Mysterious engine miss -97 Merc Villager (Nissan Quest clone)

engines
mercury

#1

My '97 Mercury Villager (Nissan Quest clone) with 127K suddenly developed an engine miss in 3rd cylinder. Local mechanic changed spark plugs, wires, distributor, cap, rotor, fuel injector, and checked for vacumn leaks and cylinder compression. Now wants to check to see if timing chain slipped a cog. This mystery is getting expensive. Any suggestions regarding the source of this mysterious miss?


#2

This vehicle should use a belt, not a chain.
It’s not likely a slipped belt and even if this were the case, it would affect more than one cylinder.

Did he by chance give you the compression readings? Whenever this is done the readings should always be written down to avoid any problems later with memory.
Often people come on this board with engine performance problems and state that the compression was “good”, and often those readings are not good at all.

A vacuum leak could do it but it is unknown how he determined there is no leak. My opinion is that a vacuum gauge should always be used. It eliminates guessing and tells you in in instant if there is a problem or not.

Another question or two. Does the vehicle run rough at idle and smooth out or does it idle rough and buck/jerk on acceleration? Any Check Engine Light on?


#3

Check engine light is on. The V-6 runs rough under all conditions – at idle, acceleration, and stable speed. The mechanic probably said “timing belt” and I inadevertantly wrote “timing chain” in the posting. I can request compression readings and verify how vacuum leaks were investigated if that might be helpful. Thanks for considering this mystery!


#4

Considering the CEL is on and is running rough under all conditions, I would run this car by a local AutoZone, Advance Auto, Checkers, etc. auto parts house that is nearby and have them pull the codes. Sometimes a different perspective may be needed.

Any of these places will do this for you free but they will not, nor should they, diagnose your problem.
Post any and all codes they give you back here for discussion.
And I would advise holding the driving to a minimum until the problem is resolved.


#5

IF #3 fuel injector is easily swapped with another cylinder, do the swap. If the scan, now, reveals that other cylinder is MISFIRING, then, it’s the fuel injector. IF they are NOT easily swapped, a 'noid light, inserted into the disconnected wire to #3 fuel injector could be observed for regularity during engine idle. If it doesn’t have erratic flashes, it DOESN’T prove that the fuel injector is good. The fuel injector’s spray action could be poor, causing misfire. [Basic data: 3.0L V6 engine, with a distributor and a single ignition coil, each fuel injector individually controlled].


#6

Mystery solved. The mechanic rechecked his diagnostic work and found that it was a bad fuel injector. Thanks for your helpful comments!