XF Ignition Advance..

[Anonymous]

G'day all

Vehicle is an '89 XF Van. Dual Fuel. Its got the computer controlled ignition. Basically my issue with it is that the computer advances the ignition until it hits 2500rpm, then it takes timing out until it retards it back to initial timing at roughly 4000rpm. Makes it go like a wet weekend, to say the least. Only just noticed it at work today, when I was doing leads and plugs, decided to put a timing light on it. The boss says he's never seen anything like it, out of 25 odd years of being a mechanic. Anyone got any suggestions?

I'm thinking XD alloy head, XE EFI/carb dizzy, recurved to suit LPG.

 

[Anonymous]

Hullo Disco,
Best advise, ditch the electronical controlled ignition and fit the XE electronic distributor, recurved for your application.
The ignition timing could be all over the place due to being revved to these speeds with no load.
Vacuum signal could be all over the place.
May be an idea to look further before changing anything.
I am thinking catalytic converter.
These block up with a few ks and especially bad with lpg.
Look into the the exhaust, not literally.
Noel.

 

[wagon]

Hello! How good is your timing chain?? A flogged out chain will cause variations in the signal from the dissy and manifold vacuum variations. These things will conspire to make the thing run like a busted arse.

 

[Anonymous]

Hello all,

Not sure to all. I reckon I should run a test to see if I've got excessive slack in the timing chain; the motor is of an unknown age. VIN and engine numbers don't match, so its been swapped sometime in its 350,000km life. Same for the cat, although it makes sense if its banking up the exhaust flow, it'd hurt VE and therefore manifold pressure. Thanks for the tips fellas!

 

[Anonymous]

I would say your test done with the timing light in the shed was done under a no load condition right? Engine free revving away int the shed. Of course the engineers who designed those computer controlled ignition would pull timing out of a free revving and engine as free revving is no good for anything.

If you look at the timing at 4000 rpm under full load then you would have what you would expect to see, somewhere areound the 30 degrees or so.

 

[Anonymous]

yair, thats also a very valid point. I guess you had to put it like that for it to click. Okay, onto the dyno it is..