Hello all,

I've been driving my '91 XJ-S as my main car for a few months now, and I'm having to contend with pinging at operating temp and a very strange revving at low RPM.

Pinging:
As noted in a previous thread, my car is staying within operating temps; so, it's not like the engine getting crazy hot is causing early detonation. The pinging usually starts after fifteen to twenty minutes, and it can get kind of annoying in stop-start traffic. It's only noticeable at idle. I live in Long Island NY, and everything has ethanol in it around here. I always go with the highest octane generally available, 92-93 by US measurements. However, I'm considering taking a fifteen minute drive next fillup to a station that sells high octane fuels and putting some high 90's or 100 octane in along with standard premium. I'm wondering if I'm crazy for thinking that standard pump gas is too weak or if other XJ-S/XJ12 owners have had similar problems. This engine does not have a knock sensor, but I could try retarding the timing to alleviate the problem. Looking for opinions and suggestions.

Revving:
At times a very light application of the throttle will cause the engine to shoot up from ~1000rpm to 1500, then down to 700, back up to 1500, and so on. It's easily demonstrated when I open the bonnet and slightly move the TPS. This is getting to be fairly annoying when I'm driving along and the car suddenly revs then bogs down when I try to minutely adjust my speed. It doesn't happen a lot, but enough to be an issue. Strangely, it can also happen when, after a drive, I shift from drive into park. The revs increase to that sour spot where the flutter begins. It seems like when trying maintain ~1000rpm, the engine sometimes responds in this strange way. Any ideas on what could be the cause?

 

Being a 91, it has the Marelli Engine Management System. This takes care of timong etc.

Fuel octane, mmm, maybe. Worth a shot of real fuel to find out.

In need of a decent long hard run, maybe.

The revs:
1) TPS is out of range, or just plain worn out.
2) Throttle cross rods are in need of a GOOD CAREFUL adjust. REMEMBER, its a Double Six, and that is the key to its simplicity. Those 2 engines need to be balanced propery.
3) The 2 throttle bodies have a good dose of V12 Black Goo growing on the inside. Petrol soaked rag and get into it.

Some mentions of all this stuff in the Stickies at the top. If not, let me know I will attach some here.

 

The USA 92 octane is fine; shouldn't be a problem. And ethanol won't cause pinging.

You might have a case of "carbon knock". Hot carbon particles causing pre-ignition. There are lots of products for de-carbonizing the combustion chambers. I haven't used any in decades so I have no specific recommendations. Others will chime in.

If carbon cleaner does the trick....it might take more than one treatment....you can prevent future carbon problems by utilizing the ITU: Italian Tune Up. Find a safe road and give the engine 2 or 3 full throttle blasts right up to 5000-6000 RPM in first gear. You'll see the crud from the exhaust in your rearview mirror. I do this once or month or so, or whenever I feel the engine isn't running quite right.

Do NOT use the ITU if the engine is still pinging.

Cheers
DD

 

Which engine does your car have please, 6 or 12?

 

It's a 5.3 V12. I'll try decarbonizer and I'll pull the plugs to see if they're fouled. Before it was driven so regularly, the car ran for probably ten minutes at a time once every few months. So, there's a decent chance the plugs are fouled. I'll also give the Italian tune up a try. Despite these issues, the car isn't lacking for power; I've gotten it up with ease to 130mph on a totally, definitely, not at all public, private track in a totally legal manner. The only reasons I didn't press on was I didn't know if there were any upcoming bends in the highw-I mean track and the unknown age of the tires.

Speaking of which, I've got some Cooper Cobras on right now, but I'm in need of some new ones. Wet weather grip ain't up to par anymore. Not bad tires, but just old. Any suggestions on good but not break the bank tires? I'm already allocating most of my tire budget this year on some Michelin XVSs for my Rolls.

 

Ethanol is your friend!!! It has 105 octane and does a great job of cleaning the engines carbon.
Try an ITALIAN TUNE UP.

