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Discussion Starter #1
I have a 2005 I6 that has a misfire in cylinder 2 and all the common stuff that comes with it, We have changed the Coils, Spark Plugs, I am getting no spark in Cylinder 2 and have a few questions. I see on the forums my next step is looking at the wire and ECM and maybe a crankshaft sensor. I'm going to test the connections tomorrow as soon as i pick up the tools to test them, My Questions are

1. As I've already looked at the wire starting at the Pig tail and down to were the wires join at the front of the car before the Oil cap is there a more common place that the wires go bad? Such as on the ECM side near the plugs and such.

2. Looking at the wire Diagram I need to test connector "42" and the Red/White wire on the Coil plug, But where is Connector 42 on the ECM side i cant find a help full picture or diagram.

3. If I have no spark at all could it even be a Crankshaft Sensor?(May sound like a dumb question but this is the first car I've had that has had coils sit over the spark plugs like this and also my first Inline I've owned.)

Thank you in advance for all those that help.
 

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Discussion Starter #2
Update 1: We got a few testers and we get spark on 2 its just really weak even with a new plugand coil and also spark on 3 is weak but all others are good. Any Ideas?
 

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2004 chevy trailblazer_lt
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I would take the ignition coil from the #1 cylinder, hook it up in place of the coil for cylinder 2 and see if the spark is good or bad. Then do it for #3. Then take the ignition coil from the #2 cylinder and test it on # 1 cylinder to see if the spark is any better. You need to determine if the #2 & #3 coils are weak, if the #2 or #3 spark plugs are causing the trouble or if you are not getting a full 12 VDC to those coils.

FYI, TrailBlazers are finicky about spark plugs so be sure and only use an ACDelco 41-103 or the NGK equivalent plug (BTW NGK makes the ACDelco 41-103 plug). As far as the ignition coils go, I would only use a coil from one of the following brands - ACDelco, Delphi, Standard Motor Products (non T series parts) or BWD (non P series parts).
 

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Discussion Starter #4 (Edited)
The Spark really does not change when the coil is switched Coils 2,3 have weak spark and 1,4,5,6 have strong spark, we also found a sensor had been unplugged near the oil pan i think it has something to do with the VVT the pig tail was green and mushroom shaped, we have to replace that one as it was packed with dirt and but cant find the name for it as every thing I look up for the VVT shows the one on top next to power steering.

Would bad VVT sensors cause a Misfire in 1 Cylinder?
Edit: I feel stupid it was the oil sending unit but if that's fault could it lead to the vvt solenoid acting up?
Edit 2: Ill have to do a CASE Relearn as im going to replace the Cam Shaft sensor, Does anyone know a good scan tool that can do it that's not in the 1000's of dollars or would it be better to have a dealership do it?
 

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Since only 2 of the 6 have weak spark, I would be inclined to think the problem is more electrical. Have you checked the wiring from the #2 & #3 coil connectors back to the PCM to make sure it is intact and not shorting out or opening up somehow?

I think the sensor for the VVT solenoid is the camshaft position sensor and while I do not have a definitive answer, I would say anything is possible. I had to replace my camshaft position sensor because I broke it while replacing my water pump and I did not have to do CASE relearn. If I am not mistaken, the CASE Relearn is for the crankshaft position sensor, not the camshaft position sensor.

Regarding the sensor that is/was unplugged, it could be one of the knock sensors. Knock sensors are on the driver's side of the engine. Google is your friend here as there are many drawings and photos of knock sensors for the TrailBlazer 4.2L I6 engines around.

Just as an FYI, the oil pressure sending unit is located on the passenger side of the engine block near the oil filter. If it is/was unplugged, yes, it would cause the VVT solenoid to behave abnormally since it is controlled by oil pressure.

Also, if you do not already have one, purchase a Haynes manual for your TrailBlazer. It will save you a great deal of heartburn.

Good Luck!
 

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I just thought of something else (thanks to reading another thread) - have you visually inspected the coil plugs for the #2 and #3 coils to make sure they are not corroded? Corrosion could very well drop the amount of voltage and current going into the ignition coils resulting in weak spark. Compare them to the #1 coil connector.
 

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Discussion Starter #7
Wires are good. My idea now is Bad oil pressure sending unit ---Causing---> Bad VVT Solenoid ----Causing-----> Misfire by telling the ECM something is one thing when its the other? All the Sensors and Solenoids are in a cart to buy on pay day so i guess we will see.

The VVT had some of the ports in the middle had alittle bit of stuff over the screens but not much
gonna do 6 spark plug, The oil sending unit and the VVT Solenoid and the 2 Coil packs and see what happens,
 

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Possible for a bad oil pressure unit to cause the PCM not to tell the VVT solenoid to move the camshaft properly, and misfire, BUT, I do not believe it would cause a weak spark out of a coil (although I could be wrong).

OK on replacing the VVT solenoid - they do get gummed up and don't function properly if the oil is not changed regularly with a decent motor oil.

If a coil fires weak on one cylinder but fires normally on another cylinder, that tends to mean the coil is OK, and there is something wrong with the wiring (or the connector) to the coil to the cylinder that shows weak spark.

Please remember to purchase decent parts. Mid to low tier parts can cause all kinds of problems. I already told you my preference for spark plugs and ignition coils, but for sensors, I recommend the same product lines. FYI, the SMP T series and BWD P series are "value oriented" parts aimed at those looking to spend as little as they can in order to get a vehicle running for a short time. The "regular" SMP and BWD parts are top of the line replacement parts that meet or exceed the OEM part's specifications (plus SMP and BWD parts come off the same assembly line and are manufactured by the same company; they are just marketed differently).

And as always, Good Luck!
 

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2006 gmc envoy_denali
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Wires are good. My idea now is Bad oil pressure sending unit ---Causing---> Bad VVT Solenoid ----Causing-----> Misfire by telling the ECM something is one thing when its the other? All the Sensors and Solenoids are in a cart to buy on pay day so i guess we will see.

The VVT had some of the ports in the middle had alittle bit of stuff over the screens but not much
gonna do 6 spark plug, The oil sending unit and the VVT Solenoid and the 2 Coil packs and see what happens,
The advice to stay with the brand names mentioned is SO IMPORTANT because manufacturing standards vary so widely, especially with replacement parts for older vehicles! Purchase wisely among the brands recommended and price won’t be an issue. You should perform a continuity measurement on each coil pack wires:
REMOVE BATTERY NEGATIVE CABLE
FOR COIL PACK 2 (measuring from each connector pin) to end point provided)
BLACK to ground/common at fuse box
RED/WHT to Pin 42 of PCM
PINK to battery positive
These are the wire colors for a 4.2L 2004 should be same as 2005.
Readings should be <1.0 ohms,
 

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Discussion Starter #10
We replaced the VVT solenoid and changed the oil and cleared the codes and so far no misfire codes or codes in general have reappeared. It still has a rough Idle We are going to clean the throttle body and see what that does for it.
 

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Discussion Starter #11
Just an update, The Codes came back we've slowly been getting the car to run better and I've just gone ahead and ordered a new ECM from Flagship one cause now at idle the oil pressure gage will drop to 0 till I press the gas but I'm not overheating and no oil burning smell can be smelt.
 

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In the case of low oil pressure the very first thing to do is check the pressure with a real gauge.


 
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