Well,today I happened to pick up a nice 1988 XJ40 Vanden Plas. I was a bit skeptical after hearing so many stories about electrical problems on the early XJ40's,but the car was in pretty nice shape that I decided to take a chance. It does have some very minor rust/bubbling on the trunk lid lip and around the taillights but it's not as bad as most that I've seen. The interior is in excellent condition and all electrical seems to be working ( lights,windows,signals,sunroof,wipers,air conditioning blows cold,etc. ) I purchased it through a dealer who got it from a woman who was the original owner. He passed on the original title issued in June of 1989. I was told the issue with the car was a clogged catalytic converter. It starts and runs but it runs very rough,almost like it's running on two cylinders,but once it revs to about 2000rpm it starts to run a bit smoother. I've noticed that the exhaust seems to be particularly hot too. Is this a common issue for the cat to clog? What's the best cure,gut the cat or just replace it? Not new to Jags by any means having owned many different models over the past thirty years. I do most of my own work too. Opinions?

 

Hi 95Leaper,

Congratulations on your new Jag. That's very cool that you received the original title from 1989. Did you by chance also receive full service records for the car? I ask because my first question would be how recently the car has had a full tuneup?

The first thing I would suggest is that you check the Vehicle Condition Monitor (VCM) for any stored Diagnostic Trouble Codes (DTCs). To do so, turn the key to Position II (ON or RUN) but do not crank the engine. Depress and release the VCM button on the trip computer panel to the right of the steering wheel. Now watch the small display window below the speedometer for any messages to be displayed. DTCs will be in the form of a single digit number, possibly preceded by the words Fuel Fault or the letters FF, as in "Fuel Fault 2" or "FF8." If an asterisk appears with the code, more than one code is stored. Report anything you find here and we'll try to help.

There are some basic tests you can perform to check the function of the catalytic converter. Unfortunately, the diagnostics protocol is OBDI, so modern OBDII scanners with bi-directional Live Data communication are of no help. But with an inexpensive non-contact infrared thermometer you can check inlet and outlet temps:



With a vacuum gauge, you can check for excessive exhaust backpressure:

Catalytic Converter


If you can determine that the catalytic converter is not obviously clogged, it may be worth spending some time checking for some known issues and giving the car a good tuneup to see if things improve. Here are some basic tasks I would suggest:

Carefully check the air intake plumbing for cracks/leaks between the Mass Air Flow sensor (MAF) and intake manifold gasket
Check the torque of the intake manifold nuts and hex screws (the torque spec is low and the fasteners can loosen)
Check all vacuum hoses and crankcase breather hoses for cracks or leaks
Clean the carbon buildup in the EGR port on the underside of the TB (see photos in my albums at the link in my signature)
Check the EGR valve to ensure it is closing and opening properly
Remove and clean the carbon from the Idle Air Control Valve (IACV) and stepper motor plunger (see my photos)
Clean the Throttle Body (TB) and check the butterfly valve clearance
Clean excessive oil buildup from insides of air intake plumbing and crankcase breather hoses

Tuneup items:
Spark plugs
Spark plug wires
Distributor cap and rotor
Air filter
Fuel filter
Adjust the accelerator cable to eliminate any slack
Clean the grounds in the engine bay, including the engine ground strap
Clean the battery power connections

Additionally:
Drill drain holes in the plastic case of the Throttle Position Sensor (TPS) and flush it with zero-residue contact cleaner (see my photos).
And if you're really adventurous, clean your fuel injectors (fuel tank additives are of dubious value - see my photos for how I cleaned my injectors at home).

Please keep us informed.

Cheers,

Don

 

An 18 year old, one owner vehicle.

You don't mention the mileage but I suspect it either could be low or the vehicle has had little recent use.

As Doug says, did you get the service records? It would help you to know if you are troubleshooting an issue the PO has given up on or are effectively recommissioning a laid up vehicle.

