7.4L MAF Issue?

[Tom P]

Just got the truck back from the shop. Key switch was the death issue. Tech said he test drove it and could not get the truck to hesitate after it warmed up. Going to go grab my scanner and see what I can read. If I'm really lucky, the key switch some how affected the run issue to but I highly doubt that

 

[Tom P]

Here's some hard data for the experts

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[Tom P]

Now the o2b1s1 and s2 readings are all over the place. s1 reads as low as .000 and as hi as .87. S2 is much more stable but still makes jumps. The first pic shows possible issues with O2 and whatever HRT means (newbie here, remember?)

 

[Christian Steffen]

I think HRT is o2 sensor heater? They 02 voltages are supposed to constantly jump up and down, if one isn't jumping up and down very quickly that probably means its bad. Also the heater code would point to bad o2s as well.

 

[Tom P]

Both Appear to be jumping all over the place and at very regular 1/2 second intervals. I would think if the heater circuits were bad then I'd be seeing more fault in the readings? Regardless, I was able con one of our techs into helping me do the extraction (beer is a powerful ally) on Friday night. If that doesn't work I'm taking it back to the shop and having them hook their scanner up. Diagnosis charge was estimated at $100 so I can't really dick around too much more for that money. I'm running out of time before my camping trip.

 

[Christian Steffen]

Well hopefully you can figure something out. I guess there should probably be a DTC present. I'm not particularly sure what to think. Have you had the "misfire" issue show up again after getting the truck back? It'd be interesting to scan during that.

 

[Tom P]

Yes, extensively. I was scanning during that period and found similar results to the pictures I posted. I will run it again tonight and try to pull up a graph of each o2 sensor reading so you can see more of a snapshot of whats going on. According to the manual for that scanner, a red x next to each system with the yellow "!" indicated shows that there is an issue with the system but no diagnostic codes available. It also says that it could mean a scan of that system is incomplete. I have no way to tell if its a issue or an incomplete scan....

 

[Tom P]

New information for the class. On my drive home from work tonight the HRT system checked out ok. Truck seemed to be running as it has but I was not able to drive it long or hard enough to draw any hesitation or power issues.

 

[Christian Steffen]

Did you ever check the spark plug gap?

 

[Tom P]

Not yet. Haven't had a chance when the truck was cold to actually start pulling plugs. I will check that this weekend though.

Finally got a chance to change my coil last night and some interesting things happened. First, the truck seems to be running better albeit far from what I would expect. Even in when the truck made it to Closed Loop, I still had enough power to almost spin the tires going around a corner. Truck does have locking diff though. Second, I got both the HRT and the O2S readings on my code reader to check out. Then the scanner popped a Pending DTC of P0131 which said low voltage in O2SB1S1. Checked the live data and saw .000. Confirming the original diagnosis. Still planning on swapping them out Friday after work. I don't want to get my hopes up that changing these stupid things are going to give me more power. I suppose thats all possible but I drove our shops 1997 C3500 flatbed towing the same tractor and trailer that i was towing when my truck stranded me. This truck has a Vortec 350 but easily did better than my 454 in its current state. Hoping that by the time we are said and done here, I'll run circles around the shop truck.