Hello all. So I bought ($2,500) a 1999 XJ8 with a perfect body but a messed up mind. Rather than try to diagnose and fix all of her schizo problems, I'm looking at giving her a lobotomy in the form of 4 Weber IDF carburetors and an aftermarket stand-alone ignition. I'll run the transmission with my own controller, which will also be completely brain dead.

This is an entertaining project for me. I'm not depending on this car for transportation. I've done this kind of thing before, just not on a Jag, so yes, it will work.

Manifolds for running 4 Webers on a small block Chevy are well known. Making (single) manifolds is no big deal. I hope they don't stick up through the hood though.

The VVT will be locked in place.

The reason for my post is to ask if anyone has done something similar on the Jag 4.0, just to discuss any situations that came up and how they dealt with them. I'm particularly interested in the transmission control. Having read how the Jag controller works, there is a lot of fancy clutch and brake management going on that I won't need. I'll just take my foot off the gas and flip a paddle shifter (switch) on the steering wheel to shift up or down. (I'll have to take responsibility for being in the right gear at the right rpm.) But this ZF tranny uses solenoids and pressure regulators to shift, so if someone has already worked out a simplified "turn these off and turn those on" kind of truth table to get this thing to shift, I'd love to see it. If not, I'll just give it my best shot and if it melts, maybe go to a manual tranny instead. (I'll be opening it up soon for the A-drum and regulator repair.)

Why not just drop a small block in it? Been there, done that (XJ6). The AJ27 is actually a neat little engine. All aluminum, overhead cams, shim and bucket valve train (very cool), and plenty of potential. I want to see what it does "uncorked".

Getting the doors to open without the computer will be fun too.

 

And that is the main issue, security. It's all linked via the Can Bus so this project you're thinking of undertaking will be a head scratcher - guaranteed.
There are conversions about I understand, here's one...maybe contact the dude that did this for a security hack/advice...

Also, this chap has converted an XK8 to run a standalone ecu with a manual tranny so he should be able to help, although the models are different is some ways.
https://www.jaguarforums.com/forum/m...xkracer-70408/

Personally I'd look at removing the engine and sticking it in something else to see what it can do like a Cobra rep if you want to run IDF's...

 

Definately a serious project, the only input I have would be if you don't already have is this... http://www.mediafire.com/file/bu2w7j...hop_Manual.pdf

I do have to ask, why the Weber's (they are classy and perform), but, like you say they are kind of tall. Why not consider a low profile FiTech unit (Holley has one now also), which calibrates and works on its own? Definitely not as classy looking as a Weber, but may be easier to accomplish what your doing?....simply a suggestion.

 

I totally agree with you about the AJV8 being a , erm, 'neat little engine' and I would much rate it over the over rated LS unit every time. It actually breaths. I would recommend using or contacting one of these LS converstion places, like Jaguarspecialities. They may be able to help with interfacing devices, just like the security system or the seat moving.


Perhaps best not to tell them that you intend to keep the Jag motor: I contacted them last week and got the distinct impression that they were less interested in helping because I wasn't doing the obligatory LS conversion. It's almost like " I show my individuality by putting a chevy engine in and shoving a finger up at the English establishment- but if you don't conform to me- you're an outcast!
Good luck!


BTW- you will lose low speed, mid range and/or top end power- depending on where you lock the cams. This will be significant. if you leave the cams retarded- they are retarded away from optimum power- so you wont get the 290 bhp rated or the mid range torque by quite a margin. If you lock them to 290 bhp- you wont get the mid range or low speed torque- the engine will feel very peaky. Your peak torque speed may be at 5500 rpm and peak power at 6500 rpm.

 

Count, if the VVT are removed and the 3.2/S-C 'flywheel' sprockets are installed, where are we at with power curves on the 4lt? I saw no loss of performance through the range and felt it actually pulled more freely compared to VVT. Gas mileage was the same prior to removal.

@Doomer Count was one of the original design team for this neat little engine, just so you know

 

I can testify to this, it was fast as F**k. It was my car we did this to

 

Doomer,

Here are links to a few references on the ZF 5HP24 transmission that may be helpful:

http://www.thejagwrangler.com/upload...on_control.pdf

http://www.jagrepair.com/images/Auto...r%20Manual.pdf

https://www.zf.com/global/media/zf_m...sa_4/5HP24.pdf

http://akpp-ivanovo.ru/wp-content/up...5HP24-diag.pdf

https://www.zf.com/global/media/medi...t_50145_EN.pdf

I'm also attaching "Jaguar Technical Guide: AJ-V8 Engine and 5HP24 Transmission Introduction."

I hope you are able to keep the Jag engine and to successfully complete your project!

Cheers,

Don

 

Thank you, gentlemen. I am grateful for all the information. I thought I might be in the wrong place with this, and might encounter some purists who took offense at my project, but I am really blown away by the support.

I was joking about the carbs sticking up through the hood. If that is the case, I'll go with something else. The X308 is an absolutely beautiful design, and I would never put a hood scoop on it.

Why Webbers? They are easy to mount on little manifolds. I don't have to make a dual plane manifold with a common plenum. That would be a pain for me. A lot of the tuning problems with these carbs come from running too large a carb on the application.

I have nothing against fuel injection, and running the Jag system with an aftermarket controller is easier than setting up 4 Webbers, but I want to try the Webbers. I'm looking at the local salvage yard for an engine to modify, then I'll swap it into the XJ8. The engine in the car now is running quite well, with a "restricted performance" condition which I'm pretty sure is due to the tranny problem. My understanding is that the '01 and '02 X308's had engines with iron cylinder liners and the control system is the only thing that makes these engines incompatible with the earlier cars. Is this correct?

