TBI throwing code 42

[green55]

Any tips on a code 42? I was pulling out of my neighborhood, had only been driving a mile or two and felt the Jimmy kinda stutter like it was losing power then went back to normal. Service engine soon light started flickering, went out for a sec, then stayed on. Went right back home so didn’t drive it long, but felt like it had less power than normal.

First code I’ve had the Jimmy throw since I brought it back to life almost 2 years/7k miles ago.

 

[88Silverado]

Code 42 is Electronic Spark Timing. Could be the ignition module however there are more items that can cause this code. More of the experts will slowly chime in and provide guidance.

 

[green55]

Thanks - from some googling, it seems like that’s a really common cause. And YouTube makes it look easy to replace.

I’d be curious to hear from others though if there’s something else I should try first. I found the diagnostic flow in my service manual, but half the time that thing is useless to me because I don’t know enough

 

[BoondocK5]

First sign of a "heading south" ignition module.
Check all the grounding/bonding straps to the engine and frame, replace the ignition module, with one of known good quality(read:good brand name) choose your own, anymore. Don't forget to apply a film of heat-sink gel, not dielectric grease. Clear the code, press on with your life.

 

[green55]

K - ordered one from RockAuto. Will report back on how it runs after install

 

[green55]

Back on this. I just finished installing the new ignition module. I still have the exact same problem. Not sure what to do next. It seems to run ok at higher RPMs, but as soon as it tries to settle into an idle it stutters and wants to stop, then roars back, stutters again, etc.

Y’all have any clue?

 

[green55]

Was going to see if fuel delivery looked ok but now it doesn’t even want to start . If I give it some gas it’ll run but otherwise it dies

 

[dyeager535]

Quick search of that code seems to indicate it's going to be an electrical fault. However, it should still start and run on the "base" timing.

I think I'd put a fuel pressure tester on the fuel line fitting at the filter and see what happens when you have someone turn the key to "run".

Obviously ignition is working or it wouldn't start. I don't mess around anymore, anything that sounds like fuel, I test fuel. The newer pumps are garbage, and the older in-tank hoses are very prone to splitting with ethanol and the age these things are. It's a relatively quick and easy test to make. Go to one of the chain auto stores and borrow their fuel pressure tester. Just make sure it has the GM fitting adapter.

 

[green55]

Ok - I’ll see if I can figure that out. Doesn’t sound difficult, but nothing is easy for me because I don’t know how to do anything .

The reason I was thinking fuel is because I didn’t replace the tank when I got it running again (although did have pump & sending unit replaced). Who knows how long gas sat in there. Something crusty could’ve broken loose in the tank and clogged filter or something else

 

[dyeager535]

Worth a shot, one would hope if it was all replaced things would be in good working order.

Tank really shouldn't need replaced, but if I had the pump out I would certainly have inspected it for dirt and what not.

 

[green55]

I haven’t checked fuel pressure, but decided I should just do what the factory service manual says for a code 42. I was kinda trying to skip ahead by replacing the ignition module, because lots of people have fixed it with that. Also skipped ahead because I only kinda understand what the flow chart is telling me to do. I don’t even have an ohmmeter or test light, but they’re on the way. Hopefully I’ll have some time over the long thanksgiving weekend to mess with it.

 

[scouthead]

couple threads on this over in the injection section. also, ive been chasing some similar problems - it comes up that you need to make sure none of your plug wires are touching or in close proximity to the harness that plugs into the distributor and coil... can cause interference. I believe that was my issue when the code 42 was thrown (but i wish i had some other codes recorded to help diagnose the other problems!)

 

[green55]

Finally have have a couple hours this morning to work on this again. I did have some plug wires that were touching or very close to the dist harness so loved those. No big improvement, all though it’ll sit there and idle again while surfing & sputtering.

I did look at the fuel injector spray pattern. Seems when it sputters the injectors are spitting out air or just dribbling, when it’s running normal they look fine. So wondering if this is pointing to a fuel issue too, or if it’s a side effect of the bigger issue.

