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Good morning, First of all I'm sorry for my bad English. when you first start the engine ,(cold start) my jaguar xj6 3.2 vibrates, shudders. runs bad a few moments then goes smooth.
warm start up are ok.
the exaust terminals are black. (like old diesel)
Sometimes ,the car stalls at intersections when you stop.(only with cold engine)
I see dark smoke when I accelerate.
fuel consumption is very high (6 km/liter) all the spark plugs are covered in soot
i think the car running very very rich.
For these reasons, I changed the temperature sensor (2 pins),
the spark plugs and ignition coils
I cleaned the throttle body very well and the idle motor
I replaced the MAF with another used one in good condition.
new standard air filter and fuel filter
i tried lots of additives for cleaning fuel injectors..
I'm desperate, I don't know what to do anymore.
could it be the o2 sensors?
(I just ordered them from England and they should arrive in the next few days)
I'm desperate, I don't know what to do anymore
please help me
Strange. When the car starts, it fuels the car from a program stored in memory. It uses only the Coolant Temp Sensor, TPS and MAF and checks to see if the oxygen sensor heaters are working, but doesn't use them until car is warmed up and everything has passed the tests to go closed loop.
It seems like your car is NOT working well when the car is in open loop, running off of the program, but runs better when the car is in closed loop and taking readings from sensors to fuel the engine?
Have you checked the ECU connection for corrosion on the pins? It is under the passenger footwell and is a common problem.
Sounds like you are just throwing parts at the car without doing any diagnostic tests to identify the problem.
For example, just changing the Temperature sensor doesn't mean it's not the problem. There could be a broken wire or corroded plug etc. You need to plug in a diagnostic scanner and read what the ECU is seeing as a temperature to prove it is working.
Sounds like you are just throwing parts at the car without doing any diagnostic tests to identify the problem.
For example, just changing the Temperature sensor doesn't mean it's not the problem. There could be a broken wire or corroded plug etc. You need to plug in a diagnostic scanner and read what the ECU is seeing as a temperature to prove it is working.
Unfortunately in Italy there are very few cars like mine. Local mechanics don't know how to diagnose. Even the local Jaguar dealer doesn't know where to put their hands
Sounds like you are just throwing parts at the car without doing any diagnostic tests to identify the problem.
For example, just changing the Temperature sensor doesn't mean it's not the problem. There could be a broken wire or corroded plug etc. You need to plug in a diagnostic scanner and read what the ECU is seeing as a temperature to prove it is working.
Ideally, if you could see what the ECU is seeing, through the use of an OBD2 reader, that would be ideal. If not possible, then you'd have to start taking readings with a multimeter. If it's as bad as you say, you will want to invest in diagnostic equipment yourself. A wireless ELM27 reader and an app on your phone wouldn't cost too much.
As a cold engine and the fuel ratio set ( my assuming )
Your closed loop tripping point is 88 C
The O2 sensors will not be used at this time but as Vee mentioned is tested
Engine CEL codes , they can be read and cancelled by a ELM - 327 device otherwise a auto parts store can read , write them down as memory can be fleeting
Vacuum leaks ?
The MAF will read 1.2 volts DC ( at proper idle ) on the middle wire , still connected so you can stab the connector as the wires come out , about 4 grams / second at proper idle ) on a ELM - 327 but can be errored by a factor of 10 or 100 ( device software issue ) whatever numbers make sense
The valve cover is not a valid ground point for your meter
The rear most coil wires swapped ?
# 6 Light Green / Purple , rearmost
# 5 Light Green / Orange
The rear O2 sensor connectors can also be swapped , swap back up top
So on the car side of the connector it has 4 wires , 3 being the same and the 4th return signal wire is different color
I had the same problem ( Still do!!!). I found out the hard way not to drive the car cold in that condition because you'll lose the O2s then the catalytics up front, which in turn will plug the rears. My obd reader showed a evap warning but no code. I'm thinking the Carbon canister and the purge vale and the lines connecting them is the real problem as I have replaced all the parts that you mention and then some. I'll have to get at least 2 new O2s, new cats front and rear, charcoal can, purge valve (if its not working), vacuum line and the Rochester valve as a kicker. If that doesn't work my XJR6 will become another LS swap...then I'll have the excuse to drop the AJ into something vintage and Damn the Torpedoes!!!
you would be thinking 88c as that is one option for thermostats.
all the thermostats i have are 87c or 88c
We are discussing at what point is the temperature hot enough for the ECU to begin using sesnors for fuelling adjustments, not at what point does the thermostat open.
