Head scratcher

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#1
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MAKE:Chevy
MODEL:Lumina(car)
YEAR
:1996
MILES:101000
ENGINE
:3.1
DESCRIBE ISSUE....Loss of midrange power- car starts right up, idles great. Get rolling, step on gas, bogs. Press gas hard, takes off. Things already done: intake gaskets changed, fuel and air filters changed, fuel pump changed, MAF sensor cleaned, plugs and wires changed (stock AC plugs) trans filter and fluid changed, coolant and hoses changed. Had car at two different independents, they can't figure it out. Took to Chevy dealer, they guessed knock sensor, changed it, no difference. They disconnected knock sensor, runs fantastic, like normal. This is my daughters car 80 miles away, so I can't work on it, but I thought maybe someone had seen this before or might have some ideas.
 
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nickb2

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#2
Hi Deano. Can you be a bit more specific?

Any check engine light on? Any work done to it lately? Like tune up, tranny oil change, gas filter, etc?
 
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#5
What is fuel pressure? What is compression? Do you possess tools to check this?

Do you have a scanner or a code reader?
No codes - I assume the Chevy guys did the basics. Grasping at straws - maybe bad wiring between knock sensor and computer?
 
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#7
Any number of things could cause "a loss of mid range power" condition.

Clogged air filter, clogged fuel filter, clogged catalytic converter.
Both filters changed. Thought about cat, but runs perfect with knock sensor disconnected, so not cat.
 

nickb2

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#8
If it was a Knock sensor issue, the PCM would have coded either a P0325, P0326, P0327.

The knock sensor module is located within the PCM.

If the PCM detects a faulty wiring/or a knock sensor faulty. It will code a P0327.
 

nickb2

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#9
Ok, no codes and suspect knock sensor system. Does it ping/pre detonation when pushed or going up and incline?

Read the following pdf flow chart. Ace 0 pdf.

I will be white on black, my virtual printer is screwed up that way. But they are readable.

Check everything listed in the flow chart. Like torque lock up, tightness of engine grounds and other such things.
 

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#10
If it was a Knock sensor issue, the PCM would have coded either a P0325, P0326, P0327.

The knock sensor module is located within the PCM.

If the PCM detects a faulty wiring/or a knock sensor faulty. It will code a P0327.
I had a reader on it a couple of weeks ago - no code. Called daughter, Chevy dealer said no codes. I did say it was a head scratcher!
 
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#12
Ok, no codes and suspect knock sensor system. Does it ping/pre detonation when pushed or going up and incline?

Read the following pdf flow chart. Ace 0 pdf.

I will be white on black, my virtual printer is screwed up that way. But they are readable.

Check everything listed in the flow chart. Like torque lock up, tightness of engine grounds and other such things.
Nick, thanks for the chart. Thought of all those things, but just disconnecting the knock sensor makes the car run perfect, so all those things must be okay. Right now, my daughter is just driving it with the sensor disconnected and we're hoping for the best; it is a twenty year old car.
 
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#14
Hot weather can cause a knock if EGR is not up to par, if fuel quality is poor, if engine if running a little too hot, if compression is high due to carbon on piston heads. But if engine sounds good, nice and quiet during moderate acceleration at full temperature, I would just drive it with knock sensor disconnected.
 
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#15
Hot weather can cause a knock if EGR is not up to par, if fuel quality is poor, if engine if running a little too hot, if compression is high due to carbon on piston heads. But if engine sounds good, nice and quiet during moderate acceleration at full temperature, I would just drive it with knock sensor disconnected.
That is the plan - thanks