That looks like a carbon build-up on the plug.

How is your fuel usage? If it's running rich, it should show up as reduced efficiency.

 

I'm not an expert by any means, but if I pulled one of my plugs and it looked like this one, my past experience would tell me this engine is running very rich and my corrective actions would be to correct the problems that can cause this. I don't believe it has anything to do with bad fuel or fuel delivery or such, but with what can cause a car engine to run so rich. Fix that and I bet you would be good to go. Wrong plugs would be a good start. Forget the "better performance stuff" and use the plugs recommended for the car. Side note: I bet the tail pipe tips look much the same way.

 

At this point after loud detonation Id pull all of the plugs and take a look. They really shouldn't be that dark if all is running well. And at least with that plug from what I can tell there is no signs of detonation. Pull all of the plugs and remember which came from where and post some photos. Can you log fuel pressure through RPM and boost reference? That can rule out a variety of issues

 

Cam,

The XJR runs rich so some buildup is normal. Id suspect a coil is on its way out but thats just a guess. If you have spares swap them over and see what happens.

Re the pressure ill take mine for a blast today and let you know but from memory its a steady 55psi and never goes under or over

On another note had the adsl connected this morning at the new house so I'm back online

Cheers
34by151

 

I'd hope OBD will tell you how it's running. Is it closed loop and what are the fuel trims.

 

I've been trying to think of things that could cause your issue, but still not throw a code.

Given that the car runs fine, and it only happens when you give it the beans, the only things I can think of are a functioning but sticky MAF, a vacuum leak that only manifests itself under WOT, or a weak vacuum hose that collapses under WOT.

 

Cleaning the MAF element cant hurt for sure. You definitely can see what voltage you are hitting

 

The climbing would be correct ... to a point.

You are measuring absolute pressure. But, the pressure relative to "atmospheric" rises due to the need to match boost.

This is normal in boosted vehicles.

The 70 psi would just about match 1 bar boost.

But, the drop off at 5000 rpm is not healthy.

A possible cause is not being able to keep up with volume demand at the fuel injector
duty cycle at 5000+ rpm.

If you can, monitoring fuel pump duty cycle from 4000 rpm up would be useful.

If you hit 100 percent before 5000 rpm, that's a problem.

I speculate that two things are at play here. Current/voltage and PWM
duty cycle. If you hit 100 percent, the way to get a more efficient pump is
to increase current, which can be helped by reducing voltage drop to the
pump side as opposed to the control side. This is done first by cleaning
and checking both supply and ground circuits. Next is to use a larger
wire gauge. In tuner circles, the use of 8 gauge wiring is not uncommon.

This is preferred to any voltage boost devices sold in the aftermarket.

What modifications have been done to your engine again?

Sorry, no opinion on the plugs because the pictures are not visible
to me.

++

++

 

In absolute terms yes, but the SDD reading is only what the pressure sensor knows and it is a differential measurement to a manifold reference.

The system is also supposed to do closed loop control to the pressure sensor and vary the pump speed to maintain 55psid, so if the pressure sensor says that it is much above 55 then either the pump is running too fast or the sensor is wrong.

 

Fuel rail pressure is absolute. The ECM also references MAP and in turn modulates the PWM circuit in
hopes of maintaining the required pressure.

In the AJ27, this is simpler because it is a bypass return system. The fuel pressure regulator has a
diaphragm that modulates the fuel pressure in reference to a pressure port in the manifold after
the blower.

On the AJ26/AJ27, the expected fuel pressure is ~55 psi relative to sensed atmospheric pressure.
When the blower is spooled to 15 psi, it would be 55+15 psi, or 70psi. Just about the values being
seen by Cam up to 4000 rpm.

I expect that although the fuel system is different on the 4.2 returnless systems, that the required
curve is no different to achieve the desired fueling strategy. The difference lies in how the pressure
is regulated. This would be via PWM to the fuel pumps with the inputs derived from inputs to
the ECM as opposed to a direct atmospheric pressure port acting on a mechanical fpr.

Regardless of any inadequacies in my explanation, the fact that there is a falloff in fuel pressure
towards 5000 rpm is significant in that it is not the behaviour that would be expected in almost
all fueling strategies used in boosted engines.

The short way of saying it is that the fuel pressure must be 55 psi net of boost.

 

The sooty plugs isn't too much of a suprise to me, it hasn't had a good long highway run in a while and these things seem to run rich, so pootling round town I'd expect em to be a bit sooty. The picture didn't really reproduce the colours, the ground electrode was also a brown colour, but darker brown than the ceramic in the middle.

This engine is basically stock, only got the upper pulley and the intake tube, and the Bosch intercooler pump (which is working fine).

Long term fuel trims measured at idle at 0%

I have no codes for misfires, no codes for anything really apart from the P1235 and it had been there for ages, long before it started playing up.

I'm 90% sure the fuel pumps just aren't able to keep up with demand, simply worn out. 10% that there is some other blockage in the fuel system. So i'm going to change the fuel filter.

Pressure sensor failing? Maybe but even if it's not reading accurately, it showed the pressure dropping as the hesitation & detonation occured, that's a giveaway to me.

With no codes i'm shooting in the dark abit. But when I think of an old school carb engine doing this, it's because it's not getting enough fuel...