There was a quick note in the 801s doc about a buffer or something on the thermostat about a 20 degree F difference
See page 50 last note 801s doc
The thermostat opens in increments to further complicate things
The rating on the thermostat the full open ?
Not related to the coolant temp sensor determained closed loop coolant temp but still has to regulate in concert with to keep it above closed loop temp but not overheat
So this increment notion points to 160 F...............170 F the thermostat opens further driving coolant toward 160 F
Wide open is throwing buckets of water on the fire keeping engine cool , your already past the point of closed loop and may never return except at stoplight ( ? )
So it's this just starting to crack open thermostat temp just above the closed loop temp that determains the closed loop temp value
Someone has taken a V - 12 thermostat and micrometerd the opening gap vs. water temp in a water pot as a PDF table back on an older broke computer
going to dialysis now
Last edited by Parker 7; Jan 10, 2025 at 12:50 AM.
V12 thermostat fiasco explained This is my findings, AND the solution to temperature gauge “floating syndrome”, that many people are frustrated by. Remove both your thermostats. Note the by-pass disc on the bottom, THIS IS THE MOST IMPORTANT PART OF THE THERMOSTAT. Look up inside the housing you just removed the thermostat from, and
Link does not work
Last edited by Parker 7; Jan 10, 2025 at 03:59 AM.
There is reference to 2 Jaguar V - 12 thermostat parts that has 82 C and 88 C , this is probably related to the 2 different engine ECU manufactures ( early M and later Denso ) and their specific engine regulation sensor values
In his text :
" Just to clear up another “story” that persists out in mechanic land, the opening temp of a thermostat is in fact its “crack temperature”, meaning that is the temp at which the thermostat actually STARTS to open, commonly known as the “crack temp”, and the thermostat is “fully open” 12degC above that. So an 82c stat will crack open at 82c, and be fully open at 94c, follow, good, it is simple. Now if your cooling system does not do as it should, the engine temp can get above 94c, which causes the stat to “fully open” and stay there, IT HAS NOW LOST CONTROL OF THE COOLING SYSTEM, and overheating is just up the road. "
Last edited by Parker 7; Jan 10, 2025 at 04:53 AM.
There was a quick note in the 801s doc about a buffer or something on the thermostat about a 20 degree F difference
See page 50 last note 801s doc
The thermostat opens in increments to further complicate things
The rating on the thermostat the full open ?
Not related to the coolant temp sensor determained closed loop coolant temp but still has to regulate in concert with to keep it above closed loop temp but not overheat
So this increment notion points to 160 F...............170 F the thermostat opens further driving coolant toward 160 F
Wide open is throwing buckets of water on the fire keeping engine cool , your already past the point of closed loop and may never return except at stoplight ( ? )
So it's this just starting to crack open thermostat temp just above the closed loop temp that determains the closed loop temp value
Someone has taken a V - 12 thermostat and micrometerd the opening gap vs. water temp in a water pot as a PDF table back on an older broke computer
going to dialysis now
yes the rating is full open.
a 87c thermo does begin opening at 87c.
the idea in a real world is to keep the coolant at that designated temprature.
so if for any reason the coolant drops below that temp it will fully close to heat up again
if you recall from my thermo testing before i had a 88c thermo that was actually opening way earlier preventing my car from warming. i tested this in a jar of water. i had one starting to open around 65c so the car would never infact warm up and was always in closed loop.
Last edited by Spud Maat; Jan 10, 2025 at 05:45 AM.
HELP ! bad cold start up , run very rich
