Error code 42, no spark

Tiny
94_K1500
  • MEMBER
  • 1994 CHEVROLET SILVERADO
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 216,000 MILES
I drive the truck listed above k1500. My truck shut off on the road and threw a code 42. The engine will crank but I get no spark. I have replaced the ECM, the battery (which was dead), and every ignition component except for the distributor. A friend of mine thinks it is throwing a false code and I need to replace the distributor, but I want to get opinions from anyone I can before throwing more money at it.
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Saturday, November 30th, 2019 AT 3:00 PM

28 Replies

Tiny
DANNY L
  • EXPERT
Hello, I'm Danny.

I've attached a step-by-step picture diagnostics for Code 42 below. This will help you to troubleshoot before buying more parts or something else. Hope this helps and thanks for using 2CarPros.
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Saturday, November 30th, 2019 AT 6:39 PM
Tiny
94_K1500
  • MEMBER
My apologies for taking so long to reply, but it looks like these instructions require for the engine to start. I have no spark at all thus the engine wont run at all in bypass mode or not. If I'm missing something in these instructions please let me know thanks!
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Thursday, December 19th, 2019 AT 6:02 PM
Tiny
AL514
  • EXPERT
Hello, code 42 is referring to the EST bypass circuit, it is the tan/black wire in this diagram. This wire controls the timing advance from the ecm. The ecm is seeing an open circuit or short to ground on this wire. So you're going to have to check this wire from the ignition module to the ecm before changing anymore parts. If this wire is touching the frame somewhere or is broken it is going to mess with the ignition timing and cause a no start.
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Sunday, December 22nd, 2019 AT 5:46 AM
Tiny
94_K1500
  • MEMBER
I'm currently living 45 minutes away from where muly truck is (because of Christmas vacation) but i'm trying to go to a nearby salvage yard tomorrow to pull and entire engine wiring harness, which contains the wires from ECM to ICM. Is replacing the entire harness myself a good idea?
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Monday, December 30th, 2019 AT 5:30 AM
Tiny
AL514
  • EXPERT
Well, it would probably take more time to replace an entire harness, than fix the one wire that's shorted out. The EST is the wire by the distributor that has the little plug you would take out to set the base timing. What you would want to check is anywhere the harness has a contact point with the engine or chassis. These are the spots that wear threw because of vibration from the engine. I would go after a single wire versus changing the whole harness. Try unplugging the est timing plug and see if the truck starts, let me know if it does. It's the tan/black wire.
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Tuesday, December 31st, 2019 AT 2:58 AM
Tiny
94_K1500
  • MEMBER
I tried unplugging the tan and black wire like you said and still couldn't get it started. What's next? Is my next step still replacing this wire? If so how hard will that be i'm not a wiring expert and actually hate doing anything with wiring normally, but I want to fix this without hiring someone else if possible. Also I talked to a person at a local AutoZone and he said any wire running to the ECM should be grounded but when I checked every wire I checked was hot. I do not know if this means anything but could it possibly be that my ECM connectors are shot?
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Wednesday, January 8th, 2020 AT 9:02 AM
Tiny
AL514
  • EXPERT
Okay, so going back to your original post, you said you've replaced everything except the distributor. It sounds like the pick up coil in the distributor is bad. Do you have an automotive test light? I can explain how to test the pick up coil with a test light. There's a purple/white wire coming from the ignition module, with your test light hooked to battery negative, and back probe this wire, your test light should pulse while cranking. I'm assuming you have replaced the ignition module as well?
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Wednesday, January 8th, 2020 AT 10:56 AM
Tiny
94_K1500
  • MEMBER
With my truck still at college almost an hour away itll probly be a couple days before I can get to testing that because im working full time during xmas break but if I do and the pickup coil is bad then it will be as simple as replacing that without having to do a bunch of wiring right? Ive lifted my cap a couple times but never really took time to look at the pickup coil. And do you reccomend getting a brand new one or would that be a part im as well off getting from a salvage yard? Thanks!
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Wednesday, January 8th, 2020 AT 4:32 PM
Tiny
AL514
  • EXPERT
The pick up coil is located inside the distributor, so getting a remanufactured distributor from the parts store is the safest bet. A junkyard distributor will not last long. Also take off the distributor cap and make sure the distributor spins while cranking. Since you've replaced every part except the distributor, that's most likely the issue, you can test the ignition coil to see if there's a signal. Test light connected to battery positive, and the negative side of the ignition coil should pulse while cranking. Same as the purple/white wire at the ignition module, this wire should pulse while cranking as well. Test light connected to battery negative. These tests will give you direction in diagnosing this. Also check the engine to body ground wires and make sure there's no corrosion or bad connections.
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Wednesday, January 8th, 2020 AT 6:07 PM
Tiny
94_K1500
  • MEMBER
I also must have forgotten to mention that I have checked my coil for spark (disconnected the coil to distributor wire and put a spark plug in it and held it against the engine block to see if it sparks) and couldn't see any spark. I don't know if I just missed it or if I did it wrong but it seems like the problem is somewhere before the distributor possibly. The ignition control module was the first thing I replaced BTW.
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Wednesday, January 8th, 2020 AT 6:27 PM
Tiny
AL514
  • EXPERT
The pick up coil in the distributor is the main input for spark and fuel injection. If you connect your test light to battery negative and back probe the purple/white wire at the ignition module, you should get a pulse on the test light while cranking. This is the reference high signal wire, if there's no pulse then most likely the pick up coil is not functioning. You should also get a pulse on the negative wire of the ignition coil.
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Saturday, January 11th, 2020 AT 9:17 AM
Tiny
94_K1500
  • MEMBER
Okay, so upon inspection I found the pickup coil was bad. It was a stock coil so it was riveted instead of screwed but no problem I just replaced the whole distributor. Now I have spark but i'm not getting fuel. My guess is I just haven't ran the truck in so long the fuel pump went bad but i'm looking for any tips and or suggestions. Thanks!
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Tuesday, January 14th, 2020 AT 9:46 AM
Tiny
AL514
  • EXPERT
Good to hear, those pick up coils go bad pretty easy. How long has it been since it ran last? I would think if it's been over a year, it just has bad gas. Replacing the fuel filter and some fresh gas might be all you need to do at this point. You can run a fuel pressure test to rule the pump out. There should be a test port on the fuel rail.
https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator
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Tuesday, January 14th, 2020 AT 10:34 AM
Tiny
94_K1500
  • MEMBER
It has been about 6 months since it ran. I was able hear the fuel pump kick on just last week but today I couldn't. Would a bad filter cause it to stop pumping?
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Tuesday, January 14th, 2020 AT 4:23 PM
Tiny
AL514
  • EXPERT
It can be a number of things, but doing a fuel pressure test is where I would head next. There could be a corroded fuel pump relay that's not working any more, any number of power issues. You can actually rent automotive tools, like a fuel pressure test kit. From AutoZone and advanced auto. You just have to pay the price of the tool, but they give you your money back when you return the tool. Making sure your fuel system is functioning correctly is crucial. A fuel filter issue will show up on a pressure test.

