Misfire Cylinder 5 - 96 Mercury Villager

I took car to O'Reillys, reader said I have a PO305 misfire on cylinder 5 & code PO325 knock sensor. With the mileage figured it was time for a tune up. I have replaced spark plugs with Bosch Double Plats, new wires, new dist. cap & rotor. Cleared the memory and took off driving, then check engine light comes back on with same codes. At 65mph the check engine light will blink 10 times then remain on. I have read the blinking may be indicating it is harming the cat converter. In park the car idles fine, but when you put in gear it idles rough just a little bit. When take rpms past 2000 the engine seems to smooth out. Used SeaFoam on van as per instructions in gas, oil and brake booster. Helped running quite a bit, but codes still there.

1996 Mercury Villager
92,000 miles

Any and all help greatly appreciated on how to proceed from here.

Have you checked the condition of the distributor cap and any dust on the optical sensor?? Have you checked the injector on #5?. Try switching #5 plug and wire with a different one to see if miss follows the plug or not. I believe the best plug to use is the NGK brand, bosch seem to create problems on some engines. Probably try another injector cleaner like Chevron or B12.

DO NOT worry about the knock sensor code as that is from the vibration of the miss. Replacing knock sensor would be a wasdte of money.

How long since you used the SEAFOAM??

Thank you for your help. The distributor cap is brand new. Not sure where to check the optical sensor for dust, if you could help me with that one I will check and follow up. I have not checked Injector #5, at the back of the motor its a pain to get too, was hoping it was just a plug or wire, but I guess that is my next step. I used the SeaFoam about 8 days ago. I will try the Chevron or B12. When we removed the plug the sound of the motor did not change at all, when moved to wire #5 to another plug the miss did not follow. We did make sure the contacts on the dist. cap and the rotor were free of any build up. The miss was there, first tried AutoLites, but did not fix so tried the Bosch doubles and still did not fix. Afraid it might be injector.

definately check #5 injector but dont ignore the knock sensor code it is located under the intake between #5 & #6 cylinders

The optical sensor is located in the distributor:

remove the dist. cap, rotor, then there is a cover that needs to be removed. If you see brownish dust on it, that is a indication that the bearing in the dist. is bad. You can try blowing it off and see what happens.

In these engines the knock sensor is very rarely bad, the reason the code was set is because of the vibration caused by the miss. Concentrate on the miss, once that is fixed and the codes are erased see if it comes back.

Hopefully this link will work, it should help with the optical sensor & Camshaft sensor:

http://f1.grp.yahoofs.com/v1/UG_WS4CFR05XjFkiYxrWZIM8nJ1pmDJM3vm_nXAld5k2LGyYt4 z8MukxDFTVDbEhMvAlbw9IQHWc1AgA0OB3_zcsQIhVMn_kjGc/%21Engine%20Related/Ignition%20System/All%20About%20CMPS.pdf

I could not get the link to work, but thank you for the reply. I removed dist. cap & rotor and gold casing on top, the optical looked clean of any debris. Did not see any kind of discoloration on the silver disc either. Pulled spark plug from #5, it is a darker color with a bit of white in it. Pulled the #5 injector connector and hooked node to it. It is working properly. Not sure how to check injector without pulling it. Running B-12 through it. When you pull any other wire you can hear the engine stumble, but when you pull off the #5 wire, the engine really does not change.

Is it possible the fuel filter is bad and the engine is not receiving enough fuel? I read on the ODB code website one of the causes may be lack of fuel. Thanks again.

You could test the fuel pressure after the fuel filter with a fuel pressure gauge but I do not think that is you problem. (I am by no means a expert, just a opinion)

To test the injector use a wooden rod and place it on the injector and listen for a steady clicking while running. If it does not click while running the injector is bad. test for resisitance it should be 10 to 14 ohms.

PM sent

I had the same problem. The chances of #5 fuel injector failing rather than
one of the other of the 6 cyl. is slim.

the answer is moisture coming under your hood, leaking past the seal for the hood and ending up on #5 spark plug.

Just stop the moisture from dripping onto #5 spark plug and you are good to go.

I wish someone had given me this advice before I fought the problem with money.