Mechanics

NO LOW END POWER

1990 Jaguar XJS

Engine Performance problem
1990 Jaguar XJS V12 Two Wheel Drive Automatic 140, 00 miles

My 1990 jag 5.2 began to perform slugishly. I legged it home (did not overheat) Upon investigation I noticed that the hoses for the air injection ( two silicone hoses at rear of engine)were busted and blowing smoke. I replaced them along with the two rubber hoses for the manifold crossover pipe. I then started the engine and it idled better than it had in a long time. It used to idle excessively until it warmed up. Now the bad news: It took it out for a test drive and it can barely climb a hill. Once going it is okay but lacks power. I also noticed a low exhaust noise( like a small leak would sound) from the drivers side near the front of engines. Catalytic converter issue. And why suddenly after repair noted above. Need some advice / ideas.
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Ahkirby
June 25, 2008.



Let us do a simple test get a vaccum gauge attech to an intake manifold port. Start engine raise RPM up vac. Should as you approach 2000rpms what happens to vac?
Let me know

Docfixit
Jun 25, 2008.
Checking the Catalytic Converter with a vacuum gauge

EXHAUST SYSTEM BLOCKAGE: high reading when engine first started, falling back to 1 or zero and gradually increasing to 15 or 17.


http://www.2carpros.com/forum/automotive_pictures/12900_vac16_1.gif


Rasmataz
Jun 25, 2008.
Hooked up vacumn gauge and started engine. Vac read around 12 lbs. Reved to 2000 rpm and reading fluctuated about 1 or 2 lbs and steadied at 12 lbs.

Tiny
Ahkirby
Jun 25, 2008.
You need to take RPM up slowly not hard. If you did slowly and it falls as you increase then it indicates exhaust restriction Cat probably. Hoses where burned yp due to hot gas basking up in exhaust.

Docfixit
Jun 25, 2008.
I like your theory. Perhaps it was the cat from the start whiich led to the deterioration of the air rail hoses. However I did the vacumn test again. If I rev the engine slowly it starts at 12# and will only drop to 10#. If I gun the engine it will drop to zero.R

Tiny
Ahkirby
Jun 25, 2008.
That does indicate some restriction coupled with the air injection hoses I think you got it. The drop to 0 when you gun it is normal but it should rise after a coupl sec. Also nornal vac reading is 15 to20.
Good luck

Docfixit
Jun 25, 2008.