Ok..so icheck everything (fuel psi,regulator psi,spark) and even replaced my cts. The car will now start but idles rough and shuts off. I m thinking of checking my o2 sensor now and see if it is working properly. How will i know if i have a good 02 sensor or maybe a bad cat ? I cannot even adjust my AAV because the car will not stay running that long. Please advice..Also, i hear a noise in my alternator and everytime i start the car and rev it..the dome light inside the car flickers..is bad alternator affects rough idle too...

 

UMMMMM, I'm game.

What year, engine, etc we trying to fix PLEASE.

Put those details in your sig, or a details somewhere, so we can use more of our brain sorting the car, not trying to work out what it is.

 

1988 xjs coupe...thanks

 

Ok,thank you.

Fresh bottle of necta opened, so here goes.

On top of the LH inlet manifold is a "black box" (yes, it is painted black), and this is the Ignition control box.

Coming out the rear of it is a loom plug, and inside that loom is a "shielded wire", and that wire provides an ignition pulse to pin #18 of the fuel ECU in the boot. NO pulse signal, NO fuel injection pulse, NO running of said engine, other than the initial fuel in the rail from the pre start priming, which may give you a few seconds of running at best.

This wire is fickle, and the loom it is contained in runs to the rear of the LH side of the engine bay, across the rear, travelling between the heater tap, and the 2 oil pressure switches, where it picks up the TPS wires, then onward to the RH inner guard (near the RH bonnet lock), and disappears through a grommet and then on to the rear of the car via the interior of the car.

Most ALL V12 cars I have been involved with, have had this coax (shielded) wire damaged, by old age and HEAT, and I ALWAYS replace it all the way to that grommet. I use simple TV antenna coax, solder the joints, seal with heat shrink, and re-wrap.

This is fiddly, and time consuming, but a V12 will simply not run without this wires integrity being 100%.

Obviously other items may be at play here, but that is always a starting point for the symptoms you mention.

 

More thoughts.

The TPS (throttle position sensor) may be flaky as hell, and that would give those symptoms.

The fuel ECU needs a steady 0.32-0.36volts at idle to drop into the idle fuel map. If that "split voltage" is too high, over fueling and cutting out will happen. Too low and crappy running is guaranteed, including cutting out.

There are heaps of write ups on this in the archives.

 

Not to say that anybody is wrong but there are more basic stuff you can check:

jaghelp.com: That pesky rough idle

 

[QUOTE=Grant Francis;944844]Ok,thank you.

Fresh bottle of necta opened, so here goes.

On top of the LH inlet manifold is a "black box" (yes, it is painted black), and this is the Ignition control box.

"Coming out the rear of it is a loom plug, and inside that loom is a "shielded wire", and that wire provides an ignition pulse to pin #18 of the fuel ECU in the boot. NO pulse signal, NO fuel injection pulse, NO running of said engine, other than the initial fuel in the rail from the pre start priming, which may give you a few seconds of running at best."

....... I traced the wire..is it a green and red wire ? Then it's connected to a black and red wire going to the distributor..is this the wire you're talking about ?... where's the boot ?..im sorry this is my first jaguar and i only owned it for 5 months .

 

k

How can i check this TPS and how can i check the fuel ecu ? Thanks

 

[QUOTE=jomia092306;945221]OK, your up there, so a different language is required.

Jaguar talk is NO different to any other car, trust me.

BOOT = TRUNK, or back end storage compartment.

BONNET = HOOD, or bit what covers the hole where the engine sits in a "normal" car.

LH = Left side, as when sitting in the car facing FORWARD, and NOT related to what side the steering wheel is positioned.

RH = Opposite of LH.

That shielded wire is in a black heavy wire, with a WHITE inner core, and a VERY THIN single strand inside that WHITE core. The WHITE core has a copper woven shield between it and the BLACK outer casing. There are other wires in that same master loom, and the colours I simply do not remember. You are looking for that shielded wire. It is maybe 5mm thick, and really does stand out when you strip the covering off that loom.

The wires going TO the distributor are worth checking, as they have a bad habit of breaking INSIDE that rubber plug at the entry to the distributor. This is NOT easy to find, and some clever probing with a pin (or some other sharp pointy object), will aid the search here. Definately NOT a 20 second look and fix.

