I ran out of time today to run the truck with the O2's unplugged. But I got videos of the O2 readings at idle and while running - with O2's plugged in.

The connectors are pretty tough to get off. I fought with them for a while and conceded as I was running out of time. The connectors both have 15 years of engine bay residue on them, and I also found out that the brackets they are attached to are not bolted down, although both were tucked away from the exhaust system and don't seem to move. Need to do something about that.

Here's the video of the O2 readings at idle after start up. Hot weather and truck had run a few minutes, water temp is somewhere between 125-140 in the video:
https://www.youtube.com/watch?v=vlLm...ature=youtu.be

This video is causing down the the road. Some acceleration, followed by harder acceleration, followed by coasting. Truck is at operating temperature here, between 180-190 degrees water temp.
https://www.youtube.com/watch?v=mgpR...ature=youtu.be

The readings look normal to me, but I wouldn't be posting here if I didn't welcome input.



Also this morning I replaced my MAF with a new Bosch unit. I cleared the check engine light and have driven about 20 minutes so far without it returning, although I am confident it will.

Another note (different topic): My coolant temps are solid. Severe duty fan clutch, recent coolant flush, new water pump, recent HG job, low mile P38 block, 180 thermo etc. While driving my temps have always been sub 200 no matter what conditions. At idle they would creep up to 202 max, and then cycle back down to 194. I thought this fluctuation was weird, as the cooling system seemed to be functioning perfectly. I had what I thought was a coolant leak, but only after the truck had been idling for a very long time (30 minutes). If I let the truck idle for a long time the temps would creep up to 210 or so, and some coolant would drip out of the hoses going into the radiator (best I could tell, it was a very small amount so it dried. I never saw it actively leaking). I found that these hoses needed to be a little tighter, so I snugged them up, and did not see the leak happen again, even when I tried to replicate the conditions.

I noticed my coolant reservoir cap was faded and the seals looked rough. I bought a new one, replaced it this morning. My coolant temps are noticeably lower AND more consistent. Now at 20-50 mph I am seeing no hotter than 194 - ever. Hard driving, easy driving, does not matter. Temps while driving are now 186-190 most of the time. At idle the temp never fluctuates higher than 194 either.

I am confident the coolant overflow cap was allowing air into the system causing these temperature fluctuations. I now feel really good and confident about my temps and the system seems to be working great. All of this being said, spend the $5 or less on a new cap!

Happy Fourth!

 

Quick update. Put another 30 minutes in driving the truck this afternoon. The SES light has not returned. Looks like the MAF could have been the problem...

I can still hear the pitter patter noise under acceleration of an exhaust leak at the manifold. Although not significant. Very confident there is a small exhaust leak, but as I suspected not significant enough so far) to cause the lean codes.

I need to drive it more to confirm the issue is resolved. Could it have really been that easy?

Another note: I had to replace the intake elbow, as my truck had a P38 intake elbow and the MAF I bought was for a D2. The previous MAF I was running was also from a D2 but had a larger diameter and fit the P38 intake elbow. I swapped out the MAF and the P38 elbow, as I had a D2 elbow ready to go. Maybe the MAF was fine and there was a leak somewhere in the old elbow?

 

Hey guys, just following up.

I install a new MAF and per my last post, the code went away.

Well, after driving a few hundred more miles. the codes have come back. I have been unable to locate a vacuum leak, but have not performed a smoke test. The O2 sensors read properly, so I have no reason to believe they are inoperable but I do have two O2 sensors and might install them just to be sure.

 

So the only way you get lean codes is if oxygen sensors think the truck is lean, but you say the oxygen sensors are working correctly. So are they starting normal and trending to lean? If that is what is happening, it would occur because the lean condition is not compensatable by the ECU. The ECU fuel trims would go to max which is 10%. So there are some questions that need to be answered to further troubleshoot.

1. Do the oxygen sensors show lean at idle only or also at cruise? What about WOT? We need the charts for those conditions. Would be good to export the data in excel via the Torque app.

Engines start out needing a lot of fuel when cold, and then need less as they warm up due to intake air temperature heating up. Cold air needs more fuel, hot air needs less. Assuming it does not start out lean, your engine is saying it needs more fuel as it gets hot, which is opposite of physics. So there are only a few ways that can happen:

1. As it gets hot, air begins getting in to the engine by bypassing the MAF. Highly unlikely
2. As it gets hot, less fuel is delivered even though it is commanding increases. Fuel is commanded by longer fuel injector pulse width .i.e. fuel trims.

Something is not making sense here. We need more hard data, I prefer charts.

 

1. Great info, thanks @Extinct. I can easily take video of the O2 sensor voltage readings from the Ultraguage during the described conditions. Will that be sufficient? Charts would be better. I’ll look into an Bluetooth obdii device that works with torque.

2. Is it worth doing a smoke test? The truck had motor mounts and HG’s done right before I bought it. Seems like the most likely source of an issue is in something that has been taken a part and put back together.

I have new upstream O2’s (came with the truck) and a set of reman fuel injectors. I am hesitant to throw parts the truck before diagnosing further, so the testing procedure notes are helpful. Thanks!

 

In lieu of a chart, I took three videos this morning. Links are posted below.

O2 sensor readings look like they are doing there thing. Something the video did not capture is that every 2-3 minutes while driving the readings for all four drop to 0.000. Then slowly increase back to normal. I cannot tell if this is the UG being funky/ cheap or the actual reading.

Videos:

Cold start O2 readings

Normal Driving conditions. truck at temperature O2 readings

Wide Open throttle O2 readings

 

Those cold start readings are not correct, they should be near 1.0. WOT is too quick to be useful really, but good to see it go to nearly 1.0 At temperature looks normal, but can't tell without the graphs. I know people really like the UG, but I personally find it borderline useless. Autool guage is better for temperature monitoring IMHO and Elm327 with the torque app is better for troubleshooting. You can get in to an ELM/Torque/Android setup for less than $30 if you buy an old android off ebay, $5 elm off Amazon. Then we can chart 02's, MAF, LTFT and STFT simultaeniously, which is what we need.

 

@Extinct yeah, understood on graphs. I guess you need to see the trends of the voltage readings more clearly and completely?

I'll see what I can get. Looks like OBD Fusion is a very similar app and available for IOS. I might have a OBDII dongle that will work with it. Offers a CSV format.

 

My business sells a data logging product for Motorsports, and our Bluetooth obdii interface works with the Fusion OBDII app.

I have not found out how to export the data into a spreadsheet. But I captured this video on the way home from work of short term and long term fuel trims, and O2 sensor voltages:

 

Yeah, ok so your oxygen sensors are functioning normally, and it looks like STFT is functioning normally. I can't tell which scale is related to the LTFT but it looks like it is bottomed at -20%, which would throw the codes but does not jibe with the STFT and 02 readings. I assume temp readings are showing normal, would be good to see IAT as well. You might want to consider swapping in an ebay ECU/BCU/Inst cluster. You can always resell it on ebay.