V12 Blues please help!!!
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V12 Blues please help!!! - 5/22/2008 3:42:09 PM
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beeturbo
Posts: 4
Joined: 5/22/2008
Status: offline
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I have a 94 xj12 it hard to start when cold, once its startedit
will eventually idle smooth but when accellerating off idle it
spits and pops back through the throttle body. if u slowly press
the gas it gradually increase rpms from idle to about 1800 acts lik
eits fuel starved but once it reaches 2100 or so it revs strong if
u rev between 2000 and 5000 rpms it will continue to rev but if it
falls below it pops and misfires.. I've installed 12 New Ngk
Plugs .025gap new fuel filter, New cap and rotor (borg warner)got
numbe 1A culinder up and alighed rotor with notch on distributor
housing. found that B coils wasnt firing so I replaced both coils
with new round 12volt universal coils both coils now
firing ..cheked vacuum lines even resealed A bank Intake gasketnew
hoses on intake balance tube..i started the engine with the balance
tube off when I accelerate it pops back through the pasenger side
i can fill the backfire when I hold my hand over the rear of the
intake where the balance tube fits on..i figure water or bad
injector .. when do a power balance test by pulling an injector
wire off at a time on the A bank(passenger side ) pulling each
injector wire drops the RPMS so I know that the 6 are working but
when ipull the injector wires on the B Bank (driver side) the
engine rpms doesnt change but wheni hold a scre driver to the
injectors all 12 of the injectors are pulsing..i removed the fuel
tank and drained and found that their was some misture in the fuel
so I draind the tank completely and filled it with about 5 galons
of premium fuel ..noticed that the tank has 2 fuel pumps in
it ...one thing did get my attention though ..i tried cleaning the
throttle body with carb cleaner on the A bank the side that
misfires and pops back through the intake; while spraying carb
cleaner into the intake it it revs fine without misfire and poping
thru the intake from idle well and up intothe rpms but when I stop
spraying the carb cleaner and rev from idle it spits and pops. but
spray carb cleaner into the intake and it takes the gas every
time .. im wondering if I have a fuel pump out? bad injector .. I
ruled out burnt valve since it accels wit the carb cleaner I just
dont know fellas this is my first V12 Jag has anyone run into this
or can shed some lite on good possibilities all healp grealy
appreciated bacause I havent a clue.. 2 things I havendone yet I
havent cheked fuel pressure but pulling the vacuum off the pressure
regulator doesnt make a difference .. and I havent did a
compression test only being that I doubt its a valve
problem..sometimes if u floor it in park it spits and misses then
all of a sudden its like every thigns clears out and it revs like a
scaled ape like its starving for fuel .. another question is I
dont know the timeing procedure for timing this v12 as relates to a
timing gun I cat seem to locate a timing mark or scale on the
frontpo of the engine mayb im over looking it u can also respond
to me by email (turbobeepee@aol.com
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RE: V12 Blues please help!!! - 5/22/2008 6:56:32 PM
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Stuckonbrits
Posts: 13
Joined: 5/22/2008
Status: offline
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Wow! It seems like you have done a lot of work with that engine. It does sound fuel starved. The carb cleaner result sort of leads me to think clogged fuel filter or fuel pump. Could be as simple as that.
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RE: V12 Blues please help!!! - 5/22/2008 9:53:52 PM
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JagtechOhio
Posts: 473
Joined: 3/12/2008
Status: offline
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That was all a little hard to follow, let's get basic for a minute.
I don't think I ever saw a '94 V12 XJ40, I know they exist but are not plentiful in the U.S. Is this a U.S. spec car we are talking about?
If it is, and since you mentioned a failed B bank (left bank, driver's side in U.S.) coil, that suggests you have a Mirelli ignition system. There is no timing adjustment or reference marks for this system: timing is digitally controlled by a dedicated ignition ECU.
If you have a Mirelli ignition system and the B bank coil failed, the B bank catalytic converter is , in all probability, bad. The ceramic honeycomb material inside has melted, and is restricting the exhaust to the extent that the left bank may run OK at idle, but that's about it.
The stock Mirelli coils are HOT, I have seen cheap aftermarket clones but no other kind of round replacement coil. What you have installed is probably good enough to make the engine run, at least for now until you solve the bigger problem(s). You should do a little investigating to find out whether they have a voltage output anywhere near the stock ones. I don't know, I only use factory coils.
If you pull the vacuum hoses off the fuel pressure regulators and fuel runs out of them, that is a bad thing: it means the diaphragm is ruptured. That's about the only thing you will learn, there will be no marked change in engine performance if you pull the hoses off, so long as you block them to seal the vacuum leak you are creating which increases the idle speed a little.
There isn't any substitute for fuel pressure gauge readings, either you know exactly what you have by watching the gauge or you waste alot of time guessing.
If the car is all assembled and idles reasonably at the moment, start it up cold and go back and feel the temperature of the exhaust. The right side will come up to temperature faster if the left bank converter is blocked. I wouldn't call that an absolute test, but it may be different enough to help confirm the suspicion. Looking inside the cat will be most revealing.
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RE: V12 Blues please help!!! - 5/23/2008 8:46:58 PM
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beeturbo
Posts: 4
Joined: 5/22/2008
Status: offline
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I pulled the dist cap off today and found that the rotor button has melted the pointer completely off that fires the b side ..maybe the after market round coils that I installed r to hott ..
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RE: V12 Blues please help!!! - 5/24/2008 5:26:12 PM
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beeturbo
Posts: 4
Joined: 5/22/2008
Status: offline
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thanks.. i put the old marelli rotor back inand now it fires.. did a compression chek and all culinders are fine .. heres what ive found .. i removed the fuel return hose from the presure regulator and started the car no fuel came out of the pressure regulator return port at idle .onlyabout 3 drops was all i got after idling about 3 mins.. i placed my thumb over the port and held it could feel no pressure at all when i accelerate the engine it popps apparently it is indeed fuel starved .. when i floor the pedal once it finnaly makes it up to about 2200-2500 rpm fuel then gushes out of the pressure regulator return port...after reseach ive found that the 2nd fuel pump inthe tank works on demand of the engine and turns on at 2500-2800 rpms and delivers xtra fuel back down to 2000rpms .and below 2000 rpms it shuts off again .well it appears the 2ndary fuel pump is working fine but the primary doesnt seem, to have any fuel pressure ..now i know that i do need a fuel pressure gauge to accuratley see how much pressure is onthe system but even if it was low as 20psi at idle i wouldnt be able to hold my thumb over the return port at idle i wouldnt think ? is it possible fornthe primary pump to be bad .. when i take the supply line off of the fuel rail and crank the egine wit the line in a clear container the fuel begins to fill the container so their is volume but not strong pressure it just pours slowly .. all advice appreciated
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