More Truck Revelations

"Future Heap Owner" (aperiodic) 08/16/2018 at 17:24 • Filed to: None

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Last night I poked around the engine bay a bit to try to narrow down why I’m getting the code 43, and, well, I sure found a problem:

Apologies for midnight potato pic

This is the wiring connector for the Electronic Spark Control module. See that slot at the top? That’s where the wire to the knock sensor should go, but there’s nothing there. So, I’ll need to fix that. I’m not sure if I’ll be able to thread a new wire into the harness somehow, or if it’s a horrible idea to route a wire down to the knock sensor without any sort of protection.

I think this dangling connector on the passenger side of the engine that’s hanging down near the knock sensor is supposed to go in the knock sensor, but I’m not sure:

It, uh, took me a while to actually find the knock sensor, and then I spent a good 10 minutes trying to get a resistance reading between it and ground, but as I was lying on the ground without jacking it up, I couldn’t reach both the sensor and a place on the engine block where I could get a good connection. Which is all to say that I didn’t try plugging this in to the knock sensor. Nothing else is plugged into the sensor , so I’ll give it a shot tonight.

The other concerning discovery was this other loose connector on the top of the engine:

I have no idea what it should go into. Either it’s another part of the ESC / knock sensor circuit, or it’s not that important, since I’m not getting any other codes. The wires to it are red w/ black stripe and black. I didn’t see anything matching that in the engine control wiring diagram of my Haynes manual, but who knows how accurate that really is (yeah, the factory manual is looking pretty nice right now). Anyone have any ideas?

Duck Duck Grey Duck FTMFW! > Future Heap Owner 08/16/2018 at 17:29

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Yeah the black connector looks like it’s definitely for the knock sensor. I have a Chilton’s I can check out the orange? connector if you want.

LOREM IPSUM > Future Heap Owner 08/16/2018 at 17:34

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Obviously a completely different vehicle manufacturer, but fwiw many BMW’s have an unused mystery connector sitting on top of the engine. I’ve NEVER heard or read o f anyone determining what it’s for o r why it’s there either, but it is.

So, it being there intentionally unused is not necessarily out of the realm of possibility.

Either way, mystery connector is mysterious.

Future Heap Owner > Duck Duck Grey Duck FTMFW! 08/16/2018 at 17:36

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I’m not sure when they merged into the same company, but worth a shot! I think the connector was red but has faded a bit ( and the lighting & exposure were weird), but I’m pretty sure on the wire colors (Red/Blk and Blk).

Future Heap Owner > LOREM IPSUM 08/16/2018 at 17:43

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Oh interesting, I had no idea that might be a possibility.

Akio Ohtori - RIP Oppo > Future Heap Owner 08/16/2018 at 17:56

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I might have the factory service manuals for this truck at home.  I have them for my 1999, but I’m unsure if they’re 1995-1999 of if they cover all GMT400 vehicles.

Future Heap Owner > Akio Ohtori - RIP Oppo 08/16/2018 at 18:37

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Ooh could you check whether it covers the 88-95 V8  TBIs  for me?

Urambo Tauro > Future Heap Owner 08/16/2018 at 20:18

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Pretty sure those manuals are year-specific. I know a guy with a set of factory manuals for a 1995 C/K that I’ve borrowed a couple of times. I’m sure a lot of the information would still be applicable to your truck.

I just took a quick peek under the hood of my ’95 , but I’m not seeing a connector like that in that area? Maybe I need to take another look ... Which engine did you have, again ? Mines a 350, but it’s been messed with a little by the previous owner. More so than I originally thought, if it’s supposed to look like your pic...

Future Heap Owner > Urambo Tauro 08/16/2018 at 22:24

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Here’s a better pic . The connector’s resting on the air filter housing. It’s not very long so there’s not many things it could go to...

I don’t think the previous owner of my truck did much to it, but who knows what he left out of the stack of paperwork he gave me. Or that the original owner did.

Urambo Tauro > Future Heap Owner 08/16/2018 at 22:51

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Wait, is that connector red? It looked grey in the other pic. Do you n o t have a p u r g e v a l v e solenoid on the intake, n e x t t o the thermostat housing?

A l s o , y ou might want to double-che c k your wire colors. M y p u r g e s o l e n o i d w i r e s a r e r e d a n d g r e e n / w h i t e , b u t l o o k b l a c k w h e n t h e y ’ r e d i r t y .

Akio Ohtori - RIP Oppo > Future Heap Owner 08/16/2018 at 23:01

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Yes, unlike any other manufacturer’s manual I’ve laid hands on, they appear to be for one year only. Wild.

