Contour Enthusiasts Group Archives Forums General Troubleshooting Knocking ... and not knocking ...

I've been having some problems with my Duratec recently, at first I wasn't getting the top-end power as good, then it started knocking when I took it back to the dealership.

The mechanic there mentioned it could be water in the fuel system and to put some flush through to get rid of it, and run on higher octane for a couple of tanks.

I got home, went straight to Canadian Tire and put in a bottle of STP Water Remover and filled up on 91 Octane.

Everything got a lot better, the knocking died down a lot but was still present for a while.

I'm on my second tank of 91 now, and the knocking is still there, but intermittently. Sometimes it knocks, other times it doesn't. Sometimes it's noticeable, other times it's just like a little rattle.

Today for instance, I drove over to see my parents-in-law and it didn't knock one little bit. Then coming home she did, but only between 2k and about 3.5k.

I'm pretty much at a loss now, and don't really want to fork out loads of cash at the dealership as we are practically broke.

When I first got the car, I did put through MotoMaster Ultra Fuel System Treatment, that was about 2,000 KM ago though.

I'm thinking I should maybe change the sparks to see if that will help.

Any ideas as to what may cause it to come and go, or what else I could try ??

'98 Mystique Duratec - 119,000 KM (73,943 Miles)

Thanks,

Rabbit.

Does the CEL work?

Pinging and knock happens when the ignition of fuel in the cylinders happens while the piston is still moving up. This is usually because the mixture burns too fast after the spark plug fires (I'm ruling out incorrect timing because it's not adjustable).

The two common reasons for this are carbon buildup, and EGR malfunction.

Carbon buildup in the cylinders increases compression causing the fuel to burn faster. This is known as "octane creep" because higher octane gas is required to keep the knock from happening. Carbon can be removed from the cylinders by using water injection, a decarboning treatment, or a gas additive like Marvel Mystery Oil.

The EGR system reduces the peak temperature in the clyinders. If it is not working, higher octane gas is required to resist knocking. If the EGR is malfunctioning it should light up the CEL. The EGR passages in the UIM behind the throttle body get clogged eventually and need to be cleaned out. With your mileage you can safely assume this needs to be done. Other parts or the EGR system can go bad also.

The CEL works as it comes on at the pre-ignition stage, so I'm happy with that for sure.

I'm interested in learning more about both parts that you talked about.

I'm not too sure about the Marvel Mystery Oil, purely based on the fact that I haven't seen it available, and so that makes it out of the question at the moment. Can you elaborate at all on the water injection cleaning method.

As far as the EGR is concerned, I've not received any CEL but I am presuming, from what you said, that this could be a contributor to the issue, so I'm interested in the idea of cleaning this for sure.

I am seriously, very, very grateful for any more info.

Thanks so much,

Rabbit

Decarboning an engine can be accomplished many ways.
Marvel Mystery Oil is an old standby, Chevron Techron fuel additive is the latest and greatest. Shops often use a quick clean decarboning fluid. Car manufacturers each have their own, available at a dealership.

Do a Google search for abundant reading material.

Water injection has been around forever. It is primarily used on high compression, turbocharged, and supercharged engines to eliminate detonation and increase fuel charge density. As a byproduct, the steam tends to "steam clean" the inside of the engine. The common backyard mechanic method of implimentation involves putting a clean water/alcohol mixture in the windshield washer tank and feeding it into the the intake through a spray nozzle while running the engine at 1500-2000 RPM. This was easy on carburated engines but is trickier to accomplish on fuel injected ones. Many companies sell water injection kits. A little searching and reading would give you ideas on how to do this yourself. The water may be simply sucked into the vacuum system, a method not appropriate for driving around, but you still must limit the ammount of water with a spray nozzle or oriface.