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E042 Help


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1) My original ECM looked brand new and only had 20K miles on it. But it kept giving the dreaded E042. Manual said to replace it.

2) The first one I received from Blue Streak on Rockauto acted totally strange. It set off chimes for no reason and made the throttle go crazy. Car wouldn't run unless I kept foot on the gas.

3) Second Blue Streak "remanufactured" ECM from Rockauto was corroded inside. I didn't even try that one.

4) Fourth ECM from Swanauto (I assume is a salvage yard) looked like it got run over by a truck, but it worked beautifully and I haven't had a problem since. Code E042 is gone.


As you can see, it took four tries to get a good ECM but I eventually got lucky. Since you purchased it on Ebay, you should be able to let the seller know it didn't work and they will send you a replacement at no charge or refund it so you can buy another.

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I got two additional used ECM one from 88 riviera and another one from a bonneville. These ones looked pretty good compared to previous ones I had. 

I plugged them in and I got the dreaded code again.


I swapped between magnavox and delco ICM. I noticed that with the magnavox coils it took 5 seconds to set the code while the engine RPM lowered. With the Delco ICM the code set instantly when the engine started. 

I do not think the EPROM is the issue because  I ran with the 88 riviera EProm and the E042 still came up in the CRT but not the instrument panel.


any ideas what else I should check? 

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I think Ronnie's previous post about the CPS signals not getting to the ICM makes the most sense. Would probably need an oscilloscope connected to Pin G and H would show which pin is missing the signal.

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I noticed that you tried all the ECMs with wrong PROMs. Have you tried transferring the correct PROM (ASSU) to the new ECMs?

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The ICM synchronizes the 18x and 3x pulses to time the first fuel control reference signal to the ECM and thereafter just sends that 18x signal for RPM determination and a separate fuel control signal calculated by dividing the 18x signal by 6 that determines crankshaft position. 


If either the 18x or 3x signal are not working, the injectors will not open and the car will not start because no fuel control reference signal can be generated. 


The 3x signal is used by the ICM at startup only and is not passed on to the ECM or used in any way after the engine starts.


Since the 18x signal is required in order to calculate engine RPM and crankshaft position, the engine won't run at all if that is lost. 

Edited by Anthony
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