Misfire on Cylinder 5/Knock Sensor

[JenniferH]

Help! My van is suddenly causing me tons of headaches!

About a week ago, I drove the van almost down to empty before I stopped and put gas in it. As I was pulling out the gas station, I noticed that the van was acting like it had no power and idling very rough. I talked to my husband about it, and he assumed that I had either gotten bad gas, or that I had some trash in the bottom of my tank that got into my fuel system when I let the tank get so low.

The next day, I was still experiencing the same rough idling problems. I stopped at a stop sign, and as I pulled off, the Check Engine Light started flashing. That evening, my husband took the van and had the codes checked. I had a misfire on cylinder 5 and a knock sensor code. He purchased and installed a new spark plug and installed it on cylinder 5. He also put a canister of fuel injector cleaner (HEET) in the gas tank. The van is still idling rough, although not as rough as before. The van also still misfires, but only when you have to hit the gas pedal very hard (going up a hill, pulling out in traffic....).

We have had so many people suggest different things. We've been told that the spark plug wires should be replaced, all 6 spark plugs should be replaced, new fuel filter, distributor cap or clean the photocell on the distributor...and the list goes on. Problem is, I can't afford to take stabs in the dark and randomly replace parts hoping it solves the problem. Nor can we afford a mechanic. My theory is that if it is a spark plug wire or distributor problem, the van would misfire all the time, not just when the engine is under load.

Has anyone ever experienced these kind of problems? Any and all advise is greatly appreciated. Thank you in advance for your help.

[tempfixit]

What year and mileage?

Do you know what the code was by chance?

Don't worry about the knock sensor, that was activated because of the misfire.

Do you have a multimeter?

All the ideas mentioned are propable causes. Tune up would be the best possible solution. What did the old plug that was replaced look like< wet, gap size>? What does the distributor and rotor look like,< corrision on the spark plug terminals, corrission on the inner terminals>? Try switching the spark plug wire from #3 to #5 position on cap and plugs see if the miss moves from 5 to 3. Check the injector for proper pulsation. Check fuel filter, if you can blow thru it should be ok.

Best would be start with wires since you already changed the plug on # 5.

Number 5 clyinder is on the head closet to firewall closet to driverside, correct?

[JenniferH]

I’m sorry – I do not know the exact code. My husband took it to the auto part store to have the codes pulled, and when he came home he simply said that it was a misfire on cylinder 5 and a knock sensor code. I have learned from reading these forums that the knock sensor alone would not set off the check engine light.
We don’t have a multimeter – in fact, I’m not even sure what one is. As for the other stuff, I’ll have to check with my husband and get back with you. He did tell me that the gentleman at the auto part store suggested that he inspect the distributor. He said that things appeared fine to him – but again, he is no car expert.
I suggested changing the spark plug wires to different cylinders to see if the misfire occurred on another cylinder, and he mentioned that suggestion to the auto part store man. Apparently, the auto part store man thought that was a bad idea and may end up causing more damage. I’ll forward your post to my husband, and maybe he will see that my idea wasn’t all that bad!
Since my original post, I have spoken again with my husband, and he intends to change the park plug wires this weekend, whether or not they are the cause of the problem. By the way – the van is a 1999 Mercury Villager with 93K miles, and still has the original wires. My husband feels that they need to be replaced regardless of the root of our problem.
Thank you for all of your help. I’ll let you know how things turn out.

[tempfixit]

When your husband changes the spark plug wires have him put dialectric grease on the boots at the cap and spark plugs, this keeps any moisture from creating a problem.

Also when he replaces wires disconnect the battery for a few minutes to clear any codes that may be present, that way you know if any new or repeat codes are activated.

Another tool you could use is a spark tester, they are inexpensive and tell you if there is proper spark at the plugs. I believe it is yellow spark = poor spark and blue spark is good spark.

Switching the plug wires at the cap and spark plug for a short period of time should not damage any thing in my opinion. Just don't do it while engine is running as this can cause damage.

[JenniferH]

Well...this weekend my husband replaced the spark plugs and spark plug wires. He did use the dialectric grease, as you recommended. The only problem he had was with the plug in the #3 position. Apparently, some engine degreaser residue was around the plug, and overtime baked onto the plug, effectively gluing it in place. He was unable to remove the old one and change it out. He feels like we will have to take the van to a machine shop and have the old plug removed.

Anyhow.....I was very skeptical that this would solve our problem. But, to my surprise, the van started up and runs fine! Thank you so much for all of your advise.

As a side note - about 2 months ago, we had the tensioner pulley and the belt replaced. Shortly after that, we had to replace a coolant hose. It was leaking directly onto the belt. Ever since then, the belt has squealed at start up, and for about 5 minutes afterwards. We did take it back to the shop that replaced the pulley/belt, and explained the situation to them. They found nothing wrong with the belt and/or pulley. Ironically, since the plugs and wires have been changed, the squealing in the belt is no longer present. Don't really know what one would have to do with the other, but I am very grateful. I'm sure our neighbors are, too!

[tempfixit]

Was the engine cold or warm/hot when spark plugs were changed? Did he try getting the socket on while the engine was warm? If he can get it on when engine is warm try breaking the plug loose then let engine cool so not to damage threads in the head.

[steamplant]

I would change the fuel filter first,

[drcoffee]

Incredible! The exact same thing happened to my wife this morning. #5 and knock sensor. When I looked down at the plug, it was surounded with 1/4" of water. Don't know why. After replacing the plug with a new one and all new wire set, it runs smooth again. Now I need to have a parts store clear the codes.