lakeffect2

I am simply at a point of frustration with trying to get basic startup and idle routine into my sbc406 with 32lb/hr injectors. So tonight i went out, and did some basics to do the IAC and Minimum air, and idle routine reset. I pulled the ignition bypass connector as well as the IAC. to set the baseline. It held anice idle4 seemed "happy" at 900 rpm ( 230/236cam siamesed runners etc)
it around the block. But it ran. Acceleration has not what I was expecting, very sluggish. It was then that I realized that I'd forgotten to reconnect the bypass line.


reconnectedit
It barely caught didn't want to hold the idle, unlike moments before, idle dropped off to 500-600 and hitting the gas caused nothing but stumbles, roughness, hesitation and bog leading to stallouts.

How could I be so far off on the idle routine ? I would have expected better performance on the full program It really, really sucked. Where have I gone wrong that t limp home runs better than a burn? What spark advance is in limp home that works, vs how to change my 7730 Super AUJP.V4 to the same spec?

RBob

iTrader: (1)

Drink much?

Appears to be that the distributor pickup coil to the ICM wires are reversed. That causes the SA to be reduced rather then advanced once the ECM takes over.

With $8d the minimum idle speed and TPS setting are not important.

Most important for idle is the injector compensation values.

RBob.

Six_Shooter

iTrader: (2)

When the bypass is disconnected you are simply running on base timing. Base timing is only one part of LHM.

Things like fuel, IAC, fans, etc are still running from the programming of the bin, not LHM, when the bypass is disconnected.

Tuned Performance

iTrader: (92)

lakeffect2

ONLYSEVENCUPSOFCOFFEEANDAFEW5HOURENERGYDRINKSEVERYMORNINGWHYDOYOUASK?

Actually, RBob, You are a genius.
Physically my ignition system is capable of having the connector from the trigger coil within the distributor to the ignition module reversed.

Two years ago I had massive hot start issues and moved the ignition module to the fender well, making it remote and now computer fan cooled. I also moved the MAT sensor to the grommet of the air filter, per advice here on this forum. The new plug I used to make the connection to the module was not polarized and could be installed either way.

It was connected the wrong way. Flipping the connection around to reverse the plug polarity IMMEDIATELY resolved the problem.

YOU DA MAN!

Thanks ever so much for taking the time to read and answer my question.


Dave Buchholz
Rochester NY

JP86SS

iTrader: (1)

Not remembering well on the connector inside the distributor but how can you tell if it's reversed before testing it?
I had wierd timing problems last time I started it up. Hmmmm...

RBob

iTrader: (1)

Other then using a scope to observe the signal I don't know of any other way to test it without running the engine. With the scope the distributor needs to be spun. Of course this is easy to do with it pulled from the engine, otherwise require cranking the engine.

The key is that the falling edge needs to be the fast one. The rising edge will be oddly shaped and slow. I posted a picture of this someplace here on TGO. I'll see if I can find it.

After start up, just see which way the spark timing goes. If it retards then the connector pins are likely reversed. Can get brand new pickup coils with them pinned incorrectly. Which is how I found out about it.

RBob.

RBob

iTrader: (1)

Found the picture, it is of a reluctor pickup for a DIS system, but it is the same waveform that a pick up coil in a distributor has. With this waveform the scope probe tip is on the P terminal of the ICM, ground on the N terminal of the ICM.

Be sure to spin the distributor in the proper direction, clockwise from the top for a SBC. Note that the spinning can be done by hand. I've done that with the distributor out of the engine but connected to the harness. Need to ground the distributor body via a jumper clip.

Picture:

https://www.thirdgen.org/forums/atta...sc00136_a1.jpg

Then the thread which is an interesting read:

https://www.thirdgen.org/forums/v6/5...rong-your.html

RBob.

Edit: OK, the picture link now shows the full size picture.

lakeffect2

JP, the nature of my results were that before flipping the connector. It would start and idle Ok with the bypass disconnected. As soon as it got replugged (wrongly) it would want to stall. When it did, it was hard to start. Touching the gas would make it bog or stall worse. Now it makes sense, that were was no advance of spark, just a question of how badly it became retarded instead.

Flipping the connection was an immediate change in response, like it was before my teardown.

JP86SS

iTrader: (1)

Thanks RBob for the info.
I was thinking mine might have the issue because I was needing almost 30* at idle and my EGT would rise very quickly upon excellerating (like timing was dropping or something) then power would just not be there.
Advancing the timing up too high and it seemed to run better, but it was way too much >40*
Might not have been the cause, just something that's been bugging me.
Now that my engine is back in and running (as of right now, Just finished Yea!) I can begin playing with my tuning stuff again.