I have not done a compression test, I’ve heard of them but didn’t know much about them and I just did a bit of reading. It seems to be something worth trying, I may ask whether my mechanic that is going to look it over would be willing to do that or at least loan me a kit to do it myself. Online it just says that you remove a plug and test each cylinder by turning it over and record all the pressures. And it mentioned a tip that if one of the pressures is lower than 100 psi that you could pour a teaspoon of oil down the spark plug hole and test it again. If the pressure jumps it could be your piston rings, if not it maybe be valve issues.

 

There is no direct link between compression and engine knock. However, if a cylinder is not firing it will produce a kind of knock until it "catches up". You might have a case that, due to low compression, a cylinder is initially not firing and later starts firing when the engine warms-up.

In such a case, the knock would disappear suddenly at some point. If your knock gets quieter gradually as the engine warms-up, then it is not due to one cylinder not firing. Perhaps, at the time of the compression check, you should replace all spark plugs if not replaced fairly recently.

Otherwise, a general rule for the compression test is to be done on a still warm engine and with the throttle fully open.

 

Its only about a 20-30 minute procedure generally. So most likely your Tech won't have an issue to do it (especially if he's charging you). Some auto parts stores will provide a loaner tool if they have it. They have you buy it so they get it back and return the money afterward.

To do a proper compression check, warm up the engine and shut it down.
Remove the fuel pump and ignition fuse.
Remove the plug, examine the plug, look for discoloring and/or buildup and check the gap. Plugs are the eyes of your motor and can tell you a lot. They should be fairly clean and have a light ash color. If you find yourself resetting the gaps, it may be time to replace them.
Screw the tool into the spark plug hole hand tight, no wrenches.
Roll the engine over at least 5 or 6 times. If you can see the gauge while rolling the motor (preferred), you do it until the gauge stops rising. If you have an assistant, even better. Usually it takes just a few seconds, ...at max, about 7-8 seconds. Reset the gauge before removing the tool and you can move on to the next cylinder.
Record each cylinders pressure. Your looking for continuity of the cylinders, they most likely all won't be exact. They can be a few pounds off, but no more than 10% after all readings are taken.

 

Better to remove all spark plugs then do the compression tests.

 

Yes it is, its easier on the battery and starter, but not necessary

 

Ok, thanks for the tips. I replaced all the timing components about 3000 miles ago and swapped the plugs out for some new ones at that time. (It was knocking before I swapped the plugs) I will fill you in with what I find hopefully by the end of the week. I also got some adhesive to reattach my third brake light and I got 3 new side marker lights so I have a lotta extra work for me to do this week.

 

Just to eliminate the possibility of a cylinder not firing (which is very hard to notice by just listening of the sound of an 8 cylinder engine), perhaps you should do a scan (if not done) to see whether there are any misfiring codes.

 

a scan with an autel scan tool reports one code, p1111. It labels that code as “system check complete since last memory clear”

 

i really can’t hear anything that weird in the video

do a longer cold start and drive and upload it to youtube

 

Hey guys I’m back, sorry for the long delay.

The jag got buried in my driveway in snow so that got put on the back burner for a while. Although when I finally got around to plowing the driveway and getting the jag free, when I started it there was no knock but after about 1-2 minutes it started to knock again and then once it got warm it started going away.

Anyways I called my mechanic again and let him know that he could take a look at it whenever he wants, and while I was on the phone with him I told him it started without a knock when I first fired it up and he told me he was almost certain it was a lifter and that he didn’t need to examine it because that’s what it is.

So I guess how would I go about fixing this lifter? I don’t know much about it but I will watch some YouTube videos online, I believe these xjrs don’t have hydraulic lifters so I figure I can find someone that’ll show me how to do it, although I didn’t find anything on the forums about it yet.

thanks

 

they’re cam operated buckets with a shim.

look up “adjusting valve shims”

 

+1 xalty.....its not a Chevy.

BTW....was stationed in Minot, so I know the cold and snow.

 

Yeah the cold and snow have not been agreeing with the jag haha, that’s what I expected though.

I watched a few YouTube videos on it, I tried to find it being done on an AJ-v8 and I found one guy who kinda explained it but it was pretty difficult to understand his accent so I tried another video and it seems like you just have to pull the cams and replace those little shim things that come in contact with cam lobes. That doesn’t seem very tough as I already have timing tools so it’ll be easy to set the timing again. Although I’m not sure where to get the little shims and would I have to buy a new valve cover gasket even though I just put new ones on 5,000 miles ago?

 

Measure the valve clearances first, that may not be the problem. You shouldn't have to replace the gasket, but do renew the RTV at the front cover joint.

 

Ok, thanks for the responses. I will check them all with feeler gauges first.