Slots are now right at the end - which is another indicator that the current set-up is not 'natural'
Here's an odd one. During the period that this car was off the road one day I came to start it and it suddenly ran like an absolute dog misfiring
throughout the rev range. I traced this to a static advance of 40degs! The timing was originally set to 10degs.
In order to get it running temporarily I had to swing the dizzy back (retard) to pretty much the end of its slots (where it normally sits about half
way) to achieve 10degs again and thats how it was left. Since getting the car back on the road I had kinda forgotten about this strange phenomenon
until I noticed its detonating at 4500rpm which it never used to - this then brought back all of the above.
To run through the basic set-up - its an XR2 engine, still running the standard late spec distributor (with small amp module bolted on top) with the
only mod being a saab turbo vac/pressure advance retard unit as opposed to the standard vac advance only unit. The dizzy is obviously run off the end
of the cam.
Now initial thought was its jumped a cam belt tooth, but to achieve that sort of advance it'd need to be 2 teeth, which would cause it to run
terribly - and the belt is tight and in good condition. Besides jumping a tooth would actually retard not advance. So I think/hope I can rule that
out. Likewise it runs a vernier pulley but this appears tight and there are no marks to indicate it has recently moved - and besides, that would have
the same (retard) effect as jumping teeth.
I have stripped the dizzy and nothing appears to be out of place (weights are all well sprung etc). I even did a direct swap for a spare dizzy (but
used original amp module) to no affect.
So, im thinking perhaps that its a fault with the ignition amp module - would I be right in thinking this little unit picks up a signal from the dizzy
internals and tells the coil when to fire? I have a spare but ran out of time to swap it yesterday and wont have access to the car for a few days. In
the meantime I thought I'd put it out there and see if anyone agrees, or has any other suggestions?
If it's a Bosch dizzy with a four point trigger wheel, I know from experience the trigger wheel can slip round on the shaft. In my case, same
dizzy on a Pinto. It's happened a couple of times.
With the dizzy cap removed, one of the spring retaining clips can "flop" in and jam the trigger wheel, if you happen to be turning
the engine over, eg adjusting valve clearances etc.. If it has moved, you could find when it lines up at the firing point, the rotor arm is not
pointing at a plug lead contact in the cap.
quote:
Originally posted by Andy D
If it's a Bosch dizzy with a four point trigger wheel, I know from experience the trigger wheel can slip round on the shaft. In my case, same dizzy on a Pinto. It's happened a couple of times.
With the dizzy cap removed, one of the spring retaining clips can "flop" in and jam the trigger wheel, if you happen to be turning the engine over, eg adjusting valve clearances etc.. If it has moved, you could find when it lines up at the firing point, the rotor arm is not pointing at a plug lead contact in the cap.
I'm pretty sure the amp' doesn't control the advance in any way. It's just triggered by the dizzy.
All the alternatives I can think of would, you'd expect, cause retarded ignition but I'd check them anyway; Stranger things have happend!
Given an alternative dizzymade no difference, start with cam timing and if thats ok check the crankshaft belt pulley; The key on the shaft has been
known to start to sheer giving sudden changes in timing. Did you use the original rotor in the new dizzy. If not check the key in that as they've
been known to fail/break.
Maybe it was stuck (and had been timed to suit) and has now freed off?
The ignition amplifier controls dwell in these, but timing is purely mechanical.
quote:
Originally posted by MikeRJ
The ignition amplifier controls dwell in these, but timing is purely mechanical.
Dwell is merely the recharge time for the coil and unless its decided to reverse polarity (open = closed) then that won't affect it.
Very odd...where in the slots are the bolts now if you've had to dial that much advance out?
Would a reduced dwell not advance the timing though?
Slots are now right at the end - which is another indicator that the current set-up is not 'natural'
quote:
Originally posted by FASTdan
Would a reduced dwell not advance the timing though?
Slots are now right at the end - which is another indicator that the current set-up is not 'natural'
quote:
Originally posted by FASTdan
Would a reduced dwell not advance the timing though?
Slots are now right at the end - which is another indicator that the current set-up is not 'natural'
Granted - you don't have that much adjustment on the slots, i'm sure. How the heck does it run at all with 40 degree out?
quote:
Originally posted by ss1turbo
Granted - you don't have that much adjustment on the slots, i'm sure. How the heck does it run at all with 40 degree out?
There are two different Bosch dizzys used on Pintos, not sure about CVH. One type has springs, weights and a vacuum unit, and the other doesn't.
The advance is controlled by the ecu/ amplifier on the latter.
Easy to tell which is which. If you can twist the rotor arm against springs, it's the first type. The other one will have a solid spindle. Rotor
arm wont turn.
quote:
Originally posted by Andy D
There are two different Bosch dizzys used on Pintos, not sure about CVH. One type has springs, weights and a vacuum unit, and the other doesn't. The advance is controlled by the ecu/ amplifier on the latter.
Easy to tell which is which. If you can twist the rotor arm against springs, it's the first type. The other one will have a solid spindle. Rotor arm wont turn.
I would definitely check where the trigger wheel is in relation to the rotor arm.. compare your two dizzys, see if they are the same?
quote:
Originally posted by FASTdan
Would a reduced dwell not advance the timing though?