Hello again all! It's been a while since I posted here, as I was overseas without my XJS for a good 12 months. We have been reunited though, and it's time to get to know each other again. Apart from a pretty ineffective aircon, it's running as sweetly as it ever has, except....

I have a hesitation at part throttle. Yes, I will check that my throttles are opening simultaneously this weekend, but I don't think it is just that. At part throttle at low revs it just feels... laggy. If I keep the throttle there, and steadily build the revs it "catches up" around 2-2500rpm, and from then on feels like full power. It doesn't seem to happen at high revs with a similar part throttle (it is a converted-manual, so dropping gears resolves it), so where should I start? Vacuum lines look and sound ok, so should I have a look at the dizzy (i.e. does it sound like an advance issue), or does this sound like a throttle/throttle potentiometer issue? Or (fingers crossed) is this symptomatic of bad/restricted vacuum to the ECU?

Thanks!

Dave

 

Long time to be away from your BEST mate.

TPS out of range etc is high on my list. Make sure its at 0.32 - 036V at idle position.
When you do the throttle rods, dont forget the spacer between the stop and the capstan ear, very important.
VAC to the ECU, nah, usually overfuel to hell if that is clogged/restricted.

Dizzy mechanicals sticking, hell yes.
Vac advance capsule gone legs up. maybe.

After 12 months fuel filter would be a must to me. Just because, no other reason.

Other than that, it needs a good long hard run, not easy at the moment I know, but it will be all webbed up inside.

 

Sage advice, as always!

Fuel filter is ordered, just because. Plus it's an easy job!

I'll drag out the DMM on the weekend to check the TPS and will look at the throttle rods too.

I had the dizzy serviced and vac advance replaced 2-3 years ago, but I'll whip the cap off and give it a little oil.

Dave

 

Good boy.

I reckon Beer O'clock will be early.

Have fun.

 

Well the TPS seemed ok (a little high at 0.39V closed, but steady linear increase), the dizzy mech advance was fine, but the vac advance unit was shot. I reckon I got no more than three years from it too, which is irritating. Anyway, a new one will be on the way shortly (not cheap!), and I’ll get it fixed.

Any tips on swapping these out? It looks a bit tricky, but can the vac advance be changed with the distributor in place, or do I need to pull the whole thing out (I’ve not done it before).

Dave

 

Well found.

Some claim that teh angle of teh dangle akkows it to be done as is, NEVER for me.

I have a write up somewhere on R & R the dizzy. It is simple, time consuming, but simple.

I will go look and return.

 

Grant's document will be the real deal, but this is what I did:

• cap off
• rotor off
• clear away anything round the point the capsule attaches to the outside of the dizzy casting.
• with a 2mm punch knock out the tiny roll pin that attaches the vac capsule to the protrusion on the dizzy casting. When replacing the new capsule, drill the hole out a touch and use a small self tapper to replace the roll pin, as this is easier to remove next time!
• there is a small U shaped spring that holds the star wheel onto the rotor shaft. CAREFULLY compress this with snipe nose plies and remove, ensuring the thing does not ping off and disappear. Store carefully on a closed box.
• remove star wheel CAREFULLY, it will break if you are rough or use metal tools. Just rock it with your hands while gently pulling upward
• you may or may not find a wavy washer under the start wheel, if you do put it back when you come to replace the star wheel, if you do not, forget it.
• You can now see the end of the vac tube that sticks into the dizzy casing and engages with the advance retard mechanism on the pickup. You may have to undo the pickup retaining screws to get the vac capsule arm off it's peg on the pickup mechanism. If you do have to, note the gap between the pickup magnet and the star wheel point so you can replace the pickup in the right place. Use a piece of paper for this purpose, not metallic feeler gauges.
• take the new capsule and poke the arm in from the outside and engage the hole in the arm over the pickup peg.
• a few drops of synthetic oil on the moving parts round the rotor shaft base
• replace the pickup retaining screws, if they were removed
• If all good then fix the vac capsule into the dizzy casing using a small screw (or roll pin).
• after that, rotor, cap, done.

 

Cyber space stole the bloody thing.

Rewrote it, glad the memory is still there, HA>

3 attached for some light reading.

I need a BEER.

 

Well the vac advance is replaced. It’s a much better oem part than the generic part I replaced. I can’t remember whether I ordered this for my mechanic a few years ago, or whether he did, but either way it’s (another) lesson in buying proper parts.

I now need more advice though! I got it all back together and it started (first win), but it has a horrible ramping idle, going from 500rpm up to 1500rpm and back, oscillating every second or so. Revs our evenly though, and holds steady on the accelerator. It all goes away and seems fine when I disconnect the vacuum line from the advance unit.

I’m guessing the advance never worked properly and the idle speed was dialled up with this in mind. Now that my vacuum is pulling on the advance, clearly something else needs adjusting. But what? AAV? The engine was warm, having driven it three hours ago, but not hot. Have I got a vacuum leak somewhere? The vacuum for the advance module comes from the back of the A bank manifold, where four other vacuum lines are (drivers side in a RHD car).

Help please!

Dave

 

Dave,

Well done.

My thoights, in NO particular order, AND based on the fiddle factor (thanks Doug) of the "mechanic".

TPS is too high, Any higher than0.36V at idle stop position, and the "smart" ECU will hunt.
AAV is stuck. Easy fix, I have a PDF for that.
Throttle rods etc are out of sync, or just plain wrong. PDF for that.
Timing is too far advanced. PDF for that.

I run the Vac hose from the engine side of the A Bank butterfly, UNDER the throttle body. There are 2 spigots there, 1 is engine side, the other is atmosphere side.

FOR NOW

Unplug the vac advance hose, cap that spigot, and start it up. If it now behaves, the timing is waaaaay advanced. This could be as simple as the OE vac capsule pull rod MAY be shorter than the old capsule rod, and it only takes 1mm to throw the thing into chaos.

Drive time the thing IF the vac hose unplug solves the issue.

Lets know, and I will keep thinking.

 

BTW, what color wires do we measure this .32v across?

 

AAAAAAH, its 1AM, Red and Yellow from memory. Choice of 3, better odds than the Lotto.

I will look tomorrow, oops, later today, if no-one else confirms.

 

The attached from AJ6.

 

red and yellow works. The colors from AJ6 do not match either side of the harness for me.

Thanks Greg and Grant.

 

Another huge thanks to Grant and Greg. My AAV is clearly an issue, and maybe it was just coincidence that it started playing up around the time I tackled the failed vacuum advance module. It is capped off for now, and since I'm living in a place where the temperature is 22C to 32C all year long, I am not too worried about it. When we move somewhere colder, I'll be looking to get a solenoid in its place to give the car a little extra air.

The TPS is now in spec (that was a fiddly job... add it to the list of fiddly jobs on an XJS!), the car is idling smoothly, and tomorrow I'll get it warm, flog the throttles, and get the timing right.

Thanks again!