Sorry everyone, but I'm back to S3 XJ6 (1985) Ignition timing.
Can anyone tell me what the (engine running/no AC/in Neutral) Ignition timing should be at a hot idle? I still don't believe I've got it right.
If I start from cold, she fires right up, but once warmed through, she doesn't want to fire and just as she catches, the engine rocks violently (the exhaust manifold bangs against something). After that, I have to jeep a close eye on the idle at stops and when in gear at a stop. Also, unless I turn the AC off, she will die. No smoke/no smell.

Sorry to drag this up again!
Ian

 

Assuming the Canadian versions are the same as USA for 1985, it should be 17ºBTDC at idle, vac advance disconnected. Non-USA spec was something more along the lines of 10ºBTDC.

A few degrees one way or the other wouldn't cause the (rather severe) symptoms you are describing.

Cheers
DD

 

Possibly among other things, the motor mounts are busted.

 

My first thoughts are lean idle mixture when warm... at 17* timing, my idle is 800 in park, 700 in D brake on, and 650 in D with A/C and brake on
1. just to keep you going, increase Idle RPM to 850
2. adjust idle mix on top-aft inboard side of Air Flow Meter box one full turn CW... this will reduce air at idle, hence increase fuel mixture.
3. Take spare new Coolant Temp Sensor (CTS, usually less than $ 20) and with engine fully warm and hard to start, disconnect two leads to the installed CTS on water rail, and plug the leads onto the room temp spare CTS ( rapped in a rag and laying on water rail)..... If restart is normal and Idle is healthy, then CTS could be the problem.

I always carry spare CTS in Glove box .. if not CTS, then full blown T/S checklist for EFI engine will be required.
Rgds
David

 

Is the duct between the throttle body and the Air Flow Meter in good shape? No leaks?

Cheers
DD

 

Thanks gentlemen. Doug, duct is good. David, looks like I'll have a busy day in the garage. It's raining anyway. Will report back. Ian

 

Yesterday I got around to following up on Doug and David's advice regarding my ignition timing issues.

This issue prompted me to install a Pertronix distributor and coil setup 2 years ago. It improved somewhat but is now regressing.

Please bear in mind that once on the roll and at all speeds, she performs perfectly smoothly - no pinging no stumbles - solid as a rock for hour long outings. This only affects me at a stop, in gear with AC on.

I did find a very slightly loose band clamp on the flexible bellows as it attaches to the airflow meter and tightened it. That made no noticeable difference.
I then checked the idle timing when hot and it was 10-11 degrees BTDC at 800 RPM (a little rough but no more so than normal). Ported vacuum reading was 6 inHg (not zero as I would have expected). I don't know how much, if any additional advance would occur at such a low reading, cause I forgot to recheck it after reconnecting the vac line.

Slackened the distributor clamp and reset to 17 degrees BTDC as per Doug's advice and it ran a tad sweeter at this setting - not quite as lumpy. Idle increased to 850 RPM. I reset it to 825.
Foot on the brake (no noticeable change in speed) and put her in gear and it drops to 700-725 RPM Still stable and will continue to idle smoothly.
Selected AC on and idle drops to 650 -700, slightly rougher. 15-20 seconds after selecting AC on, she wants to die and will do so unless I immediately switch the AC off or take her out of gear. This is repeatable.
It is almost as if the ignition is suddenly switched off (it wants to shut down, not stumble to a halt).

So, I figure there are a few things in play here and only at a stop. Intermittent Ignition failure, fuel interruption, transmission drag, AC engine drag and my big foot on the brake. If I take her out of gear or switch the AC off I can prevent the stall. But, my foot is still on the brake (and vacuum booster) and I cannot release that and still have her in gear. Sooo.....

Ignition timing now reset (and ignition system in general) I don't believe to be an issue.
Fuel delivery - if so, that should be apparent at other operating parameters so I'm tending to ignore this one.
Trans drag - possible but only intermittently at idle?
AC drag - sure, but why only with my foot on the brake and only after a certain time and resettable?
Foot on the brake - Could I be causing a vacuum drain from the booster (and hence the engine) that resets once I take my foot off the brake? I suppose that would hiccup the injector pressure but that should be somewhat gradual - no? Vacuum loss should not affect ignition setting at idle as its using ported vacuum.
Can I clamp off the booster vac line and check again.

David, you suggested richening the mixture. I cranked it one full turn CW with no change then one more then back to original and then CCW 2 turns and still no change. Also, that screw is much more loose than I would have imagined such a critical item to be.
Is there a way (without an exhaust analyzer) to reset it? Assuming it is functioning, if I lean it out it should begin to stumble. If I mark it there and richen (counting turns as I go) it should smooth out then become rough again - no? Somewhere as it rises to the sweet spot should be about right (mixture wise).
Is it possible that that air passage is blocked up? Can I clean it?

I will try the Brake booster isolation today and report back.

Once again thanks for your insight.
Ian

 

I sense the engine lacks power to operate the AC compressor at idle. Or the compressor is in some manner absprboinmg way too much power.

At idle what is the Hg read. Low, signifying a 'weak" engone///

To my way of thinkit, idle speed is not anumber. Just low enough so that the ecar does not dreepat a stop in gear., And fast enough so as to not stall...
Carl

Carl

 

Thanks for your input Carl. I agree that the compressor puts an additional drag on the engine, but why does it only consistently quit after 15-20 seconds with my foot on the brake? I'm going to isolate the booster and try once more. The car will happily idle for ever with the AC on and in gear and yes it does want to creep so I do have to depress the brake, but it seems to struggle to stay alive 15-20 seconds after I depress and hold the brake.

