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Old 09-18-2022, 10:24 AM   #1
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Engine Hesitation on P32, 8.1 Vortec

Hello,

I am having a performance problem on my 2004 P32 8100 Vortec with roughly 15,000 miles. The problem is big hesitation and usually occurs while accelerating from a stop or at low RPM. It occasionally occurs at higher RPM while climbing a hill as well. Also noticed that when the problem occurs while accelerating from a stop it affects the speedometer meaning it reads 0 until you hit around 5-10 MPH. Oddly enough the tach is not affected even though the it is loosing RPM.

I have replaced the spark plugs and wires, fuel filter, and ran some Lucas fuel treatment through a tank of supreme fuel. The plugs and wires and fuel treatment seemed to help initially but problem returned. Replaced the fuel filter which did not help.

Have read that the problem could be Idle Air Control (IAC), Mass Air Flow Sensor (MAF), throttle position sensor, or the crankshaft positioning sensor. Also have read about updated software helping?

Anyway, does anyone have a suggestion which part to swap next or if I need software? I like to do my own maintenance so hoping everything mentioned can be done without taking to the shop.

Thank you,
Brian Weirth
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Old 09-18-2022, 11:33 AM   #2
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So you don't mention if you have a scanner.. if not.. it's time you do.. now don't cheap out here.. buy the best you can budget for.. you need one with live data capture and web support.. and one with good book.. it will save you a small fortune.. many recommend here your next thing would be.. clean maf... but I think your next move is to get scanner..
Good luck and keep us posted
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Old 09-18-2022, 01:37 PM   #3
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The MAF and Air Intake valve (butterfly) can be removed and cleaned rather easily.
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Old 09-18-2022, 08:59 PM   #4
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So you don't mention if you have a scanner.. if not.. it's time you do.. now don't cheap out here.. buy the best you can budget for.. you need one with live data capture and web support.. and one with good book.. it will save you a small fortune.. many recommend here your next thing would be.. clean maf... but I think your next move is to get scanner..
Good luck and keep us posted
I have an INNOVA 3100 which has been helpful when the check engine light pooped up. It was diagnosed as a knock sensor twice.

No check engine light pooping up now but will check.
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Old 09-18-2022, 09:07 PM   #5
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The MAF and Air Intake valve (butterfly) can be removed and cleaned rather easily.
Easily sounds good to me. I will research this although may take a bit of time to actually apply the fix. I am not very good but I am slow.
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Old 09-18-2022, 10:16 PM   #6
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Start with the throttle position sensor. sounds exactly like the symptoms that I was having until I replaced mine. Might want to consider a "sensor replacement program"... buy all the sensors new from amazon or such and replace them... the get old and weak.... I did this was so surprised at how well my engine ran!
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Old 09-18-2022, 10:23 PM   #7
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Are you getting a Check Engine Light?
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Old 09-19-2022, 01:58 PM   #8
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Are you getting a Check Engine Light?
Negative on the check engine light.
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Old 09-19-2022, 03:16 PM   #9
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Start with the throttle position sensor. sounds exactly like the symptoms that I was having until I replaced mine. Might want to consider a "sensor replacement program"... buy all the sensors new from amazon or such and replace them... the get old and weak.... I did this was so surprised at how well my engine ran!
I am going to start with the throttle position sensor since you were having similar issue until you replaced yours. I am looking for an OEM part now.
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Old 09-19-2022, 03:43 PM   #10
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Problem

The worst thing you can do is just throw parts at the issue without confirming this is the problem. Scanner will tell you what is wrong BUT not all scanners are the same.

The sweetness of low price is long lost and poor quailty after you throw parts at it not knowing that is what is needed.

My suggestion is get it to the OEM dealer, which I believe is GM. They have the proper scanners and OEM tech bulletins. In the long run you will spend less. As Clint Eastwood said as Dirty Harry movies, one must know their limitations.
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Old 09-19-2022, 05:14 PM   #11
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The worst thing you can do is just throw parts at the issue without confirming this is the problem. Scanner will tell you what is wrong BUT not all scanners are the same.

The sweetness of low price is long lost and poor quailty after you throw parts at it not knowing that is what is needed.

My suggestion is get it to the OEM dealer, which I believe is GM. They have the proper scanners and OEM tech bulletins. In the long run you will spend less. As Clint Eastwood said as Dirty Harry movies, one must know their limitations.
Good point. I actually talked with Workhorse Parts. They had the same great technical advise you have given. Check the fuel pressure (should be no less that 45 psi) that is easy, and check the reading from the MAF sensor (no less than 230 grams/second at WOT). Problem is finding someone with a scanner that can measure the MAF output. I think a scanner that can measure that is very expensive.
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Old 09-20-2022, 09:11 AM   #12
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I am going to start with the throttle position sensor since you were having similar issue until you replaced yours. I am looking for an OEM part now.
wouldn't worry about OEM part, just get one that will work correctly.... most OEM parts of this kind are manufactured in China anyways. Just replaced a MAS sensor on my chevy truck, OEM $125. amazon $27... works perfectly...
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Old 09-20-2022, 09:17 AM   #13
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The worst thing you can do is just throw parts at the issue without confirming this is the problem. Scanner will tell you what is wrong BUT not all scanners are the same.

The sweetness of low price is long lost and poor quailty after you throw parts at it not knowing that is what is needed.

My suggestion is get it to the OEM dealer, which I believe is GM. They have the proper scanners and OEM tech bulletins. In the long run you will spend less. As Clint Eastwood said as Dirty Harry movies, one must know their limitations.
I don't agree, the worst thing you can do is to not record what parts you have replaced. Moho's sit a lot, the sensors age and become weak and will give intermittent readings not failing completely. most sensors will last dependably for about 10 years, after that it is a crap shoot as to which ones fail and how soon. I'd buy a higher dollar code reader or better yet buy program for your laptop. It will help find any sensors that have completely failed but ones brain is the best diagnostic tool....
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Old 09-20-2022, 11:13 AM   #14
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Scanner

Yes, scanners are expensive. Cost of a proper scanner most likely cost more than paying a shop with the proper scanner to scan for you. then complete the repair yourself.

If you still want to attempt repair without having to spend a lot of money I would first if not already done, purchase a quality contact cleaner and clean all sensors and harness.

I have doubts that this will solve your problem. Most connectors have electronic grease applied. If so and choose to clean you will need to reapply the grease.

Most likely once a good scanner is used the repair will be easy. At the same time consider cleaning the throttle body.
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