Help. Engine misfiring after washing

Take the car to autozone, they will pull the codes for free.

Odds are that you got a coil pack wet or water standing in a spark plug hole.

It should be said that the electrical connectors under the hood are water resistant, not water proof and that any "power washer" setting is likely going to result in water getting into these connectors and causing problems, if not immediately then later on when the water evaporates leaving behind corrosion and salts to muck up the connection.

For your immediate problem, the easiest place to start is the spark plugs. Pull each of the COPs/plug wires out and check for water in the spark plug wells. If you see any, dab it out with paper towels being careful not to put any side force on the plug. Once you get the worst of it, pull the plug and dry it and the plug well thoroughly. Try to get any water out of the COP/plug wire. Smear some silicone dielectric grease on the tip of the plug, re-install it, torque it to spec and re-install the COP/plug wire. Repeat for all 8 plugs.

What year model? IDK what year they changed but some Mustangs have coil packs while some have the coil on the plug. My 98 GT has the coil packs and my granddad's 01 GT has the coil on plug. He did the same thing on his car (washing under the hood) and apparently some water got in like 1 or 2 of the coils on the plugs. This caused a misfire, just like on yours. He replaced the two coils and problem solved. Thing that sucks is that they were pretty expensive, like 80 bucks a piece.

Getting water in the spark plugs could also cause misfire. When I swapped my NPI intake manifold for the PI intake manifold, apparently I got a little water down in the spark plug hole. It did the same thing yours is doing also. I needed to replace the plugs anyway, so I swapped all of them out, and problem solved.

To figure out which cylinders are misfiring, you need an OBD-II code reader to figure out which coils are messing up. I can't remember what the code will be, but you should be able to find an entire list of the codes and each's diagnosis somewhere on the net, or in the back of the code reader instruction booklet.

I don't know for sure if this is the problem, but it was for both me and my granddad. Hope this helps.

-Will

water & 4.6 dont mix

I washed my 99 gt some years ago it was a bad mistake , the coil packs dont like water & will short out also ford says water in the holes where the spark plugs are located should be blown out with a air hose , actually the 4.6 with all the electronics is not fond of water ...PERIOD ! I never washed it again..... the coil packs failed so I replaced them ........ just a rag & some hand cleaning after that .. a lesson learned .... you will probably need a coil pack which you can get on flea-bay for cheap , check all the conectors to the fuel injectors you can use a hair dryer to dry up any of the other stuff ..... good luck

squeak93 said:

Take the car to autozone, they will pull the codes for free.

Click to expand...

they cant in CA btw. Autozone does not hire smog techs so they legally cannot pull or diagnose OBD2 codes.

I clean under the hood regurlarly.... I just take precautions like covering my coil packs, alt, and air filter. Do that and you should be ok. (as long as you have check all electrical connections for tightness).

Nothing wrong with a clean underhood... You just have to be careful about it.

Change the plugs, get all the water out and try that. You may of got lucky and just fouled out the plugs. Odds are that you popped a few cp's though.

I don't know that you need to replace plugs or coil packs at this early stage. If you have a leaf blower or some other source of compressed air, blow out the plug wells, dry them and the cops off as well as you can, reconnect, and start up your car. It'll probably run rough for a little as it idles, but hopefully it'll get better as it warms up and dries off. If after it warms up and still runs rough, see above. Good luck.

this is exactly why i don't wash my engine anymore. first time i did it i got water down 3 plug wells and killed a coil