Sonny_T

Per manual, when key is on/engine off, MC solenoid's Port A gets 12 volt from ignition, and port B gets 12 volt from ECM pin 18. If both side has 12 volt, how does it click/work. What ECM does to MC Solenoid via pin 18.

naf

iTrader: (7)

The ECM provides the ground to energize the MCS at a frequency of 10 Hz, varying the dwell time based on mixture requirements.

Sonny_T

naf,

thanks.
---------
That means if MC blue cable is shorted to either '+' or '-' of body/battery, clicking will not happen. This blue cable should only go to MC plug and dwell wire, and not touching anyhting. I am going to unplug ECM connector and test this blue cable.
---------
If this blue cable is not shorted to any where, then ECM is shot for MC circuit.
----------

Am I thinking correct.

naf

iTrader: (7)

or the MC is bad. you should be able to manually short the ecm conductor to the MCS and cause it to click (w engine in run)

Sonny_T

---------
I put battery +/- to MCS and it clicks.
-----------

Sonny_T

After having MC solenoid not working, I did a deep investigation of all wiring in engine bay. Starting from fuse, wire isolation, continuity, wire short, test light of all ECM related component, and relays, fan, switches...name it. All passed. Did ECM connector voltage test with engine running. MC clicks perfectly when connected directly to battery. Wires going to ECM port 18 is not shorted, or spliced, but MC simply will not click.
--------
Am I right to say that my ECM port 18 is not 'grounding', or 'pulsating' as required. Then it must mean that ECM is fried of what ever circuit port 18 supports.
--------
I have not modified any wiring or component in my car, but with ECL on, I know it will never pass emission, and I want this to be a daily drive car.
--------
Car runs 'OK' and has no other issues. I may try another ECM, with the existing prom.....
------------
What else can I do.

Damon

Did you check for continuity from the NON-12V side (grounding path side) of the MC solenoid plug to the ECM pin? If that check out OK, I think your ECM replacement theory is valid.

FYI- many cars used the same ECM as your Camaro over a period of years. Buy an ECM always entails swapping over your existing PROM into it prior to install, since they always come without a PROM installed (unless you get one out of a junkyard car).

Sonny_T

Damon, yes, non 12v cable from MC to pin 18 had been checked for short and continuity, and it is ok.
--------------------
Finding an ECM is not the problem, but finding a DLB prom is where I am stuck. Finding an ECM with DLB is almost impossible. I do have two DLB and tried both with present ECM. I wish ECM had a self check process to verify weather itself, or prom is bad and send a code, but it doesn't.
-----------------------
I even thought of buying some tool and blank chip, but there are no bin file for it, and even if that solve prom issue, there are no tool to check out ECM 1226865.
--------------------

Damon

I don't understand. What's wrong with the PROM you already have in your existing ECM? Why would you think you can't reuse it?

Sonny_T

Original ECM wasn't working as shorting AB would never blink. So I got a 2nd ECM and put the original prom into the 2nd ECM, and at least it has been responsive with code 12, and any other stored code it picks up when engine runs. It also causes EGR to click when Engine off/AB shorted, but EGR click never stops as Shop Manual says it should stop after 25 seconds. If I remove MC it gives Code 23, I put MC back it gives 54. Now, I do not know if the 2nd ECM is bad and that is why pin 18 never gets ground. I never get click in MC when key on/engine off. I am also waiting for a 3rd ECM and try it out. I have already went through a thorough check up of all engine bay cables for shortage, open, and MC does click with directly connected to battery.
--------
If 3rdECM doesn't make MC click, then I am lost and just do not know what should be my next step.

Damon

Are you sure it's not the MC solenoid that's clicking? That's the one that should be clicking when you go key-on for about 30 seconds or so (at least in Chevys- Olds, Buick and others don't do the key-on clicking because it drove old people nuts and they kept bringing their cars back to the dealership for repairs!).

I don't recall the ECM cycling the EGR solenoid at key-on (which gets it power from a common source with the MC solenoid, but grounds through pin T at the ECM). I'm not even sure you can get an EGR fault just sitting with the engine off. I could be wrong about that, but I don't recall getting one under those conditions.

Sonny_T

As for EGR & Per shop manual key on/AB shorted EGR clicks for 25 seconds, then stops if engine is not started. This happens only during code check. If AB is not shorted there are no click of EGR.
-------------------------
Per shop manual MC should click whenever a key is on/engine off also for 25 seconds if car not started, as part of normal operation.
----------------------
Yes shorting AB causes EGR to click per shop manual. How I know it? I remove EGR cable, now shorting AB doesn't cause clicking any more when key on/engine off.
------------------------

Damon

OK, got it.

So you have 12V+ at the MC solenoid, but the negative (ground side) through the ECM isn't causing the MC solenoid to click. BUT the solenoid itself has tested good by doing a straight battery test.

Do one more thing before you throw in the towel on this....

Remove the ECM harness connector from the ECM. Check for continuity to ground on the ground-side pin at the MC connector. You should NOT have any continuity to ground when you check this. If you do, you just found the problem.

Here's my thinking... the grounding-side wire from the MC Solenoid connector back to the ECM may be grounded against something PERMANENTLY. Like the insulation has rubbed through on something or some dingbat tried to use is as a ground wire for some add-on accessory. That run of wire will still test good for continuity if you use a self-powered continuity tester (a test you already did), but it'll never switch the MC Solenoid on and off no matter what the ECM calls for. (Kind of like having an internally shorted tachometer constantly grounding out the neg side of a coil and never allowing the coil it to fire).

