Hello:
I own a 1996 3.5L trep with 84000.
After replacing the spark plugs (checked the gap at .035), wires, coil pack, and successfully tested the Throttle Position Sensor, and Intake air control sensor, and the resistant at each injector (12 ohms); I am still getting the bothersome code 43 from the ECL.
The engine idles rough, but there is something funny about it.
While in P or N, it idles rough at around 1000 rpm. In any other drive gear, the rpm's drop to around 750 and it idles rougher. I have not notice any stall while driving on the highway or at acceleration. As far as I am concern, it is normal.
Something else, when I first start the engine, the rpm's jump to 2000 and then drop to 1000.
The scanner indicated a misfire at the #5 cylinder. I tested the spark plug wire signal with an induction light. It missed. I went on to test the spark plug wire for the #2 cylinder and it did not missed. Since the 4 wire connector from the PCM the coil pack uses the same primary connector for cylinders 2 and 5 could it be that the timing signal to the #5 cylinder is bad, because the timed signal to the #2 cylinder seems OK?
I would greatly appreciate any help on this.
El futbolero

Exact same thing mine done. Misfire on #5, engine revs to 2K-2.5K RPM on start-up then drops to 1.2K and idles there, 750-800 while in gear. I have replaced plugs & wires and all tube seals while I was changing valve cover gaskets. engine runns better but still a tad rough and still revs on start-up :dunno: normal maybe. But it does have more power now and 43 hasn't come back on yet.

 

intake manifold gasket?

 

intake manifold gasket?

Was gonna replace that as it is in the plenum gasket kit....BUT....the rails looked like something I didn't wanna be messing with..LOL. a bit of flake on them so I didn't want to disturb them any.

 

I believe the plugs for 2 & 5 should fire at the same since they have a common signal.
if one is firing consistantly and the other not, could be a bad coil pack. Others have said they have seen half a pair fail before. Have you ohmed the coil pack. The values are in the service manual. Although don't know if that test is alway reliable but worth a try. .

 

I'd vote dor the intake gasket.

 

Thank you for all of your replies.
I am willing to replace the gasket.
However; I do not understand how a faulty gasket may be resposible for a misfire in one of the cylinders.
I did forget to add this piece of information when I first wrote the post:
When I checked the new spark plugs for the correct gap and replace the wires, I found a liquid substance at the bottom of the spark plug chamber. I cleaned it off with a rag and a long screw driver. It did not smell like oil, or fuel, so I would say that the spark plug had been torque to specs. I assumed that it was melted silicone grease.
How does the PCM times its signal to cylinders 2 and 5?
I am thinking that if the PCM is faulty when the timing signal goes out to the #5 cylinder, it may be the cause of the misfire.....
Any thoughts?

 

It is common for the intake gasket to leak only on one cylinder. The few that i've replaced all leaked on #5, causing that cylinder to miss. #2 and #5 both fire at the same time. The spark plug on the cylinder that has no compression on that stroke is the ground path for the other cylinder.

 

Thank you for all of your replies.
I am willing to replace the gasket.
However; I do not understand how a faulty gasket may be resposible for a misfire in one of the cylinders.
I did forget to add this piece of information when I first wrote the post:
When I checked the new spark plugs for the correct gap and replace the wires, I found a liquid substance at the bottom of the spark plug chamber. I cleaned it off with a rag and a long screw driver. It did not smell like oil, or fuel, so I would say that the spark plug had been torque to specs. I assumed that it was melted silicone grease.
How does the PCM times its signal to cylinders 2 and 5?
I am thinking that if the PCM is faulty when the timing signal goes out to the #5 cylinder, it may be the cause of the misfire.....
Any thoughts?

The PCM gets the signals from the cam and crank sensors. The cam tells PCM which cyl is next. The crank tells PCM when to fire. To check coil(s). the primary side from B+ terminal to each pin should be 0.45 to 0.65 ohms. The secondary is measured between the 2 towers of an individual coil, should be 7,000 to 15,800 ohms. One thing I've noticed is that of all the posts about a misfire on the 3.5 is that 95% of the time it's cyl #5. I gotta wonder if there's a design flaw with that plug wire routing. Just a twisted thought.

 

The PCM gets the signals from the cam and crank sensors. The cam tells PCM which cyl is next. The crank tells PCM when to fire. To check coil(s). the primary side from B+ terminal to each pin should be 0.45 to 0.65 ohms. The secondary is measured between the 2 towers of an individual coil, should be 7,000 to 15,800 ohms. One thing I've noticed is that of all the posts about a misfire on the 3.5 is that 95% of the time it's cyl #5. I gotta wonder if there's a design flaw with that plug wire routing. Just a twisted thought.

yeah jed, was wondering that same thing myself...awfully "odd".

 

Hey Folks:
Thank you again for the second wave of replies and explanations. You guys really know your stuff.
I am going to replace the intake manifold gasket.
I would like to add that I tested the injectors by unplugging each individual electrical connections. When I got to the #5 injector, the idle roughness did not change. So a misfire on the #5 cyl is the problem. I am going to test it further with a noid light, to make sure that the coil driver in the PCM is working properly. I called the guys at auto zone and advance auto and they told me that the coil drivers are an integral part of the PCM, which cannot be replace. So I would have to replace the entire PCM. I wonder how true this is.
I won't replace the PCM just yet. The gasket is much less expensive and it definetly seems like the logical thing to do.
Thanks again and will let you know how it turns out.
El futbolero

 

They are correct. The output of the PCM driver provides the ground for each injector circuit and is quite durable. Unless you connect it straight to +12 or the components actually fail there is not much to go wrong with the injector drivers.

 

intake gasket, mine misfired on #5 last year, repalced plugs, wires and coil only to find out it was a $5 gasket set >_<