97 Grand Prix With Intermittent Miss

[doctorhrdware]

You can also purchase the connectors from Mouser, at a considerable reduced price. For example I paid for the blower motor resistor connector with pins, secondary lock, if my memory serves me correctly I paid around $5.00 complete. That was the housing, pins and the secondary wire lock.

[srlash]

Originally Posted by CrazyHorst

I would check knock sensor(s) and see if they have the proper torque. I would probably replace them if the price is right.

I can't recall the variants which are used over the years...some actually are bathed in coolant and obviously you can't check the torque on those...but others bolt to a boss on the outside of the cylinder block and if they get loose, the resulting vibration can simulate false knock events.

If the knock sensor is freaking out...it may be pulling out spark like mad in an attempt to compensate...this would explain your red-hot manifolds when I wouldn't think they should be that way.

Hey Guys,

Just a quick update on my car with the number 4 cylinder misfire. I put a
scanner on my fathers 2003 Caddy and checked the timing advance.
Pretty interesting what I discovered. In closed loop at idle the car will
advance timing anywhere from 8-10 degrees. When raising the idle it will
increase up to 20-30 degrees depending on rpms. Note these are all
positive numbers. Now for my Grand Prix, at idle in closed loop the car
reads -22 degrees yes this is no typo. When raising the rpm the car reads
upwards of -30 degrees advance. Wow is this even possible that the car
could run with this much spark advance being pulled out. I guess this
would explain the glowing exhaust manifolds. So I guess either a knock
sensor is defective or it is hearing some abnormal knocking from the engine.

Let me know what you guys think !!!

Steve

[tblake]

Yes, I think you better have a look at the knock sensor. I'm not even sure where it is. I'll see if I can find the location for you. BTW, does the 3800 have 1 knock sensor or two?

[srlash]

Originally Posted by tblake

Yes, I think you better have a look at the knock sensor. I'm not even sure where it is. I'll see if I can find the location for you. BTW, does the 3800 have 1 knock sensor or two?

Hey tblake,

It has 2 knock sensors 1 by number 3 cylinder and 1 by number 4.
These readings don't make any sense, I can't believe that the car
wouldn't set a code with these readings much less run. I did double
check my fathers car with my car and the readings are accurate.
Negative 22 degrees at idle for my car versus 9 degrees for my dad's
car. !!!

Steve

[tblake]

I'm not sure how much the knock sensors are, but if I were you, I would maybe just replace them. Are they easy to access? If they are the same part number, you could swap them around, and then see what happens. ie: does the same cylinder seem to be misfiring....

I took a digimoto scan tool reading with my laptop of my 2000 GTP back in febrary. Here is a snapshop of the scan tool data to compare yours too. My car was running just fine and I was just toying around with in.

[srlash]

[quote=tblake]I'm not sure how much the knock sensors are, but if I were you, I would maybe just replace them. Are they easy to access? If they are the same part number, you could swap them around, and then see what happens. ie: does the same cylinder seem to be misfiring....

I took a digimoto scan tool reading with my laptop of my 2000 GTP back in febrary. Here is a snapshop of the scan tool data to compare yours too. My car was running just fine and I was just toying around with in.

Hey tblake,

I have the GM service manuals and tested both of the knock
sensors and they both appear to be good according to the manual.
There is 3 tests you run,make sure you have 5 volts at the connector,
check the resistance of the sensor should be close to 100k ohms and
the AC voltage test. The darn things passed all three. Oh well I guess
I will just keep plugging away at this problem. I wonder if the the
scanner I am using is not displaying the correct info. I see you have
22 degrees at idle and I have -22 degrees, although the scanner
appears to work properly on my fathers car !!!

Steve

[tblake]

Odd problem isnt it?

[CrazyHorst]

This is a high-effort thing to try...but a possibility is to remove the front cover and see about the base engine timing from crank to cam.

There should be a nylon tensioner "foot" which takes up slack on the slack-side of the chain drive, if it is damaged or missing there's a possibility you have jumped base time on the engine

I can't recall ever removing a front cover in the vehicle before...so you'd probably be into dropping the cradle or pulling the engine. I am also wondering out loud if you could do a study by rolling the engine over to check crank position vs. the pushrod displacement, check via dial indicator or other.

The red-hot manifolds hint at some kind of timing shift where either the ECM is modifying the spark time unexpectedly or else the base time of the engine is wrong.

[tblake]

Think a good compression check would point out jumped cam timing?