Error Code 42 Ignition Bypass Circuit Error

[Tom Stacy]

Has anyone experienced this error code on their Esprit? Symptom is after starting, idles high, drops to 1200-1400RPM, then sputters and eventually stalls. Did this to me while driving for 10 minutes or so. Read code as DTC-42 : Ignition bypass Circuit error. I thought about replacing the IAC and TPS since both could cause this condition, but error code tells me that it may be ECM related. Any thoughts from experience out there?
Thanks.
Tom S.
'89 Lotus Esprit Turbo x180

[Erikl]

Curious what that code means?  If you look in the service manual I think there is a list of things that could be wrong for each code?  I think that is how it works.

[Bibs]

There's a list of the error codes in the Freescan manual which is available from here...

https://www.thelotusforums.com/freescan_manual.pdf

Code 42 ELECTRONIC SPARK TIMING (EST) CIRCUIT Ignition module sends a reference signal to the ECU when engine is cranking or running. When under 700rpm. The ignition modules controls the ignition timing. When the engine speed exceeds 700rpm the ECU send a 5 V signal to switch the timing to ECU control. An open or ground in the EST bypass circuit will set a Code 42. Engine will run in “limp home” or “bypass” timing.

[Tom Stacy]

Tested EST circuitry, no opens or shorts. Ran Freescan, reviewed data, nothing out of the ordinary except IAC stuck at 170. Swapped IAC, ran freescan and found no longer stuck but error 42 still persists with rough idle and stall. Removed ECU, swapped out with spare unit and installed MemCal chip. Started car, idle immediately leveled out at 1350RPM, with no stalling. Faulty ECU was the issue for code 42. Will buy another spare on EBAY to keep on hand.

[Erikl]

Also, i believe Esprit engineering will rebuild the old ECU.  Probably not inexpensive how ever.

[Tom Stacy]

Probably not inexpensive as you say, but they are cheap enough and available on EBAY. I found one (#1228707) for under $25 and free shipping. Can't beat it, worth the investment for future insurance.

TS

[lovemonkeysd]

On 15/10/2023 at 08:19, Tom Stacy said:

Tested EST circuitry, no opens or shorts. Ran Freescan, reviewed data, nothing out of the ordinary except IAC stuck at 170. Swapped IAC, ran freescan and found no longer stuck but error 42 still persists with rough idle and stall. Removed ECU, swapped out with spare unit and installed MemCal chip. Started car, idle immediately leveled out at 1350RPM, with no stalling. Faulty ECU was the issue for code 42. Will buy another spare on EBAY to keep on hand.

Hello,

I have a 1990 Esprit SE. The check engine light recently illuminated, so I jumpered A and B of the ALDL, and code 42 was the result of the check engine light flashes.

I drove it for about 15 mins, and the only thing that seems wrong is the boost gauge needle barely moves now. It used to show correct boost. I didn't want to drive it further with the check engine light on. 

Can you please educate me on how to test the EST circuitry? I don't know where to start.  I don't have freescan.

I really appreciate any help.

Thank you, 

Dan

Edited July 20 by lovemonkeysd

[Tom Stacy]

Hi,

    Error code 42 denotes Ignition bypass circuit error. Mine was associated with a faulty(original) ECM unit which I replaced from a 1991 chevy beretta. Detail troubleshooting is available in the Lotus EMH service manual which I included for your discretion. Freescan is a useful diagnostic tool free to download, also included. You will need to reach out to SanJ to obtain the interface cable for ALDL to laptop interface. His email is <turboesprit@earthlink.net>. He also sells them on EBAY.

 

     ECU removal is shown here and also on Youtube. http://www.lotusespritworld.com/EGuides/EModifications/chip_install.html

Lastly, I picked up a spare '91 chevy beretta ECU on EBAY, had SanJ program the EEPROM, then installed it into the circuit and plugged it in to validate functionality. Now I have a spare unit in the event that I need to replace the unit in the future.

Good luck,

Tom S.

Section EMH - Electronic M.P.F.I. With Chargecooler - B082T0327Z.pdf freescan_210.zip

[lovemonkeysd]

Thank you for replying!

