my thoughts exactly.

if it works like any other potentiometer ive evr hacked up, then .38v should be the very bottom of the track with the high side of the wiper contacting bare metal. in theory, it should move any farther than that.

 

fuel pressure is 38 psi, passthrough between the left hand fuel rail and left hand regulator during key on, engine off.

running the fuel pressure is 30 psi no change until after it dies and the fuel pump primes for a restart.

twenty bucks and a perfectly good fuel hose wasted.

 

Wasted? How? Are you gonna throw the pressure gauge away and never use it again?

I'm sorry that nothing significant was revealed but it had to be eliminated as a possibility.

Cheers
DD

 

well its been eliminated. im more upset about that rubber hose than the fuel pressure gauge. tools will always have later uses.

compression test next i guess. i suspect to find that the drivers side bank isnt drawing enough air.

the right hand side is much louder.

 

did a quick compression test cold. Its far too dark out to do a proper one, but i was curious to see if the left hand bank was getting even remotely enough air from the cam.

so i did cylinder 1a and 1b. engine cold. both were spot on at 160psi. i know that the compression will drop when its warm. like i said, i just wanted to make sure the left hand valve train was allowing air in since the left hand pipe is nowhere near as loud as the right.

 

Mmmmmm, 160 sounds a tad low for a 12.5:1 V12. \\OH I forgot, the US got a detuned version, about 11:1 I think.

Even so mine is around 240 DRY, and 245 WET.

I assume this was done with the fuel relay OUT, and the throttle jammed WIDE OPEN. If not, another dud.

If the LH exhaust is quieter than the RH then a restriction is a "maybe", although the AAV on the LH side can give exhaust oddities, until operating temp is reached and that AAV closes, and since the time frame I hear of the thing running is NOT getting anywhere near AAV closing temps, it should be wide open.

Unplug the CTS, and see if there is a difference. Mine WILL NOT run with that unplugged, and if it is unplugged with the engine running it STOPS, it is a PRIME ECU signal, not sure what the USA market got here. Then plug a 100K ohm resistor into the plug, which will simulate "N" temp and prove maybe something is out of whack at the cold side of that sensor.

 

HAHAHAHA, I just had an offer to move to Las Vegas, seriously.

 

mine wont run with the CTS unplugged.

WOT testing of course. although i did it twice. once at WOT and once closed and saw no difference.

 

Considering how rich its been running it probably washed the cylinders out wouldn't you think? Have you checked the oil level lately?

 

I've trawled through this as I have had loads of similar problems that are now fixed. My best friend throughout was a simple automotive type multimeter with a pulse width setting. With everything I do to the engine I monitor the effect on injector pulse width. Have you checked that as it may suddenly change dramatically just before it dies? As you say, a tool will always come in useful later.
Also, just to try to put to bed all the stuff about injectors firing in groups of three, they don't. Each bank's two groups of three are connected directly together in the ECU, so injectors just fire A bank or B bank, both at the same time as it happens although they are driven by different pairs of power transistors.

 

my uncle was reading the injector pulses with this tool he had. it was like an old TV with a readout. i cant remember what he called it. weve briefly looked at the injector pulse with it, and all we really found was that both banks were pulsing good. we havent played with it much since it started shutting off so quickly. its hard to troubleshoot when it wont stay running.

thank you. i didnt want to be the one to say it for fear of getting flamed, but i discovered this when rebuilding my injector harness.

 

I remain in the 'work methodically through each system from front to back and verify it' camp, and I still have a suspicion that you should bite the bullet and check the ECU loom all the way through the car... BUT I do not want to be thought silly, but have you tried disconnecting one bank's injectors' loom plugs, and then tried starting it? Maybe it would at least show if one side or the other is worse?

Greg

 

i have tried that, but not in an attempt to see which bank runs worse.

 

ive checked the CTS and it reads good. it matches the values of the chart exactly.

i started up the Jag, let it run for 3 or 4 minutes and ran to get some water to top off the rad pipe. as soon is i poured cold water into the pipe, it flipped a switch and started surging. it surged 3 or 4 times and shut off. now it wont start. im gonna buy a new CTS for the hell of it and triple check all my CTS wiring.


also, i unplugged the left hand side hose from the vacuum regulator (this is the one that my Vac advance is plugged into) and it ran one heaping heck of a lot better. less backfiring, much more throttle response. still rich and some backfiring above 3500rpm, but much better. the other 3 hoses had no effect, except for a slight increase in idle RPM.

 

OK, that sounds like the "base timing" is far too far advanced, and then when the vac advance pulls it some more (can be 15deg depending on capsule installed) it is nearly on the next cylinder.

I would be sorting this out without teh vac advance plugge din at teh moment, and then work up from there.

Also sounds like there is air in the cooling system, which would be causing a little grief to the CTS getting a stable reading.

 

To share my experience with air in the cooling system, I've had numerous cars that do run worse before properly bled (oddly, some VERY old and carbureted) but when I swapped out the rad on my '85 it took me nearly a week to get it bled properly. The entire time it ran perfectly normal, and my root issue was a big air bubble stuck behind the drivers' stat right where the CTS is. In fact I removed the CTS and topped up through the hole with a turkey baster to bleed out that coolant rail properly.

Not disagreeing with Grant at all (in fact he was the one who pointed out my air-bubble issue a while back) but my car seemed to run fine with a dry CTS against all logic. I just knew I had air in the lines.

Secondary point - when you do bleed, remove the CTS, look for coolant, then with the engine running keep the CTS cracked until coolant squirts out around it then tighten it back down. After my experience this should go into the XJ-S bleeding FAQ, especially since it's quick and effective at removing a large portion of air.

Great news on the advance front - we now have a new clue - let's get the coolant bled and the base timing set properly and work from there. Did you put a vac gauge on that advance line? It should only be 11"hg, no more no less at idle.

 

sorry to say, but your on the wrong track

i put a vacuum load on the advance module with a vacuum pump and it had almost 0 effect on the way the engine ran, but if i plugged off that regulator port, the engine ran like crap again.


my engine really seems to love the timing.

 

it also runs different today than it did yesterday. thats another problem i cant figure out.

 

Grant, what would the symptoms be if the CTS and the ATS were reversed?

 

thought of that too.