Hi All,

My 1989 XJS Convertible runs good, but is too rich to pass the california smog test. Does anybody know what may cause this or how to lean this out?

Thanks Much,
Andrew Janoski

 

Hi Andrew

A little more information is needed. There are a lot of causes for an engine to run too rich.

Is it a I6 or V12
If a V12 is it rich on both banks or just 1.
How long since it has been tuned, spark plugs etc replaced

Cheers
Warren

 

Warren,

The engine is an early 89 V12 with the Lucas distributor. I just gave it a quick tune up. I had to unfreeze the centrifugal advance (most common Lucas distributor problem) and replaced the vaccum advance (2nd most common problem), so while I was there I relaplaced the cap,rotor,spark plugs and wires. I also set the timing.

I still have an occasional stumble at idle when in gear. Most of the time the idle is perfectly smooth, but once in a while it stumbles like a minor miss on one cylinder.

As for being rich, I did check the voltages at the EFI Lambda Feedback Monitor Socket. These voltages with the Lamda Disable plug removed should be around 2.5 volts. My car runs around 4.10 volts which means the computer is over richining the mixture. Not sure why. If I try to set the Idle mixture using the adjustment on the ECU, Bank A stays at 4.10, while Bank B starts to swing between 2.20 and 3.95. Thinking I might need to replace the O2 sensors.

Any suggestions would be greatly appreciated.

Regards,
Andrew

 

Hi Andrew,

I am only going off what is listed in the ROM as I have a later car. Cold start has an additional injector in each inlet manifold between 3 and 4 intake runner and a relay to drive them. The ROM states that the coolant temp sensor (located on the LH water rail) has a bearing on Cold enrichment.

I would check in this order

The Temperature senors - if either sensor is high resistance or open the engine will run rich
Cold start injectors for leaks
O2 sensors

cheers
Warren

 

I get that too. According to Kirby Palm's book, an occasional stumble on a 5.3 V12 is normal. Did you get the smog issue sorted? I've had my mechanic test every sensor I have and now it's down to either the EFI ECU or the cats...

 

Can't really help on the mechanics but have you considered moving to another State?

 

As Warren says, could be a number of reasons.

Does the car get up to operating temp? If not your stat(s) may be stuck open. The coolant temp sensor can go bad and report the wrong temps which definitely cause the ECM to enrich the fuel mixture.

You could try the old Italian tuneup technique Run some fuel injector cleaner through the tank then take the car on the highway for a high speed/rpm drive. 80-90mph for half an hour or so then immediately go get your smog test. Works for many.

 

The Italian tuneup is great, LOL, but I would first try one bottle of Redline Sl-1 fuel cleaner in a half a tank of fuel and run it every day or so for 10 miles. Don't run the half tank in one day, its good to let the cleaner sit in the fuel system for a week or so to loosen and clean things up. When you get down to an 1/8 of a tank or less, you may even want to get a second bottle of Redline to then use in a full tank of fuel for a second application... After 100 miles you should feel a difference in idle and how smooth it runs. I did this after buying my XJS and it now runs great...

 

Of course. Friends, family, mortgage and career be damned, I'll give it all up for my XJ-S. That's the insight I was looking for! :-/

 

Nobody talks about TPS sensor check here for some reason.
I'd check if TPS sensor reading .33v (+/-.03 volts), at idle. If TPS is reading more then .36v at idle, engine is going to run rich.

 

I would say your o2 sensors have failed within operating range so there's no engine light . Your o2 sensors keep the engine running within a proper fuel mixture. I would replace them

 

I had done that. What it turned out to be in my case was disconnected ground eyelets on the wiring harness that the O2 sensors heating element grounds to (sloppy previous mechanic) so while the sensors were new and functioning, they were never getting up to operating temperature to work correctly. An EFI ECU that couldn't be adjusted wasn't helping matters.

The TPS, coolant temp, air temp and everything else down to the spark plugs .... They were all tested before my mechanic ended up pulling everything off the top of the engine and finding the fault.

 

What about the microswitch on the throttle pedistal? It's there to turn up the fuel when you stomp it, but if the switch is broken, it will run rich big time.