That’s where you accelerate as fast as you can FOOT TO THE FLOOR! Right up to freeway speed limits
Do it several times. Once the car is fully warmed up. Take an off ramp and get back on the freeway several times with your foot flat to the floor.
There is an app that will tell you who has E85
That’s right, 85% ethanol. But don’t fill up!! Only put 5 gallons in and then top off with the highest octane fuel you can buy.
Be careful though. E85 will noticeably increase the power.
First don’t worry about hurting the engine that way. If you’ve ever worked on real race car engines. The Jaguar V12 is built stronger than anything I’ve ever worked. It’s unbelievably Strong!
The crankshaft and connecting rods are made from Forged EN 30 steel. Then hardened after machine work is finished Just like NASCAR ENGINES. Except the bearings are bigger, massively bigger. The valve train is so light and simple that I’ve never had a single problem with my race car.
( Yes I race Jaguar V12’s. I’m currently building a Group 44 tribute car to go vintage racing).

A serious issue is with the intake valves. Jaguar batch fires injectors and lets the valves and camshaft sort out which cylinders get fuel and when. What that means is cold fuel is sprayed on the back side of intake valves and some stays especially when not fully warmed up.
That ugly build up really hurts power development. (And fuel mileage). It doesn’t come off instantly. It takes a long time to to slowly wash off.
Carbon remover is typically some form of alcohol. Typically methanol. ( it’s cheaper than Ethanol) METHANOL IS REALLY HARD ON THE FUEL SYSTEM. MAKE SURE IT DOESN’T STAY IN THE TANK.
Ethanol is not hard at all. It’s what’s in WINE, BEER, SCOTCH etc. stuff you can drink.
Methanol is poison drink it you die!

 

Well, I tried the ITU, with a mixture of ~4.5 to 1 of premium and E85. While very fun, it hasn't alleviated the issue. The pinging problem did seem significantly better right after the E85 fillup and before the ITU though. However, after the ITU, which consisted of six runs, with the engine now fully warmed, the pining was back to usual levels.
I noticed this afternoon before the ITU and before the E85 fill up while running errands that there was a puff of smoke from the exhaust on hot startup. Likewise, I noticed it again when I pulled into my driveway, only this time the smoke puffed when the engine pinged. It stopped puffing soon after, but maybe they're connected. As for the pinging, it seems to be coming from the B bank, judging by the exhaust on the B side. The putting of the ping is only coming from the B side exhaust, and I take it the car has true dual exhaust. It almost smells richer right after a ping. Perhaps an injector sticking open?

On a related note, I didn't believe automobilecatalog when it said 1st is good for ~60, but boy did I find out they were right. Locking the car into gear, planting my foot, and pushing to 6.5k rpm, I wasn't expecting that kind of acceleration. Almost makes me wish for a manual. The engine has a surprisingly flat powerband and pulls strong at all RPM. Really gives me new appreciation for the car and engine. Fantastic sound too.

 

Jaguar 🐆 injectors are batch fired. So it wouldn’t be one injector it would be the whole set. ( I’m not sure if that’s 3 or 4 in injectors per batch).
White smoke on the exhaust indicates coolant. Is there any loss of coolant?

 

No loss of coolant. It's not white, more grey. But also not blue like oil burning. I've seen both before on other cars, and I'm confident it's neither.

 

Whilst the injectors are batch fired, igt can still be one injector of the batch of three that is faulty.
Have you removed the loom plugs from the B bank injectors and clmeaned the contacts? If not IO would do this. ,If that does not help, remove the injectors and have them cleaned and tested. It is highly likely that this is an injector problem, from what you have just posted.

If, after all that you still have a problem, then it lill be the loom. Which is very worthwhile renewing anyway.

I am glad you have discovered what this car is capable of! No need to baby it!

 

I replaced these injectors a few years ago, but the car hardly moved between then an a few months ago. Perhaps it was enough time for them to get gummed up. I luckily have a brand new injector wiring harness. So, I'll put it on and see if things improve. Then I'll pull the injectors.

 

Smoke more grey than white could be that injector problem others have talked about. Unlikely, because it’s rare for injectors to fail in that short of time. I would try the new Injector loom first.
Jaguar injectors really are a painful removal and replacement process. That’s why I’ve switched to Chevy Injectors and 2 Chevy Atlas fuel rails. It’s not a bolt in.Fabricating is required. And you need a GM fuel pump. Not worth it for the street but racing is a whole different story.
You mentioned the fun of flooring the throttle and running it up to 6500. Thought about a manual.
Maybe you don’t need to spend $5500 plus the cost of installing, yet? The GM Turbo 500 can easily and cheaply be modified to manual select.

