My 1996 XJR starts up and runs fine until it warms up and when I press on the accelerator it starts misfiring and blowing black smoke any ideas on what could be the problem?

 

I've moved your question from X350 to X300 forum. This is the place to post technical questions about your model.

I've also deleted your identical posts in New Member Area - Intro a MUST and General Tech Help forums. Do NOT MULTIPLE POST THE SAME QUESTION across different forums.

Graham

 

Most likely the coolant temperature sensor. That controls the cold enrichment, so it's possible the ECU is thinking the engine is cold and adding extra fuel. You can measure the resistance it should be ~ 200 ohms at operating temperature. It's a standard Bosch sort of curve that changes with temperature.

 

Changed the coolant temperature sensor car runs better but at 3000 rpms it starts missing and blowing a lot of black smoke and no power!!!

 

Next likely culprit in the air flow meter. It's unique to the XJR and now NLA, so your only option is a used one off ebay or a place like Coventry West. As a quick and dirty test, try unplugging it and see what happens. It shroud run a bit rich all over, but not black clouds rich.

 

The xjr model uses 2 fuel pumps, one for low speeds and the other cuts in about 3000 rpm. Could it be a fuel pressure problem?

 

I know this sounds silly, but make sure the battery is fully charged. I once had an issue where my XJR felt like it had hit a rev limiter at around 4000rpm. The fault developed after my water pump failed wetting the alternator - short story charging the battery fixed it.
Also the only other time I had a running issue was due to corrosion on the ECU connectors - It felt like fuel contamination and caused me a lot of messing. Use contact cleaner on them, not WD40 or similar as the residue cause issues believe it or not!

 

Any fault codes?

There has been an TSB (18-53) from jaguar regarding rich or lean running conditions, which in most cases is not the air flow meter, but the fuel pressure regulator leaking/sticking. Pull off the vacuum hose at the pressure regulator and smell if it smells like petrol which might indicate a leaking pressure regulator and excessive petrol entering the system.

It might also be a good idea to check your rochester valve.

 

Replaced the alternator it was bad but not the problem battery is also good where is the ECU located?

 

Where is the pressure regulator and rochester valve located?

 

The ECU is behind the plastic trim panel by your feet on the right hand front door post. I guess this will be the same for left hand drive cars. The ECU connections are covered by a 'security strap' with special screws that you need to carefully drill out. The plugs are on the top and water leaking in can track down the cables and corrode the connectors. Unplug and carefully clean with contact cleaner. That cured my problem, I guess the water gets in once the drainage tray section of the firewall starts to rust through. I try to keep my car as dry as practical!

 

hi any news on the main post as I'm having the same problem I need help...

 

Codes ? Might consider a EML327 live data reader to see if something goes out of wack at the point of failure , 8 dollars free shipping Ebay . There is a learning curve . Perimeters to look at are :

STFT 1 and 2

TPS

MAF

Coolent Temp

RPM

An example of one being used on a X300 page 2 :

https://www.jaguarforums.com/forum/x...ong%5D-184729/

A example of it's all around features , cheaper software :

 

Here is a TSB for a recall here in the US.

The remove/replace procedure is in the document for reference.

bob

 

I have suffered this problem twice, firstly caused by a defective pressure regulator (mentioned by Dutch-R) & second time it was the oxygen sensors (2) which I replaced.
You have a classic case of "over fuelling", & replacement of the above immediately cured the problem & I was lucky in that they were my first calls to replace.
Best start with the simple & obvious first, try not to "overthink" the problem (ie talk of ECU's etc)

John Herbert
1996 Jaguar XJR

 

can I ask please what was the part number of your original sensor and what p/n of new one thanks

 

update.! Changed the air flow meter with new unit.cts confirmed ok.timing ok.runs but with intermittent misfire due to running extremly rich!!!
Stft= -25 plus but when I take revs up the the trims come down near or the -7 to 0 at approx 3000 revs.what else can make this thing rich I'm now thinking ecu...

 

No ECU yet . What someone told me was 24.2 fuel trim at idle and goes toward 0.0 at throttle up is vacuum leek on the intake side . On the higher RPM could be a different issue . Can you see if the fuel trim goes to close loop on the ELM327 and it my have not meet the requirements to do so .

 

I've got negative fuel trim on idle which means 02 sensors are detecting rich running and telling ecm to reduce fuel he ce the negative trims. which is confirmed and present due to smell of exhaust and plugs are black. When I pick revs up it goes down due to more air going in which compensates for the extra fuel that shouldn't be there..ill 're check for leaks when back together.

 

negative trim is opposite of what I picked up on in your post . Mine was positive 24.2 with obvious rich exhaust . My bad . Scratch on the leaks ? FPR too high for the minimum pulse length of the injectors ? 43 psi at idle and bumps up bit on throttle up . TPS reading 0.60 + or - 0.2 volts at idle ? Sticking open butterfly giving biased TPS readings to give it a longer pulse length ? Never mind that would cause higher idle RPMs .