Author Topic: Intermittent OBD1 Code 42  (Read 5192 times)

Offline Jon87V20

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Intermittent OBD1 Code 42
« on: July 28, 2018, 07:45:21 PM »
Hey, guys.

A while back, my '87 Suburban V20 w/ 5.7 threw a Service Engine Soon light on me and was running really rough. When I checked the code, it was a 42. I replaced my ignition control module and that seemed to clear it up and it has been running pretty well.

Over the last few weekends I replaced all my front brake components (calipers, pads, rotors/hub assemblies, and master cylinder) so the truck had been sitting for a while.

When I took the truck out to test drive it to see how the brakes were working, I left a tool or something on the bumper and heard it fall off. I jumped out to grab it off the street and the truck suddenly shut off and would not start again. It was cranking but wouldn't fire. I popped the hood and didn't see anything out of the ordinary and tried again. It was cranking and kicking a little bit like it was trying to start but just wasn't quite able to. After sitting for a few more minutes, I just held the starter and it finally fired up and I got it back to my house.

The next day, I took it to work. No issues whatsoever. The day after that, when I started it in the morning, the SES light was on again and it ran terrible all the way to work. It took twice as much throttle to accelerate up to the speed limit etc. and seemed to be missing a lot between 1,500 and 3,000 rpm. It wasn't jerking or anything while it was missing, but you could hear in the exhaust that it wasn't firing consistently.

When I got to work I checked the code and it was 42 again. After I checked the code, I started it again and the light was off and it ran fine again. That was Tuesday and it's been fine all week driving it everyday for about an hour each direction in heavy traffic until today when I took it to the dump to get rid off some garbage. It drove fine the whole way there and then the light came on again right when I was about to park it. After shutting it off and starting it again, the light is again off, and everything is fine.

It seems to be happening so randomly that I'm wondering if this could be my ECM failing?

I found a thread on here from Vile that shows a workflow on how to isolate the fault, but I can't get it to throw the code in a situation where I can perform that process at home and what not.

Is it possible it's the ECM, or maybe the new ICM is faulty? I put the thermal paste on the ICM and everything so I don't think it's getting too hot.

From what I understand, 42 has something to do with the ECM's ability to adjust the ignition timing. Could this be an issue with the distributor itself?

Luckily for now, it seems that turning it off and back on clears it up. I haven't had another episode (yet) where it will not start back up, but I'd like to get it resolved before that happens!

Thanks, everyone in advance!
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline VileZambonie

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Re: Intermittent OBD1 Code 42
« Reply #1 on: July 28, 2018, 09:58:03 PM »
Sounds like the pickup coil is toast. I'd replace the distributor altogether.
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Offline Jon87V20

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Re: Intermittent OBD1 Code 42
« Reply #2 on: July 29, 2018, 04:09:30 AM »
Okay. Thanks, Vile. Are there any brands in particular I should consider above others, or are they about the same as far as quality goes?
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline VileZambonie

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Re: Intermittent OBD1 Code 42
« Reply #3 on: July 29, 2018, 06:49:07 AM »
If you are buying local, just get whatever is readily available at the parts store you use.
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Offline VileZambonie

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Re: Intermittent OBD1 Code 42
« Reply #4 on: July 29, 2018, 06:52:31 AM »
Here is the diagnostic strategy for DTC 42
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Offline Irish_Alley

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Re: Intermittent OBD1 Code 42
« Reply #5 on: July 29, 2018, 02:31:08 PM »
hey vile do you have these diagnostics on your pc for all of them?
If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline Jon87V20

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Re: Intermittent OBD1 Code 42
« Reply #6 on: July 30, 2018, 01:11:07 PM »
One more question. Can I buy one of those distributors with the internal coil as a replacement, or does it have to be the same one with the external coil? Just thought it might be nice to get some clutter out of that area if possible.

Thanks!
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline VileZambonie

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Re: Intermittent OBD1 Code 42
« Reply #7 on: July 30, 2018, 06:12:38 PM »
hey vile do you have these diagnostics on your pc for all of them?

What exactly are you asking?
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74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline VileZambonie

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Re: Intermittent OBD1 Code 42
« Reply #8 on: July 30, 2018, 06:13:36 PM »
One more question. Can I buy one of those distributors with the internal coil as a replacement, or does it have to be the same one with the external coil? Just thought it might be nice to get some clutter out of that area if possible.

Thanks!

Although you could make it work, they are not interchangeable in that way.
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Offline Irish_Alley

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Re: Intermittent OBD1 Code 42
« Reply #9 on: July 31, 2018, 01:01:00 AM »
say for the "tech" section ? or are they there already?
If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline VileZambonie

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Re: Intermittent OBD1 Code 42
« Reply #10 on: July 31, 2018, 05:37:33 AM »
Unfortunately I don't have the time to pull all every diagnostic strategy, too many variables. They can be found in the drivability and emissions manuals.
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74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline Jon87V20

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Re: Intermittent OBD1 Code 42
« Reply #11 on: August 06, 2018, 09:32:10 PM »
So I haven't had the time to go pick up a new distributor yet. Today I was driving home, and the truck stalled badly for about one second (going sixty on the freeway) and then I felt it give itself a bunch of throttle momentarily. Next time I had to stop in the gridlock, I noticed the engine was idled up quite a bit. It was trying to idle at 1,500 (in neutral) and 1,200 (in drive). It stayed like this for quite a while but eventually came back down to about 800 (in drive).

It seemed to be okay until later on in the day I was in traffic again and it gave itself a bunch of throttle again. I put in neutral because I was going to give it a light revving to see if it would calm down again. When I put it in neutral, the idle dropped sharply like it was going to shut off and I saw the SES light blink and go out. I had to keep my foot on the pedal to keep it running. It was missing terribly until I got out of traffic.

When I got it home, I popped the hood and I think I'm hearing some rod-knock now. I got down on the ground and got close to the oil pan and it's definitely coming from the bottom-end. Needless to say, I'm feeling really discouraged at this point. I still need to get the rear differential rebuild on this and the steering still needs attention...

Part of me wants to sell it, but I'm kind of attached to this truck and also I spend about $1,100 on the transmission a few months ago, put in a new steering gearbox, and replaced everything for the front brakes and I don't want to just eat it on all that.

Do you think it's better to pick up a long-block, or get this one rebuilt?

In the meantime, is there any of those products that thicken up the oil and what not helpful to keep this going for now?

This may seem like a silly question but is it dangerous to drive it like this? If it throws a rod on the highway, is it possible it will lock up the rear end and put me in my grave, or would the transmission let go of the engine when it stopped moving?

Thanks.
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline Irish_Alley

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Re: Intermittent OBD1 Code 42
« Reply #12 on: August 07, 2018, 07:48:08 AM »
if it is indeed the engine it will be cheaper to stop driving it now and a little easier to remove the engine when the time comes. it will also be cheaper to rebuild the engine vs buying a long block. but it you want more power anyway then think about what the OEM engine can do
If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline VileZambonie

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Re: Intermittent OBD1 Code 42
« Reply #13 on: August 07, 2018, 08:29:16 PM »
If you just replaced the transmission, I would check your flex plate bolts. Take the infection cover off and tighten all 3 bolts very tight.
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              ⌠¯¯¯¯¯'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline Jon87V20

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Re: Intermittent OBD1 Code 42
« Reply #14 on: August 09, 2018, 03:42:38 PM »
The transmission was rebuilt and installed professionally at a shop earlier this year, but I'll still get under there and check when I get a chance. That would be great if that were the case!
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208