Vacuum advance canister replacement

[MikeNo9]

The plastic linkage on my vacuum advance canister '82 Spider 2000 failed. It was probably original. I replaced the canister with an new one and now I cannot get the advance to extend into the high rev range. The advance works OK, not great up to about 3500 rpm but will not run beyond that.
Has anyone else run into this problem?

I've adjusted the the linkage to provide maximum movement before it bottoms out into the canister. A friend thought the advance plate appears to be be sticking, but I'm not sure about that. Could this be a problem with the distributer that needs replacement too?

Mike D
1982 Spider 2000

[18Fiatsandcounting]

Mike, I think you might be mis-interpeting how the distributor advance works. The total advance seen by the engine (what you measure with the timing light) has three components that all add together:

1) The "base" or "static" timing which is what you measure at very low engine speeds with the vacuum advance temporarily disconnected. I believe for an '82 spider that is 10 degrees before top dead center (BTDC).

2) The centrifugal advance, which is a set of rotating weights inside the distributor that push outward as the engine speed increases, thus increasing the spark advance. The centrifugal advance adds about 22 or 24 degrees advance on top of what the static advance is set to in (1) above. The centrifugal advance will max out at around 3500 engine rpm, as you don't want any more advance than that.

3) Some engines benefit by have vacuum advance, which advances the spark timing about 10 degrees, but only when their is full or partial engine vacuum. So, this is in effect only at low speeds, and there is no vacuum advance when you open up the throttle the whole way.

The upshot is that you would set the static timing at idle with the vacuum hose to the advance canister disconnected, to 10 degrees BTDC. You then verify that the timing advances as you rev the engine, up to a maximum of around 34 to 36 degrees total at 3500 rpm and above. If that is happening, chances are the advance at other engine speeds is correct.

There are no timing marks for anything over 10 degrees BTDC, so you just have to estimate. Or use what is called a "dial back timing light".

-Bryan

[spider2081]

I have seen the plastic rod adjusted too long, on some new chambers, so once its popped onto the ball on the advance plate one has to push the chamber in to get the 3 mounting screws to match the screw openings in the distributor case. I think that limits the advance travel and in some conditions conditions lock the distributor in full advance. When the distributor is installed in the car and the timing light is used to set the timing the Distributor has no vacuum advance or limited vacuum advance depending on the rods adjustment.
I have also see the wrong screws used to mount the pick up coil to the advance plate and or the lock washers under the head of the screws missing. This allows the screws to pass through the plate and hit the distributor case, limiting the advance travel of the advance plate. If this happens there is a distinct mark in the distributor case under the advance plate.

[MikeNo9]

Thanks for the replies. I am beginning to question if timing is the problem. Here's what I have done after seeing your responses and looking at other posts. Near the end I have possible diagnosis questions/ideas.

Checked the vacuum advance canister adjustment. I can't say for sure that vacuum advance is not partially restricted but the plate begins to rotate at about -5psi then continues to full rotation around -15psi. Guessing 5 to 10 degrees CCW rotation.

Checked vacuum from the manifold. Idles about -5 psi at 1000 rpm then up to -15psi near 3000 rpm.

Checked the centrifugal advance. It moves fine. I have not checked the pulley timing mark at different rpm.

I tried to check base timing as Brian described. Really I checked around 1200rpm as low as I can get a decent idle. Tuning by ear, the mark looks to be about 10 deg off the pointer. I used the advance function on my Innova timing light (dial back?) to align the pointer and the mark on the pulley. It read about +20 deg. Maybe OK at 1200 rpm?

If I rotate the distributer CW to align the pulley mark to the pointer, the idle drops and tends to stall. I hope to get adjust idle speed screw and idle adjust screw to check timing at low idle. Then I can check the centrifugal advance with a timing light.

Keeping in mind that this was a sudden change. My car was running OK, rough idle but plenty of power and able to rev high, drive freeway speeds... One day while warming up there was a pop, probably a backfire then lousy idle, barely running. I fiddled with the timing. That helped then noticed the vacuum advance was not working and replaced it. No significant change after replacing the canister.

My next steps
1. Try to get 850 rpm idle. Continue to check the timing.
- Is it possible the timing belt jumped? It's about 5 years old, maybe 10k miles. My approach would be remove plugs and rotate to #4 TDC measuring with a wood dowel.
- Did something break the distributor? Unlikely.
3. Check the fuel system: injection, fuel pump... I just found the Mirafiori L-Jetronic injection guide. Checks do not look too difficult.
- Considering the cold start idle it's possible the injection was messed up and got worse.
- When I got this car about 15 years ago the "mass air balancer" had been recently replaced. I'm guessing this is the Air Flow Sensor.

I'm sure I will have a bunch of questions before I am through with this. Thanks for reading this far and your advice. I'm looking forward to seeing your thoughts.

How about the Bay Area Weather Brian? I'm in Oakland.
Mike D

[ORFORD2004]

Check the door of your AFM for free movement maybe the backfire bent it.

[18Fiatsandcounting]

Mike, as Orford suggested, you could have bent the flap in your AFM with the backfire. But, the reason I called, let me know if you want me to come out to Oakland and take a look. I do house calls (within reason), my labor rates are free, and all I usually ask is a Thank You and maybe a burrito and a beer for payment.

Send me a PM if you're interested. You're welcome to come out to Livermore if you'd like, and there are always multiple engines and transmissions in various states of repair. Keeps me off the streets and outta the bars as they say. I'm currently building up a 1608cc engine to go back in my '71 spider.

-Bryan
PS: Adjusting the idle on a FI engine is somewhat counterintuitive. Various adjustments must be done in the correct order or things get goofy. It's not like adjusting the idle on a carbureted engine.

[MikeNo9]

Thanks again for all the advice. The AFM plate is bent and binds at about 40 deg open.

I checked timing (again) and can get an OK low idle with 10deg BTDC base. The centrifugal advance works. The problem remains 4000 rpm max then it bogs down. I checked O2 sensor output. It's minus 50mV. A google search hit some results that negative O2 sensor voltage could indicate bad AFM.

I ordered an AFM and will know if it's the problem next week and report back.

Mike D

[ORFORD2004]

I ordered an AFM and will know if it's the problem next week and report bac

It is