P0771 - Engine Running Lean

[hufhouse]

I have a Service Engine Soon light on and I need help.

Here's what happened:

I did the Intake Manifold repair and I had a gas leak afterward. I repaired the gas leak and the SES light came on.

I went to AutoZone and they said it was P0771-Engine running lean.

The guy at AutoZone said to use Fuel Injector Cleaner. I did that.

Someone in another thread said to clean the MAF sensor well. I did that.

Here are some things that I know:

1. The MAF sensor has a little screen in the front. That has a very small area (about half the size of a dime) that is a little dented. (Chalk that up to it being virtually impossible to replace the air filter. :-()

2. There is a vacuum hose that comes from the passenger side fender (around the window washer fluid tank) and enters the plenum on the back left side (as you are looking at the engine). It is very small. When removing it to do the gas leak repair, the little rubber boot tore a little.

3. When I did the gas leak repair, I put in all new o-rings.

4. When I took the car for a test drive after fixing the gas leak, I did not get a SES light. It was only when my wife drove it the next day. After I cleared the code and cleaned the MAF sensor, I did not get the SES light. It was only on the next trip that it came on again. In other words, it doesn't come on right after clearing the code...it comes on in the next trip. Weird.

I keep assuming this has something to do with the fuel repair, but maybe it doesn't. All I did was remove the fuel rail, replace all twelve o-rings on the injectors and the o-ring on the input and put everything back. Of course, this required that I unplug virtually every electrical connection on the engine. That's probably the source of the problem. However, I'm confident that everything is plugged back in.

So, lay it on me. What's my problem? How do I troubleshoot this?

I'm headed to Mississippi to help rebuild after Katrina in a couple of days, so I won't be able to troubleshoot this until after 3/13 or so. I also won't have internet access. However, please give me your thoughts so I can tackle this when I return.

[hufhouse]

Just some additional info...the vacuum tube that I tore is for the heating and cooling vent dampers. I doubt it has anything to do with my SES light being on.

Anybody got any ideas?

[GTP Dad]

Did you clean the MAF sensor? If they get dirty they can set the P0771 code by allowing too much air to enter the engine. Remove it and spray the wires with electronics cleaner. Don't touch the wires and spray gently. You will also need a security torx bit. Available at Sears for about $30 per set.

[hufhouse]

Originally Posted by GTP Dad

Did you clean the MAF sensor? If they get dirty they can set the P0771 code by allowing too much air to enter the engine. Remove it and spray the wires with electronics cleaner. Don't touch the wires and spray gently. You will also need a security torx bit. Available at Sears for about $30 per set.

Well, I THOUGHT I cleaned the MAF sensor. What do I use the torx bit for? I figured that you just spray cleaner on the wires. Sorry for my ignorance, but I have to admit that I just took it off and sprayed it down with choke cleaner. Obviously, that's not what you had in mind. Duh. Where do I get electronics cleaner and what do I use the torx bit for?

Also, I have another puzzle. I took the van to pick up a pizza, and the SES light is still on. I pulled into the garage when I got home, and thought to myself that maybe if I just "rev" the engine up a little bit I can "blow the carbon out" as my Momma used to say.

So, I gave 'er the gas, and it went up to about 3800 RPMs, and then all of a sudden it acted like it lost power, then went back up to 3800 RPMs, and started alternating back and forth about 2x per second. Kind of a vroom-vroom-vroom-vroom-vroom thing without moving the gas pedal.

What's up with this thing? Is it possessed of demons or something?

Any answers would help. I'm leaving in the morning to do Katrina relief. I'll be back in a week for lots of great answers!

[maxwedge]

There is a rev limter to stop someone from blowing the engine racing it neutral, be thankful! What spray cleaner? You need electrical parts cleaner, Radio Shack has it. You need to access the heated wires in the maf that stick out into the airstream. Any vacuum leak can also cause this. What engine is this ? If it is a 3800 you may have left out one of the "o" rings for the pcv under the map sensor in the manifold.

[hufhouse]

I stopped today at Radio Shack, and they no longer sell electronics cleaner due to environmental concerns. I'll keep looking for it.

[hufhouse]

I took another look at this problem today, and I seem to have licked the problem. The light went out this evening, and I've successfully made 2-3 trips without it coming back on.

I did three things, and I don't know which helped. I will put them in order of what I THINK did the trick first.

1. I had torn an "L" in a vacuum hose that controls the heat damper. I have the part on order, but it hasn't come in yet. Today, I "duct taped" the part really good. I had ASSUMED it wasn't related, but I could have been wrong.

2. I cleaned the MAF sensor again. I still haven't found electronics cleaner, but I did have some aerosol battery terminal cleaner. I sprayed that on, then "rinsed" with some choke cleaner.

3. I poured another dose of fuel injector cleaner into the gas tank.

I'm just hoping the light stays off. Those things are SO annoying.