I don't post here much. My 01 has only 90K on her, and this is the first real diagnostic problem I've had.
Last Christmas, driving into the mountains, the D started bucking on me--RPMs fluctuating, felt like it was missing, losing power, etc. I had to go up a lot of the hills in 2d. Before long I got an MIL too. I read the code the next day, and got P0121. The FSM wasn't really helpful, so I just scratched my head for a day or so, and drove the car a bit more, with the same symptoms. Then, on the second morning, the MIL was off, and she drove fine. And has been fine since. This started just after I had filled up, so I figured I just got a tank of bad gas (even though I had only gone through maybe a quarter tank) and forgot about it.
Then, coming home this weekend, the same thing happened. I managed to make it home (about 125 miles), but there were some moments when I was about to lose hope, although it did seem to get a little better towards the end. When I got home and read the code, I got the same thing -- P0121.
From what I can tell, that means the TSP and MAP sensor aren't getting the same voltage. I tested the TSP and I think it's OK. The first couple of times I thought there was a flat spot or a dip in the voltage, but I didn't have a good grip and I'm not sure I was rotating the throttle smoothly. The next couple of times it read fine. It's conceivable I loosened something up the first time or two though.
When I tried to read the MAP sensor, I got nothing. No voltage across the terminals on the connector and none when I backprobed the middle connector. I guess that would explain why the two aren't getting the same voltages, but I wonder if the truck will even run if the MAP is reading 0. I also wonder if I'm not missing something.
In the process, I also noticed that most of the clips on the air filter housing were loose and the underside lip of the bellows between the air filter and intake wasn't on properly. I assume either of those could have resulted in problems with the air-fuel mixture. The bellows has probably been on wrong for the last month or so since I cleaned the TB. But I spent some time on some fairly nasty washboard this weekend, so that might explain why the problem suddenly got worse.
After doing the testing, I took it out for just a couple of minutes at freeway speeds and it seems OK, although the MIL is still on. I'd like to think it was just the bellows and I fixed it, but it's too early to tell. And that wouldn't explain why I'm getting the same symptoms as I did a year ago, or why I'm getting the P0121.
Any ideas what my problem is? It still seems unlikely that I'm getting 0 voltage at the MAP, but I don't know what else to conclude. And if that's the problem, how likely is it that it'd appear for a couple of days, disappear for almost a year, and then show up again? Any other thoughts?
Last Christmas, driving into the mountains, the D started bucking on me--RPMs fluctuating, felt like it was missing, losing power, etc. I had to go up a lot of the hills in 2d. Before long I got an MIL too. I read the code the next day, and got P0121. The FSM wasn't really helpful, so I just scratched my head for a day or so, and drove the car a bit more, with the same symptoms. Then, on the second morning, the MIL was off, and she drove fine. And has been fine since. This started just after I had filled up, so I figured I just got a tank of bad gas (even though I had only gone through maybe a quarter tank) and forgot about it.
Then, coming home this weekend, the same thing happened. I managed to make it home (about 125 miles), but there were some moments when I was about to lose hope, although it did seem to get a little better towards the end. When I got home and read the code, I got the same thing -- P0121.
From what I can tell, that means the TSP and MAP sensor aren't getting the same voltage. I tested the TSP and I think it's OK. The first couple of times I thought there was a flat spot or a dip in the voltage, but I didn't have a good grip and I'm not sure I was rotating the throttle smoothly. The next couple of times it read fine. It's conceivable I loosened something up the first time or two though.
When I tried to read the MAP sensor, I got nothing. No voltage across the terminals on the connector and none when I backprobed the middle connector. I guess that would explain why the two aren't getting the same voltages, but I wonder if the truck will even run if the MAP is reading 0. I also wonder if I'm not missing something.
In the process, I also noticed that most of the clips on the air filter housing were loose and the underside lip of the bellows between the air filter and intake wasn't on properly. I assume either of those could have resulted in problems with the air-fuel mixture. The bellows has probably been on wrong for the last month or so since I cleaned the TB. But I spent some time on some fairly nasty washboard this weekend, so that might explain why the problem suddenly got worse.
After doing the testing, I took it out for just a couple of minutes at freeway speeds and it seems OK, although the MIL is still on. I'd like to think it was just the bellows and I fixed it, but it's too early to tell. And that wouldn't explain why I'm getting the same symptoms as I did a year ago, or why I'm getting the P0121.
Any ideas what my problem is? It still seems unlikely that I'm getting 0 voltage at the MAP, but I don't know what else to conclude. And if that's the problem, how likely is it that it'd appear for a couple of days, disappear for almost a year, and then show up again? Any other thoughts?
