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1973 C10 "The Purple Truck"

Basic build
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Headed to the shop to change the oil and the O2 sensor failed. I was able to get a replacement at O'Reilly and swapped it in. That cleaned up some poor running issues I was having so it was in the way out for awhile.

We took the C10 out on some country roads to practice filming. In case you are wondering, I sped the video up in editing. After watching again, it was probably too much. In reality we were driving about 20mph.

 
Another failed O2 sensor? Is that maybe 3 of them? Something is not right.

How do they look when you pull them out? Sooty? Wet? Clean?

Remind me, do you have it mounted on the top of the exhaust?

Is your cold cranking too rich?

Do you give it any time in the morning between key on and firing?
 
I just looked back and it was January I had the O2 sensor fail. Did not realize it was that recent. I didn't record the odometer but it should have been about 10K miles since then.

I have the PF4 rigged up on a switch, and I turn that on for a bit before hitting the key.

I haven't messed with the cranking fuel, so it should be at factory default.

The sensor is on the top part of the pipe, about the 10 o'clock position. It is a few inches after the collector flange. I was thinking maybe I need to move it into the header collector. That would only be moving it 4 to 6 inches.

This engine is burning some oil. Never visibly, but it needs a quart about 3,000 miles.

Pictures of the failed sensor.

20241203_130707.jpg

20241203_130700.jpg

20241203_130712.jpg
 
I've been having a backfire on deceleration since awhile before the oxygen sensor failed. It suddenly occurred to me I cranked up the vacuum advance timing as high as the system would allow, 15°. I backed it off to 12° and the backfire went away! Sometimes you miss the obvious. :doah:
 
I think 1qt in 3k mi is fine for these old engines.
 
mrk5 said:
I've been having a backfire on deceleration since awhile before the oxygen sensor failed. It suddenly occurred to me I cranked up the vacuum advance timing as high as the system would allow, 15°. I backed it off to 12° and the backfire went away! Sometimes you miss the obvious. :doah:
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That's surprising, what is your base timing at?
 
I want to say 22°, maybe 24° base timing. I noticed it was running about 48° total advance on decel after I dropped the vacuum advance to 12°.

The backfire was happening if I decelerated when the RPM was over about 2200 to 2300.
 
mrk5 said:
I want to say 22°, maybe 24° base timing. I noticed it was running about 48° total advance on decel after I dropped the vacuum advance to 12°.
Click to expand...

Is that what your idle is set at 24? That's a little high for a low end torque engine.

mrk5 said:
The backfire was happening if I decelerated when the RPM was over about 2200 to 2300.
Click to expand...

Was it popping in the exhaust, or actually backfiring into the intake manifold?

There is a big difference, and its not always obvious to tell the difference.
 
folkenheath said:
Is that what your idle is set at 24? That's a little high for a low end torque engine.



Was it popping in the exhaust, or actually backfiring into the intake manifold?

There is a big difference, and its not always obvious to tell the difference.
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It was definitely the exhaust.

That would be idle spark. I wish the values showed without having the app connected to the ECU. I left the C10 at home today so I can't verify precise numbers. I just know I generally set idle timing in the low 20's. I'm guessing total spark is around 38°.


skunked said:
what brand O2 sensor are you using?
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Bosch 17025
 
Okay, I gotta figure out what's going on, because I just lost another O2 sensor. It also means their life is getting shorter with each sensor. I wonder if I put it too far back in the exhaust.

2022-03-04 copy.jpg

This is how it's orientated in the truck.
 
I have long tube headers on my '01 with a 6.0. The O2 sensors are in the header collector. 25K miles so far hasn't bothered them, so I would assume that yours are fine position wise.
And you have it tipped up to keep condensation out.
 
On the truck with ProFlo 4, my O2 is just past the collector on mid length headers. No issue to report however I don't drive mine like you do.
 
I have mine in about the same position behind the collector, same O2 sensor for over 15 years so far....

When you key on, do you wait 5 seconds for the fuel prime to stop, or you key on and crank at the same time?
 
It does run for a bit. I usually get in the truck, flip on the switch for the PF4, put the key in the ignition, and then crank. So there's a bit of time for the pump to run before cranking.

I don't have any kind of discharge out the exhaust tips. I would think if there was something from the engine contaminating the sensor, I'd see other signs. On the flip side though, I don't know what else could be causing the failures. It has been running good lately after I fixed my timing issues.

I just had a thought. I posted back just a little bit about figuring out I had the vacuum advance timing too high which was causing backfire on deceleration. Could that have caused the sensor to fail?
 
I was surprised you could even get the vacuum advance too high with the PF4, I usually have the opposite problem.

If it was popping and banging out the exhaust, yes, because it's raw fuel being ignited. But that is usually caused by misfires or fouled plugs.

If it was backfiring in the intake, then I wouldn't think so. You have had this problem multiple times, so its unlikely to be the latest timing change correct?

What is your actual cruise timing with the latest timing settings? I don't mean the setting, I mean the actual timing it says while cruising down the road at low load?
 
folkenheath said:
I was surprised you could even get the vacuum advance too high with the PF4, I usually have the opposite problem.

If it was popping and banging out the exhaust, yes, because it's raw fuel being ignited. But that is usually caused by misfires or fouled plugs.

If it was backfiring in the intake, then I wouldn't think so. You have had this problem multiple times, so its unlikely to be the latest timing change correct?

What is your actual cruise timing with the latest timing settings? I don't mean the setting, I mean the actual timing it says while cruising down the road at low load?
Click to expand...
I want to say it was around 40° most times.
 
Yeah, thats pretty mild for low load lean cruise, I have it around 50 in my truck.
 
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