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Discussion Starter · #1 · (Edited)
I have an interesting situation here and hopefully some one has some more ideas.

The car was brought home running rough. It has since only been started once in 3 months with lots of smoke.. I wasnt there but was told it was white. All plugs were replaced prior to that start so they have 5 minutes on them.
Owner put a scanner on the car and produced no codes other than scanner stated all cylinder timings were off. (I wish I was there)

Here is a preliminary list of things looked at by myself.
Spark = yes
Plugs looked good except one a little dark. All had fuel.
Checked firing order.
Fuel = yes
New pressure regulator (by owner) but pressure not tested yet.
Oil changed by owner for fear of water contamination.
Compression all equal at around 175 psi

My initial thoughts:
After doing the compression test with all plugs removed. I replaced the plugs and tried to start. Obviously this didnt work but I can rule out any flooding or water in cylinders.
My thoughts turned to timing issues. A good compression test should rule out a timing chain.
Now onto ignition timing.
Today I am going to look into testing the Crank Posistion Sensor
Assure there is spark from all 3 coils ( I know I forgot)
Possibly pull valve cover to ensure correct valve timing.

Initially the owner wanted me to pull the intake as someonehas convinced him it was a coolant leak from there as these engines are said to be prone to that.
After clearing the cylinders I should be able to run the engine even with some water present. At least long enough to get the running engine codes.

Im having a real problem with taking a engine apart not knowing for certain what is wrong, even with him wanting this.
The trouble shooting would grow by a factor of ten after doing that and I dont think that is the real problem to begin with.

I realize the computer could be the cause but Im trying to save that for last.
(I dont have the ability to test this or a spare)

There must be some thing I havent thought of yet or a easier way to disprove some of my ideas.
Could the circuit board under the coils affect the timing?

Any and all sugestions will be considered and tested so dont be shy.
There will be beer.:pray:
 

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Hi Pat,

Did you check the gap on those plugs he put in? They came out with lean burn in 96 and the gap moved out to 60 thousands. Closer than that would give iffy spark. Need to jump across a large gap in a lean mix.

Crank position sensor sounds like a good candidate.

Any way two of the three spark signals to the coil packs could have been switched?

SABL will be offering help when he finds out about the beer. :)

Best regards,
Mack1
 

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Hi patmcgroin

Q:The car was brought home running rough. It has since only been started once in 3 months with lots of smoke.. I wasn't there but was told it was white.\:Q



The Buick appears to have has a blown head gasket. If there was lots of white smoke then its a clear indication of it. You must perform a leak down test on all cylinders before you do anything. Check radiator coolant level and see if the engine has overheated at some point. If you cannot perform a leak down test, open the rad cap while having someone cranking the engine, ( make sure battery is fully charged, coils disconnected, pedal to the floor while cranking for maximum intake) and look for blow-by coming out of the radiator. If it shoots out the rad, the gasket or the cylinder heads are gone.
 

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Discussion Starter · #4 · (Edited)
Thanks for the respones guys.
Here is what I have learned in no particular oreder.

mack1: The coil packs are the C3I type with all 3 mounted to the same plate with the ignition control board underneath, so if there is a mix up its internal.

octaneman: I have thought of that and did a sort of a modified version in that I made certain the radiator was/is full. I used the burp screw to be sure that it was as full as possible and have left the cap off to keep an eye on it. That was the first thing that I did as I know that is a pretty dependable way to detect blow-by without a radiator pressure tester. The coolant has a good color and no bubbles. So I am going to need to get it running for further diagnosis of that.

Im fairly certain that I have made progress. I got a schematic from Auto Zone and even though it it wasnt completely accurate it was pretty good. Im not sure if GM got it wrong or Auto Zone but I guess that doesnt matter. If anyone has a different ignition schematic for a 98 3.8 I would like to see it.

Any way The vehicle has a 2 sided crank posistion sensor. One half sends a 18x reference and the second half sends a 3x reference. (each per revolution)
I nicked the wires and put a volt meter to them.
Not having a graphing multi meter I cranked the engine by hand.
More blood and more beer later I dertermined that the sensor was operating correctly going into the ignition control module but that the 3x reference was not coming out correctly and going to the main computer.

I have been told that Auto Zone can test the ignition control module but with only about 50% success.
I would think that the 3x signal on a 6 cyl. would be standard and should fall in the 50%.
In the schematic it shows the 3x signal as basically a pass through but there isnt enough detail to be certain.

The owner cant get one until Tuesday due to the holiday and payday so keep those cards and letters coming because I just am not yet certain and I hate to throw money at a problem..

EDIT: 2 things I forgot.
The plugs are gapped correctly and I looked into the cam posistion sensor but the manual say it only controls the injectors and will revert to a standard pattern. Enough to allow it to run.

