I'm working with a 1999 XJ8 VDP 4.0L AJ-27 with 90,000mi. I don't have much history on this vehicle. Previous owner said that he started it up one day and it started knocking so he parked it, let it sit, and then I bought it.

It makes a loud knocking sound when running. It is not consistent, and it does not entirely increase with revs. Sometimes it changes to include a squeak/squeal.

I have done research and am not satisfied. I have removed valve covers and the timing cover to inspect. I have not noticed anything unusual about valve train and the timing chains appear to be in-tact and tight. The tensioners seem to be solid and were replaced 30 thousand ago. the guides looked good as well. Was considering the possibility of a head gasket problem, but does not run rough and the noise did not change with a cut-out test. I cannot pin-point the location of the noise but it sounds like it's coming from the top front of the engine.

I'm wondering if this could be caused by a bad VVT solenoid or not. I just replaced oil with 10w-40 diesel, high-detergent oil, and the sound did not change. Tomorrow I am going to start trouble-shooting with the vvt using the information that I can find on them. Help would be appreciated, who doesn't enjoy a good puzzle?

 

VVT operation is often described as a 'ticking' and it usually occurs at the threshold of operation of about 1200 - 1500 rpms.

A description of 'knocking' is usually reserved for connector rod bearing failure. For whatever reasons that I do not understand the front end of this engine seems to be more susceptible to rod failure.

Removing the serpentine belt would quickly eliminate the accessories and idle/tension pulleys.

Your description of the tensioners did not mention if they were metal or plastic only miles. Lots of plastic tensioners have been replaced with plastic ones.

 

VVT noise would disappear at just under 1500 rpm. If your tensioner are good then u have bigger probs.

 

About ten years ago when I was at the dealer I saw a car in for a 'knocking noise'.
The guy at the other end of the shop tied alot of things and eventually pulled the head on the side the noise seemed to be coming from.

I went over to see what was going on and we determined that the piston was pretty loose in the bore so the noise turned out to be 'piston-slap'

Called Tech-Line and was advised to install reman engine.

I don't remember if it was a nikasil engine or not but it was replaced with iron liner engine.

Just something you might want to check.

bob gauff

 

I understand what a rod knock sounds like and have heard them before, this is not close to that. At first I thought it was a broken chain guide that was allowing the chain to hit and rub against the timing cover, but it is not. It is a loud, almost hollow, sort of sound. and the reason why it can't be rod bearings is because it is not consistent enough and does not change with the revs in the correct way.

I visually inspected all tensioners, and they seem to keep tension after the engine has been running. The two primaries look like newer plastic tensioners and the two secondaries are newer metal-body tensioners.

Already removed serpentine belt, none of the pulleys.

I'm not considering VVT ticking; I'm wondering if a complete failure would be enough to cause timing problems or in any other way make a loud knocking.

Do you know if there is a way to check if this vin had a nikasil engine?

Any other thoughts? I'm thinking of pulling off the intake manifold to have a peek inside before I go and do a whole lot of work on it.

 

I didn't see in this thread where you removed the accessory belt and ran the car- did you try this?

 

The last nikasil was on Aug18 2000, so unless the engine was replaced .......

If a cylinder is eroded enough to have piston slap it should have low compression and/or severe leakdown.

 

You asked if it could be a VVT solenoid... I do not know how a solenoid itself would make such a noise, but you will do no damage if you simply unplug the solenoid. The VVT will just fail to advance on that side. It will probably throw a code,but I expect that will reset itself after a few run cycles.

 

Yes, I ran the car with the serpentine belt off. The sound was still there.

I am going to leak it down next, once the weather brightens up again. Plugs did not seem to be washed, but I will see if the leak-down gives me anything.

I was wondering if the VVT would be able to retard or advance it enough to cause the timing to be off enough to make things hit. Or if there was something broken with the VVT that was creating a rattle. I cut-out the VVT's with it running and the noise did not change. I'm assuming that unplugging them just leaves the timing in a neutral position.

At this point I'm hoping that the leak-down will reveal a bad head gasket, or at least give me something to go on. Thanks,

Till next time...

 

The valve timing does not hit anything at either extreme (obviously?) so it can't hit anything in the middle either! I am pretty sure that with the solenoid disconnected, you would be at the retard position.

 

I would suggest unplugging one ignition coil at a time to listen to each cylinder for a change in noise.
At least you can maybe narrow your noise to a certain cylinder?????

If no change then maybe it is rotational and not firing related.
Rod bearings tend to be louder when the cylinder fires.

bob gauff

 

sparkenzap, it is nice to know that I'm at the retard position. Haha.

I already tried a cut-out test for each cylinder, that did not change the sound.

I'm turning away from a bearing issue because the noise is so inconsistent. Yesterday I had the car running and for a little while it didn't make the noise at all. Then it started again and got louder and more persistent when I revved it up. I'm going to do the leak-down tonight, and possible then try to get it up at operating temp to see if it gets hot, meaning head gasket.

Thanks chaps!

 

I did a leak-down test and it did not tell me anything terribly important. It leaked down pretty good. The worst two were 13% and 14% leakage. The rest were between 5% and 10%. I think my next course of action is to start taking things apart. I did an oil change and the oil didn't have any metal in it (though it did need to be changed).

I'm going to start pulling the intake tomorrow and keep going until I find something broken or get to replacing the head gaskets. Wish me luck, hopefully I'll find something definite. That is, unless anyone has any other ideas...

 

Well, I ran the car a little more and diagnosed at least one bad head gasket. Once at operating temp on a hot day the coolant wouldn't stay in the reservoir, it was shooting out like a volcano--couldn't even keep coolant in it long enough for a block test. I've almost got the heads off. I will probably make another thread about my experience, I decided not to buy the set of timing tools and am making out okay thus far.

Thanks for the help, we'll see if this is the only problem...

 

I found that the head gasket was leaking at cyl. #6 and combustion was pushing right into the water jackets. However, I also found rod play in cyl. #1. I'll be pulling the rest of the engine in the next week and will be surprised if there is any bearing left. There was almost a quarter inch of play. Sounds like I'll have some fun in the lower end as well as with the upper--luckily this is one sexy lady...

 

Sounds grim, bad luck.
Out of interest how did you detect the con rod play - rocking the crank back + forth and watching the piston move?

 

Not that grim. I got the car for a hell of a steal and was expecting to at least have to re-build the lower end but diagnosed the head gasket first. I'm an ambitious young mechanic surrounded by supportive (and experienced) mechanical talent so it's not scary to tackle the job myself in my free time.

I was going to rotate the crank to a point where it was pulling a piston down and then push down on it to check for play and do that for each cylinder, but I was walking through Harbor Freight Tools and found a 2.5" suction cup for $3 (like you would use for pulling dents) and so I snatched that up and just stuck it on to the top of each piston and pushed and pulled.

 

Good luck with the rebuild, keep us informed.
You guys in the US don't know you're alive with places like Harbour Freight.

 

I started a new thread about the engine re-build here: https://www.jaguarforums.com/forum/x...96/#post755086

 

https://www.jaguarforums.com/forum/x...96/#post755086