Hi all,

Im looking at sticking a aj6 engine in my series 3, haven't decided on a 4.0 or 3.6 yet.

The problem is always going to be the spedo and this is probably the biggest reason the conversion turns me off.

I was wondering a few things maybe others would have input on:

1. Where does the xj40 actually take the spedo reading from. Some say diff, some say tranny on the 4.0. If its tranny on the 4.0 then it would probably be easiest to stick a 4.0 in and just modify the guts of the s3 spedo to take the xj40 mechanism. This is probably my least preferred option as you loose the odometer and would probably need to house the circuitry from the xj40 dash somewhere to drive the spedo.

2. Make a reluctor that sits on either the transmission output flange or diff output flange behind the brake disc and then send this signal to the series 3 electronic spedo. this would work if the series 3 spedo looks for a digital or pulsed signal, rather then a variable voltage. Obviously the ratio of pulses to revolutions is critical and would need to be worked out. If the series 3 unit relies on voltage then this plan won't work as turning the digital signal into a variable voltage is hardly easy.

3. Mount a reluctor on the transmission flange and use a pickup to run something like an aftermarket autometer spedo mounted in the frame of a series 3 spedo. These are programmable and probably the easiest option electronically, although making it look original is another thing.

The most important question is does the xj40 ecu require a road speed pulse to adjust the fuel trim and what not? If it does then the original xj40 system will have to be replicated as close as possible. Anybody who can post a link to a wiring diagram or a pdf would be much appreciated. I cant see why the 4.0 would be more complicated even if it is electronically controlled, apart from mounting the tcu and wiring. Apparently it gains its speed information from the transmission and this is what runs the spedo and tcu.

Any input would be appreciated,

Thanks,
Jay

 

From memory, so take care please.

We fitted a few 3.6 with the cable kickdown 4HP22 transmission.

There was an adaptor on the extension housing for a sender, or cable drive, if needed. It mattered not the donor car layout. That transmission is used in sooooo many Euro cars, and like Jaguar, some had trans speedo drives, some had diff senders.

We stayed away from the 4ltr and the 4HP24, due to the electronics needed to drive that trans.

I think we found a Merc, or maybe BMW, speedo drive that did the task just fine.

 

So all you need to do is knock the plug out and find a sensor? Did you use the original series 3 spedo and was it accurate? Did the ecu need a pickup?

Thanks for the reply,
Jay

 

1) Thats the fuzzy memory bit. I reckon we fitted a transducer and that was it. The speedo accuracy is DIFF ratio dependant.

2) One of them went in a S2, so a cable adaptor was found and filled the hole, again, the diff ratio remained as was, so the speedo was as accurate as it was before the spanners touched the car.

3) The engines came with the ECU junk, so fitting to the ":new" car was simple enough, but which wire went where just took some logic, and time to back off and ponder. Usually with a few JD's.

It was/is a time consuming task, and I would NOT do it again, REALLY. I would rather rebuild the XK, or V12 engine, and be done with it. Do that properly, and drive it another 25-30 years, maybe more with modern oils/coolants/etc.

The 4 speed 4HP22 trans into a BW65/66 is a top idea, and that is always a consideration, but as with all this car stuff, $$ talk.

 

I almost finished my conversion. I used a 4.0 aj6 with 4hp24 transmission. This box takes the speedo reading from the box, at least in my car which was an 1994 model. I intend to combine the original s1 spedo reader with the xj40 one. So integrate the xj40 mechanism in the s1 looks. Keep in mind though, the speed is measured at the transmission. The diff is not taken into account. as the S1 diff is different from the xj40, your actual speed will be higher then the displayed speed. I am not sure if the box ecu is programmable, which means you can change the diff ratio. If not, I will simply adjust the numbers on the dash.

I didn't have the box working at once. First, it didn't shift. Still, the engine ran fine, also on higher speeds. The engine management is really a standalone unit. will work fine outside the car.

reason why I choose for 4.0 liter was simply that at the time I wanted an aj6 engine, a scrapper xj40 with 4.0 was the cheapes I could find.

I would, however, recommend buying a complete car, and not just an engine. I would have had to buy so many things I now simply took of the xj40, it saved me money in the end buying the entire car.

Biggest challenges in the conversion:
- Wiring
- engine mounts (people say you can take xjs mounts but didn't work for me. I used them, and then the sump fully rested on the anti-roll bar, instead of on the mounts.)
- driveshaft needs to be shortened and balanced.
- rear engine/tranmission mount is also a challinging job. But again, when you have the complete car, you can almost use complete mount from the xj40, and then it's fairly simple.

tip: use xj40 steering rack. I drove my converted car first time yesterday, and it steers like a dream! amazing how the handling has improved, compared to the original steering rack. on top of this, you wont have to adjust connectors to steering pump etc.

good luck and keep us updated

Edit: In response to Grant Francis: I would do it again tomorrow. So far (I am only 25 yet) this has been the most fun job to do on a car for me!

 

Hi grant and Wilfred,

I was working on an xj40 at work today (just got the head on and getting it running) and it all looks relatively strait forward. Only thing that concerns me is hooking up the air con, although it doesnt work at the moment so if I got rid of it all together I wouldnt be too heartbroken.

As to the rack my car is a series 3 so already had a different rack in it that has a very nice steering feel anyway. Here in australia you need to have all sorts of engineers reports for modifying vehicles and steering racks are no exception. Technically as the 4.0 was offered in the xj6 you can get off having to have the car 'engineered' as you can use a combination of original mounts and engines in the swap, you just have to sign a form that states you have not modified the chassis or any structural aspect of the vehicle. Its all a bit ambiguous when it comes to modifying engine mounts, but by using xjs ones I dont think there will be any issue. Are you sure you got the later 4.0 xjs mounts that were designed for the aj6 engine, maybe you were sent some 5.3 v12 ones?
I have seen the xk engine mounts collapse to the point that the engine sits on the cross member.

Personally I too love having to make up parts and modify things to work. I would probably use the series 3 radiator and install an separate trans cooler and just make up a coupling for the power steering lines. As you say the transmission mount cant be too hard. The rest of it seems to be as easy as the chev conversions everyone seems to love. As far as wiring goes ill probably just untape the whole look and cut and splice things in and out to suite the installation. I hate nothing more then redundant wiring left in place for no good reason.

At the moment im eyeing off a 4.0 wreck that has been t-boned pretty seriously. Hopefully I can strike a deal on it.

I will be very sad to see the xk motor go as I really appreciate the engineering of the thing and it actually runs very well, just the auto is pretty sad and by the time I get a decent rebuilt one in there its probably cheaper to stick an whole new power plant in. I have thought about a 5 speed conversion keeping the 4.2, but these are not cheap!

 

I am sure I got the right engine mounts. But as I said, I put them in place and the engine would just rest on the anti roll bar. There was no way it was gonna fit.

I put things 5 cm back, drilled new holes in the subframe and now it sits very nice.

yesterday I had the first ride with it, and it's quite comfortable. No irritating noises or vibrations, plenty of power and nice handling.

 

now I'm sure the 4.0 will do. I got mine shifting today....... Turned out the gear computer wasn't powered. Now all works. So the rpm and speed info comes from the box itself. For me it's up to the instrument panel now. the speed signal can thus be taken from the box, connected to the xj40 speedometer and integrate this into the s1 dash.

 

for a different approach on the speedo hack, see my thread:

https://www.jaguarforums.com/forum/xj6-xj12-series-i-ii-iii-16/series-i-aj6-engine-107712/page4/#post959658]CLICK