EDIT: I forgot to mention, this is a 1999 Blazer 4x4.

Alright, in the past couple of months I have bought a new catalytic converter (catalyst efficiency error), distributor (missing on wet/humid days, is now fixed), both upstream O2 sensors, new air filter, new plugs, plug wires, distributor cap, and a rotor.

During a two hour trip over the weekend, it started running rough at idle and while sitting at stop lights. I could let it cool down for a while and things would smooth back out, but at operating temperatures it would go right back at it. Note that it never overheated. While running rough the oil pressure would drop to around 17-18 PSI at idle (according to the factory gauge). Pressure would go back up when accelerating. Finally I got yet ANOTHER CEL, and when I scanned it today I got codes P131 and P171.

Any suggestions on where to start? I'm VERY quickly coming to despise this piece of junk.

 

p131 02 Sensor Low Volts Bank 1 Fault
p171 The code says the fuel mixture is too lean on bank 1 of the engine. The O2 sensor is not switching at this point and the fuel adjust is maxed out.

 

I read the code descriptions. Since I have brand new O2 sensors (including that bank 1 sensor), the only thing I can figure is that for some reason I'm getting too much air, or too little fuel. That means it could be a vacuum leak ANYWHERE, or absolutely any fuel system component. I was hoping the combination of the two errors might help narrow that down a little, if someone has had experience with it. God help me if its a vacuum problem.

 

First off what brand replacement parts did you use? Ac Delco or Delphi is the way to go just ask everyone on here. these trucks are very picky when it comes to that.

But the next thing you need to do is (with the engine off) unplug the Mass Airflow sensor and drive it around for a while and see if the problem continues. if it does not, then you most likely have a vacuum leak. then you just have to listen for it, generally pretty easy to find, and if its enough to throw a lean code then the leak will probably be good sized. (when you unplug the MAF sensor the tranny may shift into D and R pretty hard, so dont worry thats what happens)

If the problem continues then you probably have a faulty part if you didnt use one of those two brands or you need to get your fuel pressure checked.

If it turns out to be a vacuum leak, listen to where the spider injector head comes through the intake and plugs into the harness (back of the intake) the seal went bad on my 2001 project blazer and caused a vac leak. 5$ for the seal and about 1 hr to take the intake off replace and put back on and its fixed.

 

It seems to do it more on longer interstate drives, and since I've mainly been driving around town the last few days, I've not had much trouble with it. My CEL even turned itself off, but like I've said, I've not taken an extended trip yet to know if things actually improved. Most problems don't fix themselves, lol.

I'm going to start by changing the fuel filter. I already have the replacement part in the garage; I just hadn't got around to installing it yet. If I'm lucky, maybe that will be the problem. If not, I'll move on to your suggestion of unplugging the MAF sensor when it starts doing it again.

Incidentally, does this model have an IAC valve, and could it cause these symptoms? I seem to only have trouble when idling at a stoplight (after the engine warms up); when driving down the road or accelerating, it doesn't have driveability issues.

 

UPDATE: I replaced the fuel filter; it made no difference. Still getting the same codes yet again.

After it threw the code this time, I pulled over and disconnected the MAF sensor. The symptoms got A LOT worse instead of clearing up.

Oil pressure seems to be back up, but it seems to be idling rough all the time now instead of just when its warm. I've also noticed a sweet smell when I come to a stop, but it doesn't look like antifreeze is getting into the oil. It also doesn't seem to be losing antifreeze.

Is it just time to haul this thing to the scrap yard and start over?

 

In caseyou missed this.

 

I can't even remember what brand they were, but they likely weren't AC Delco. So, I guess thats about $100 in the garbage when I replace them and $250 if replacing with AC Delco doesn't fix the problem.

EDIT: They were Bosch.

 

While its easyto do and a good idea I would check your fuel lines,if they are totaly rusted on the outside then more than likely they are rusted and corred on the inside causing low fuel presure.This happens as a result of watered down gas constantly being ran through those metal fuel lines.The water will rust them from the inside blocking the lines with junk.As mentioned in an earlier post I MADE this discovery while replacing mine.Good luck

 

Thanks for the tip. I recently replaced the fuel filter, and today I traced the lines to my intake to find the fuel pressure port. The lines looked good all the way down without any rust. I do appreciate the suggestion though. Now I at least know where to connect my pressure gauge to check fuel pressure, as soon as I can borrow a gauge from someone to do it.

I found a rotten vacuum line going from that (thingy?) connected to the PCV hose to a check valve that (according to another topic on here) runs to the HVAC vacuum control and the 4x4 actuator. That makes sense; neither one of them has worked right as long as I've had it. I replaced that vacuum line and plugged off the nipple on the check valve in line with the source line (apparently the port for the 4x4 actuator, since my HVAC started blowing correctly). Even with that fixed, its still having the same issue. Its not even waiting to warm up anymore; as soon as I drive to the end of the street and stop at the stop sign, it starts idling rough.

Since its done it more often, I've had a better chance to get a whiff of that weird smell. "Sweet" isn't necessarily the best word to describe it, because it doesn't smell like antifreeze. It doesn't smell like electrical burning, but it smells like a hot electric motor. If you ever played with electric trains or remote-controlled cars as a kid and got a whiff of the electronics after running it for a while, its kind of like that.

Before someone suggests it, I find it unlikely to be the alternator on its way out. Its not emitting any strange noises or smoke, and my voltmeter stays steady at 14 volts.

Also, there isn't any smoke from the tailpipe, and it never has trouble starting.