91 GL dropping cylinders when wet

[disneyd]

I have a 91 GL (fuel injected, manual trans) that just recently developed a problem. Several weeks ago I got caught in a downpour for several hours and had no problem with the car at all. Last week the same thing happened (downpour) and it felt like I dropped down to running on three cylinders... loss of power and the exhaust note changed. I kept driving (was on the interstate) and after a while it felt like it dropped down to running on two cylinders and I could barely make it up slight hills at 45 mph.

It would occasionally pick back up to 3 cylinders and sometimes would run normally (all four). Seems like it got worse when the rain really started coming down hard or I was right behind someone who was throwing up a lot of spray/mist. Once the rain slacked off and/or I managed not to be behind anyone the problem improved... if the rain picked back up the problem got worse.

I stopped and checked the engine. With it missing (while idling) I checked and appeared to have spark on all plug wires. Distributor cap, wires, and spark plugs looked dry. The connector on the air flow meter was slightly ajar and I thought I'd found the problem. Someone had put the metal retaining wire on the wrong way and it wasn't locking the connector onto the air flow meter properly. I fixed that (and noted there was no moisture in the connector and reconnected it... but it didn't change the problem. The weather improved and I was able to limp home on 2, 3, and sometimes all four cylinders.

I've since driven the car in the dry several times and it has run perfectly.

I'm looking for advice on what to check for next time this happens. I found a previous thread here mentioning the throttle position sensor, so I will put that on my list.

What else could cause loss of fuel or spark to only one or two cylinders at a time? Looking at the wiring diagram, it looks like the injectors are batch fired (1 & 3 together and 2 & 4 together), so I would lose two cylinders at a time if there was a wiring problem there (also, the injectors were dry). I assume if I had a coil problem it would affect the entire engine rather than a few cylinders.

Any ideas would be appreciated.

Thanks

[roycehof]

Well, sounds like the classical moisture in the distributor cap, sundrome. I would replace the cap and when installing the new one put some THICK grease on the lip of the cap where it attaches to the distributor itself (the thick grease acts as a seal). If the problem continues, change the wires. Since it runs O.K. when it is dry, your problem, most likely, is in the high voltage (Spark ignition) area.
Good Luck and Happy New Year.

[phantorn]

try spraying the wires witha spray bottle filled with water and see if 1 of the plug wires is arcing

[miami man]

i have had two festivas die in my driveway because of corrosion inside the center tower of the distributer cap where the coil wire goes in. pull out the coil wire and examine it closey in the inside of the tower and the coil wire itself.

[jglutz]

Agree with all of the above.....best bet change the wires, rotor and cap.....you said an interesting thing...you have spark at all the cylinders....believe it or not.....that may not be a good thing....why...maybe you have spark when your not suppose to....corrosion or moisture could cause two plugs to fire at the same time. In stead of 3 cylinders, you may have 2 cylinders + 1/2 cylinder + 1/2 cylinder.

Might as well change the plugs while your at it.

Normal acceptable maintenance is (if you go to auto zone) change plugs-rotor-cap and wires every 12K or 12 months, what ever comes first........................period
If you spend a few dollars more, purchase ford, NAPA, Carquest.......18-24K or 18-24 months.
Plugs......though many may not want to hear this.....Buy autolite or championbrsand, and change them every year...anything else is a waste of money (thier about $1.75 each)
(those expensive plugs....maybe for a FWD V6 where 3 of them are impossible to get to....also...if you don't improve the coil/solid sate ignition, the $$'s plugs are a waste.)

Good Luck!