I will look at section EMH. I have a partial manual, and it doesn't have that section, so thanks. 

Is that connector a 15 pin, 3 row connector? I have an old laptop running windows xp that has one. Will that port work?

Thanks,

Dan

Edited July 20 by lovemonkeysd

[fjmuurling]

The port (15 pin Sub D) in the above picture is for connecting a (VGA) Monitor.

Any more ports on the laptop? Ideally you need a 9 port Sub D port for connecting the interface.

 

[fjmuurling]

First of all I would be checking the wiring between the DI module and the ECU. Make sure the connector pins are clean and not corroded / dirty etc.

[Tom Stacy]

You need to attach the cable to a USB port on your laptop. Look at the picture below and you will see there is an interface cable that converts from serial (DB9) connector to USB. You can order this from SanJ on EBAY here:  https://www.ebay.com/itm/175448207955?itmmeta=01J3AEQNWFN72M3EFY1CJQ94D4&hash=item28d9873253:g:u44AAOSwgVdfZjYW&itmprp=enc%3AAQAJAAAA8DoVo2cWm9pJ1hxrlUnksw00EvIvmZ94yE5I49lL9CFQSuOOXgi1f6MqJRGzbdrTSLt%2BkzXsS72dk%2BUhxrbg38BT2GWELAIvbTzPDRp2Lp5puAFOQ9AuPGCMf66pvwcmISSGEJYGsCtRBxTGmtugEtXzAf9hHmNVNj4T%2BxeZfFvexspRwcrYZBA7Tbly9qL7wkXWnARjUrUhIbqxuw6c2auo%2Bof2qGxIfWtskBcE0D4aO6cis%2BJJbkFhZMwlwuXUZK3hD%2BBLnCkIkLYCae7GPddtrGOdjPP1mcEL0KXLMtQ8GaijPaBMeP20vG5O30TisQ%3D%3D|tkp%3ABk9SR6je3s6aZA

 

[fjmuurling]

Even better, 2 options, serial port (9 pin) or USB connection.

 

[lovemonkeysd]

Thanks for the replies!  My old laptop doesn't have any other ports than usb, so I'll plan on using that, or my newer laptop (it only has usb ports, too).

I followed the instructions in section EMH, the circuitry tested properly, and the Check Engine Light still illuminated. So, it indicates the ECM is faulty.  I found one, #01228708, on ebay, so I've ordered it.  I'll update after I have installed the new one.

The interesting thing is the car seems like it's running fine, even though the CEL light is on.  It accelerates normally, and the turbo kicks in like normal.  The only difference is the boost gauge barely moves when the turbo kicks in, and it used to indicate proper boost.  I didn't read anything in the code 42 section that referenced the boost gauge.  The car isn't in a 'limp' mode at all.  I just wonder if there's a slight error in the signal for the spark, not enough to notice while driving, but enough to cause code 42.

I'll wait for the new ECM, which says it's from a 1990-1991 Pontiac, but written on the ECM in the pictures it says 90 Cutlass.  Some searching made it sound like the Pontiac, Cutlass, and Esprit SE all use the same ECM.  The pictures show the same connector ports that my ECM has.  After installation I hopefully won't have a CEL anymore. 

P.S.  I ordered SanJ's cable, too.

Edited Monday at 05:49 by lovemonkeysd

[Tom Stacy]

Remember to swap out the Memcal chip from your ECU into the "new" ECU. Use proper grounding when doing so. You may want to search this forum for "turbo boost" and see if there are any other threads on this topic to aid in your troubleshooting.

[Chillidoggy]

The boost gauge is not connected to the ECU. The MAP sensor supplies boost information to the ECU.

[lovemonkeysd]

Tom Stacy, yes, I definitely will remember to swap the Memcal chip.  I knew that, and have already read the procedures for doing so, but I'll take a reminder any day. Thanks!

And Chillidoggy, thanks, that explains some things.  After doing the diagnostic procedures for code 42, I got an intermittent code 34, which is the MAP sensor circuit that you said.  I'll diagnose that after I get the replacement ECU.  I'm hoping it doesn't come back.