If the pumps are unable to deliver enough fuel flow then i'd expect the ECU would request to spin them faster. Could be the reason for "fuel pump control out of range". And then when they just can't deliver enough, the pressure drops off, and it goes lean...

I don't know...

 

Just for clarification, it's important to know which duty cycle and what each means. The ECU to REM duty cycles are only valid from 5% to 50% and 75% is OFF, while the REM duty cycles can be interpreted as percent off so 25% might mean 75% ON.

Here's a good explanation (it's for a Ford Returnless System, but it should be valid for Jaguar):

Under Pressure: Maintaining Ford?s Electronic Returnless Fuel System

 

This statement is not correct.

It is true that I am speaking from experience with an XKR but on the AJ33 the fuel pressure transducer has the same part number between the XKR and XJR.

Part AJ87977 bolts to the fuel rail and has a manifold pressure reference port.

The reported pressure should not change substantially as a function load or RPM.

 

What does the reference manifold port line look like? Is there a vacuum hose that connects between the sensor and the manifold? If so I'd take a look at that.

 

If it's any consolation I have the PWM code on mine right now and the car runs fine but I don't have the SC engine.

 

Mine does not quite look stock, but you get the idea.


Sensor has a port facing inboard and a rubber elbow.




Connects to the supercharger outlet on the right side.

 

Got the fuel filter out, it was an aftermarket Mahle item (surprised me!), but after draining it & blowing through didn't seem like much of a pressure drop through it, maybe a little less than the brand new genuine Jag filter.

Drained ~37L out of the tank by cycling the ignition on/off about a million times. Fuel looks clean, now a light green colour from the mix of yellow 98 & blueish Sunoco. Couldn't get any more out & the pumps sounded like they were sucking a bit of air. Car was up on ramps at the front so the angle might have something to do with it. Gauge was down below E when I got it off the ramps.

Cleared the codes and the ECU "flight recorder" creeped it over to the closest Caltex (didn't think i'd make it to the Shell) and with the computer hooked up to watch the fuel pressure, got on the freeway for a 2nd gear WOT throttle run. It hesitated from just under 5000 and made a loud rattle at 5500. Fuel pressure peaked at around 70psi and fell off to just over 60psi with the rattling.

So it wasn't the fuel. It wasn't a blocked fuel filter. 99% sure the pumps are finished.

No codes thrown up during the drive. And the flight recorder only had data about how long it took to start; 807ms by the way...

I won't rule out the fuel pressure sensor, but it seems unlikely to me. If the fuel pressure was reading "too high" why don't i get a code for that.

Come to think of it, why aren't I getting codes for the detonation? Or the loss of fuel pressure???

Shopping around for the best price on pumps now...

 

Cam,

Glad you're narrowing things down but sorry it sounds like it's going to be somewhat expensive.

Do I recall that you have a scope, and if so, would it be worth scoping the fuel pump drive signals to see if any anomalies are visible? I'm just wondering about the odds of both fuel pumps failing at the same time.

Also, for the record, as far as I've been able to determine, Jaguar doesn't make any of its own filters. Mahle is an original equipment supplier and in addition to filters, the parts they have produced for Jaguar include pistons and other engine parts, and the ill-fated Nikasil cylinder coating. It's very likely that the Mahle filter was installed by a Jaguar dealer. Other Jaguar filter OEMs I've been able to confirm include Bosch, Delphi, Mann+Hummel, Valeo and Visteon (and in the old days the carb manufacturers like SU, Solex/Zenith-Stromberg and Weber).

Cheers,

Don

 

I know this is frustrating, but before you spend the money on pumps, you need to take a step back.


Those questions are likely the answer. If it were your pumps, you'd have a code. I also don't think you would have a failure of BOTH pumps that would only manifest itself at WOT. One possibly, but not two. It also doesn't make sense with a PWM pump as it would with an old school one (i.e. the pumps work fine being modulated X times per second, so they should work being modulated Y times per second).

I would think, that the only way you are not getting a code, is that the ECU and ECMs in the system are all seeing signals that are within range or expected.

The pumps may not be failing, but doing exactly what the ECU is telling them to because the ECU is making decisions off of valid appearing yet false data. Keep in mind that the ECUs main purpose is to run the engine for emissions efficiency, not performance. So if it thought there wasn't enough air, it would dial back fuel regardless of throttle demand to make the most clean burn possible. So if MAF says there is X air, but there really is >X air you'd get detonation.

A slightly wrong signal from one or more of the following sensors; ECT, MAF, IAT, fuel rail pressure, fuel rail temperature might be enough to see a problem only under WOT.

Since you have a supercharged engine, something we haven't thought of is the Intercooler. The whole point of the Intercooler is to prevent detonation, if you are getting insufficient cooling of the intake air, that might explain your symptoms.

 

The first impulse would be to say "monitor short term fuel trim".

But there won't be any answers there because under high demand, the ECM goes
into open loop and depends solely on fuel maps.

What might be possible is to monitor the wideband sensor directly.

Also monitor voltage sag at the power connector at the pump. If there is
insufficient current, it will sag. That would point directly at a need to
upgrade wire gauge to something bigger ... or that the connections
need attention.

In addition to the fuel filter, I would go ahead and clean all power
connections as distinct from signal connections. Remember the
ground side is just as important.