96 Buick #4 misfire

Just found this problem, engine light on showed a misfire. Had shop double check all of the injectors and fuel pressure, all good. Install
a new fuel filter. Then did a new plugs. Thought it might be a spark
plug wire, installed a know good one, no fix. Then swapped with the one next to it, still no fix. Replace coil, no fix. Replaced the ICM, no fix. Thought this could be related to the plenum problem noted here, not the issue, the engine is not using any anti-freeze. Tonight, I listened to all of the fuel injectors, all sound good.
Can a timing chain cause this kind of issue? It has never been replaced on this car and it has 165k miles on it. However, why just #4 misfire. Overall, the engine runs great at highter speeds, only misfires at idle.
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Not the chain, do a compression test first, check for vacuum leaks, switch injectors see if the miss moves.

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Should the timing chain be replaced maybe the better question. I did not thing it could case this problem, but I was wondering about the life. Shep wrote:

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snipped-for-privacy@gmail.com wrote in

The Mass Airflow Sensor(MAF) is dirty or needs to be replaced. If it's the 3,8, it screws in above the PCV valve. Check & replace that too.
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The map sensor is above the pcv!!, the maf is in the air intake duct, be careful with your advice.

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snipped-for-privacy@gmail.com wrote:

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steve_f wrote:

is this the 3100 eng
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No, it is a 3.8 steve_f wrote:

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snipped-for-privacy@gmail.com wrote:

if the exhaust stinks like sulfur then you are getting fuel but no spark and the catalytic converter is trying to burn all the excess fuel in the exhaust stream ......if this goes on for too long you will burn up the converter and possibly cause a restricted exhaust making the car sluggish or if the exhaust smell gassy like a beat up old pick up truck the converter is already burned up ...if the exhaust smell normal, then you are not getting any or enough fuel to that cylinder. try this...... your car has three coils one coil for each pair of mated cylinders...2 and 5....6 and 3....1 and 4. try removing the wires from 2and 5 only at the coil.DON'T MIX UP THE WIRE LOCATION...have someone try to start the car while you watch the coil . you should see a sharp blue spark jump from one tower to the next. if you do, put the wires back on hte 2 and 5 coil and move on to the 6 and 3 coil ... do the same thing remove the wires from the 6 and 3 coil and have someone try to start the car ...you should seee the same sharp blue spark. if you do , put the wires back on the 6 and 3 coil and move on to the 1 coil and 4 do the same thing and look for a sharp blue spark ...if you dont; see a sharp blue spark at the coil tower then you have a bad coil or ignition module .....as long as you dont; mix up the wires you can move a coil you think might be bad to another location on the ignition module .....like if you think the 2 and 5 coil is bad you can move it to the 6 and 3 location as a double check ..if don;t see a spark with the coil in a new location the coil is bad . if you do see a spark at the new location you have a bad ignition module ... .....as long as the wires stay in the same order as they did when you started ...... the coil locations are interchangable they are numbered only from the factory for convenience however the sparkplug wire locations cannot be moved . try that first ..if all check good you may have a bad injector and if you have not replaced one before take it to a shop .....i know a guy who set his car on fire because he nicked an injector o-ring . let me know ..
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sounds like timing to me.What do you think group.
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Todd A. Delk
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Thanks for all the feedback. On the electrical part, I have already been done the path of moving coils around, put in a new coil, seeing if the misfire followed the coil (if it is bad). It proved not to be bad. I bought a new ICM, and no fix, so I swapped back in the old one and go credit for the new part. I am almost sure it is not a injector problem now. After listening to it, doing presure check at a shop, it seems to be o.k. The exhaust on the car smells normal to me. I have two Buick's, one old and new, so I compared the two. I am going to check the PVC value and the intake components this weekend. Also, will check the EGR value. I did find small crack on a vacuum line that hooks up to the high pressure sensor, but it was pretty minor. The crack was right at the connector. I will replace that line also. I appreciate all you support here. I will keep you posted. Tom
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I have a 94 LeSabre with 230,000 miles that I went through all the things you did about 30,000 ago. I was pretty sure the injector were OK, they sprayed fine, I though, but not well enough because I finally decided to get a set for $165.00 from eBay and the car hasn't misfired since. I can't say yours has the same problem, it may be something else, but just keep my case in mind as you search for the solution.

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I decided to bite the cost and install a new injector. No fix. Still have the problem. At this time, we have replace or at least swapped with a know good, all the parts assoicated with misfire to #4. The problem stays there. Guess we will live with it or until the problem tells us more.
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I did swap injectors all over the place and the misfire continued usualy on two cylinder, forgot the numbers. The misfire did not go with the injectors. It's wird. I think that's because several injectors , if not all, were not working properly, but they were good enoug to keep the engine going. The computer must be trying to compensate but couldn't, so it messed up or thought the cylinders were misfiring. The sapark never failed but the computer said it did. I checked these things using a timing light and a scan tool. What I know is that once I replaced all 6 injector the problem ended.

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If you have a miss in two cylinders, it could be a coil. Each of the three coils fire two cylinders at the same time. Remove all the wires from the coil pack and check Ohm resistance across the two posts of each coil. They should all be similar. Then look for carbon tracks down the sides of the coil posts. If you don't find any problems, check the resistance of each wire. All the wires should show an Ohm reading. (longer wires will have more resistance)
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