Engine knock after spark plug change Topic is solved

MoosePond123 · Post by **MoosePond123** » 07 May 2016, 17:11

Hi, Need your help!

I changed the spark plugs on my 2000 S80 today. After installing the new plugs I started the engine it and there was a serious knock. When I shut the engine off air rushed out of the engine thru a valve in the front drivers side. I thought the problem might be the new spark plugs so I put the old ones back in and the knock remained. When I installed the new plugs I gently loosened up some dirt in the spark plug wells and vacuumed it out. One of the spark plug wells was dirty which I was told was probably blow back from one of the spark plugs that was not seated properly due to dirt or debris which made a lot of sense.

Does anyone have a suggestion as to what is causing this sudden engine knock? It wasn't there before I changed the plugs.

Thanks!

Post by **matthew1** » 07 May 2016, 17:21

I would double-check the connection to the wires. Make sure they're seated on the plugs.

MoosePond123 · Post by **MoosePond123** » 07 May 2016, 18:16

I pulled a coil pack boot off the spark plug one at a time while the engine was running and each time the engine ran rougher.

Post by **June** » 07 May 2016, 18:25

Could somehow a nut or screw fallen into one of the open plug holes?

MoosePond123 · Post by **MoosePond123** » 07 May 2016, 18:32

The reason the air was rushing out when I shut the engine off was because there was a connector from a small black vacuum hose to a nipple on the drivers side of the manifold that had split. I was able to cut off the bad section and reattach. Engine is still knocking.

MoosePond123 · Post by **MoosePond123** » 07 May 2016, 18:35

I don't think so. All bolts for the coil packs and covers are accounted for.

MoosePond123 · Post by **MoosePond123** » 08 May 2016, 05:09

I think further investigation will require removal of the cam cover which is probably best left to a Volvo specialty mechanic. Do you agree?

Post by **June** » 08 May 2016, 13:34

I agree. I would not start it again and let your mechanic start it. In case the engine is damaging itself.

difflock54 · Post by **difflock54** » 09 May 2016, 04:43

Was going to suggest that the new plugs were the wrong ones (i.e. too long so hitting the pistons at the top of the stroke) but as you replaced the old ones without the knock dissappearing that theory is unlikely.

MoosePond123 · Post by **MoosePond123** » 09 May 2016, 15:39

My mechanic looked into the spark plug holes with his scope and didn't see anything unusual, so he turned the car over a few times with the plugs out to blow out anything that down there, then shot some compressed air into the spark plug hole. He reinstalled the plugs, started the car up and it quieted right down. He thinks it was a piece of plastic. I had recently replaced the plastic hoses that surround the coil wires because the old ones had disintegrated into tiny bits, some of which were hidden under the coil packs. So he didn't have to get into the cam cover which is good news. Thanks for your input.