I originally started out with a cylinder 8 misfire code along with a random multiple misfire, egr circuit A, and something about emissions out of limits, and restricted performance flashing under load or acceleration. I purchased a new coil pack for cylinder 8 and a new set of NGK plugs. I installed them yesterday and reset the codes. Now the check engine light stays off but it has a dead miss on one cylinder. It is NOT throwing any misfire codes. Under acceleration you can feel the dead cylinder. But the strange thing is as soon as it goes into 4th gear, it starts going into a pulsating random misfire and the engine violently shutters and bucks. It will do this for about one second followed but about 2 seconds of running smoother (still with dead cylinder issue). While it is doing this the engine light flashes. When I get on a smooth level road it does not do it. And the check engine light is off. It only does it under load like acceleration or climbing any incline. It was doing this also before I changed plugs and cylinder 8 coil pack. The check engine light is not on when in is not bucking and shuttering. And it ONLY happens in 4th 5th and 6th gears (why?)I have no codes for any particular cylinder or egr mass air or anything else. I have never seen a situation like this. I will try to isolate what cylinder is missing at idle today by pulling the injector plug on each cylinder and listen for no chamge. Have any of you experienced this. The pulsating random misfire is baffling me. My code reader is not leading me in any direction. Thanks in advance for all advice.

 

Your code reset means you also reset the OBD monitors.

If they set OK again then it has a decent chance to flag codes.

Most codes only flag after 2 warm ups.

In case it can't set all the monitors it may or may not be able to flag codes such as what you had.

You can perform drive cycles to speed up setting monitors and you can use OBD to see which have not yet set.

 

Thanks for the tip. I didn't know it took multiple watm up cycles to st the codes. I only drove it last night for 5 his without ever shutting it off, so that was the only cycle the engine had since putting the plugs and coil pack in. I will see what it does today. Thanks.

 

OK, I ran the engine this morning and pulled each injector pigtail one at a time and got an rpm drop on all cylinders except for cylinder 4. So that is my dead cylinder. Didn't throw a code until later. So its either a bad coil pack or bad injector. All of the coil packs look just as old. Surely they are not original with 230,000 miles. But they are old. So I just ordered a complete set of coil packs and a new injector just in case. Hope to have them by Friday so I can get it all knocked out on my next day off. Driving to the gym just now I had cylinder 3 throw a misfire code. So I guess these coils all fail very close together. Spark plugs are all new so a coil pack swap will hopefully cure this. Still can't figure out why the bucking and surging is only occurimg in 4th 5th and 6th gears, and why it is intermittent. Is it drastically altering the timing trying to compensate for the misfire?

 

Mechanics do recommend changing all the coils together if you get a problem with one coil.

Having said that I changed just one and the rest have been fine.

They do live in a very hot spot!

 

They swell up from heat and age, they could very well be the original coils, as well as plugs.
A guy i worked with had a truck he bought new & never changed them in 280,000 miles.
Truck ran fine, he sold it at almost 300,000 miles with the original spark plugs still in it.

 

I got a confirmation that my coils will be here on Friday, so I will install them as soon as they get here. I also noticed there is a vacuum leak noise coming from the pcv valve on the passenger valve cover. Is it supposed to leak by a little at idle or is it supposed to plug itself until vacuum pressure drops? If its not supposed to leak by, then that could be adding to my issues.