 

Assuming a so-called "Federal" spec engine with an oxygen sensor and cat convertors.

These fuel systems were configured very lean to begin with; there's barely enough mixture to sustain life when everything is up-to-snuff. Any fault that would increase the lean-ness can put things over the edge and the engine will die. I did battle with a couple such XJ6s many years ago. Behavior virtually identical to what you describe. After much effort I never did find out why; they weren't my cars and the owners didn't have unlimited time or resources. I increased the idle speed and they were happy that the engine merely stayed running.

As an experiment I'd disconnect the oxygen sensor and see if anything changes. This puts the system into open loop and it should revert to 'base fueling' which is usually a bit on the rich side. If the problem goes away then perhaps the oxygen sensor is faulty (leaning out the mixture excessively). Or, perhaps, the new-found richness is masking a different problem. The sensor can be tested with a volt meter. Or, as guess go, is fairly painless in terms of expense and labor.

The fact that the mixture adjustment makes no difference is significant. It suggests that air from another source has more influence, rendering the mixture adjustment impotent. This is where isolating your brake booster....a possible vacuum leak.... would come into play. As for cleaning the passageway for the mixture adjustment....I dunno. You might be a trailblazer here !

Have the injectors ever been tested or professionally cleaned? Lack of fuel flow due to minor clogging/degradation might be enough to put things over the edge.

I'll do more thinking

Cheers
DD

 

Quote: Have the injectors ever been tested or professionally cleaned? Lack of fuel flow due to minor clogging/degradation might be enough to put things over the edge. Unquote

When I sent my injectors out for test and clean, they ranged from 19 to 24 lbs. flow before cleaning.
Ian, did you eliminate the CTS sensor as possible source of lean idle mixture?
Rgds
David

 

David, I don't have a spare CTS sensor. Can I just bypass it somehow ?

 

Remove the connector and use a small paperclip to jump the terminals. Some paperclips have a plastic coating which would need to be scraped off.

A cold engine will not like the CTS being bypassed so it'll be easier to warm the engine up first.

Cheers
DD

 

This likely has no relevance but it should perhaps be noted that the Canadian spec. cars did not have an air pump (neither the 6 nor 12 cylinder cars).

 

Ocasionally I have found customer cars with similar symptoms. In some (not all) the cause was the micro switch on the throttle butterfly (so that when the accelerator pedal is released; it informs the ECU to lean out to avoid overfuelling on the overrun). Often heat and age causes the plastic casing of the switches to crack and they jam or misalign. A quick, simple test is to disconnect the two wires (do not join/jump them) and see if the engine is able to maintain idle under a/c load. They are a generic microswitch, easily bought from any electronics shop for under $5). If not this, then usually it was a vacuum leak, most commonly from a split on the underside of the concertina bellows where you mentioned tightening the clamp. Fuel residue seems to pool in the bottom over the years and the cracks always seem to form on the underside as a consequence (and annoyingly where they can't be seen without removal). On cars with this as the root cause, it was a similar story to yours - fine at higher revolutions and usually OK at idle (free) but stalling with a/c load on.
Best of luck getting it sorted!

 

Just surmising here, are the brake light electrics working OK? Ian states there's dramas when brake pedal is activated.

Maybe there's a short in the wiring that's adding load/ excess current drain that's affecting the ignition system?
That's what I liked about the (now out of favour) ammeters fitted to the dashboard, any electrical faults would easily show up with excessive discharge, usually full scale deflection!

Sorry if it is apparent I have NFI what I'm on about. Nothing new.

Pete

 

Finally, after 2 years of back and forth, I believe I can state that my idle issues when under load in gear, with ac on and brakes applied, may have been resolved.
I installed a new CTS, that read the same values at different temperatures and cleaned up the connection. I don't believe that the CTS was at fault.
Concentrated on the vac line between manifold and brake booster. There are 2 vac non return valves in that run. The one closest to the manifold was open both ways. After huffing and puffing it freed up and now holds lung pressure only in one direction. Plus, all the clamps on the hose connections were a bit loose.
After an easy cold start and an uneventful warmup. She idles at 800 smoothly, foot on brake, no drama, aced in gear rpms drop to 725. AC selected on, drops to 675. I can now stay in this situation indefinitely. Smooth a silk!
Took her for a quick blast down the back street and my God, it feels as if I changed the engine. No pinging, but a substantial increase in power! Really very noticeable.
I was so pleased that I forgot to shut her down to see if the difficult hot start was still there.
Gives me an excuse to drive her again tomorrow.
Just for reference, ignition timing set at 17 degrees BTDC, at 800 RPM with dist. Vac disconnected and plugged.

Will update after my blast tomorrow.
Thanks everyone! Ian

 

Great sleuthing !

Cheers
DD

 

Doug, As all I found were a few slightly loose hose clamps and a dickey vac valve (which I plan to replace with a generic one today), and the replacement of the coolant sensor, I don't understand what I actually fixed! The new CTS readings were identical to the old one (albeit I did not check the entire operating temp range) so perhaps it was a poor connection at the sensor connector? Plus, a non sealing booster Vac valve should only become problematic if there was an air bleed within the booster itself, which I could not check. In all fairness, I suppose if I had a mitey-vac, I could check if the booster does actually hold vac. Perhaps it's time for a new tool toy! Thanks to everyone for their assistance. Nice to know your not alone out here.