1988 Chevy Silverado code 42

It seems that code 42 is related to the ground of the control module mounted on the distributor. Now what I need you to do is disconnect the 4 pin connector to the distributor and use the pic below to find pin A and check it. What you do is use a digital multi meter and ohm between term A and gound is there continuity? Get back to me with what you find. We will check the ESC Module next if this checks ok. I do need to know what size truck 1/2 ton or ? and what engine as the 305 has a different ESC then the 350 and so on.

do i check on the ign module or the connector side ?

the eng is a 350. 1/2 t

checked the a term. on the ign module, checks ok

Ok so I need you find the ESC module shown in the pic below. Before we get to far with this I also need you find the knock sensor on the passanger side of the engine block see pic. Now hook up a timing light and tap the block with a hammer near the knock sensor what does the timing do? ESC Module,

Knock Sensor,

well i haven't been able to do that knock sensor test,nobody around to give me a hand, i can't hammer on the blk from the top to much in the way, so i just replaced it, along with the map sensor.
it's kind of frustrating it runs great with the set timing connector off. could it be a worn out dist. it has 250K plus mi. on it?

solved the problem myself dist. is shot.

So the distributor shaft was worn? Great job glad it is fixed. Have a great day.

I would like to know what code 42 means, that is the code that keeps comming up on my truck. it is hard to start and when it does start it will run fine for a little while then the check engine light comes on and it runs real rough and it starts back firing and then after a while it will take off and run like a new one for a little while and then it will act up again. I have had a tune up put on it a new ecm, new mapp sensor, ect.

DTC 42 Electronic Spark Timing (EST) or Bypass Fault

I have a 90 Chevy Silverado, 5.7 Truck is running sluggish, has a code 42, with vehicle running I unplugged the EST wire and it almost died so i would say its getting a good connection between the distributor and the ECM. I replaced the module in the distributor, still runs the same. Not sure where to go from here.

Do you have a multimeter to do some testing?

yes

Yes I do

I posted the wire diagram and troublke tree for you follow them and let me know what you find.

When I conect the temp unit it wont idel in gear, But if I disconect the temp unit it will idle fine when in gear, ANY IDEAS IM RELLY GRASPING FOR A ANSWER, the codes show a 15 it is the temp unit

Saturntech9, I'm not able to read the text in the diagrams, real blurry and blotchy

Code 15 is Coolant Sensor Signal Voltage Low.

When the ECM gets this signal, it would think that the engine is cold and would induce a richer fuel supply hence the poor idling. Did you replace the sensor and/or checked its wiring? It could be the sensor, its wiring or ECM fault.

I replaced the unit by the thermastat housing (auto zone), same thing wont idle in gear, I replaced the ecm, still the same

Are you still getting the same code?
Did you test the wiring?

checked wiring all ok, still getting same code 15,,,,new info ,,,,sometimes it will idle fine other times it will not

Well, I think I got it, I started looking at the wires and all the connections, and noticed that the EST wire had a flat spot in it from being pinch under the black cover that covers all those electrical goodies on the firewall. so I replaced that section of wire, cleared the code, drove it around for a bit, seems to be fine now. I even checked the timing again just to make sure. And yes I cleared the code again after I check the timing. Thanks guys for your help.

This means the problem is most likely intermittent and could be due to a loose wire, ECM or the charging system.

The chart below shows how to go about testing the circuit.

Your welcome thats what were here for nice find.Hope you have safe and happy new year.

Hi
I borrow this thread, hope it´s OK. I have the same problem with my TBI code 42. And I have checked the Pin A blk/red from the control module to ground and theres no ground there.. is my ECM bad or can i hook this blk/red cable directly to ground and see if this solve my problem?

Yes, try to introduce a new ground to see if that fixes it. If not I would try a used/rebuilt ECM. Please let us know what you find we are interested to see what it is.

Cheers, Ken