While it only has 3 gears, it is a far more solid shift and actually easier on the transmission. That smooth shift is caused by the clutches slipping for a bit until the modulator forces them to lock up.
To have a transmission shop convert it to manual shift is only a few hundred dollars. They don’t need to pull the whole transmission. All they do is drop the valve body ( modify or replace it with a modified valve body.) and change the modulator.
It’s actually something you can.if you have a set of taps. Harbor freight has decent ones that are very affordable. Then other than a pan gasket and some ATF it will cost you less than $10 at your local hardware store for the Taps.
If interested go on U-Tube and find How to convert a Turbo 400 to manual shift.
It’s not a 1 way conversion. If you find yourself not liking to move the lever for every shift it can be reversed.

 

I figured it out!! You have a H.E. correct? Your vacuum retard isn’t working. Replace that or check the vacuum hose for leaks or connection?
In order to prevent pinging the distributor retards ignition on the HE. ( on the pre HE the distributor advances the timing on acceleration.)

 

I'll check the vacuum line. The pinging is worse at idle. It's smoother as RPM increases. It pings every few seconds, and in between it's pretty smooth.

 

Being Msrelli, there is NO vac capsule.

 

Having thought about the situation, I have a couple of ideas.

Concerning the fluttering: I think the over-run cutoff may be being activated due to a bad throttle potentiometer. The ECU may be receiving what it considers a "throttle closed" signal and an RPM it considers too high, though it is only around 1500RPM. Thus, the ECU cuts off the injectors, RPM falls, and the over-run condition is no longer present. Then the injectors come back on, the RPM shoots up, and, with the potentiometer still sending a "throttle closed" signal, the cutoff engages again. etc

As for the pinging: I suspect the lamba sensors aren't functioning properly, causing excessive richness. I suspect this, as the catalytic converter on my car has been "hollowed out", not by a ne'er-do-well but intentionally by a previous owner. Thus, the hollow cat may not be getting hot enough for the lamba sensors to function properly, causing the system to become overly rich to compensate. I may try bypassing the lamba sensors and see if that makes a difference.

 

After consulting that big XJ-S guide, I decided to try adjusting the throttle butterflies and linkages. Someone has definitely monkeyed with things on the left linkage. On the left side, the linkage is missing its return spring, there's play between the butterfly shaft and the splined shaft connected to the linkage, and the throttle rod is slightly bent. The right side looks untouched. Here are the results of the adjustment:

The good news,

There is no pinging or rev fluttering. I had to also adjust the black switch activated by the lefthand linkage. I guess it's an idle enrichment switch. Adjusting it to stay on for longer has eliminated the fluttering. I found the sweet spot by opening the TPS wheel and adjusting the stop on the linkage until there were no more deadzones.

The bad news,

I fear this has caused an issue with cooling. The exhaust is much hotter and the engine bay is heating up extremely quickly. A few minutes of idling and it got hot hot hot. Of course, it was idling in park, and, not having adjusted the idle speed, it does so at 1500 RPM. However, it never got this hot, even after long hard drives. It sorta reminds me of when my RR had FI issues and was running insanely rich, causing the catalytic converter to get so hot it melted wiring inside the car.

I will check the cooling system again tomorrow. Perhaps something has gone wrong while the car sat for a few months.

 

Idling at 1500 rpm is a disaster for any engine, let alone a V12. You have disguised not solved your problem.

 

Perhaps I didn't make it clear before that the rev fluttering and pinging would occur at idle in park at similar rpms before. The idle in park has gone up a few hundred RPM from its previous of 1250, but it goes down to 750 when in drive. I sat in park and in drive to wait for the pinging, and it never happened. I also tried to get it to flutter in drive and park, and it wouldn't. However, when idling in park at the previous park idle of 1250 RPM for an hour, it would never get hot, just up to normal operating temperatures. And the exhaust is much hotter than it used to be at this RPM, again like extra reactions occurring in the catalytic converter due to overfueling. I suspect someone has set the idle adjustment screw too high, and I think I know why. This car is in need of a new bearing where the driveshaft enters the diff, and I suspect the shadetree mechanic who royally screwed with the left linkage raised the idle to compensate for the extra drag at idle in gear. I will check the cooling system and lower the idle. Then I will let it idle for a while and see how hot it gets.

 

Quick update:

We've still got issues. Both problems are back, but I think I found the issue. I tried reaching towards the distributor with the car running to feel the temp, and I got the shock of my life, literally. I then found the insulation on leads going to the coil stripped. Let's see if some DIY insulation repair works.