Topic: Distributor cap issue

[sharpxmen]

the pcm has no way to "know" what wire go to which cylinder.

[dwtaylorpdx]

Let me re write that, what I was trying to say was that if you are a
tooth off the PCM can pull enough timing to get things synched up, if
for instance you were a post off in putting on the plug wires, the PCM
cant correct 90 degrees of timing, so it would pop bang and backfire....

It would be the equivalent of having the distributor 4 teeth off or so...

Does that make better sense?

Later
Dave

[sharpxmen]

Let me re write that, what I was trying to say was that if you are a
tooth off the PCM can pull enough timing to get things synched up, if
for instance you were a post off in putting on the plug wires, the PCM
cant correct 90 degrees of timing, so it would pop bang and backfire....

It would be the equivalent of having the distributor 4 teeth off or so...

Does that make better sense?

Later
Dave

it makes more sense but this is my thinking: the advance has to occur at the same angular point bfore TDC for some given engine running params (rpm, temps, etc)
now if you move the dist 1 tooth ahead or behind the PCM will still give the spark at the same point for the same engine running params - the spark would occur at a different position inside the dist cap but the ignition advance is the same relative to the TDC for a cylinder (and that is given by the flywheel teeth and the crank sensor and these have not moved).
the cam sensor is only used for injector sequence, has no input/influence in the ignition timing.
I don't see what/how would the PCM do with the timing to correct that (the spark would still occur at the same point, so you still have the same ignition advance)

i don't even think the engine would run with the cam/crank out of sync (i read an article for a 4.0 where the dist was not set properly and the engine would run for 2 seconds and then cut out, once they fixed the dist position started to run fine) - have not tested this so it's only from what i read.

[dwtaylorpdx]

When I rebuilt my engine I got the distributor in a tooth off,
It ran, but when I used my cap with the hole in it the spark was jumping
from the leading edge of the rotor not from the face of the rotor to the contacts.
It was also wicked rich and fouling plugs at idle, which I attributed to
the injection firing way out of sync and puddling fuel in the manifold?
It would run ok if ya revved it enough to get it up to firing more continuously...

At least this is what I observed and kinda guessed was happening,
I corrected the distributor and it went away. Now I don't know for sure what
was happening with the injection but that's what it looked like it was doing...

My understanding is the cam position sensor in the MPI distributor only fires
the injection, and the ignition is all off the crank sensor. A mopar mechanic
told me once the ECU is really like multipe small computers in one box, the
Ignition is one the injection is one and there is one that runs some accessory
stuff like the alternator. Thats why they act sort of phsychotic because they just
talk on a local buss to sync their activities.

The Renix uses a continuous pulse system that is related to RPM and sensor feeds. So its not timed right?
And I'd assume it has a regular distributor that fires the ignition?

Dave

[chardrc]

The Renix uses a continuous pulse system that is related to RPM and sensor feeds. So its not timed right?
And I'd assume it has a regular distributor that fires the ignition?

Dave

tbi distributor has no electronics, just the rotor and cap. just uses cps and other sensors like you said. i know the timing is computed in a box that the coil connects to which receives a signal from the computer and 12v.. so maybe its just a dumby but a similar system (renix / bendix)  was used by Volvo and computed timing with cps and map outputs.

what do you mean by timed? (im guessing you are talking about timing for injector pulse on / off... but not sure)

[sharpxmen]

When I rebuilt my engine I got the distributor in a tooth off,
It ran, but when I used my cap with the hole in it the spark was jumping
from the leading edge of the rotor not from the face of the rotor to the contacts.
It was also wicked rich and fouling plugs at idle, which I attributed to
the injection firing way out of sync and puddling fuel in the manifold?
It would run ok if ya revved it enough to get it up to firing more continuously...

At least this is what I observed and kinda guessed was happening,
I corrected the distributor and it went away. Now I don't know for sure what
was happening with the injection but that's what it looked like it was doing...

My understanding is the cam position sensor in the MPI distributor only fires
the injection, and the ignition is all off the crank sensor. A mopar mechanic
told me once the ECU is really like multipe small computers in one box, the
Ignition is one the injection is one and there is one that runs some accessory
stuff like the alternator. Thats why they act sort of phsychotic because they just
talk on a local buss to sync their activities.

The Renix uses a continuous pulse system that is related to RPM and sensor feeds. So its not timed right?
And I'd assume it has a regular distributor that fires the ignition?

Dave

yeah, that's what i'm saying - the timing has nothing to do with the dist position - sounds about right from what you describe (spark being offset off the rotor).