Poor running XJS at idle.
 

I am new here and hopefully somebody of great wisdom can help me here.

I have a 85 HE that I bought a few months ago.

It drives OK apart from the way it idles.

I have been through various things and found the idle air valve was stuck solid, I replaced it with a new one and managed to get the idle down to 750rpm. I then found it was popping on the the left hand bank of cylinders and the Fuel air ratio was lean at about 20 to 1 where as the right hand bank was running rich at about 12 to 1. ( I have a wide band exhaust gas tester ) I have tried adjusting the mixture and could make the Right hand bank better but the left hand bank was always very lean.

Tested the fuel pressure and it was less than 20 psi so I am surprised it was even running. Replaced the regulator and now I have both sides running rich all the time ( 12 to 13 to 1 ) The ECU is set fully lean and the car seems to be doing about mid teens on a run.

Where should I go next?

My first thought is the temp sender for the Fuel Injection but before I spend any more money I would be grateful of any suggestions.

Thankyou in advance.

Steve P

Have you tried cleaning the carbon buildup inside the motor ? maybe with some seafoam or MMO.

I'm no pro but I've been reading up on both these past days and just added Marvel Mystery Oil to the oil on my 04 XJ

The coolant temp sensor is a possible culprit, yes. It can be tested...I can find the specs, if you want. Don't forget the check the terminals inside the connector as well. Loose fit or corrosion will give a "cold" reading and the mixture will be rich.

The same applies to the air temp sensor in the left side air cleaner.

There are two enrichment switches, wired in series, that richen the mxiture about 10%. Look at the right side of the throttle turntable for the first one....a little snap action switch. At the rear of the right intake manifold is a blue/white electro-vacuum switch. That's the other one.

The throttle position sensor, under the throttle turntable, might be faulty. Not uncommon. Backprobe the red and yellow wires...you should have about .32-.35 volts with the throttle closed and about 4.8-5.0 volts with the throttle wide open, and smooth readings as the throttle is opened.

There's a barometric sensor inside the ECU. I'm not sure how to test it but make sure the vacuum hose is in good shape. It runs all the way from the back of the big vacuum balance tube at the rear of the engine.

You can check for proper voltage swing of the oxygen sensors but remember that you'll need to do this with the gearshift in "D", as the system goes into open loop in "P". As I recall there's a jumper wire in the trunk to bypass the system for testing.

That's all I can think of for now.

Post back if you need more details and I'll try to help. I'm going from memory here, though.

Good luck
DD

Hi Doug

The specs for the temp sensor would be good if you have them. Good thinking about the plug connections, had not thought of that one.

I dont have a Lambda sensor in mine so mine runs open loop all the time, this is normal UK spec until cats were fitted .

All I need to do is get it to under 4.5% CO for the MOT and it will be OK, I would like to see 1 to 2% CO but from what I can gather this is a bit of a pipe dream on a mid 80 XJS.

Steve P

The first number is Temp (Deg C) followed by Resistance (kilo ohms)

0/5.9
10/5.9
20/2.5
30/1.7
40/1.18
50/0.84
60/0.60
70/0.435
80/0.325
90/0.250
100/0.190


One more thing.....

How about a couple of drippy injectors ?

Cheers
DD

Yep could be but it is unlikely to be almost equal on both sides.

Might run some injector cleaner through it though for good measure.

Thanks

Steve

I checked the temperature sensor and though not much was out of spec, I have replaced it with a new one but I still have this problem. This has brought the emissions down a bit but still to high.

I have checked the fuel pressure and it is running at about 35psi, had a look on the internet at the weekend and this seems to be a bit high according to some web sites but correct on others. What is the correct fuel pressure for a mid 80's HE V12? Some say 30psi and others say 35psi.

As a buy the way when I now start the car with its new tempertaure sensor it starts as if there is to much petrol going in but drives better once warmed up. I have checked the connection on the sensor and there is no probolem there.

Steve P