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Discussion Starter #1
First off I want to apologize if I have posted this in the wrong place as I'm new to the forums here, if it needs moved to a more appropriate place feel free to move it. Second, both "I'm sorry" and "thank you" for reading this entire post as it's a bit long and complicating! I am still a novice when it comes to cars so I will be as detailed as I can while I explain my problem.

I have a 1989 Buick Electra (Park Avenue sub-model), it came with a V6 3800 (this one to be precise), and it has 145k miles on it. Back at the beginning of October I found I had a leaking head gasket, oil had leaked all through my radiator and back to my coolant reservoir before I got it home to get fixed. The advice from my other mechanically-inclined family members was to replace the engine itself instead of the head gaskets (which by the way this is the one and only time I ever make that mistake, if this happens again I go with my gut and change the gaskets). I had the old motor replaced with one of the exact same, another V6 3800 Pre-Series that was pulled from a 1990 Buick Reatta. I looked over both engines and they are similar from top to bottom, every single plug, mount, bolt, hole, etc from what I could see is identical between the two. I bought it used, it has only 45k miles on it, and looks to be more in shape than my old one. The yard I got it from said the Reatta it used to be in was totaled from the side and that it sat on their shelf for a little over a year before I bought it. I'm inclined to believe them about the mileage on it because this engine does in fact run, it makes no obscene or out of place noise, and looks well kept.

The problem I am having right now is that we have misfires on cylinders 4 and 6, and if I change gears the car will stall unless I hold the pedal down. We have tried pulling my car's engine codes and the only two codes we got were 12 and 34; my mechanic said 12 was not important because the engine was off when the codes were pulled and 34 is Mass Air Flow Sensor. Before replacing the Coil Pack and ICM my car would backfire and idled terribly (and my old coil pack, showing its age, straight up overheated and melted! haha), and with all these new things on it it is certainly running a lot better at idle and we've eliminated the backfiring.



This is the layout for my cylinders and coil pack. Cylinders 4 and 6 (top right corners) are the ones misfiring.

Items replaced:
(some links are provided so curious minds can see the shape/build of the items)
- Spark Plugs
- Spark Plug Wires
- All Air Hoses
- Knock Sensor
- Mass Air Flow Sensor
- Ignition Control Module
- Coil Pack

Items restored (removed and/or cleaned):
MAF Sensor's chamber
Throttle Plate & chamber
Battery terminals & cable ends

Bought but not yet replaced:
- Crankshaft Sensor
- Camshaft Sensor
- EGR Valve

We do not know if it will be worth our while to change the Cam/Crank sensors and EGR Valve because these would not cause only two out of six cylinders to misfire. Of course the MAF Sensor wouldn't do that either, but since it pulled a code for that specifically we changed it. We're pretty much down to changing these simply because we can, because they're the only things left to change before we're completely out of ideas. What's baffling is that we have spark, fuel pressure, and compression in all 6 cylinders and yet are still having problems with misfires. I even did research to see if we had unknowingly swapped an even-fire with an odd-fire engine because my mechanic faintly remembered there being this issue in older cars, but from what I found the odd-fire V6's were dropped from the Buick line back in 1979, nowhere near the 3800 series of the late 80's.

If anyone has any remaining ideas on how to fix this problem I would be grateful beyond belief, I just want Mable to run again. She was my first car and I'm not ready to let go! She's got lots of life left!
 

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Check out your lower intake manifold for leakage. Use carb/ choke cleaner and spray around area and look for a change in idle.

Check your spark plugs for consistency with the #4and #6. You must make certain that you are not leaking coolant in the cylinders.

You may have to run a coolant pressure test. You can purchase a tester for pressurizing your coolant system to 15lbs., and see if you are losing pressure.

Even though you replaced the intake gaskets when you replaced head gaskets,
you may have a warped intake or gaskets not sealing.

Easier to do than replacing cam and crank sensors...

How is the car at idle?.....
 

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Discussion Starter #3
I did not change the head gaskets. The entirety of my post explains that I swapped engines, not head gaskets. The new engine is not leaking internally as there is no evidence (at least at this point) of leaks with the new engine.
 

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When you checked the fuel pressure did you use a gauge or did you just observe fuel flow? Also it might not hurt to clean the injector(s) and I did not see if you changed the fuel filter.
As gtx500hp said, you should check for vacuum leaks and the intake gaskets fail very often on these motors.
Good Luck!
 

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Discussion Starter #5
I will check the intake gaskets as both you guys and someone at work had thought to check those next.

The fuel pressure was checked with a gauge and though I don't remember what the gauge should be reading my mechanic said when we first checked it that it wasn't that far under the mark. After letting it run for a few minutes my fuel pressure was normal and has remained normal since.

I have yet to change my fuel filter as we do not know what to replace it with yet. The last person to fandangle with it replaced the entire fuel line in that area so my filter is no longer specific to my car. I have to match one up the old-fashioned way. Fun stuff!

I bought a new fuel injector today at work and I'm hoping it will fix the misfire issue on at least one of the two cylinders. If it does, then problem solved! I'm not sure if it will though considering the ones on it now came from my old engine and they all worked up to the time I took them off.
 

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In the future, a good way to check to see if it is an injector or not is to swap it out with one that is working and see if the misfire follows the injector.

I also believe that if there is coolant and/or air leakage into the cylinder from the intake gaskets the presence of coolant in the combustion chamber could cause a misfire. The leak could be internal into the intake runner which would make it hard to see from the exterior although puddles on top of the manifold are sometimes present.
Good Luck!
 

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Really unlikely the Crank Position sensor would be the problem. You would be experiencing multiple cylinder misfires, if it was starting to fail.It would not pick on the same 2 cylinders.
The most common symptom of a bad CPS is the engine will die when it is hot. A heat related sensor failure.It will not re-start until the sensor has cooled off enough to work again.

A failing cam sensor may not even allow the car to start. You may experience erratic back fires.

I have had misfires on our 3800 Series 1 van due to a failing corroded intake.
 
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