https://www.2carpros.com/articles/how-a-fuel-pump-works
https://www.2carpros.com/articles/how-to-change-a-fuel-filter
https://www.2carpros.com/articles/how-to-test-a-fuel-injector
https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator
https://www.2carpros.com/articles/how-fuel-injection-systems-work
https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester
https://www.2carpros.com/articles/how-to-use-a-voltmeter
https://www.2carpros.com/articles/how-to-check-wiring
https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit
Here's some extra information to help diagnose this no-start issue.
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Tuesday, January 14th, 2020 AT 4:51 PM
Tiny
94_K1500
  • MEMBER
I'm going to do a pressure test this weekend. I just want to know this in advance so i'm not having to wait for a reply after the test. If the pump is not working will the gauge show 0 after attempting to prime the pump?
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Thursday, January 16th, 2020 AT 4:37 PM
Tiny
AL514
  • EXPERT
It can show 0 psi or close to it, depending on the problem. The 2 second prime is actually a different electrical circuit, so you want to make sure you have cranking pressure as well. If there's an electrical problem you may have the prime but no cranking pressure or the opposite. If you have 0 psi, you'll need to check for power and ground back at the pump connector, if there's no power (12 volts) back at the pump, you'll go to the fuel pump relay next and so on. If you don't hear the pump prime, which you should, you can go right to the pump and check for power. Bang on the fuel tank as well, it may kick start the pump while cranking. If it starts while banging on the tank, the pump will still need to be replaced. Anything else you might question during these tests?
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Friday, January 17th, 2020 AT 10:35 AM
Tiny
94_K1500
  • MEMBER
I think that's it because I have replaced the filter and put fresh gas in it and still got no fuel and I couldn't hear the pump kick on. So i'm guessing it's the pump because I have also checked the relay and fuse. I'm sure once I do the test I will realize there is something else I forgot to ask, lol. But for now I think that's all. Thank you so much you've been a huge help in trying to get this old girl back on the road!
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Friday, January 17th, 2020 AT 11:17 AM
Tiny
94_K1500
  • MEMBER
I actually do have one more question. If I do go after the fuel pump how do you recommend doing it? I have watched videos on both pulling the bed back and dropping the tank. To me dropping the tank seems like an easier method but I have also seen people cut a hole in the bed. Cutting the hole seems simple enough and easier for one person but do you recommend it?
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Friday, January 17th, 2020 AT 11:35 AM
Tiny
AL514
  • EXPERT
I don't recommend cutting any holes in anything, especially around fuel vapors. You could end up with a fire, just not safe. Dropping the tank is recommended way of replacing the pump. But make sure you have power at the tank while cranking, you could end up changing the pump and not fixing the problem. Just to be sure.
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Friday, January 17th, 2020 AT 2:28 PM

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