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Intermitant code 42 by ltlfrari
Started on: 08-22-2010 07:25 PM
Replies: 4
Last post by: tbone42 on 09-12-2010 01:52 AM
ltlfrari
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Report this Post08-22-2010 07:25 PM Click Here to See the Profile for ltlfrariClick Here to visit ltlfrari's HomePageSend a Private Message to ltlfrariDirect Link to This Post
This is a weird one.
First up, let me say I know all about code 42 and how the ecm and icm communicate etc and how you get a code 42 when an expected signal is not where it should be during the startup and running phases so I'm not really looking for info on that aspect of things.

When I start the car the first time of the day (usually in the morning going to work) the CE light comes on (pulled the code and it's 42). If I turn it off and remove the key for about 5 secs and try again then about 50% of the time the CE light will come on again and 50% it won't. If the light comes on and I turn it off, remove the key, wait another 5 secs or so and then restart it, pretty much 99% of the time the light will NOT come on and the car is fine for the rest of the day. I can drive it to work (10 miles), park it all day, get back in it and it's fine, No CE light. Next day, same thing.

So!
It only happens on the first start of the day.
It goes away after a couple of starts.
I have no other problems/CE light issues.

So I am trying to figure out, why only the first couple of starts of the day, it's not like the engine even has time to warm up so I don't think heat is a factor. But also, how the heck can I diagnose this. Since it only occurs for such a short time I am at a loss as to how I can diagnose it.
I guess I could take the 'replace every connector and wire' for this circuit approach as a start just to be sure (new icm in there too so I don't think it's that) but anyone got any ideas as to how I can really dignose it other than do ONE test per day!

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Report this Post08-22-2010 08:13 PM Click Here to See the Profile for BloozberrySend a Private Message to BloozberryDirect Link to This Post
Did you try the diagnostic procedure on page 6E3-A-59 in the '86 service manual? Looks pretty simple to do but in your case it looks like it boils down to a faulty or corroded connection, or a chaffed wire on either the white wire or the tan/black wire between the ICM and the ECM. In summary, here's the procedure:

1. Disconnect the ECM connectors;
2. Switch ign to ON (engine stopped);
3. Probe the ECM harness connector pin B4 (white wire) with your ohmmeter set to 1000 to 2000 ohms range;
4. With the other meter lead to ground, it should read less than 500 ohms;
4a. If it doesn't, either the white wire is broken, has a poor connection at the ICM, of the ICM is faulty;
4b. If it does, then:
5. probe the ECM harness connector pin D5 (tan/blk wire) with one wire of a test light and the other wire on 12V and note the light:
5a. If the light turns on the look for a short to ground on the tan/blk wire, if it's not shorted then the ICM is faulty;
5b. If the light doesn't turn on:
6.with the ohmmeter still connected to the ECM harness pin B4 and ground, again probe the ECM harness pin D5 with the test light connected to 12V. As the test light contacts pin D5 the resistance measured on B4 should switch from under 500 ohms to tover 5000 ohms;
6a. If it doesn't, then disconnect the 4 terminal connector with the ohmmeter still connected... you should get infinite ohms. If not then the white wire is shorted to ground. If you do get infinite ohms, then the tan/blk wire is broken, has a poor connection at the ICM, of the ICM is faulty;
6b. If it does switch to over 5000 ohms, then reconnect the ECM and idle engine until the light comes on... if it comes on, then you have a faulty ECM. If it doesn't come on, then check the harness and connectors for an intermittent break or short to ground on the white and tan/blk wires.
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Blacktree
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Report this Post08-22-2010 08:40 PM Click Here to See the Profile for BlacktreeClick Here to visit Blacktree's HomePageSend a Private Message to BlacktreeDirect Link to This Post
 
quote
Originally posted by ltlfrari:

So!
It only happens on the first start of the day.
It goes away after a couple of starts.
I have no other problems/CE light issues.

If I had to hazard a guess, I'd say there's a loose connection somewhere that tightens up when the ignition system warms up. The two places I'd check first are the electrical connections on the ignition module, and the general condition of the tach filter.

On the module, check to make sure there isn't any corrosion on the mounting screws, or the part of the module that the screw heads touch (the module is grounded via the screws). Also, make sure the electrical contacts on all the wiring connections are clean.

If all that checks out, take a look at the tach filter. It has a few resistors and capacitors inside. And after a couple decades, they can start to go bad. Unfortunately, you can't just pop it open and solder in new components. But you can try swapping in a known good one, or temporarily replace it with a jumper wire.

Best of luck!

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ltlfrari
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Report this Post09-11-2010 11:09 PM Click Here to See the Profile for ltlfrariClick Here to visit ltlfrari's HomePageSend a Private Message to ltlfrariDirect Link to This Post
It was the ignition module. Car died on the freeway the other night. Swapped in a spare and the car fired right back up and no more CE light for the first start of the day.
Motto: Always carry a spare module and the tools to change it!

New spare on order to replace the one I just used.

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tbone42
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Report this Post09-12-2010 01:52 AM Click Here to See the Profile for tbone42Send a Private Message to tbone42Direct Link to This Post
Just had the same problem.. SO GLAD its finally over. Unfortunately, I noticed the distributor is gonna need an o-ring change now. Going back in, coach!

[This message has been edited by tbone42 (edited 09-12-2010).]

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