I have an 03 P71. I have had what feels like an occasional engine miss when the car is in overdrive at lower speeds, at speeds where the engine might be close to lugging. It doesn't happen in the first 3 gears. Could this be one symptom of torque convertor issues? There's no chatter or rumble, and it is not a constant thing.
OR: I had a coolant leak from the intake manifold, and the car basically sat unused for about 10 days in cold and/ or wet weather. Antifreeze stayed puddled around the bottom of the boot on # 1 coil.
I finally got the $$ to buy a new manifold. I had my usual garage to replace the manifold; and now, the "miss", or "stumble", is worse, which leads me to think it's a coil/ boot problem.
The transmission has 40K miles since last fluid/ filter replacement. I know it should have been done again already; however, the fluid is still quite clean, and is full.Plus, the transmission shifts and functions apparently normal.
IMO, there was an ignition issue all along that got worse after the manifold job.
Can someone advise me. Thanks

 

OK, then. I'll try this: If a coil/ boot/ plug OR an injector was causing an intermittent miss, shouldn't the check engine light come on pretty soon? It has not set a code yet, per the mechanic's tester.
Also, I had a parts guy to "blip" the throttle wide open then immediately release it, and I can feel and hear a misfire/ stumble from the left tailpipe, but not the right one. Can also hear it in the air filter housing, very subtly. Also, engine seems to idle about 950 (per machine) smoothly and quietly. Can't afford to just jump in and replace the whole plug/ coil system just this minute. If some one can tell me how to isolate the problem to one cylinder, maybe. Can someone help me with ideas please? Thanks

 

How many miles on the clock?
You only mentioned since last trans service..

 

133K miles.

 

Since the misfire was present prior to the manifold repair/swap, would take it out of the diagnostic. Especially with no idle or driveabilty issues other then the mid range misfire.

Low mileage torque convertor 'shudder wasn't a big issue with introduction of Mercon V. In years prior, shudder was reasonably common that required frequent trans services and/or products like Shudder Guard added to the service lube. Being you can snap the throttle and feel or hear a misfire takes the TC out of the diagnosis.

Usually when you feel a slight misfire with engine load high like on the OD shift with light throttle added is generally ignition related. If you power brake/brake stand for a second or two and add light throttle can you produce the misfire?

Anti freeze sitting in the plug well for a short time shouldn't have been a problem. 133K,, the plugs have been in for? Checked at all? Knowing it had a misfire, checking or replacing the plugs would have been a first step with the manifold off. Without any misfire data, and if the plugs have some miles, might install a new set only this time move all 4 coils to the opposite side. If the misfire moves over with the coils new position then you'll know you have at least one failing coil. Buy one new one, then replace one at a time on the failed bank until the misfire is gone. I've seen coil primary connectors as well as injector connectors broken after manifold changes, plugs and such. Possibly' a cracked porcelain, boot arcing or,, Just somethings to check before spending.. If the idle is good, no misfire under high fuel demands (steep throttle angles/WOT) chances are its not injector related. Higher mileage engines though, anything can be on the table....

 

Thanks for the info. The car was a detective's car with Myrtle Beach SC PD. A friend bids on cars like this, and I bought it from him in 2010. I called Myrtle Beach maintenance super to get records right after I got the car. He said records were purged when they sold vehicles, but that they replaced plugs/ did tune up on their PD cars every 60K, so by that, plugs have 73K now. Manual says they should go 100K without problem.
Miss was there before manifold job, but only noticeable in lower speeds while in OD, and not very pronounced. Pulling the coils for the manifold job may have exacerbated the miss.
I have a plug wire tester, induction type, not wire piercing type. Thought I'd put a piece of fuel line on it for an extender/ handle/ insulator, and see what it will show when contacting the plug boots. Maybe it'll show an erratic firing pattern or something, if it doesn't shock the soup out of me!
Shop has called and offered to replace plugs and boots on his dime until I can pay him. His price on parts is not much more than I can buy them myself.

 

Hayapower, I had plugs and boots changed. Plugs were pretty burned. After that, the car ran like silk...........until! We drove about 40 miles this AM with no problem, then, out of the blue, the intermittent miss started again. We aborted our intended trip, and headed for home. It smoothed out pretty well on the return trip, but I can still feel a slight misfire. I let the car cool in the driveway for about 6 hours, then made a short test run. The dead miss was gone; car ran like a rabbit, but still can feel a slight tremor in it. I have a full set of coils ordered. I guess the original miss caused at least one coil to start deteriorating? Is there a simple, cheap, safe way to test those coils while the engine is idling? I read that there should be a resistance across the small terminals where the small plug goes, like 1.8 or so ohms, but that is only useful to see if the coil is flat dead, not if it goes out intermittently. My induction type wire tester doesn't seem to work for this system. I figured holding the tester on the boot would show something, but I can't get it to work. Thanks for your input.