As I understand it, the AJ28 VVT is comparatively simple, and only changes the relative opening of the intake to exhaust valves, not lift or duration. If this is correct, a best-compromise fixed position shouldn't have such a negative effect. I read that the VVT was primarily used to enable low idle speed quality for emissions compliance, which makes sense. But I'm very new to this engine, and maybe there's something I'm missing?

Thanks again for all the information. I have a lot to read!

 

Sorry to add to your reading, Doomer, but many of your questions will be answered in these publications:

Jaguar Engine Managment Systems and Advanced EMS Diagnostics - Book A
Jaguar Engine Managment Systems and Advanced EMS Diagnostics - Book B

Jaguar Service Training Course 881 V6/V8 Engine Management

Jaguar Technical Guide 1998 Model Year Introduction

You can download Electrical Guides for various years here:

JagRepair.com - Jaguar Repair Information Resource

Cheers,

Don

 

Why not get 8 little Mikuni carbs?

 

No comparison, there's a huge difference in actual measured torque curve VVT vs non. Check out the attached pic- orange (no vvt) vs blue- with VVT of an engine on the dyno.


This engine has been optimized- and the non vvt engine has longer duration periods to compensate for the lack of VVT (optimum duration becomes longer with no VVT).


You can see it makes up to 12 % difference. The difference is even larger with tuned exhausts.


There is a difference between 'performance feel' and real performance.


Some years ago we build a peaky Jaguar and set it up against a torquey one with a flat torque curve- EVERYONE on the clinic stated the one that was peaky was faster, emphatically. In actuality this was not the case.


If you peg the timing- infact you'll lose power as the default VVT position or rest position is set for smoothest idle/non overlap at all, which is different to the best position for peak power. Combine this with the fact that your duration hasn't been optimized for a non VVT application.Placebo effect - after being proud of something you've done would argue otherwise :-)
I wouldn't expect much of a difference in fuel economy. Exhaust VVT has a bigger effect on engine efficiency but even this is quiet small

 

Incorrect- please check my previous post- it was never done for emissions and makes a huge difference to power/torque and spread of torque.


The only way to get the torque back is to go bigger on the engine. The AJ26 had two position vvt units by unisea, and the AJ27 onwards has a continuously variable system that phased the intake cam.

 

 

Count Iblis:

So is the fact that the cams are ground for use with VVT what makes the big difference? In other words, if a non-VVT grind were run in fixed mode, could most of that 12% be made up?

I am curious because VVT has the reputation (among gear heads) for being an "emissions gadget" that can't compete with a fixed cam with a "real" performance grind. The VVT seems like it is easy to control, with only a solenoid valve regulating the engine oil to the VVT piston. Also, it seems that this is something that can be experimented with without risking damage to the engine if I get it wrong. Unlike an error in transmission clutch or air fuel ratio control, which can cause catastrophic damage, a VVT control error will just hurt power.

Instead of fixing the cams, I think I'll experiment with a VVT controller.

 

I just re-read your post and saw that the non-VVT cam had more duration, so that actually answered my question.

 

Thank you very much for these resources. I've gone over the engine management course. Quite overwhelming. I love the Jag, but the complexity of this control system is wasted on me. I honestly think this is the reason for the horrible resale value of these cars (around here, anyway). So much to go wrong, and a devil of a time to find the culprit. If Jags had the reputation of being "reliable and easy to repair", I probably couldn't afford one.

The transmission manual is greatly appreciated. "The transmission has been filled for life...it shouldn't be changed for 10 years." I guess my transmission was supposed to die 8 years ago!

 

The resale is due to such as previous bad reliability (can you say Lucas?) and that most people stay away from anything they regard as exotic.

 

Well, if it is the 5hp24, then it will die. Mine took 20 years to die...

 

Settle down Daim. Don’t get too excited........

 

After much reading and research through the bounty of materials provided by the knowledgeable and generous members of this forum, I have decided to shelve this project. The deeper I got into it, the less fun it became.

The final, large nail in the coffin was finding an immaculate 2002 XJ8. I had actually never driven a fully functional XJ8, and to say I was impressed by my first test drive is an understatement. I engaged "sport mode" and held the accelerator pedal to the floor. The engine pulled eagerly to 6,500 rpm and the sleek Jaguar leapt to 90 mph in no time. My '99 with the sick transmission and restricted performance mode gave no clue of what to expect from a working XJ8. If I didn't know better, I'd say someone at Jaguar got hold of a XJ6 with a small block conversion and said "We should build something like this." I completely blew any hopes of haggling with the owner by my inability to wipe the stupid grin off my face when I got back from my test drive and ended up giving him his full asking price. But it is a fantastic driving car.

So now, instead of figuring out how to dismantle the control system, I need to figure out how to maintain it. A scan tool will be my first step, and I'll be making heavy use of this forum again to research the best model to buy.

I'd like to try to fix my '99 to run like my '02. The '02's previous owner expressed doubts as to the likelihood of this, given the '02's iron-lined cylinders and other unspecified "improvements" over the earlier models. He owned a '98 which he described as "nothing but trouble." I do have a fairly competent local machine shop, and I will inquire about the possibility of sleeving the nikasil block, although finding a late model sleeved engine might be a better investment. I would imagine others have been down this road?