I have a 1989 XJ-S 70,000 miles, runs great. I am curious about where /or if the rpm is limited and can it be changed. It acts as if it is limited just above the shift points of the turbo 400 at about 5k rpm. Any ideas? thank you.

jack

 

I'm not aware of any rev limiter on the XJSs. My '88 certainly didn't have one. It would rev easily to 6500 rpm if the gears were held manually....although I don't think much, if any, additional horsepower is being generated after 6000 or so

I'd suspect a fuel starvation problem if yours struggles at just over 5000 rpm

Cheers
DD

 

Doug,
Thank you for your insight. As I think about it, it could also be plugs, ugh. I will do further research as I found an after market rev limiter that allows over 7k.
I also have a 74 XJ6 with a 350 , 350hp/400 ftlbs. it just flattens out at prox 6500. I will keep you posted and thank you again.

jack

 

I agree, mine revs higher, I think about 6500, and it will make WOT shifts. It could be running out of spark, but I would be at least as suspicious of loosing fuel pressure to the rail.

 

If you have Lucas ignition--- some 1989 cars Lucas ignition, others had Marelli ignition--- you might be experiencing failure of the secondary coil.

If you still have the secondary coil (many dual coil set-ups were replaced with a single coil) it'll be in front of the radiator. When they go on the fritz the engine won't rev well....although usually you can feel the problem at 3000-4000 rpm

Just a thought

Cheers
DD

 

In my ownership of V12s, it seems a rev limit caused by spark (spark plugs) would result in intermittent broken firing. All other limitation was fuel related. Have you changed the fuel filter (ever?). I installed a inline fuel pressure gauge so I could check fuel pressure at any time I have the hood open. Of course, load (driving) will effect fuel consumption more than revving the engine while idled, but nonetheless, the fuel pressure gauge allows me to watch what the fuel pressure does as I crank the throttle up.

 

Well guy's,

It seems there is an rpm limiter and I quote from the Jaguar Repair and operation manual

the PCMF (powertrain Control Module Fuel) provides engine over speed control and imposes an engine speed limit of 6,000 rpm by cutting fuel injector operation The FI begin operating again as the speed falls to 5900 rpm.

There are several possible causes of my malfunction. I will update as I continue my research.

jack

 

Relative to what years and engines?

Cheers
DD

 

I cannot find any mention of rev limiters on any xjs and can say for certain there is none on my '89. Quite easily revs to redline which is 6500 so unlikely there would be a limiter set at 6000 anyway. I think the PCM appeared in later XJ40 and XK8 models.

 

According to my manual, the 5.3 12HE should fall into this area.

My first step is to get it on the rack and check the flywheel sensor. I spoke to another owner, who interestingly enough, had the same issue and found the sensor bracket bent. He fixed the issue and solved his problem. Would that mine will be that simple. The other issue is how many times will I want the extra RPM. my trans shifts at 5K anyway. If I want to race I can get in my XJ6 with chevy vortec engine.

Thanks for all your help.

jack

 

Doug,
It appears that I was wrong about the rev limiter. I spoke to a jag shop and he feels that since I have a lucas ignition that the advance weights are frozen and thus limiting advance. I plan to pursue that approach. Apparently this is a common problem. If it isn't frozen, it will be soon.

I look forward to having a 12v that runs as it should.

Again thank you for your help.

jack

 

my standalone computer all adjustable , i can set my rev limit anywhere from 1500rpm out to 9000rpm, of course depends on if your engine can take it!

as of now set to 7000 rpm, but after 6500 its over the peak, time to shift

 

If you look at your distributor, have one center wire, and a small black box mounted on top of the engine, you have Lucas ignition. If you have two coil wires in the cap, one center, one off center, you have Marelli. Very obvious which one is which.

 

Good morning,

I have a Lucas Amplifier mounted on top of the engine. I haven" examined the dis. cap yet. I will do that today.

Thank you for you help.

jack

 

You have Lucas ignition


Cheers
DD

 

Yup, no Lucas amplifier on a Marelli car

 

I would be interested in how you install a 5 speed in your XJS. While I like the turbo 400
in both of my jags, I think the XJS would be a lot more fun and it begs to have a manual trans. I also have an XJ6 with a vortec engine (350 hp, 400 lbs/ft) the turbo 400 is more suited to it. While I have considerable experience restoring cars, I am new to the Jag v12. BMW v12, yes, I am learning the jag as I go along.

The Jag forum has been a big help.

Thanks again,

jack

 

The Jag V12 can be overwhelming at first. I found that by breaking it down to systems, i.e. fuel, ignition, etc., it became MUCH less daunting. After rebuilding a couple of them, they are now even less so. It really is just two inline 6 cylinders joined by a common crankshaft. When looking at the Jag V12, always keep in mind that the right side of the car (as viewed from behind) is the A side. The left side is the B side. The more I work on them, the more familiar I am with it.
On a side note however, the turbo 400 was phased out for a reason. It is a bulky transmission that consumes a lot of power. I am looking forward to having my conversion done. I owned a 71 V12 XKE (4 speed, then converted to 5 speed) and I know it was a LOT of fun to drive!

 

Thank you for the info. I agree that as I look at the engine more I am able to realize that it is like any other engine,albeit, with a few other systems. Are you going to convert to a 5 speed your self or have it done? If you are doing the conversion, it might make for a nice video that, would be enjoyed by many.
Thank you again for your help,
jack

 

Im doing the conversion by the piece. Not sure a video would help, as I had a couple on NOS Tremec 5 speeds that I had bought from a retired Eaton engineer several years ago. They have extra long tail shafts, and I had a friend of mine professionally relocate the shifter to work on my XJS. I am installing a 6 liter from a 94 XJ12 that I am doing the Electromotive TEC3r engine management system. Also doing a custom supercharger system by mounting a Whipple 3.3 liter twin screw in the V. This whole project is nothing but custom made pieces all the way. Enough time, creativity, and patience you can build about anything you can envision. I think it was Norman Vincent Peale that said "Whatever the mind of man conceive and believe, it can achieve".