I’ve got the FSM for a Reliant Robin, if that would be of any help!

Future Heap Owner > Urambo Tauro 08/16/2018 at 23:24

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For the evap canister? I don’t have that.  The line out from the canister is just dangling. That must be it, thanks! Another thing to pick up at the pick n pull this weekend.

Urambo Tauro > Future Heap Owner 08/16/2018 at 23:31

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Hold up. Before you get too excited, I need to tell you that while I was waiting for your reply, I took a peek on RockAuto and (if I spec’d your truck correctly in the menu) it’s listing your purge valve as a totally different type. Yours is supposedly vacuum-actuated, while mine ’s electric. My truck might not actually be such a great reference point for you after all, at least not in this particular case.

Future Heap Owner > Urambo Tauro 08/16/2018 at 23:48

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Well, it does make me put two and two together to reckon that the thing the line from my evap canister is supposed to plug in to might be the thing that the connector is supposed to plug in to as well. Gives me some more stuff to look up tonight at least.

For reference I have a 1992 K1500 Silverado with the 350 V8. I thought they didn’t change until the Vortec in 1996.

Urambo Tauro > Future Heap Owner 08/16/2018 at 23:54

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Yeah, I’m sure they’re still gonna be mostly the same. Except for this, and probably a few other things as well. Like yo ur electronic spark control module . I don’t have one.

Duck Duck Grey Duck FTMFW! > Future Heap Owner 08/17/2018 at 08:47

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Okay will look tonight

Future Heap Owner > Urambo Tauro 08/18/2018 at 00:47

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Yeah, you were right: I have a different purge valve, and the line I thought was from the evap canister is actually clipped in off to the side of the evap canister, so not hooked up to anything at all. Weird.

So no closer to solving the mystery of that red connector. Maybe looking at trucks in the yard tomorrow will let me figure it out.

Is there any chance I could have a wiring harness that’s been swapped from your model year truck? There’s got to be other things that would be different, right?

Duck Duck Grey Duck FTMFW! > Future Heap Owner 08/18/2018 at 08:15

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I checked my Chilton’s and didn’t find anything but here are the diagrams in case I missed it. I didn’t include the stuff for anything newer than 1994.

Duck Duck Grey Duck FTMFW! > Urambo Tauro 08/18/2018 at 08:19

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95 is a special year truck I have been told because they were working on implementing OBD II crap.

Duck Duck Grey Duck FTMFW! > Urambo Tauro 08/18/2018 at 08:20

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95 is a special year because they were working on implementing OBD II stuff.

Urambo Tauro > Future Heap Owner 08/18/2018 at 10:00

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Hard to say. The previous owner of my truck supposedly had the engine out at least once (for a rebuild ), so either of ours could have been modified  in ways that we  have yet to discover. (In fact, I have a mystery connector on my en gine harness too, a four-pin one . I’ve just been neglecting to pursue it because the truck runs just fine, and doesn’t trigger any codes.)

Anyway, w hen I tried to look up an engine wiring harness, I came across GM part #12150130, which is supposedly for ’92-’96 305s & 350s. The largest image of it I could find was on (of all places) Walmart.com :

If you zoom in on that red connector near the middle bottom of the image, it looks exactly like the one I’ve got, and it plugs directly into my purge solenoid . B ut even though your connector is red and seems to be in about the right place, it appears to be a different style. That’s really throwing me for a loop, since yours is supposed to be vacuum operated in the first place. And I’m not seeing any connectors in the pictured harness that matches what you’ve got .

Future Heap Owner > Urambo Tauro 08/18/2018 at 22:10

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I looked at a few trucks at the junkyard and that connector is definitely for the purge solenoid, and my year doesn’t seem to have a purge solenoid. I have no idea why I have that connector.

Urambo Tauro > Future Heap Owner 08/18/2018 at 23:36

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A ccording to the vehicle application chart, the purge solenoid that I have was supposedly used from 1990-’98 on various GM vehicles, but when it comes to C/K truck applications, it was only in use from 1993-’95. I’m seeing a little bit of overlap though- the vacuum-actuated valve that’s supposed to be on your truck has a C/K truck year range of 1988-’94.

And if you look closely at my connector, it doesn’t have a gap between t he tubes that surround the contacts, like yours does . Here’s a pic of mine, and what the valve and connector look like when new:

BUT WAIT what’s this thing ? I stumbled across it while looking for a be tter pic of my connector. Hard to tell from this angle , but it looks like it might plug into your connector to use the solenoid? The application chart doesn’t give me much confidence, but it does kinda look like it might fit what you have.

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