on a 98 XJ8 with a loud VVT, can you unplug them and just drive without it? Would it stop the noises or hurt anything? Can they be replaced without taking the timing covers off? I'm about to do a complete gasket overhaul and could do this at the same time? I should have looked when I did the tensioners but didn't. Thanks!

 

I looked at the JTIS manual procedures on the VVT removal and it says you need to remove the front timing cover and the primary chain tensioner plus all the other procedures leading up to their removal to be able to remove the VVT.

Jim Lombardi

 

can you just unplug it and drive it with it unplugged so it won't make the noise? It's fine if I rev up the engine and it builds pressure at idle but embarrassing lol

 

Try going up one grade of oil if it seems the viscosity is inadequate to maintain the required pressure.

 

You can remove the VVT system and plug the oil ways with 2 bolts. You gain around 10-15 bhp. You have to remove the front timing cover to do this. There is a Jaguar document detailing this conversion. It's an option...

VVT is only for emissions. Not gains are made to peak power or torque.

 

I've seen that statement about the VVT only being for emissions before but this is the first to say that the VVT actually costs you power.

I find it a bit hard to believe....the theory behind VVT suggests that it should improve both power and emissions. I'm confused...

 

I've experience of VVT removal and gain on the 4.0 - this is specifically the unit I'm talking about, not generalizing VVT systems or cam phasing on other units. Just personal experience of the AJ27 NA...
The 4L S/C and 3.2 don't have the system fitted...what's not to believe? I've found it an added complication and something else that can add noise/worry/expense to these engines.

 

Does the PCM needs to be reprogrammed if i decide to remove the VVT on AJ27?
On a mechanical side - am i right that i need to:
-Remove VVT solenoids and housing
-Plug the VVT oil supply (or just swap the heads from s/c engine)
-Install the valve covers from a S/C or 3.2
-Should i use the 3.2 or S/C cam sprockets?
Anything else?

 

either on the bits, I'd try 3.2 ecu as it's not programmed for vvt.

 

Hi Everybody
I also have an interest in the VVT system and how it works.

The following 2 PDF files that described the VVT system and the Associated Engine Lubrication sytem, I extracted from the JJTIS Engine Description section of the 1999 XJ8 Model Selection.

XJ (X308) Variable Valve Timing (VVT) Overview.pdf

XJ (X308) Engine Lubrication System info.pdf

Jim Lombardi

 

Interesting document Jim! It looks like if you unplugged the connector, the system is biased to retard the valve timing, basically to where it sits at idle.

 

but my question is will it hurt to unplug them and just leave them unplugged to get rid of the noise should the oil change not take care of it? I am interested in knowing more about the conversion for sure!!! I know the engine light will come on for it being unplugged but will it be ok to do so?

 

In my humble opinion, it won't hurt anything. Possible changes in power or emissions, maybe fuel economy, but I can't see any damage in any way.
They designed the system with a bias spring to drive it to the retarded position, so obviously that's where they wanted it to go in the case of an actuator or electrical failure. Unplug them and see what happens.

 

right I guess I'll try it if it doesn't go away when I put the thicker oil in there. I'm hoping it will do better with different oil. The previous owner didn't really maintain it as well as it should have been and then it sat for 2 years.

 

So it might be just gummed up mechanisms.

Try adding a quart of ATF and letting it idle for awhile before your next oil change. Then do a couple of low mile changes to get some of the varnish out.

 

+1 on adding 1 qt of ATF to your oil - use 5W20 oil and sub 1qt oil w/ 1qt ATF and drive as normal - might take a while but the ATF will infiltrate the VVT unit and passages clearing them. I have done this with success..

 

The information on VVT seems to indicate that you may create emission and performance problems if you unplug the VVT.

Here is the important part of the PDF file on the VVT System information:

The variable valve timing system improves both low speed and high speed engine performance, engine idle quality and exhaust emissions.

Engine idle is improved due to the ECM being able to retard the valve timing by an
additional 10° compared to the previous VVT system; this also reduces the internal EGR at idle, where it is not required.

However, the internal EGR system is improved at normal engine running speeds to reduce NOx emission and eliminate the need for any external EGR system components.

It also sounds like you might start getting DTC faults from the ECM reporting emissons and performance issues.

I guess you can just try it and see what develops (hopefully it does not damage or plug up any of the parts in the emisson systems).

Jim Lombardi

 

You WILL get a DTC for the VVT if you unplug the left (bank2) VVT unit.
The AJ26 ECM looks for the change for the 'B'bank intake cam when commanded and if it does NOT detect the change it will fault the VVT system.

You can drive around with the check engine 'ON' light if you want.

bob gauff

 

i just went down and unplugged both sides and the tapping persists. If i plug them back in and rev the engine to 1500 it dissappears, so I'll just leave them plugged in and change to thicker oil and see if that quietens. I've had the tensioners done a month ago so thats not it.

 

Did you replace ALL the tensioners or JUST the secondary.
The primaries can fail and the long curved chain blade will rattle at low rpm.

The newer metal primary tensioners have a 'ratchet' mechanism to prevent this fault.

Just a thought.

bob gauff