"Phantom" code 21? (High TPS voltage)

**dyeager535** · 08-14-2012

Back story:

Truck was running pretty decent, but I had just cobbled together the exhaust on the drivers side to make it last until I get to the point of the frame off, and it has a couple of small leaks. Noticed that it was slowly developing more and more frequent pops out of the muffler, like it was combusting fuel there, and getting worse.

Anyway, the truck has had a problem with pulling a particular hill. Every time it starts out climbing good, but once I hit 35-40MPH in 2nd gear (this time I paid attention to when it actually occurred), it started to jerk and buck, like it wasn't getting enough fuel. Figured it was probably just in a MAF range that I hadn't added enough fuel in. Well, I hadn't fixed it, and I came to the hill. Knew what to expect. Except this time it was bucking far earlier and worse, enough that I had to pull over. Eventually got up the hill, but it wasn't pretty. Much less load (50MPH, flat ground), and it seemed fine. It was NOT acting like that even earlier in the day while I was climbing logging roads.

Got home, started looking at what it was doing, after ensuring I had good spark to all cylinders. Noticed the MAF changes weren't working as expected...add fuel, BLM's would start increasing. I'd keep messing with idle MAF voltage, eventually it would stall out, no matter if I took fuel back out quickly or not. I went back to the "stock" APYP bin (With just VATS turned off and fuel injector pressure set correctly), which I swear would start it in the past (long ago) but now it just cranks. Try a bin from months back, and it would start and run decent. Not right, but it would run.

Eventually the thing throws a code 33 (high MAF). Turn truck off, clear code, restart, code 33 comes back. I KNEW I had a bad ECM connector terminal (had fixed it "temporarily") for one of the MAF wires (5V reference as I recall, B12) so I removed it, cut it off, and spliced in a new one. Code 33 gone, but how it runs hasn't changed. :(

Then I immediately get a code 21. But with truck off or on, the scanner shows that the TPS voltage is correct. Does anyone know if code 21 SHOULD set if the ECM is spitting out the correct voltage? You've got your reference, ground, and signal wire, if ANY of those were bad (and they'd have to be to trigger the code as I see it) you wouldn't have a correct TPS reading. I'll run the service manual test for TPS just to make sure I'm not missing something, but looking at the wiring of the circuit, I don't see what that's going to tell me.

Anyone run into something similar? Armchair mechanic-ing here, since I'm not at home to play around with it more.

Edit: Going to have to keep my eye on this one. I swapped in another EEPROM I had laying around from a previous tune, and it started right up, no codes, seems to run much better. But I didn't change anything when it started running worse initially. Hmm...

**1project2many** · 08-15-2012

Is the ALDL displaying the actual TPS, or a substituted value? Check shared grounds for a connection problem. If you happen to have MAF and TPS or CTS and TPS on a common ground, and the ground connection fails, signal voltage for both sensors can become erratic. A DVOM is often recommended as a test tool when codes are present.

Ensure all grounds at ecm are good. You changed the eprom but you also physically disturbed the box which can be enough to cause a loose pin to make a good connection temporarily. Finally, give the box a "tap test." holding onto the blade of the screwdriver, gently tap the handle against the ecm case while the engine is running. If the engine stumbles then you've probably got a classic case of bad solder connections in the ecm.

**dyeager535** · 08-15-2012

Yes, ALDL was displaying actual value, at least as far as I know....Voltage was "normal" with pedal at rest, and if I manipulated the throttle, voltage changed accordingly.

I did pull the Moates G1 to make sure all the connections were secure, and they seemed to be. Drove it to the gas station with the swapped-in EEPROM (older bin), and it's driving quite well. I have no clue for sure, but it certainly seemed like I had/have a corrupted bin. Something I did or something that happened when tunerpro crashed (does that once in a blue moon on the laptop) seems to have made the difference in triggering the codes. Swapping the EEPROM made the code 21 go away, and not return.

I was unaware that you could set a code like TPS with something in the bin messed up. I know the MAF codes can potentially be triggered when manipulating the values, but TPS is pretty basic, X voltage at idle seems to be the key trigger, and I'm not even sure where in the bin I'd go to monkey with the values that trigger the TPS code.