Anyone familiar with Code 42??

[TireSmoke420]

alright guys heres the whole story. original engine in my 87 ran awesome it would light the tires up whenever it pleased with no hesitation. i lent the truck to a friend and got it back with a cracked head. since then i have replaced the engine 2 times. first time was a remanufactured engine this time its a junkyard motor. sister was driving the truck when it lost compression on the #7 cylinder took the whole motar apart looking for a problem found nothing but that motor is in the past. i got the junkyard motor put in 3 days ago or so, and it keeps popping up code 42 the last motor the remanufactured on did this too. its what we think ultimatly screwed the last engine. code 42 is when the distributer cant comunicate with the computer and therefore it does not advance the timing. also it only kicks the check engine light on when going up a hill or when ya stand on the gas. now i have totally rebuilt the distributer...module and pickup coil. can any one this of anything else to check?

[killthewabbit]

42 is the answer to Ultimate Question of Life, the Universe, and Everything.

Sorry, TireSmoke. I don't really know. I was just hoping to make another geeky truck person out there somewhere shoot coffee out their nose.

[Captkaos]

Have you set the timing to 0 with the bypass disconnected?
If you are getting code 42, you are running on base timing plus whatever advance is built into the module, the computer is no longer controlling the timing.

Check this link:
http://www.troublecodes.net/articles...ndrstd42.shtml

[rfmaster]

Tiresmoke

Code 42 is one of the more common codes that is often difficult to diagnose. Scanner tools are of little help since the problem is in interface between ECM and dizzy. Troubleshooting code 42 requires some understanding how EST system works.

When engine is being started, RPM<400 ECM keeps ignition module in the bypass mode by applying 0 volts to by pass wire. In this mode the reluctor coil signal is being amplified by the ignition module which energizes ignition coil primary windings. ECM does not provide any timing correction in bypass mode, as amount of ignition timing is fixed into ignition module.

With the voltage low on the bypass wire, the EST is pulled to ground through a resistor in the ignition module. This keeps the voltage on the EST wire at around 300 mV. When the ECM sees the RPM over the run threshold (that's the DRP signal being received from dizzy), it will then apply 5 volts to the bypass wire that will activate the solid-state SPDT switch built into ignition module. This in turn will switch the EST from ground to the base of the transistor that controls the ignition coil's primary winding. In this mode, the primary coil winding is being triggered by the altered signal sent out from the ECM. The ECM will alter the signal to the ignition module and control the timing based on the inputs from various sensors. This is referred to as the EST mode.

Troubleshooting EST problems will require DVM for other checks that can be made when working with an intermittent Code 42. With DVM measure voltage on bypass wire, there should be 5 volts. On the EST wire, with the engine running, there will be close to 2.3 volts. The EST is a 5 volt on/off digital signal, so with a volt meter you will see the average of the high and the low. With the EST signal being a digital on/off signal, if you have a meter that will read in Hz, you can also pick up a Hz reading on the EST wire. Normally, you will see about 28 Hz with the engine idling and will increase with RPM. If the EST circuit would become momentarily grounded, or open, the engine will cut out. The voltage reading will jump down to as low as 1.3 volts and the Hz reading will jump from as low as 17 to 128 Hz. If there is a problem in the EST circuit, the voltage on the bypass wire will not change. If the bypass wire is momentarily grounded or open, the reading on the EST wire will be the same as if it was grounding or going open, but unlike a problem on the EST circuit, the bypass voltage will be pulled low if it becomes grounded or goes open. If this happens fast enough, the engine will cut out. The voltages will vary, but the SES light will not come on and no codes will be set.

With the EST circuit open, engine running, the voltage will stay low on the bypass wire and the ECM will not put out the 5 volts. With the EST shorted to ground, the voltage on the bypass wire will be high (5 volts) for a very short time (three seconds or less) then the ECM will remove the 5 volts. Using a min/max on the DVM is the best way to see this voltage. With the bypass open, the EST circuit OK, the ECM will put out the 5 volts. By using a DVM on both the EST and bypass wire, you can tap on the ECM, wiggle and tug on the wiring to see if the voltage or Hz reading will change. If it does, this is an indication that you have located the problem area.

Since your truck is 1987 I would suggest getting a spare ECM - these are widely available (1227747) and inexpensive - just make sure that it came out of V8 application and you can always transfer EPROM from your original ECM to keep emission calibrations the same.

//RF

[TireSmoke420]

sounds like a nice long night in the garage is in my near future... dang i hoped itd be simple from what i just read it sounds like i should be taking it to a computer repair shop lol. now i read something there about emissions calibration i dunno if i mentiond or not i took the emmission stuff off