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Discussion Starter #1
'82 Elky code-setting bizzaro!

Ignition-off tests at brown wire on MCS connector:

ECM plugs connected, fuse out = grounded.

ECM plugs disconnected = grounded.

ECM plugs connected, fuse in = grounded.

Ignition-on tests at brown wire on MCS connector:

ECM plugs connected, fuse out = open ground.

ECM plugs disconnected = open ground.

ECM plugs connected, fuse in = open ground.

Symptoms: MCS clicks fine during “hairpin” code check. It does not click at all when the ignition is turned on, maybe having something to do with the above ignition-on test results? Why would the circuit work with the hairpin test but not when the ignition is turned on?

This thing has been setting code 21 forever, code 41 has set occasionally, and this morning code 23. All have been intermittent, but now the 41 and 23 are persistent. I bought the car 3 weeks ago taking on the responsibility for smogging it. It has a fairly fresh 350 crate engine and has passed smog every two years up until now. I have replaced the carb, cat, and yesterday, the ECM. After I replaced the ECM, no more lights for a few hours (My euphoria was short-lived!) and then it reverted to its old behavior.

BTW, where is that green MCS dwell-test connector? There's a bright green connector in that harness, but it is located on the passenger-side inner fender, near the AC accumulator. There is no sign of any such connector “in front of the carb.” Any way of testing if this is the right one?
 

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Discussion Starter #2
More on that MCS diagnosis . . .

Also, when the ECM is disconnected from its plugs, pin 18 shows open ground.
 

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that's good that it see's the mcs now, if its not clicking with the key on engine off,,
[you know it only clicks for a few seconds when you turn the key on?? right???]

check the grounds for the tps and mcs,, should be in front of the carb there somewhere,,
trace the grounds from the plugs..

MCS clicks fine during “hairpin” code check. It does not click at all when the ignition is turned on,
maybe the ecm uses a different ground for the test and run???

can you check the wire color on the green dwell connector,, and compare to a diagram??

what is pin 18?? I don't have my manuals at home..

one thing I don't know if you know,,
be care full with the power to the ecm any time the key is on,, batt cables,, jump cables, charger,,
ecm plugs,, ang grounds too I guess??
don't pull or replace the fuse with the key on,, somehow it makes a difference??

im just guessing here and thinkin outloud now Skip..
 

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code 21 is TPS switch I'm a pro at that. code 41 no dist. ref. are the two plugs behind the dist. plugged in? MAP or VAC sensors check the connections and vac. to the MAP sensor. Check the plugs at the ECM also. Check the voltage at the MCS and ground. same at the TPS top wire to ground 5v middle wire should read key on engine off warmed up .48v and 4.8 at WOT. bottom wire ground. Check fuses #7&8 are ECM.

MAP test unplug with key on + gray wire -BLACK ON THE PLUG 5V

There's a bright green connector in that harness, but it is located on the

this is the BARO. SENSOR


Recheck all connections disconnect the battery for a few min. and then take a drive.




 

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Discussion Starter #6
Pin 18 is the terminal that grounds the MCS. Or at least I've read that several times here so I'm assuming it is the TRUTH! :}

The code 41 keeps coming back even after everything else stays clear (for a while). I have removed, cleaned and reconnected every plug anywhere near the distributor, including the module plugs inside. I have not tested the resistance of the module. That's next and I sure hope that's not the problem as I REALLY don't want to have to pull the dist.

Oh for the olden days. Distributor: 1 wire, one vacuum line. Period. I liked that! (But then, hey, I'm old!)

Regarding the green plug, mine looks just like that, has two pale green wires coming out of it, but it is over by the A/C evaporator on the inner panel. Maybe they did that so it can be tested with the air cleaner installed? Still not sure it's the right one.
 

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One thing I had to do was the connector to the ECM wasn't making good contact so I had to wedge a piece of plastic under the bottom top END of the ECM the larger plug to get my code 21/24/41 to go away I just did that today and all my codes are gone!!!!!!!!!!!!! :cussing:


I COULDN'T GET RIDE OF THOSE CODES WITH MY 87 ECM so I installed a 84 Monte SS ECM today and fixed my connection problem at the connector and ECM I been fighting these codes for months and it's the board worn down and not making contact with the plug.

I don't know how I never touched the ECM sense the truck was new but it was worn down and not making contact??????
 

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Discussion Starter #9
I keep seeing "check the MAP sensor." I thought '82's did not have an actual MAP sensor and that this check was done at the vacuum sensor? Correct?

I'll go over that diagram. I just check the pickup coil resistance. It's 946 ohms, within shop manual specs. But the terminal that is supposed to show "infinite resistance," which I assume means ground, is open.