 

The TPS is tested by probing 2 of the 3 wires, and I forget the colours, I do that, forget that is. Both my XJ-S's are completely rewired under the bonnet, and I used my own colours coz I can. I THINK it is the Red and Green of the TPS loom??.

You will need a volt meter. Preferably one of the older analogue style with a needle. A Digital will do, but you will need to pay close attention to the readout. The needle style gives a noticeable swing to the needle as erratic OHMS is detected, and the digital is slower at detecting this error.

Once probed, set the meter to OHMS, and SLOWLY open the throttle, and note a VERY SMOOTH rise in OHMS. If a SMOOTH rise is detected the TPS is deemed OK. If an erratic rise and fall of OHMS is seen, the TPS is history.

This test requires the ignition to be OFF. It is an OHMS test, NOT a voltage test. That will come later.

I have a word doco on setting the TPS, and the throttle rods if you get to the point you need to reset that item. Ask and I will attach it here. I think its small enough, if not then alternative methods will be found.

 

Hello i attached this picture, maybe some can help me on what suppose to be the reading on this(labled by letters) when the car is idling. Maybe i can start with this...thank you for all the help...

H - is the fuel psi regulator...my psi is between 27 to 35 psi when idling...(rough idling )

 

Those wires are attached to the coil which produces the spark. A coil is a transformer that takes 12volt battery current and truns it into a high voltage low amperage blue spark for the spark plugs. The ones nearest the capstan are the positive 12volt feed to the coil and the ones the other side the negative return. The hgh voltage blue spark for the spark plugs comes out of the thick lead at the top. All the terminals on the coil look corroded to me. One at a time remove first the positve
screw terminals on the coil and then the negative one and carefully clean up to shiny metal the connectors on the end of each wire, and the coil terminal. Emery paper will do the job. If there are any loose-ish terminals on the end of the wires, cut them off and replace with new ones crimped to the copper wire.

Another reason for poor idle (AFTER you have checked the TPS as grant has mentioned earlier) could be that the whole tangle of vac pipes is somehow misbehaving. This can be greatly simplified and loads of complex junk removed from the engine as a result. I would recommend that after these other things have been done if no improvement.

I do not believ this is a fuel pressure issue. If you can drive and accelerate at high revs OK, then fuel pressure at idle is unlikely to be the cause of a poor idle.

Greg

 

ok..thanks. i will clean those terminals tomorrow and go from there. How can i check for a vacuum leak ? How will i know i have a vacuum leak ? Than k you for your help. I will keep you posted.

 

Concerning the terminals, carefully check the connectors on the wires are actually attached to the copper, and not just held on by the white plastic/rubber outers. I had an intermittent start problem about 6 months ago, and it turned out to be the copper having fractured inside the white outer on these wires. Renew the connectors if any doubts at all.

As far as the vac bits go, may I suggest we leave the actual modifications until you have done all the things suggested so far? For example the TPS and shielded wire stuff is very important.

The vac simplification is quite easy to do but one thing at a time is usually best, to avoid introducing more variables into the mix! But if you really want to simplify the vac stuff right now, I'll happily explain.

Greg

 

ok...i check all the wirings and getting ready to chk the tps. btw, just for info....what should be the "bench" reading of the coil ? im getting 3.2-3.6 ohms...is that ok

 

On the HE, I have always aimed for 1.2 ohms per coil, with NO wires attached other than the test meter.

The original HE coils were in fact 2 @ 1.2ohms +/- a tad, as a single unit, and hoked together as the car had them gave 0.6 +/- a bit, but NO more than 0.9ohms.

High reading like you have indicates "toasted" coil/s.

You have probably found the rough idle??.

 

hopefully...i will get a new coil. trying to get the petronix coil...hopefully replacing the old one will improve the idle....i will keep you posted ...thanks

 

But remember, as Grant said: "The original HE coils were in fact 2 @ 1.2ohms +/- a tad, as a single unit, and hoked together as the car had them gave 0.6 +/- a bit, but NO more than 0.9ohms."

Most coils are lots more Ohms resistance than 0.6. Any more than 0.9 MAX on your car will toast the ignition!

Greg