My question is a little subtle. I am having a problem with the ignition on my 88 (165 ARAP bin).

Sometimes when I start the car and then push on the gas pedal at all the engine speed drops from idle to sub 500 rpm and acts like it has very little timing and of course wont rev. When I release the gas pedal the engine idles normally.

A previous problem I had was I used to rev the engine in park or stomp the pedal when driving and the engine would stumble over 3500 rpm or so.

To correct this problem I assumed that the computer was requesting so much timing that the rotor was actually closer to the previous post when the coil was commanded to fire. So I thought that since the phase of the rotor and post is fixed without computer input -- I would just set the initial timing higher to allow more advance with the computer connected.

So I advanced it from 6 to 14 degrees BTDC.

Now I have the gas pedal -- stalling problem and I am pondering wether the computer can actually request a lower timing amount than this static setting.

I believe that the advance signal goes over the EST wire to the 4 wire connecter in the distributor module. the module then interprets the voltage on the est wire as the amount of advance to give to the reference pulse when it fires the coil.

If this EST signal is 0 volts for 0 degrees of advance added then indeed the computer could not subtract timing from the base setting of the distributor.

Thanks for any insights and I will be setting the base timing on my car back to 10 degrees to see if it helps.

 

Question: Can 165 (or 730) retard timing further than base setting?

Yes, by a max of about 4 degrees. Not much , but it can do it. There is a max retard parameter in the calibration tables. This value is limited by the actual distributor.

RBob.

 

FWIW, to me, I don't see where you'd need to be running that much timing. And if you do need to, then you'll never get enough with a dissy, and you need to be looking at some sort of CNP, or DIS, setup.

Wouldn't it be *next post* rather then previous post, if you were requesting *so much timing*?.

 

Well thinking about it -- if the phase of the rotor and post to be fired is fixed when the computer is disconnected -- lets say the rotor points to the post it is to fire.

Then when turning the distributor with the computer disconnected you are setting the relationship of the shaft (reluctor wheel) to the pickup.

when I set this to 6 BTDC the computer then takes that number (given in code) and calculates how much additional advance it is to command at any given time.

if the computer commands 6 BTDC it would only have to signal the module to fire when the rotor points to the post in my example.

if then the computer commands 51 BTDC the computer would be adding 45 degrees of advance relative to the crankshaft and 22.5 degrees relative to the distributors rotor. This is the mid point between posts in the distributor and hence the coil will likely fire to either the intended post or the one preceeding.

IF in fact this phasing is what is present in the distributor then one would not have problems getting close to the amount of advance described.

HOWEVER if the phasing between the rotor and post to be fired with the computer disconnected was advanced (meaning firing before it reaches the post) then the situation is different.

Lets say that when we set the timing as above the rotor is now 3 degrees advanced compared to the post it is to fire and we set the timing to 6 BTDC.

Now when the computer commands 6 BTDC again it allows the module to fire as it would with no advance commanded but the rotor is already 3 degrees advanced compared to the post it is to fire.

And when the computer commands the same 51 degrees as above, it places the rotor 25.5 degrees advanced BUT only 19.5 degrees away from the previous post. In fact one should only be able to get 45 degrees of timing before the rotor is firing halfway between two posts.

I will reset the base timing on my engine but I may also check the phasing to see exactly what it is.

Thanks for the reply on the retard capability.

cheers.

 

I think the HEI is set up to put the leading edge and trailing edge of the rotor at the correct post within a range of typical ignition timing (like 0-45), where middle of rotor points directly at post in the 20-30 degree advanced range.

I'm just speculating, but I did see that on a 4 cylinder distributor setup.