Running rough (Autozone CPS thread conclusion)

[cruiser54]

I just tested the CPS with the truck running. I'm getting a rock solid 1.5 acv

 

What ye cruiser?

 

I read your CPS testing tips and it says I should be getting .5acv

More doesn't hurt. 

 

But what is it on cranking? 

[ftpiercecracker1]

truck fired right up this morning idle perfect.

 

Died before I could even get to the end of my road.

 

Jumped right out and tested the CPS while cranking. Solid .3acv, on both sides of the connector. Its a little low, but shouldn't that be enough?

[ftpiercecracker1]

More testing information.

 

Plug wire from coil to distributor 650ohms resistance. I know plug wires are supposed to have high resistance, but I do not know how high. Does this sound right?

 

 

 

Ignition coil module. The plug with three wires (yellow, black, grn w/wht stripe).

 

Yellow wire has 12v with key in run position.

 

Black is grnd w/ less than 1ohm of resistance.

 

Grn w/ white stripe has nothing AC or DC regardless of key position.

 

 

I also tested between the same plug and the tabs on the module.

 

Standing on the P-side of the truck the left tab has 16k ohms of resistance between it and the solid yellow wire.

 

The right tab has 1k ohms of resistance between it and the grn and white stripe wire.

 

 

These readings are meaningless to me without a baseline, but maybe they will reveal something to you guys.

[ftpiercecracker1]

More data:

 

On the ICM, the left tab has constant 12dcv with the key on, but the right tab only has .25dcv and only while cranking.

 

I think I read somewhere that the right tab is supposed to have half the voltage of the left or something like that.

 

 

I also tried to do a spark test. I didn't get any spark, but I am by my self so it's easy to get a false negative.

 

I tested the (brand new) coil too, just in case. Less than one ohm across the studs and around 10k between either stud and the ignition wire terminal.

[ftpiercecracker1]

More data:

 

On the ICM, the left tab has constant 12dcv with the key on, but the right tab only has .25dcv and only while cranking.

 

I think I read somewhere that the right tab is supposed to have half the voltage of the left or something like that.

 

 

I also tried to do a spark test. I didn't get any spark, but I am by my self so it's easy to get a false negative.

 

I tested the (brand new) coil too, just in case. Less than one ohm across the studs and around 10k between either stud and the ignition wire terminal.

 

 

The second solid yellow wire, square wave signal wire I believe has a steady 5dcv w/ key on.

 

Maybe it is the ICM?

 

5dcv in .25dcv out?

[cruiser54]

I don't know of a proven ICM test. 

 

The stuff below is not mine...

 

Three wire connector:

A = +bat voltage (from latch relay)

B = Ground....

C = Tach

 

Two wire connector:

only wire hooked up = spark pulse from ECM (5v square wave)

 

So, as I figured above, the ICM is just another version of the Duraspark II ICM (or more accurately, ignition amplifier, since all it does is take a TTL pulse and amplify it into ignition coil drive). 

This one just gets the pulse from the PCM instead of directly from a hall effect sensor in the dizzy....

 

So, I rechecked the ground wire to the ICM (unplugged the 3 wire connector, measured from the B pin in the connector to the - battery pole.  0.1 ohms. Then I rechecked the +voltage.  Battery voltage present when key is on..

 

So, I hooked up my scope to the 5 volt pulse line (back probed, both plugs connected to ICM) and grounded its ground clip

 

The ECM provides a nice pretty pulse both when the engine will run (it was nice enough to run for 30 seconds while I did this test) and when it has no spark. 

When the engine died, the pulses continued until the engine stopped spinning (as one would expect with the key in the on position).

 

At this point, it is my opinion that if I can send a pulse into the amplifier (ICM) and not get a spark out, then the amplifier (ICM) must be bad.... 

[Ωhm]

I don't know, but could, would or should a short to ground (STG) on the ICM Tach output signal or a faulty Tach, cause this type of problem? 2¢ worth.

[ftpiercecracker1]

ICM has been ordered, will report back tomorrow with test results.

[ftpiercecracker1]

Well it appears the ICM was the culprit. Got the new one from Advance Auto, $117 ,carquest BWD brand,

gasp <<<MADE IN U.S.A.>>> gasp stamped right into the part.

 

Installed it and she fired right up, purring like new engine. Been driving her around for the last few hours with zero issues, about to go out again. Think I finally got it nailed.

 

 

Important data:

 

old ICM

 

Square wave signal wire (solitary yellow wire) had 16k ohms of resistance between connector and left tab (tab closest to firewall with ICM installed).

 

Grn w/ white stripe has 1k ohms of resistance between connector and right tab (tab closest to front of vehicle when ICM is installed)

 

2nd Solid yellow wire that is grouped with black and grn with white stripe has 2ohms of resistance between the connector and the left tab.

 

 

 

 

New ICM:

 

 

600ohms

 

 

1k ohms

 

 

haven't tested yet.