Graham

 

The original owner was an older woman who purchased the car new. From what I was told,she traded the car in to a dealer ( the man I purchased it from ) who then tried to sell the car for a few months at $3500. Like with some used car dealers,he would take the car out for a drive once in a while. He mentioned that on this one occasion that he was out driving that he noticed smoke coming out from below the car,pulled over and the cat was nearly on fire. After running the car for about five minutes I also noticed the exhaust running hot and seeing some smoke ( nothing from the tailpipes though) coming from midway beneath the car. The car has 136K miles,not super lower but can be considering it's 29th birthday is in January. The engine doesn't seem to run hot at all with outside temps being a tad over 80*F. I guess I'll have to slide underneath and use my temp gauge to see what the cat temps are reading. Since we don't have any emissions here,do you think it would be wise to just eliminate the cat?

 

Some owners have eliminated the cat so that's a possibility. Search this forum and the archives at the Jag Lovers forum for details.

One thing I forgot to mention is that cat failure seems to have been uncommon on the XJ40s. Our '93 is still on its original cat at 197,000 miles. When owners have had problems with the cat, they have generally been associated with engine problems such as unburned fuel making its way into the exhaust due to misfires.

 

Oil or any sort of other combustible crap seeping back underneath the car on to the exhaust or even parking it over some dry grass or other flammable stuff could cause smoke until it clears/explodes ...as you saw in Eric's video, the cat is supposed to get hot and burn up the NOx so maybe all is well ...

When you say the exhaust was running hot, do you mean the actual exhaust fumes or the tailpipes?

The infra red thermometer test would be a good thing to try, you can probably rent one if you don't want to spend the cash on a new one (although I got mine on sale for $14.99!!)

Larry

 

I lifted the car and got it up on jackstands today. I ran the car for about five minutes to make sure it was completely warmed up before going to test the cats. Well,looking under the car at the cat,it was glowing red like molten lava,not a good sign. I managed to cut the rear cat out completely and she seems to run slightly better but the front cat is glowing red also. As far as the VCM, I'm getting a bulb failure( which I'm assuming is a brake light since I've checked every single light and they are all working ). I'm also getting fueling failure, low brake pressure and an abs fault which I'll address after I get it running properly. I did notice a cut brake line just behind the passengers front wheel inside the engine compartment,so I'll have to trace it and see where it goes. For now I'm mainly concerned with it running smoothly. She'll start with no problem but as soon as it starts it runs like it's on two cylinders,but when you give it gas it feels like it's stumbling until it reaches 2000 rpm's and then it just comes to life and sounds as it should. It also runs much smoother after 2000 rpm's,like it's running on all six. Aside from eliminating the front cat too,what would cause such an erratic idle below 2000 rpm's?

 

Check the number plate lights too!

Larry

 

Lawrence,that was my first thought since they always get overlooked but they are fine,even my reverse lights work. Just need to check my brake lights but my guess is that it may be the third brake light bulb. I think I'm getting that low brake pressure warning because of the erratic idle and possibly not building up enough vacuum for the brake booster unless I accelerate to higher rpm's. Still a work in progress but I'll get there.

 

Was the "fuel failure" warning in the form of "Fuel Fail," and if so, was there also a single-digit number? If so, that is a Diagnostic Trouble Code and not necessarily an indication that fueling has failed, only that the ECM is receiving an incorrect signal from one of the sensors or components involved in fueling (MAF, O2S, CTS, IATS, TPS, etc.). Check again for any numerical digit that is part of that code, such as "Fuel Fail 8).


There's a good chance the cut hydraulic line was part of the original Self-Leveling Suspension (SLS) on the rear corners of the car, which was prone to leaking. Jaguar came up with a conversion kit to replace the hydraulically-leveling rear shocks with conventional non-leveling shocks. The coil springs and some spacers were also exchanged. Part of the process was to plug the hydraulic plumbing somewhere close to the pump at the front of the car.


Probably the most common causes of rough running at idle and lower rpm are an air leak somewhere on the intake side of the engine, a vacuum leak, a clogged air filter, or a problem with fuel delivery such as a failing fuel pump or clogged fuel filter.


Unless your car has been converted to vacuum brake boost, it has hydraulic brake boost, and the system is powered by an engine-driven hydraulic pump at the right front corner of the engine. A common cause of the Low Brake Pressure lamp is a failed hydraulic accumulator, but there can be other causes. I am attaching the Power Hydraulics Manual that contains diagnostic flow charts to help you identify the cause.

Cheers,

Don