Hi all

Ive yet again found a situation that stumps me, my car sounds to be running excessively lean. Any ideas as to what can cause this? She ran fine after I changed her cylinder head, but now she's running terribly. All the temp sensors check out well. Is it possible that ignition timing can do this? The symptoms are backfiring under load, if I stab the throttle she jets off but then suddenly looses power and starts to backfire... Any ideas?

 

Some quickie thoughts, based on what you say "it takes off good and then starts to get hissy".

Blocked fuel filter.
Fuel tank venting system AWOL, sooooo, flip that fuelcap, try again, if that fixes it, the fix is simple.
Timing????, I doubt it.
Ignition coil breaking down at revs, it does happen. 3000-3500 seems to be the number.

 

Thanks Grant, fuel filter has been cleaned, I'll try the fuel cap thingy. As for coils I doubt it, she pulls hard through those revs if I stab her down through them. I should mention I'm doing this with a water leak, yip, today is the 4th time the radiator shop is going to try get her expansion tank right, so everytime I venture put she comes back with less water, my tests have been cut short many times.

 

OK, that could be a strting area.

That cooling system does not have to drop very far at all for the ECU temp sensor to be out of fluid contact, and once that happens, there will be a very strange signal to the ECU, and leaning off symptoms could be one of them That sensor is designed to sense fluid temps, not air/steam temps.

My thoughts on those fuel caps is based that even the Sedan has gravity feed from the tank/s TO the pump, so if that tank cannot breath, the gravity supply will cease, the pump will starve for fuel, and the engine will splutter and cough, and even spit back due to this leaning off.

 

That's what I'm leaning towards, once she's properly bled I'll take her around the block. Mistake on the leak, found a loose hose, feeling very intelligent at the moment haha.

 

AHA, a true V12 owner, loose hose, welcome to the club.

 

Ha! Love it! Right so my lean running is CTS related, says the motor is at 70 degrees after 5 minutes of idling... I'll be probing around for the cause. She also doesn't bleed like she used to, to get that stream of water out the bleed tap takes ages, I'm leaning towards a faulty thermostat in B bank.

 

Agreed.

Make sure you get the correct length stats, or money and time will be wasted.

Lots of stats that are too short, including OE.

Not sure if I sent you this a long time ago.

V12 thermostat fiasco explained.doc

 

Haven't got that one, but that's about to change. Many thanks Grant. I've heard about the jiggle pins etc, mine has the correct ones, I'll take B bank's one out and see what jumps at me.

 

Nathan:


The great part is that the cylinder head issue is fixed. A huge leap forward.


I saw a TV piece yesterday. "Alaskan Gold Rush". Guys wrestling huge equipment to mine gold. In this part awakening a long sleeping big diesel on a barge. Air in the oil cooler line. Bled by forcing in oil under pressure til the relief stopped bubbling!!


Jaguar application: Force feed coolant in a near end and bleed at a far end???


KUDOS on the progress.


MERRY CHRISTMAS ANDS A HAPPY NEW YEAR!!!


Carl

 

Sounds more like outright "fuel starvation" rather than "running lean".

As for the CTS, it's worth checking and/or replacing....either way is cheap and easy....but I'm not optimistic that it'll end up being the problem.

My thoughts....

Cold running enrichment, signaled by the CTS, decreases as coolant temp increases. After about 150ºF the effect tapers off a lot and by about 175ºF it's all done. After that any coolant temp increases result in increasingly minute signal changes....to the extent where the conventional warm running fueling map within the ECU totally masks any CTS influence. In other words, the CTS can richen the mixture but it cannot lean the mixture beyond the existing ECU parameters.

On the other end, if the CTS sends a "too cold" signal, the result will be a needlessly rich mixture....which doesn't fit your symptoms.

Personally I'd lean (sorry) towards a fuel *supply* issue as mentioned in other posts, including a loss of fuel pressure due to either lack of supply or a faulty regulator.

From an electrical standpoint (less likely, according to my gut) I'd look for a TPS voltage drop-out to begin with.

I'd had very similar symptoms on my XJS V12 and (long story short) the culprit was a duff inlet regulator.

Cheers
DD