Thank You thus far Pat
 

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If you haven't already try a coolant pressure test, (connected to the rad). I would think Auto Zone would have a kit available for rent cheap. In my opinion white smoke usually indicates burned coolant/water. If this all goes well your crank position sensor I would agree could be your issue. Can Auto Zone or others test your computer? Best of luck.
 

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Owner put a scanner on the car and produced no codes other than scanner stated all cylinder timings were off. (I wish I was there)
Hi Pat,

Interesting scanner. My scanner only puts out error codes and keeps its thoughts to itself :grin:

I've looked at the signal from a crank position sensor on a scope. It was a single output type and put out a 5 volt square wave. On a voltmeter, it measured less that 5 on the AC scale because of the square wave shape I'm almost certain.

Instead of nicking the wires, it is sometimes easier to push a straight pin (from a sewing kit) down beside the wire into the connector and measuring from there. In the books, they call it back probing but don't recomment it for use at the PCM connectors. Guess there is a chance of screwing up the connector and would have to change out the whole harness.

Sometimes just unplugging and replugging connectors will clear up some weak contact problems. You can try this at the PCM.

Does anyone know how much off the compression would be if the timing chain slipped one notch?

Keep us posted Pat. I think we are all scratching our heads with you.

Best regards,
Mack1
 

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Discussion Starter · #7 · (Edited)
Nextxech: I agree, though I havent pressurized the cooling system Im not currently loosing any water. I have also pulled the plugs a few times to ensure that the cylinders are clear. I should at least be able to get it running enough to see that it is running badly.

Mack1:
You are correct concerning the square wave. I dont have a scope or a graphing multi meter (more or less the same) but by turning the engine by hand I am able to do it slow enough to recreate the on/off signals.
As for the harness, I thought of that and pulled the plugs for a continuity test. Thats pretty much how I figured out that the schematic colors were backwards.
I havent pulled the PCM connecters but my mystery is the 3x signal isnt headed towards it as it should be so I believe the problem occurs before that in the ignition control module.
Ill be thinking about that though.
As for the scanner: Yeah I laughed about that myself. It turns out that it came with a book listing the codes and that was his interpretation.
I looked through the codes and if I remember correctly it was 0300 "engine misfire detected"
Not very descriptive but accurate I think.
 

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Instead of nicking the wires, it is sometimes easier to push a straight pin (from a sewing kit) down beside the wire into the connector and measuring from there. In the books, they call it back probing but don't recomment it for use at the PCM connectors. Guess there is a chance of screwing up the connector and would have to change out the whole harness.
Back probing or nicking the wires is considered bad because of corrosion after a year or less in a northern climate where salt is used on the roadways the wires will oxidize to point of effecting the signal to the ECM because of the low voltage used. The only correct way to repair the nicked wires is cut and splice them using heat shrink tubing the heavy wall type with glue inside.


Timing errors on that setup can also be caused by a defective coil pack shorting through the bottom into the control module which is usually caused by a bad plug wire to start with the coil pack can't deliver the spark to plug and burns it's way out the bottom of the coil into the control unit (another example of good engineering) usually if you remove the coil pack you can see traces of where the spark jumped similar to what used to be seen in a "cracked distributor cap" carbon traces. At times if none are seen it's easier to test with known good units.
 

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Discussion Starter · #9 ·
wrench; That makes pretty good sense and is something I never even considered.
I read this about a 1/2 hour or so ago while watching the hockey game and had to respond.
Yesterday while doing the other things I removed (dislocated) the coils while checking their mount for grounds. It never occured to me to look for a short from the coil for some reason.

While watching the game though I wondered if that would be a possible reason for the bad timing issue and the no 3x signal but then it hit me that it is probably the cause.
40K volts to a circuit board isnt good so before I put the new board to it I had better at least test each coil or Ill be right back here, just pissed off this time.

You have brought a smile to my face.
I only rolled the coils on their backs to check for ground to the plate. I didnt clean them or thei mount so I should be able to relift them and check them.
I dont suppose you know offhand how to test them individually.
I dont know what they should read.
As much as I love google it doesnt always have the right answer and the only ones I have to test with are on my car and they aint exactly on top.
 

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The readings will be the same as a good coil because they still work, but instead of traveling down the wire the spark is jumping through the bottom of the coil pack, if you still have the original spark plugs you can sometimes get a hint from them the one with the bad wire/coil will be sooty or more so then the rest. The coil packs/control module ran the same across the GM line on several different engine combos I used to (probably still have it somewhere) use a used one to test with saved a lot of time and trouble the key is to make sure to change or test(ohm meter) the plug wires to ensure you do not hook the bad one up to the new coil pack and burn the new one out. I would scour some local shops or salvage yards to see if you can find a used one cheap to test with.
 

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Discussion Starter · #12 ·
Ok no real new news but I did find a questionable coil that is going to be replaced along with the ICM and the wires.
I wont know for sure til tomorrow as I cant do it tonight so I keep you posted.
 
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