In reply to a message from JohnXJR sent Wed 15 Aug 2012:
A visual inspection will probably tell you little or nothing
unless the filaments are physically broken, checking the o/p
voltage being fed to the ECU, will tell all as it should
vary with the rev’s. You need to check either via a scanner
on the OBD11 Comms Bus or along the circuit from the MAF to
the ECM.
No easy answer here, but many chances to spend and waste a
lot of cash.–
The original message included these comments:
Neil, I meant so that I could see if the filaments were burnt
out/damaged with the unit disconected, not with the engine running.
fuses/relays. I guess that a mass flow stuck at oo and the error
code means no measurment so unless the filaments have totaly failed
I guess it points to wiring
In reply to a message from JohnXJR sent Wed 15 Aug 2012:
John,
I suggest that you get an aerosol can of electrical contact
cleaner and use it to clean the plugs and pins. WD40 leaves a
film that can interfere with a clean connection. The
electrical contact cleaner will remove any film and restore
contact.–
Jeff Schultz -1992 XJS 5.3L V12 -1995 X300 4.0L
Rutland VT, United States
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In reply to a message from JohnXJR sent Wed 15 Aug 2012:
Hello,
Re: pins on ECU
Had same symptoms…my pins just had a very small amount
of bluish ‘‘gunk’’. I cleaned them and thought all was
ok…it was not. It all looked perfectly well to the
naked eye, I realized there was still a problem because
the misfire came back, and when I took the ECU back out
and I put pressure on all the pins and they all had
resistance, the one that had the gunk all over it had no
resistance and just snapped of. New ECU with lots of ECU
connector grease (from Motorcraft, not dielectric grease)
and all is well…in that department, anyway.
In reply to a message from Mark Janzic sent Wed 15 Aug 2012:
Thanks,
I will get some contact cleaner, I was thinking that the WD40 would
protect against further corrosion and that the conectors would
easily scrape through the oil film, maybe not and the voltages are
very low.
I also used WD40 on the under hood right inner wing multiplugs and
the relays in the boot, perhapse that was a mistake, they looked in
good condittion anyway.
When you say you measured the resistance do you mean from the
inside of the plug (by opening up the ECU) to the outer pins? Or do
you mean that they felt physically secure in the housing? Mine did
not feel loose when I gave them a gentle scrape with a small
screwdriver so thought they would be ok. The small amount of
corrosion was most visible on the wire half of the connector once
the white plastic strip had been removed from the female socket.
Perhaps I should try the proper contact cleaner and if no better
open up the ECU and look at the inside of the conectors in case
there is corrosion there. If the ECU end is ok perhaps I should try
to replace the female wire conector.–
JohnXJR
Lancashire, United Kingdom
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In reply to a message from JohnXJR sent Thu 16 Aug 2012:
IMHO as an engineer with about 50 years hard experience,
very few ‘‘Snake Oil cures’’ work! The original design would
be deemed the ‘‘Best available’’ if properly conceived,
Cleanliness and Godliness (FAITH) is what you need after
that. Clean every contact with IPS or similar and burnish
where there is tarnish or corrosion and replace where
necessary, a bit of a b*gger but the best way.
Also have a logical plan and record what you have and have
not done, reverting back if there is no change! Best way to
check what is happening on route is to monitor the start and
the end, the best diagnosis is to check in the middle and
then move forward or backwards in halves to see where it
starts to go wrong.–
The original message included these comments:
I will get some contact cleaner, I was thinking that the WD40 would
protect against further corrosion and that the conectors would
easily scrape through the oil film, maybe not and the voltages are
very low.
In reply to a message from JohnXJR sent Tue 14 Aug 2012:
I have had a similar problem with a miss-fire, on my 95 XJR
auto. Traced it to the ECU. Removed ECU and saw damp
staining and corrosion on the case and connectors. Using a
good quality switch cleaner form an electronic supplier such
as Radiospares I cleaned all connector pins and contacts. I
then opened the ECU and cleaned the backsides of all
plugs/connectors. I then placed the opened ECU in a warm
oven to ensure that it was thoroughly dry. I then sealed the
box again using a silicon grease on all case edge seals, not
the connectors and replaced the ECU back into the car. No
more problems. This was over two years ago. WD40 is not the
best product for this type of problem.
Best of luck,
Kit Pannell–
Kit300
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In reply to a message from JohnXJR sent Thu 16 Aug 2012:
Hello, I meant physical resistance on the pins. Even a
small amount of ingres can do a lot of damage.–
The original message included these comments:
When you say you measured the resistance do you mean from the
inside of the plug (by opening up the ECU) to the outer pins? Or do
you mean that they felt physically secure in the housing? Mine did
not feel loose when I gave them a gentle scrape with a small
screwdriver so thought they would be ok. The small amount of
corrosion was most visible on the wire half of the connector once
In reply to a message from Mark Janzic sent Sat 18 Aug 2012:
Dear All,
Since I last wrote I have cleaned the pins on the ecu connector
with contact cleaner on looked inside the ECU to see if there was
any corrosion. It looked fine. I now runs consistantly but still
excessively rich, judging from the short term fuel trims slight
difficulty starting slightly rough running and exhaust that smells
of petrol. My scan tool now shows the MAF in not providing a
number, as stated in a previous post. I now think my problems could
be a combination of the slight corrosion in the ECU plugs and a
failing MAF. After a period of inactivity due to other comittments,
today I cut through some insulation and measured the voltage across
the three wires connected to the MAF.