 

[green55]

Ok I know I’m all over the place with this, but did a couple more things. Found a vacuum leak and fixed it, that improved things slightly but still running real bad. Also started running through what the service manual diagnostic instructions.

Pretty sure I was on the right connector for the first step checking that CKT 423 is under 500 ohms. I got a reading of 672 ohms. Which says “Open CKT 423, faulty connection, or faulty ignition control module”. I’ve replaced the ignition control module already, so hopefully it isn’t that (I know I could’ve gotten a defective one).

What do I look for to figure out “open CKT 423 or faulty connection”?

 

[shima]

Essentially that means that the circuit has an open in it somewhere - you would want to look for damaged or cut wires within the circuit.

Faulty connection is sorta obvious, you just want to make sure that the electrical connectors within the circuit are clean and are making solid contact with whatever they're connecting to.

 

[Wes Harden]

632ohm is not far off. where was your selected ground? The high reading might be ground connector/circuit resistance. Or just variance in your meter.

Also this book seems to contradict it self, in the description pic a few post up bullet #2 "Checks for a normal EST ground path through the ignition module. An EST CKT 423 shorted to ground will also read less than 500 ohms"

then the trouble tree has you testing CKT 423 from the ecm connector through the ICM to ground. and says should be below 500ohms? Make sure you distributor body is well grounded and retest.
I don't believe this is your problem.
One of my factory school instructors, loved to design diagnostic lessons around bogus service manual procedures. There were no shortages of lessons.

 

[green55]

Thanks shima and Wes. I’ll check the wiring regardless to see if anything looks like it’s on its last leg. Doing that was how I found the vacuum leak too. Hard to get a good visual on the wiring with it being tucked all the way back against the firewall.

I used a ground that’s on the firewall basically right above the distributor. I tested multiple times and got 672 every time, but didn’t test with different grounds.

How do I make sure the distributor body is well grounded?

As far as the book being off…that wouldn’t be great because I hardly know what it’s telling me anyways . If I don’t figure this out soon, I’m sending it off to the pros because I’m tired of it being down. I’m sure I’ll hate the bill though! It’s been hard to find free time to work on it with house projects that are more pressing

 

[Wes Harden]

the dist grounds to the block through the hold down, make sure it clean and no paint at contact points. Also check block ground to frame and body.

 

[dyeager535]

Thanks shima and Wes. I’ll check the wiring regardless to see if anything looks like it’s on its last leg. Doing that was how I found the vacuum leak too. Hard to get a good visual on the wiring with it being tucked all the way back against the firewall.

I used a ground that’s on the firewall basically right above the distributor. I tested multiple times and got 672 every time, but didn’t test with different grounds.

How do I make sure the distributor body is well grounded?

As far as the book being off…that wouldn’t be great because I hardly know what it’s telling me anyways . If I don’t figure this out soon, I’m sending it off to the pros because I’m tired of it being down. I’m sure I’ll hate the bill though! It’s been hard to find free time to work on it with house projects that are more pressing

You can just set your meter to continuity and touch one probe to the distributor body, the other to a clean spot on the block. Or any other ground on the vehicle.

 

[green55]

Well I’ve put myself in a worse spot somehow. Went through the wiring to ign module under distributor that I could get to. None of it had splits or anything, stiff from age but nothing that looked like it wouldn’t function.

Then cleaned the spots where the dist cap contacts to make sure that was grounding well. Not sure if dist cap is tired? Had a bunch of rust colored dust in it. Truck started but no change in behavior.

Then starting looking at engine grounds. Found what I think is the block to body ground and it looked nasty. Caked with something. So figured maybe that wasn’t grounding well. Cleaned that up some and now truck won’t start. I don’t know if it somehow isn’t grounding now and it was before? This whole thing is frustrating, I can see why people get fed up with electrical issues