I am also not looking to see detonation related timing changes. I have SDD that I'll use to monitor my normal operation timing over various loads and RPM and throttle position and Im only doing that to see what I get at WOT because zray is seeing timing getting pulled and Im not sure that normal.

Ive never watched the ign timing on a boosted car so maybe its normal. As I said earlier, in my old muscle care, (340 sixpack stroked to 416cuin with high compression and big solid lifer cam), I set my distributor to give me full advance (34 deg total) at 2500 rpm and up. I dont pull timing at wot or high rpm. His scanner shows 16 deg at 4400 rpm down from30something at lower RPM so Im just checking to see if thats normal for our cars of if he is having timing pulled (maybe due to detonation??? IDK)

Do you know what our timing is supposed to do at WOT?

 

as pointed out in the Jaguar manual (post #12 attachment), the ECU will retard the timing under the conditions of:

a) during acceleration
+
b) “at critical engine speeds”

Im pretty sure that includes WOT conditions. They are coy about what exactly the “critical engine speeds” encompasses.

the manual makes no reference to that ECU action being only done with the supercharged models.

I do know that since the advent of computer controlled (factory) ignition systems it is 100% normal for the timing to be retarded during a high engine load situation on cars that were factory supercharged.

I don’t know if all normally aspirated cars have the same feature built in to their computer controlled ignition systems, but I’d be willing to bet that they too have the timing advance reduced when the throttle is opened wide.

That technique has been around since the advent of the internal combustion engine. My dads old pre WW-I Harley had a manual spark advance on the left side handlebars twist grip to aid in starting the beast and was also recommended to be used when the road was steep and uphill (high load), according to dad.

Retarding timing when the engine under a load is the same exact thing that vintage vacuum advance distributors do under the conditions of low vacuum, ie “wide open” throttle, and for the same reason.l; it prevents detonation..


Z

 

About 20 degrees, then pending on the IAT#2 temp the ignition will be further retarded.

 

understood. But retarded from what to what is what I was wondering. On older cars like my cuda and everything else that had a vacuum advance distributor, at part throttle cruise when the vacuum is high, you can get advanced into the 40° range when you combine the vacuum advance to the centrifugal advance. Then when you stomp on it, and the vacuum goes to zero the timing is effectively retarded to only the Mechanical centrifugal advance built into distributor bc of the distributor springs and weights in the (which in my case is set for 34° total). So that’s what I was asking. It’s not like I set my distributor to 34° total and then at wide-open throttle it gets reduced from there. it’s actually kind of the opposite in that the vacuum at Cruise adds to the mechanical advance which is fine because theres no real load on the motor

 

that’s a good question, and I’d like to know that also.

My year of manufacture (2002) is covered by the 2nd edition shop manual, and I’ve found no exact mention of the ignition timing at wide open throttle. The knock sensors can take out as much as 9.4 degrees of advance, but that doesn’t really address your question.

what I’d like to know, and can find out from my dash mounted Autool 60, would be what is the maximum advance, it should be occurring at a steady highway speed with minimal throttle opening.

if I can take my eyes off the road look enough to snap a photo, I should also be able to find out what my timing is at WOT at a moderate speed, say 70 mph. I do know from my last little experiment that the timing can go from an advanced mid 30’s to a
retarded mid teens in the blink of an eye with just a throttle position change from 11 to 39. That may or may not change to a greater spread with a throttle position in the 90’s. I’ll report back on that at some point.

Z

 

Yeah when I get my *** in gear I plan on doing some monitoring of those things as well I drive around but I haven’t got that far yet. It doesn’t look like I’m gonna be able to do it today either so I won’t have any results. But I did see that section where it said that the knock sensors will knock the timing back a maximum of 9.4° or something. There’s just so much vague information in a lot of those jaguar training manuals and it really doesn’t help when you’re trying to find out what it is supposed to do when you can’t find the information.

 

I did find this info though. But I’m not sure if this is ONLY for the older 4.0 L or also the newer 4.2 L like mine.Probably both since it says that the newer ECM further enhances blah blah blah. But here i found a document that says the system will increase the timing until it hears a knock and it can determine which cylinder the knock came from. then it will reduce the timing on only that cylinder Soooooo If that’s the case what does that timing number on your monitor represent? It also means that i probably need to be monitoring all eight cylinder timing at the same time.

Hang on I’ll post some screenshots from the document in just a minute

 

Those articles were posted at the beginning of this thread.

I’ve read nothing that indicates the timing is advanced “ad infinitum” until a knock sensor detects a knock.

Z

 

Well no, Im sure someone realized that there are certain ignition timing values that are obviously wrong and therefore not possible. One or two of those screenshots actually says if the ECU sees an unrealistic value from the knock sensor it reverts to a safe base mapping. I also saw that a graphical representation of the mapping posted below . and you can see the base map gives the max timing at moderate engine load and high rpm. It also maxes out at high load and mid range rpm and drops off as the rpm goes to redline.

So if youre lucky, your car saw some implausible knock sensor readings and you went to the super safe base map

 

So far.... I’m doubting that my engine timing has reverted to a base mapping as there as been no drop off in performance from what it has been for the last 50,000 miles. The way I keep the car exercised I believe a drop off in performance would be more than a little evident.

in any case, there’s going to be a lot of “what if’s” and “could be’s” where this little 4.0 s/c’d engine is concerned; whatever the consequences are from
my little knock sensor experiment turn out to be , I’m going to accept them head on and learn a lesson if need be.

In the meantime I’ll drive the car with one ear listening for engine knock, etc. and the other ear listening to Sammy Hagar’s “I can’t drive 55”.



Z

 

@Aarcuda
The ECU has evolved with each iteration, where the 4.2 engines already had a more advanced ignition under driving then the previous 4.0 AJ27 version. You may have an even more advanced ECU called PanPag, which was introduced in 2006 (if you have VVT on your SC then you have this one), the latter is easier to tune as the master files (has a specific name which I forgot) where known by many (that describes exactly what maps there are etc).
Although I have no idea what thresholds are the ECU would use to switch to a safe map on KS signals (except for knocks), I would guess it wouldn't be on muted signals. From reading it would filter out normal engine noise to easier detect (even the smallest) knocks so take it signals left not within the typical knock frequencies would fall under that (again just guessing). Even though this was all pretty advanced already 20 years ago, as you may have read in the link, modern engines are flirting with knock limits more dynamically now adjusting for octane even.