal wire to the computer; and the black wire is just a ground.
So i measured voltage across those two wires with with the pig tail plugged into the sensor.
With the engine cold and the key on,
there are 3.4 volts across the two wires.
with the engine warm and the key on,
there are 2.4 volts across the two wires

Does this sound right?
Old 04-28-2010, 02:46 PM   #9
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Re: Help, s10 4.3 tbi hesitation problem

That sounds about right if i were you now i would replace the 02 sensor that is the only thing i can think of now how is the timing on it is that all set and have you replaced the controle module on the dizzy if that starts to go it may retard the timing
Old 04-28-2010, 03:37 PM   #10
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Re: Help, s10 4.3 tbi hesitation problem

I checked the timing the other day, and it is right on. And the control module is new.
Old 04-29-2010, 12:44 AM   #11
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Re: Help, s10 4.3 tbi hesitation problem

Check the CTS with the wires unhooked and your meters set to OHMS, compare to the chart in my signature.
Old 04-29-2010, 09:13 AM   #12
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Re: Help, s10 4.3 tbi hesitation problem

This may sound stupid, But what range of ohms am i supposed to set my multimeter to to read the ohms on that sensor? My multimeter has ohms ranges of 200, 2000, 20k, 200k....etc
Old 04-29-2010, 05:59 PM   #13
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Re: Help, s10 4.3 tbi hesitation problem

So i changed out my CTS today, that didnt help at all
Old 04-29-2010, 06:01 PM   #14
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Re: Help, s10 4.3 tbi hesitation problem

i'll try my pigtail next
Old 04-29-2010, 08:39 PM   #15
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Re: Help, s10 4.3 tbi hesitation problem

Quote: Originally Posted by skylarkmk
This may sound stupid, But what range of ohms am i supposed to set my multimeter to to read the ohms on that sensor? My multimeter has ohms ranges of 200, 2000, 20k, 200k....etc
That would depend upon what temperature you were expecting, if the engine is warmed up a 2000 scale would be good, if the engine was at 32* then you would need a higer one like 200k
Old 05-01-2010, 04:28 PM   #16
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Re: Help, s10 4.3 tbi hesitation problem

Any Luck????
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