The other test you can do while you have the ECM harness disconnected from the ECM (and you should do this one AFTER the above test) is to send 12V to the + side of the MC Solenoid connector as it normally would be (do this however you can), plug it into the MC Solenoid, and see if it shows somewhere close to 12V (relative to ground) down at the 18 pin on the ECM harness connector. Even after the current flows through the MC Solenoid, it will still be close to battery voltage all the way down that wire to the ECM connector pin (the solenoid is not a very high resistance device). This test will assure the connector itself is making good contact with the pins on the MC Solenoid as well as test the entire length of the circuit right down to the "busness end" at the ECM connector pin itself.

Two bad ECMs doesn't seem likely to me. It's POSSIBLE the chip itself is bad, but that's actually pretty rare. I've seen enough mouse-eaten wiring on these cars I never dismiss these kind of possibilities.

Sonny_T

Did that, and did it again. No continuity between ground and 'non-12v cable' of MC plug, and ECM connectors are disconnected. Also verified in case it was shorted to pos cable, and it is not. Per continuity test this 'non-12v' cable only goes to two places, dwell and ECM connector pin 18.
----------------------------------------
It defies all logic, so at this point I have to blame ECM (or prom) so I can vent some frustration.
---------------------------
1st ECM had burn me when I tried to figure out why it wouldn't blick with AB short. As I had put second ECM and it blinked, and then with same setting I went back and put the 1st ECM back, and it didn't blink....and that was the only way I was able to confirm that 1st ECM was toast at least for blinking part, and since it won't blink it had no use. 2nd ECM brought a lot of relief till the 'MC-click'..........here I go again spending many hours of troubleshooting, some blindly... some 'per shop manual', some per guidance from thirdgen.... and I am hopping that 3rd ECM will be the one......

Sonny_T

Question, is MC just clicks-no clicks 10 time and is that all, means 'full 12 volts' goes through the solenoid towards ground energizing plunger, and then no ground, then 'full 12 volt'....... 10 times, or is it more then that.
------------------------------------------------------
If that is all it does, then there are other way a 10hz clicking can be implemented without interfering ECM circuit. Where ECM port 18 can see 12 volt and then no volt....for 10 times... and MC will click 10 times. However if it is more then just 10 clicks, then ECM is only way.

Damon

Damn, Sonny, you are in deep weeds with this, aren't you? You've run me out of ideas (a pretty rare occurrance, but you did it). Everything says it's your ECM (or far less likely, the PROM itself). Or its something totally wacky like a bad ECM ground wire.... stuff there's no way we could guess at over the internet.

The ECM should be clicking the MC solenoid a lot more than 10 times when you go key-on/engine off. It should go for a solid 20-30 seconds before it gives up and stops. Weird you would see it try only 10 times and then stop. I don't know exactly how the ECM reads "proper functioning" of the MC solenoid, but looking for voltage between groundings at the 18 pin seems like a likely way the factory would have used to check for it.

Just for ***** and giggles, give me an ohms reading between the two poles of your MC solenoid (near room temp if you can). I'll go check your reading against a known-good MC solenoid I have laying around the joint. Maybe yours is too high/too low and kicking the ECM into a frenzy trying to operate it. It's just an electro-magnet so the resistance should be fairly similar across different units, regardless of age or condition (short of being non-functional).

Sonny_T

MC resistance: 23 ohm

Sonny_T

Got my third ECM with CPK prom, and MC clicks as it should be. May be CPK and DLB proms are interchangeable. For MC at least, issue was definitely with ECM. Now I have to wait to find out if other codes comes in, or not as engine runs. But I tell you man without MC, and ESC signal by ECM, this carburetor will not be civil.
---------------------

Sonny_T

I had a test run, so far no more code. Until no more ECL, I am resting this ECM/MC issues and will move to the next fix...heater core leaking, catalytic converter leaking, parking brakes no workie......

Damon

Glad you nailed it down, Sonny. It made you work for it, but you stayed methodical and did one thing at a time and you finally got it. So few people willing to put in the real time to diagnose a problem before throwing parts at it in frustration.

FYI- sorry about the long delay in replying. My MC solenoid was just a tick over 20 ohms, so you're in the ballpark.

Sonny_T

thnx Damon.
----------
what a pain with heater core, but made it.
---------------------
Do you have gasket between catalytic converter and exhaust flange, if not will it not leak exhaust?
-------------------

Damon

Wow, you're really taking me back! I think it's just a flared-type union, no gasket (I'm talking at the back of the cat where it meets the intermediate pipe back to the muffler). Pipe is flared out, end of the cat stub is flared in at the same angle, the two connect, compress and seal "metal to metal".

naf

iTrader: (7)

the replacement L69 cat I installed last year came with two gaskets but it was a four bolt flat flange on each end.

Sonny_T

as 'naf' said, mine has 4 bolt flange and not flared. Some one in 'thirdgen' advised copper spray on gasket would be the way to. Factory ones had no gasket and made sense of flanges being smooth. But after so many years, not that smooth any more so gasket is the way in my case. It is done and working great with no issue.