Any ideas on that?
 

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Discussion Starter #10
Bad pickup coil, for starters.

I just did the trouble-shooting diagram in the shop manual for a code 41 and it led me to the pickup coil. Mine shows no resistance across the terminal, no resistance from the green wire to ground. Both of these tests show a bad pickup coil. So hey, one more item to replace in this endless guessing game. While the dist is on the bench, I guess I might as well replace the module, too, right? Oh yeah, the magnet on top of the pickup coil came out in pieces. I hope I can even find one of those!

Stay tuned . . .
 

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wtg finding the pickup, you can piece it back together or get a whole distributer..
ac delco rebuild 150$ http://www.rockauto.com/catalog/x,carcode,1042625,parttype,7108

yes you have a map on the intake,, and maybe a baro on the fender.. but you don't have a map code..
the map is the vacuum sensor,, baro is pressure sensor..:wink3:
 

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One thing I had to do was the connector to the ECM wasn't making good contact so I had to wedge a piece of plastic under the bottom top END of the ECM the larger plug to get my code 21/24/41 to go away I just did that today and all my codes are gone!!!!!!!!!!!!! :cussing:


I COULDN'T GET RIDE OF THOSE CODES WITH MY 87 ECM so I installed a 84 Monte SS ECM today and fixed my connection problem at the connector and ECM I been fighting these codes for months and it's the board worn down and not making contact with the plug.

I don't know how I never touched the ECM sense the truck was new but it was worn down and not making contact??????
Tomorrow when I pick up my parts, I'm gonna install the new pickup coil and ign module, both of which were implied as questionable in my carefully-followed shop manual trouble-shooting diagram. Then, yeah, I will make sure the ECM plugs ar mashed tight. I think I'll go in there and clean each contact, too.
 

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Tomorrow when I pick up my parts, I'm gonna install the new pickup coil and ign module, both of which were implied as questionable in my carefully-followed shop manual trouble-shooting diagram. Then, yeah, I will make sure the ECM plugs ar mashed tight. I think I'll go in there and clean each contact, too.


Make sure the battery is disconnected before messing with the ECM. I THINK I HAVE AN EXTRA IGNITION COIL AND MODULE 82/87 SAME??

Does your mod. have the two plugs behind the dist. or one big sta-kon both sides. On the coil are you talking about the one with the spark plug wire to the dist. cap? Probably not I don't think the truck would start.

IU have sensors coming out my ears new installed once and the ones I took out that are probably just as good.

I pay it forward when I see someone like you spending $$$$$ I know how it feels and a little help makes me feel good.:baa:

Took this picture in the mountains today.


 

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Discussion Starter #14
Thank you everybody! WE PASSED SMOG TODAY! After only about two weeks of non-stop frustration, I carefully assembled all the info I got from you guys and finally, last night, I got the thing to stop setting codes. The end of hours of trouble-shooting paths out of the factory shop manual led me to an intermittent distributor pickup coil and a failing ignition module. I replaced both and the code 41 set again. So I remembered what one of you guys said about sometimes you need to "reboot" the ECM several times to finally dump a code. I did, and it hasn't come back. Went to get the smog check today and sat there all angsty for an hour and it passed!

YES!!!!!

Thanks again, Forum Guys! Couldn't have done it without you, and I sure know a lot more about these things now than I did a few weeks ago!
 

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wtg Skip
I think that makes you the expert now..
the mcs is working now with the key??


Robert the 87 is different, you have the small cap hei..:infinity:

Ok his is built in the cap.
 

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Discussion Starter #17
MCS working, but . . .

The MCS is working, but there is no clicking when you first turn on the key. Once the engine starts, you can hear it doing its thing. Since it does work when the engine is running and the emissions tests came out great, I'd like to assume that it is working!

Here's an interesting twist, but probably not unusual. The very nice guy who runs the smog station said it came through all the emissions tests great except the timing was not within specs. Since he is also a repair facility, I asked him to just give the distributor about a 2* clockwise twist and check it again. Right on this time, he said, but now since he made that adjustment he was required to re-run the emissions tests. He did, and it passed again, but this time just barely. I had set the timing for best performance, and he even told me that it ran better before he reset it to THEIR specs, but since it passed, just tweak it when I get home. I did! So now I'm legal but polluting more than if I could tune for performance. Go figure.
 

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Discussion Starter #18
More on that MCS

When I ran a whole series of tests on the MCS, every one of them showed that there was no 12v to the MCS with the ignition on but the engine not running. With the engine running, the 12v was there. Maybe that's why it has a tough time running smoothly on cold start? Once it's running for a minute, it's fine. I don't understand everything I know about these things. :)
 
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