code 42

[jimbil208]

Can anyone please help me.
1982 with code 42,I have replaced everything inside the distributor' I have replaced the electronic spart control module. The wiring diagram doesn't help me anymore. Does anyone have a wiring diagram? Can anyone tell me where to lok next?
Please help,Jim

 

[Rex S]

Can anyone please help me.
1982 with code 42,I have replaced everything inside the distributor' I have replaced the electronic spart control module. The wiring diagram doesn't help me anymore. Does anyone have a wiring diagram? Can anyone tell me where to lok next?
Please help,Jim

White wire to distributor shorted to ground, ECM going bad OR has corrosion on contacts. Clean the contacts with some contact cleaner and check all terminals for burnt/corroded conditions.

 

[jimbil208]

Thanks for the help,I replaced the ecm after having the trouble also replaced the spark control module behind the ecm,along with other things,someome said to check the knock sensor do you think that is a problem.The way it's acting,it doesn't seem like that to me.

 

[Rex S]

Is the car just throwing the 42 or is it acting up as well? Do you have a digital VOM (volt ohm meter)? If so I can supply you with some volt ranges.

 

[jimbil208]

I have a meter.
The car is not ideling properly.
It goes from a normal idle and drops slower.It goes back and forth that way util it stalls.If I throttle it it takes it very well,but if I hold a steady faster idle it starts to drop and go back also. Other than replacing all the parts that I mentioned,I just removed the wire from the sensor in front of the starter and it runs the same way,no change.

 

[wishuwerehere82]

A good way to test the knock sensor is to put a timing light on the #1 plug wire and watch to see what the spark advance is doing.
Whack the block with a ball peen hammer and the knock sensoe will see it as a knock and retard the timing. It will do it every time you tap the block. If it does nothing, then the knock sensor is probably bad already. The ceramic insulator tends to snap off the neck of the sensor, causing all kinds of erratic behavior.
Since you have already disabled the sensor, it sounds more like the spark advance is diong whatever it wants, or the CTS is sending the ECM some bad temperature readings. This is known as "hunting" where the ECM richens and leans the mixture based on engine temp. and TPS position at idle by opening and closing the IAC motors until it satisfies the O2 sensors. If the CTS is out of range, it will make the mixture too rich to run.

 

[jimbil208]

Thank You for the info.
Can you answer a few questions?
I received my gm 1982 corvette shop manual today.
There was a one page flow chart.
I did some of the tests that I could some need another person.
So I went through each test as if it failed.
In all I was instructed to change the ecm,hei,spark module,and controller.
Test about 4 wires between the distributor and ecm.
Every test passed,every wire tested continuity.
code 42 does not metion temp or knock sensors,although I heard other people mention that in this forum.
CVab you explain that to me please?
I am tired of testing and replacing things and nothing changes.
Please HELP_!!!!!!!!!!!!!!!!

 

[crowvet]

Code 42 can set because the main shaft in the distributor becomes magnetized. you will never get rid of the code unless you either replace the distributor or the shaft. Code 42 does not always have symptoms associated with it. I own and operate a auto repair shop and I would replace the distributor in this car. Best of luck

 

[jimbil208]

Thank You Crowvette and all others.
I have another question.
I replaced and checked wires on the trouble chart with no luck of course.
At one point someone mention the knock sensor.
What are the chances that could be a problem before I get into the complete distributor?
Again please help.

 

[wishuwerehere82]

Thank You for the info.
Can you answer a few questions?
I received my gm 1982 corvette shop manual today.
There was a one page flow chart.
I did some of the tests that I could some need another person.
So I went through each test as if it failed.
In all I was instructed to change the ecm,hei,spark module,and controller.
Test about 4 wires between the distributor and ecm.
Every test passed,every wire tested continuity.
code 42 does not metion temp or knock sensors,although I heard other people mention that in this forum.
CVab you explain that to me please?
I am tired of testing and replacing things and nothing changes.
Please HELP_!!!!!!!!!!!!!!!!

Here, read this on code 42 and possible causes.
http://www.crossfireinjection.net/ECM%20Check%20Engine%20Codes.pdf

More useful stuff
ECM troublecodes

eBay Guides - HEI Ignitions--A primer

http://www.corvettefever.com/techarticles/4688_chevrolet_corvette_efi_system_tuning/index.html


What it comes down to:
Nobody has the same exact problem everytime with the same solution.
A lot of us have had the same problems, so we can share.
Everyone and every problem is unique, in its own special way.
As Sherlock Holmes put it" when you have eliminated the impossible, whatever remains, however improbable, must be the truth.
This takes deduction, reasoning, a systematic methodology, and unfortunately time and parts.

 

[jimbil208]

OK,I have more information. The voltage on pin 10of ECM is supposed change from 0 volts to 5 volts when the engine in started.
It does not change,maybe it goes to about 2 tenths of a volt thats all.
That is the HEI BYPASS voltage. I metered the wire( a brown/black) from the ECM pin 10(circuit 424) to terminal C on the EST and it is ok. I replaced the EST and the ECM. Can anyone tell me,what tells the ECM to change from 0 volts to 5 volts when the engine is running?
I am searching on the computer and reading the manual and I haven't found where it comes from. Please Help.

 

[jimbil208]

ok,does anyone agree with this?
The ECM hei bypass lead on pin 11 of the black connector is at 0 volts when starting,when the engine reaches 400 rpm it changes to 5 volts sending the 5 volts to the EST on pin C. circuit 424. I am not getting any voltage there. The signal for this to happen comes from pin A on the EST. I am getting a signal there but the ECM is not changing pin 11 to 5 volts. This is a rebuilt replacement ECM that I installed. So it was one of the last places that I looked for the trouble, At any rate I sent it back for repair and I expect it to work when I get it back.
Does anyone agree or disagree? By the way,because of this the car is trying to run on regular timing not running on est,hei at all.

 

[jimbil208]

Sorry it is PIN 10

 

[Rex S]

All I can say is we have had really bad experiances with "rebuilt" ECMs. If you happen to find a really good rebuilder, let me know.

 

[wishuwerehere82]

I know that on my 82 the advance bypass wire was a solid wire, not with a connector on it. If you look at the article in Vette Fever about tuning the Crossfire, they make several jumpers to connect all the wires except the bypass wire. That's how I had to do it. It's the Brown Wire of the four wires on the harness that comes out of the distibutor housing and connects to the wire harness to the ECM (actually I just cut the wire and put a connector on it so I could disconnect it anytime I wanted to.)
There is wire with a connector on the distributor that is very easy to mistake for the Advance wire, but it doesn't do anything to disconnect the advance.
The EST is controlled by the ECM, and the Tach Feedback Lead off the distributor tells the ECM exactly when the coil is firing.
So make sure that you set the static base timing at 6 degrees BTDC at idle with the advance wire disconnected first. Otherwise the ECM will be trying to advance the spark far beyond or below its designed range.

Once the base timing is set, the advance will keep advancing the spark timing until a knock is detected by the knock sensor.
So it's very important to have the knock sensor hooked back up.
Once a knock is detected, the EST module retards the spark advance until a knock is no longer detected. Then it starts all over continuously while the engine is running to optimize the spark advance to the highest possible advance without detecting a knock.
You should have an advance range of 6 degrees BTDC at idle to around 36 degrees BTDC at 3200 RPM if the system is running as it should.

 

[jimbil208]

The black connector it on the ecm.
And the hei does send the signal to the ecm to change pin 11 from 0 to 5 volts that is what makes it work.