The exhaust pipe that connects to catalytic converter get's red hot pretty quickly. Never park/stop on top of anything flammable, especially if you are going to run the engine!

Now why: today, frustrated with loss of power during acceleration when car is hot I wanted to find the problem. So, I drove around until problem became consistent, then connected vacuum gauge to vacuum line that goes to distributor and observed how pressure drops at different loads (I was suspecting that vacuum was advancing to far at partial throttle), then drove around with vacuum disconnected. All seemed fine..

So I got into garage and while engine was still running I kept looking for problem... after a while, suddenly I noticed smoke coming from under engine, smelling like burned plastic....

That's when it hit me - I still had PVC liner on the floor that I put there while replacing radiator hoses!!! The damn thing could have caught on fire. Not to mention - because of small oil leak I usually throw piece of cardboard under the car anyway.

That whole experience prompted me to note location of fire extinguishers and their age. I decided to get one more, as my old ones are getting old..


So, do you ever throw something under the car? And are you extinguishers "fresh" and ready to go?

:-)

 

Well found in time.

Exhaust heat is way underestimated.

I dont throw anything under the Jags, no oil to drop. Fixed them all.

 

Though it shouldn't get that hot. Cats aren't supposed to flow red drin normal driving... Are you sure your car isn't running a little lean?

I'be never had problems with hot cats. On my old Volvos the cat was the lowest part of the vehicle and it never got hot enough to cause something in the area, no matter how far away or how close, to melt.

 

The converter should not get red hot. I bet you're running rich; the converter is burning off all the excess fuel and that's why it's so hot. Lack of power could be the cat is melting. You need to fix whatever is upstream causing the converter to run that hot.

 

It's pipe right after catalytic converter that was glowing red today (it was after dark, during highway test-run). Actually, there are quite a few warnings in the handbook about 'unusually high catalytic converter temperatures, especially under engine malfunction', pages 38-39.

No, I am not sure if car is lean or not. I was going to pull spark plugs out today, but after 'smoke scare' I just called it a day... How else can I find it out without special equipment?

Anyone has a colortune I can borrow? :-D

 

Thank you. I feel the same way.

I am trying to tune upstream part, but without special equipment all I can do is replace/check sensors, and bring to specs few 'adjustables' like TPS position, timing advance, fuel pressure. Any suggestions how to tell ECU to go 'leaner' or 'richer'?

I just received new coolant temp. sensor (5S1570, hope the right one), but old one tested ok with ohmmeter so I do not expect miracles with this replacement.

Another surprise is the absence of oxygen sensor in my car, hope it is not a 'mod' by one of the previous owners. I will pull out ECU one day and check by model number if it is supposed to have input from oxygen sensor.

Colortune is another thing I want to put my hands on, at least I can get feedback at idle..

 

Is your car a US spec car? It should have 4 O2 sensors. Even a European spec car would have at least 2. Colourtunes are not great, you're much better off with a wideband O2 sensor and gauge, it will tell you exactly what the air-fuel ratio is. AEM makes good ones.
http://www.aemelectronics.com/produc...uego-afr-gauge

 

Well, it is 'US spec' to an extend as it has sticker that it comply to us law. At the same time it is an 1985 import with 3.6L straight 6 engine (which were mostly sold in europe). I think most likely this car did not have 02 sensor, and if it was - per manual it would have just one. My xj8 does have 4 sensors, but it is newer design.

Thanks for the wideband O2 sensor and gauge idea, will definitely look into it.

 

IIRC the 3.6 had 2 O2 sensors... One per 'manifold' of you will.

 

This is exactly how mine look like:

 

For some reason I had it in my mind this was the XJ8 you were talking about!

The XJS of that vintage is known to run rich. See here: A COMMON PROBLEM WITH THE EARLY 3.6 XJS (1983-87) / AJ6 Engineering

 

Just found in the manual that idle richness is adjusted on ECU using "tool 60730551". Does anyone have it? How does it look like? (google did not see it ! )

 

The ECU adjustment tool is commonly made custom out of sundry bits from the hardware store. I assume the original is NLA.

If if you are not concerned about maintaining originality of the parts behind the carpet in the trunk then you can easily mod it.

Open up the ECU, drill out the rivet holding the bracket for the adjusting potentiometer. Remove the pot from the bracket ( small snap-ring pliers required ) and remount it in the original case opening. Now remount the plastic pointer that made it "click" and you have an external adjuster with an indicator. No more clicks though.

The pot is very stiff and will not change position while driving even without the clicky indent mechanism.

 

I made 'tool' from a pen, it fits over potentiometer just fine, but with normal effort I can turn it only few degrees (feels like one or two clicks). What is the turning range for this adjustment potentiometer? (I don't want to break it accidentally).