The black wire measured + 14V above both the pink and green which
showed 0V between them. I have not found a figure quoted, but from
general information I would expect one wire to be Earth 0V, one to
be a positive feed 12-14V and one to be an intermediate voltage
that varies with air flow.
Is this correct, and do you think that these measurments would
support buying a new MAF sensor?
In reply to a message from JohnXJR sent Sat 1 Sep 2012:
re running rich
Hey John I don’t know about the readings from the maf
I had the same problem you are describing and after
basically replacing every sensor plugs maf you name it
I was actually going to scrap the car the car had been to 4
different mechanics all saying we will fix it and a couple
grand later each time no joy only to find the reason it was
running rich was a 2 dollar valve under the back seat it was
sucking fuel from the charcoal canister IE(emissions
rubbish) directly into the manifold behind all the
electronics so what one mechanic said was add a piggy back
computer to lean it was so far from the right reason
It was Andy Stodart that gave me the idea what to look for
but in the end I had to take it to a independent specialist
that had the factory jaguar diagnostic software for this car
wish I went to him first I would have a fair bit of money
left in my bank accounts if I did
so have a look at the valve under the back seat since I have
fixed mine both of the independents that could not diagnose
the problem have since had cars with the same problem and
have contacted me to ask what it was–
XJR BOY
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In reply to a message from Roger sent Sun 2 Sep 2012:
Thanks XJR Boy, sorry to hear about your expensive experience. I am
lucky in that I go to work on the train so not under pressure. I
still suspect an electrical or MAF issue but worth a look for the
valve. Is it integral to the charcoal box under the left rear
floorpan? I guess fuel vapours from the tank are collected in it
then get emptied when the engine is running. It shouldn’t be
possible suck liquid fuel through it though, should it?–
JohnXJR
Lancashire, United Kingdom
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In reply to a message from JohnXJR sent Mon 3 Sep 2012:
re valve under back seat
If you had told me it couldn’t pull fuel I would have
believed it but it did pull fuel and the car ran excessively
rich but on another it is going like a dream at the moment
(I knew it would only cost money LOL)–
XJR BOY
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In reply to a message from JohnXJR sent Sat 1 Sep 2012:
Don’t know that I can offer any assistance with actually
fixing anything, but maybe I can waive you off of from
chasing down an empty rabbit trail.
Getting no MAF reading on your scan tool is perfectly normal
I believe. Don’t know why, but I don’t believe these cars
report real time MAF readings through the OBDII. I had
recently purchased one of those blue tooth OBD plugs that
sends data to my smart phone so I was playing with it on my
'96 XJR just for fun just last week. I was nervous when I
noticed no MAF reading and thought I had maybe discovered a
flaw in the blue tooth gizmo. So, I tried it on my other
two X300’s and neither gave a MAF reading either. So, I
tried my old trusty scanner and no MAF reading on any of the
cars with my regular scanner either, yet all three run just
fine.
The short story is no MAF reading on a scanner seems to be
perfectly normal.–
'95 XJ6 4.0, '96 VDP 4.0 & XJS, & '96 XJR w/ 45k!
Dallas, Texas, United States
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In reply to a message from jeremywatson sent Sat 8 Sep 2012:
When all three of my Jags developed a severe misfire and
almost not running and then sometimes they would seem
normal, after replacing fuel filters and pumps, thinking it
was a fuel problem, or a MAF problem, it’s turned out to be
a crank position censor. That one fooled my experienced
favorite mechanic, who thought it was a fuel problem this
last time. Sooner or later it finally goes out and the car
doesn’t start. Until then, the symptoms look like a lot of
other things and it seems to happen far enough apart for me
not to remember the CPS symptoms…–
Michael Freeland
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In reply to a message from mfreeland sent Mon 10 Sep 2012:
Thanks Guys,
To update, my ‘Elmscan 5’ gives a readout of MAF in g/sec,
which had become stuck at zero with a faut code relating to
MAF voltage. I think my problems were caused by the ECU
connnectors and the MAF was also on its way out. After
cleaning the connections the missfiring was much improved
but still rich. I have replaced the MAF now and the mixture
seems right now, judging fron the fuel trims and switching
of the oxygen sensors which had been stuck on rich
correction, and the fact that the exhaust does not smell
heavily of petrol! Sadly still has a missfire, currently
thinking that may have permanantly fouled the plugs - I hope
not as they are new iridium ones, they are all still black
although there is a shiny spot on the electrodes where the
spark has been so maybe ok. The coils had some condensation
on them along with the rest of the engine (been very wet in
the north west UK recently so lots of dew/condensation in
the morning even on a fine day), so I sprayed them with some
WD40 and left them to dry in the sun. The miss fire
emphasised the rattling from the supercharger, so I spent
the rest of my car time replacing the coupling, a job that
had been on the list for a while, so not run the engine
again yet.
If the missfire persists, I will try the old plugs back in
and also test the compression. I have already checked the
cam timing.
The other suspect is the CPS, but the rev counter works and
I get steady readings for rpm via the OBD11.–
JohnXJR
Lancashire, United Kingdom
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In reply to a message from JohnXJR sent Mon 8 Oct 2012:
To update. Swapping back to the old plugs made things worse
so the new plugs went back in. As the mixture seemed right I
deecided to take it for a drive after some use the misfire
reduced and is now only ocasionaly noticable at idle.
So I think the main problem causing the non-drivable
condition was light corosion the ECU connections and a
secondary issue of a failing MAF sensor.
Hopefully this is now resolved.
Thanks to all for advice–
JohnXJR
Lancashire, United Kingdom
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