1991 360 Pinging Questions

[Brynjminjones]

I have a freshly rebuild 360 in my 1991 Grand Wag. It runs great, but I've been noticing some pinging in certain scenarios.

It only seems to do it when the throttle is almost wide open and the revs are fairly high (above 2500-3000 would be my guess). At lower RPMs there is no pinging at all.


It has a Melling MTA1 (RV-style) cam but everything else is stock, down to the 2150 carb and distributor.
The vacuum advance is connected to ported vacuum.
The EVAP canister and EGR are both in place, but neither is connected. There is no other emissions stuff installed.

Timing is set to 10 degrees initial, with whatever that gives me as total (I will check this).

My understanding was that it would usually ping at low RPM/high load. Why would it be pinging at high RPM/high load, and what can I try to stop it?

[babywag]

could be many things
poor fuel
too much total advance(mechanical)
lean fuel mixture

try backing initial off a couple degrees.
if it stops then you know it's timing

[SC/397]

Do you have a Duraspark ignition system?
Every Duraspark distributor that we have dyno tested had to be mechanically modified to keep the timing from going to infinity.

[Brynjminjones]

Thanks both, I'll do some investigating this weekend.

I doubt it's bad fuel or running lean, as it runs on propane and gas and does it on both. I didn't mention that at the start to avoid confusing matters!

It is running a Duraspark ignition (that's the standard Ford one, right?). Is it usually the mechanical or the vacuum that you had to restrict?

My engine builder wondered if it could be applying too much vacuum advance. It's timed exactly the same way as it was before the rebuild, except now a load of vacuum leaks have been fixed and the engine is of course much healthier.
He thought that this increased vacuum could be bringing on too much timing.

Does that seem possible?

[wiley-moeracing]

Yes, can you find someone over there with a distributer machine to fine tune the unit and make adjustments.

[SC/397]

We had to limit the mechanical by taking the distributor completely apart and welding a limiter slot smaller. That probably doesn't make sense but I will try to get a picture of what I am tying to describe.

[Mikel]

Low compression engines love a lot of initial advance. Greatly increases low end torque. Centrifugal advance has to be limited for this.

[babywag]

there are 2 slots on a duraspark everyone i have seen has been on the larger one.
if disassembled and on larger slot it can be swapped to smaller one.

ristow has pics here...

http://www.ifsja.org/forums/vb/showthread.php?t=84586

[babywag]

My engine builder wondered if it could be applying too much vacuum advance. It's timed exactly the same way as it was before the rebuild, except now a load of vacuum leaks have been fixed and the engine is of course much healthier.
He thought that this increased vacuum could be bringing on too much timing.

Does that seem possible?

@WOT or even hard acceleration vacuum advance is just not there.

[Brynjminjones]

Thanks everyone. I will check out my total centrifugal advance once my new dial-back timing light arrives this week.

SC/397, I know exactly what you mean with the limiter slot - I've played with that previously in our '74 Ford F100.

babywag, I've thought about changing to the other slot in the distributor, but I thought that after doing that I'd need to rotate the whole thing back 180 degrees.
Looking at mine, I think the vacuum advance would interfere with other stuff if I did that. How are others managing?

[babywag]

Thanks everyone. I will check out my total centrifugal advance once my new dial-back timing light arrives this week.

SC/397, I know exactly what you mean with the limiter slot - I've played with that previously in our '74 Ford F100.

babywag, I've thought about changing to the other slot in the distributor, but I thought that after doing that I'd need to rotate the whole thing back 180 degrees.
Looking at mine, I think the vacuum advance would interfere with other stuff if I did that. How are others managing?

If done in engine simply lift distributor, rotate shaft/rotor, drop back in(after swapping slots). Vacuum can location won't change.
If done out of engine simply reinstall distributor like normal.

[Brynjminjones]

If done in engine simply lift distributor, rotate shaft/rotor, drop back in(after swapping slots). Vacuum can location won't change.
If done out of engine simply reinstall distributor like normal.

That's incredibly obvious now you say it!
I'll check it out soon and see how mine is set.

[nograin]

Timing is set to 10 degrees initial, with whatever that gives me as total (I will check this).

My understanding was that it would usually ping at low RPM/high load. Why would it be pinging at high RPM/high load, and what can I try to stop it?

It will ping under load.
When it does, then the spark is being lit too early for that condition.
It rarely happens at low rpm because its difficult to heavily load the engine at low rpm, especially for any length of time. With a manual transmission and the right situation it can be done, but an automatic is going to rev toward the torque converter's brake stall speed.

So if the pinging is occuring at full throttle or close to it, then there is too much mechanical timing at that rpm. (initial plus mechanical advance).
---------------------------------------------------------
If the pinging is occuring at part throttle load, then its too much mechanical plus vacuum advance. Even though EGR brings back in hot exhaust, my understanding is it generally slows the burn.

Therefore you could try using the EGR (EGR valve should be open above idle, when the engine is warm. It should be closed when any of the following conditions exist: the engine is cold, or at idle, or at WOT)

or you could change the vacuum advance and/or part throttle timing.

[nograin]

Thanks both, I'll do some investigating this weekend.

I doubt it's bad fuel or running lean, as it runs on propane and gas and does it on both. I didn't mention that at the start to avoid confusing matters!
...............................
He thought that this increased vacuum could be bringing on too much timing.

Does that seem possible?

Its possible the vacuum advance is coming in sooner. Easy enough to dial it back.
I had to do that with my original engine to eliminate part throttle uphill pinging at 50 mph and up.


Having two fuels does confuse matters!
The time it takes for pressure to build by burning depends on what is being burned!

[Brynjminjones]

Thank you, that's very helpful.

I've tested the vacuum advance with a hand vacuum pump and have some numbers.
It starts moving around 7" of vacuum, and stops advancing somewhere between 15-20 (sorry that's a bit vague).
Until I get my new timing light I can't figure out how much advance it's actually giving.

Do those vacuum numbers sound about right?


I looked at reconnecting my EGR, but it wouldn't hold vacuum so looks like it needs replacing first.

I've also noticed that my distributor wasn't actually tightening down very well. I almost stripped the thread of the bolt and I could still turn it by hand. I've now bent the hold down tab and it's much better.
It's unlikely, but I'm wondering if the distributor could have been rotating by itself.