Running rich..

It is immediately aft of the left side thermostat housing. I'll look up the resistance specs and report back....

Doug Dwyer
Longview Washington USA
1987 XJ6 Ser III
1988 XJS V12 Coupe

Doug-

Can you tell me where to find the "ccolant temp sensor" on the engine? also, you mention that I could meter it out to check its functionality. In what range should its resistance be?

Thanks

Rodd Leeds
1988 XJS 5.3 Cabriolet

The enrichment switch has black and white/slate wires. The switch is wired in series with a vacuum switch serving the same function....it's just a redundant system. The black wire goes to ground, the white/slate goes to the ECU

I use AC Delco oxygen sensors but any brand will do. Most are semi-universal...you'll have to splice the Jag connectors onto the new sensors; no big deal. Before replacing you can test them if you have a digital volt meter.

Even though there is no fuel in the vacuum hoses to the pressure regualtors they may still be faulty. That's where the pressure gauge would come in.

Many regular repair shops have an exhaust gas analyzer.

Doug Dwyer
Longview Washington USA
1987 XJ6 Ser III
1988 XJS V12 Coupe

Doug:

Thanks for the detailed response! I noticed that the micro switch on my throttle"turntable" is disconnected electrically and mechanically. It is sitting up top, and I see how it would close as the throttle is advanced, but there is no wire connected to the male spade terminal, and there are no wires in sight that may have fallen off. Where does the electric wire come from that is su*pposed to connect to this switch? Also, do you happen to know its color?

I pulled the vacuum hoses from the fuel pressure regulators, and there was no sign of any fuel in them. Next I thought I would replace the O2 sensors. Can you recommend where I should puurchase them, and what brand I should buy?

Also, absent going for an inspection at a State facility, what is the best test tool to determine the correct fuel/air mixture? Would it be an exhaust gas analyzer? In other words, how do I know when I have corrected my problem??

Thank you very much!

Rodd Leeds
1988 XJS 5.3 Cabriolet

Doug:

Thanks for the detailed response! I noticed that the micro switch on my throttle"turntable" is disconnected electrically and mechanically. It is sitting up top, and I see how it would close as the throttle is advanced, but there is no wire connected to the male spade terminal, and there are no wires in sight that may have fallen off. Where does the electric wire come from that is su*pposed to connect to this switch? Also, do you happen to know its color?

I pulled the vacuum hoses from the fuel pressure regulators, and there was no sign of any fuel in them. Next I thought I would replace the O2 sensors. Can you recommend where I should puurchase them, and what brand I should buy?

Also, absent going for an inspection at a State facility, what is the best test tool to determine the correct fuel/air mixture? Would it be an exhaust gas analyzer? In other words, how do I know when I have corrected my problem??

Thank you very much!

Rodd Leeds
1988 XJS 5.3 Cabriolet

The coolant temp sensor is a common culprit as they often fail "skewed cold".....sending a cold signal to the ECU which, in turn, dutifully commands extra fuel....regardless of engine temperature or demand. Make sure the connection is clean and tight. The sensor itself is easy to test with an ohm meter. Or, for $25 and 10 minutes labor you can replace it. I'm not advocating shotgun diagnosis but as guesses go, this one isn't too hateful in terms of expense vs. labor vs. success rate.

On the throttle turntable is an "enrichment" switch which activates at about 3/4 throttle. Make sure it is not jammed closed or you'll be 10-13% rich.

Remove the vacuum hoses from the fuel pressure regulators. If raw fuel is present in the hose then you obviously have a ruptured diaphram.

A fuel pressure test will tell you if one of or both of the regulators is allowing too much pressure. A fuel pressure test is not convenient on these cars as there is not ready made acces port. You'll have to remove the right regulator and fit your pressure gauge between the inlet pipe and the fuel rail. Quite doable, just not convenient. I might add that the right side regulator is redundant and can be eliminated completely. It is for noise control only. I might add, too, that a vacuum leak at the regulator vacuum hoses will cause higher fuel pressure.

On the left air cleaner inlet pipe is the air temp sensor. If the connections are poor or the sensor is skewed you'll get a *slightly* over-rich mixture.

On the left side of the fuel rail is the fuel temp switch. When the fuel is hot the switch closes, cuts off vacuum to the regulator, and allows full fuel pressure to prevent fuel vaporization. If the switch is faulty (stuck closed) you'll have excessive pressure at all times. It would be a simple test to see if it is stuck closed (it is either open or closed---no intermediate modes)

There are other possibilities but this should be good enough to start off with. Hope it helps,

Cheers

Doug Dwyer
Longview Washington USA
1987 XJ6 Ser III
1988 XJS V12 Coupe

Start at the begining1 You have to do a pressure test and find out where the problem is otherwise you'll waste time, money and tranquility! Jaguar affectionado and etc.