My car has suddenly started to lose power dramatically when the engine is warm and will literally just limp along on idle once the engine temp increases. When the engine is cold it will run, I wouldn't say 100% OK, but much better. No engine light and no codes, at least that my scanner will pick up.

I've read lots of articles on this site and others about loss of power and misfire causes. I observed when the car limped to a stop the other day, exhaust fumes coming from the area highlighted when I first opened the bonnet. Just prior to this quite an unpleasant exhaust smell entered the car.


I'm thinking the CAT may well be screwed and causing the issue. I just wondered if anybody else had a CAT fail (melt) and what happened / what were the symptoms.

Its a UK car. Is there a CAT near the engine as well as under the car?

Cheers, Richard.

 

Check for loose or broken manifold to downpipe joint bolts that contains the donut gasket

The only way I found was to go underneath with a 13 mm universal on a long extension

one of the 4 nuts will have little side clearance and I used a short straight socket with the extension bearly engaging the socket so you get the needed 15 degree angle

The gaskets can be blown or a crack in the manifolds

New exhaust studs I obtained from Welsh and were cheap

Search Genuine Exhaust System Parts For Jaguar Xj 1995 - 1997 (from 720125 To 812255) Classic | Jaguar Land Rover Classic Parts

 

It's probably the cats.

It's a little bit of work if you want to tackle this yourself. You'll need some socket extensions for sure. Its doable over a weekend if you have all the parts ordered. There are some one time nuts, and some donuts you'll want to order in advance. Someone else will confirm, but if you will probably have to remove the exhaust manifold to replace the cats. You may as well replace the metal gaskets while you're there... If you have an EGR, you may need some new parts as well.

Here's where I reported what I needed....without replacing the cats.

https://www.jaguarforums.com/forum/x...cement-200933/

I replaced the exhaust manifolds and gaskets. The cat might be a little easier than that, but probably not by much.

 

Confirm , to remove the forward cats the manifolds has to come out fully first

If manifolds remain attached to the downpipe you can't move the manifold far enough to the cars right to clear the head to manifold horizontal studss

On reassembly it is easy to error but is important to not damage the flair on the downpipe with the 4 down pointing studs interfering with your wrestling

I had to cut the webbing between the fwd and aft pipe for assembly

This damages your donut seal to have proper engine regulation , biases a rich mxsture or fuel trim

Don't forget to inspect for cracked manifolds , common from reading as was mine

The manifolds come in a couple different versions based on EGR and secondary air ( smog ) pump fitting

The supercharged version is I think the same as normally aspirated so that helps

 

Thanks Parker 7 and Vee for the advice. I'll be looking at this over the next 2-3 weekends and will update on the solution (hopefully).

 

So to recap, my car would drive OK with the engine cool. As soon as it warmed up it would misfire very badly, with pretty much complete loss of power and pressing the accelerator would cause the engine to make this terrible misfiring farty noise. The solution thus far has been to replace the Crank Position Sensor. It is running fine again now, although running way too rich. Hopefully get lambda sensors changed this week to try and sort that one.

 

Beforechanging sensors there are some things to help them out

There is 1 fuse for the 4 sensors to heat them up so they will operate and read correctly

This single heating wire passes though the Papa Indy 1 connector that has a TSB for corrosion

You can put a meter on the sensors heating elements to confirm if you have a target sensor in that aspect

Only 2 of the 4 sensors are used in engine regulation and the other 2 are for Cat effecientcy comparison code

The grounds that protect the return signal can be cleaned and I found green corrosion on the aft sensor connectors

important to not mix the connectors installation as they can be and this will give you some mid time ECU relearning of the sensors operating parameters

Vacuum leaks ?

cracked exhaust manifolds ?

donut gaskets or loose downward pointing 4 exhaust studs ?

Editing

 

Is the Check Engine light lit?

 

G’day Richard,

I had a similar problem with an XJ6 SIII I owned years ago, it would start and run when cold but as it warmed up it chugged and finally died.

The problem was a failed coolant temperature sensor (CTS) always telling the ECU that the engine was cold so as the engine warmed up it was progressively overfuelled to the point where it wouldn’t run properly.

If your exhaust is smoky black when the engine is warm then I’d start by replacing the CTS.

Cheers,
Jeff.

 

The 2 aft O2 sensors are for engine regulation

See page 80 - 81

801S TITLE (jagrepair.com)

The ECT sensor can be calibrated against page 79 using a resistance test driven by a 9 volt battery

So above 88 C closed loop trigger point you should see below 250 ohms

 

The rich running is highly likely due to a cracked exhaust manifold, a common complaint on these engines. Counterintuitively, although exhaust gas leaks out of the crack, oxygen is also sucked in between exhaust pulses, and tricks the O2 sensors into thinking the mixture is weak, resulting in the fuel being trimmed to rich.
Remove the chrome “vanity” cover, and cracks will be easily detected from the carbon deposits.
See the various threads for cracked manifolds for the next steps.
BTW, your car doesn’t have egr.