Well, that's a good thing.

 

If it were me, I would probably replace the O2 sensor at this point. Especially if it is of unknown age. It was/is considered a basic maintenance replacement part on these trucks, with a similar replacement schedule as a spark plug.

 

That's Correct.

A code 41 is a lean code, if I remember rightly. If it's plugged or fouled it could think the truck is running too lean and increase the fuel mixture on you.

I'd remove it from the manifold and if it's chalky white or sooty I'd definitely throw a new one on it.

 

I'm going to run the koer test again just to be thorough, but since a new o2 sensor costs between $18 and $32 I will just replace it anyway.

 

Just remember on a truck this old, take care in removing it. You dont want to pull the manifold threads out with it. Best to use some heat.

 

When you take it to be retested bring your previous tests and ask that they test the way they did in the first test, as the rpm spread is inappropriate for the type of test the state wants. The purpose of doing the dyno test was to see different loads at similar rpm and I've never seen one look like that unless it was in a car that had a failing transmission and was missing a gear, in which case the state would normally fail it anyways.

 

That bothers me too. I can verify the transmission works fine, so the first guy chose a different gear than the second guy for some reason. Question is why and does that impact the results?

 

Well it all has to do with powerband, it requires a richer mixture to turn 15 mph @ 1200 rpm vs. the 1900 or so that were looking for. Essentially the way you're supposed to do it is what ever gear you're in for the 15 mph test, you then accelerate to 25mph and shift to the next higher gear. This also allows a more complete sampling, lets say you had blow by issues and when it shifts gears, you get a puff of smoke, the state wants to catch that. If they give you any lip about it, once you get this taken care of, I'd write to the California department of consumer affairs, bureau of automotive repair and complain because the second test should not have been tested like that.

 

Re-ran the koeo and koer tests. The koeo test came up clean (code 11) and the koer test returned code 41 again for the o2 sensor and returned code 13 this time for "Cannot Control Revolutions Per Minute During Key On Engine Running Low Revolutions Per Minute Check" according to Actron. Don't know what that's about, but I'm not going to worry about it unless it turns up in the koer test I will perform after I change the o2 sensor, since this is the first time the truck has returned code 13.

 

You sound like you speak from experience grasshopper.

 

Since the o2 sensor is being replaced, I plan on hitting the old one with some pb blaster then letting it dry before I install the new one.

 

Yup, pulled the o2 on a Tuesday evening, was replacing the manifold on Wednesday morning...

 

What transmission do you have? I don't see it mentioned. One of the 4-speeds?

I've seen people complain that a smog tech would wind the crappola out his engine in granny gear and failed it, because he didn't know any better.

The rpm drop you are experiencing seems to be a starting in 1st or 2nd issue.

A regular 4-speed (T-18 / T-19 / NP435) is normal to start in second.

A 4 speed overdrive (Clark/Tremec) you start in first.

Starting and lugging (or winding) the crap out of the engine could definitely skew the test if he starts out in the wrong gear, and would account for the RPM drop for the second test.

 

Its the 4 speed overdrive

 

I replaced the o2 sensor, which turned out to be original to the truck, with a universal Borger Warner unit from O'Reillys. The universal model, which I used because that's what they had available, is different in that it needs the plug to be attached before the sensor can be used. No big deal I figure I can cut off and re-use the original plug. I cut the plug, with about 6 inches of wire, off the old sensor. I intended to solder the old plug to the wire leading from the new sensor, but I discovered I was out of solder so I used the crimp style plug (sorry, I forget the proper name, but I can post a photo if necessary) that was was already attached to the wire of the new o2 sensor. I then installed the new sensor, reconnected the battery and brought the truck up to operating temperature.

I then re-ran the koeo and koer tests. The koeo test came up clean (code 11) and the koer test returned code 41 again for the o2 sensor and returned code 13 again for "Cannot Control Revolutions Per Minute During Key On Engine Running Low Revolutions Per Minute Check" according to Actron.

I'm wondering if crimping the wires together rather than soldering them could be making a difference and causing the new o2 sensor to throw the same codes as the old sensor? Is there another reason code 41 would appear? Also, does anyone know what's up with code 13?

The old sensor looked trashed. Based on what my nose was telling me, the truck is running richer with the new sensor than it was with the old sensor.

Any thoughts?