Thanks! I checked it, and it went kinda fast, but I think I got code 13... What is that? I'm not sure if it actually pulled a code, though, because at first, I got what I thought was 13, then it just kept flashing 3 times, pausing, flashing 3 times, pausing, so on and so forth until I finally turned off the key. The check engine light hasn't been on, but it is simply running weird.

 

A code 13 is the O2 sensor, but the norm is to check the wiring and the connections to the O2 sensor, but you might have seen the code 12 as you first started the the testing....Possibly you saw the code 12 that flashes 3 times before going to the stored trouble code....It can fool ya if you're not watching closely...

But, the 3 flashes, pause, 3 flashes is a code 33. That is MAP sensor. Look real close at the vacuum hoses from the MAP sensor and the wiring connection. The MAP sensor (Manifold Absolute Pressure) is a device that monitors intake manifold pressure and sends info to the ECM with changes in engine needs for fuel and such via voltage output from the sensor to the ECM. The ECM will use this info to change and control the fuel system and ignition timing.

If the MAP sensor is acting up this may be related to your problem, but I feel that your problem is vacuuum related. Most vehicles I worked on back when I was spinning wrenches (a part time job from '85 to '93) had some hidden vacuum leak that would defy logic. Look real close at the vacuum lines for buldging (too soft) to cracking lines (dried up) and where the lines are connected by the plastic couplings. These little pesky connectors are famous for being broken, but still holding a line to them, but....leaking. If you suspect you have a leak at a spot, take a glass of soapy water and a brush and coat the spot in question. You should see bubbles coming from the bad hose or connector. Timing can be a cause as well for rough or loping idle, but I always look at the vacuum first. You spot a leaking line, replace it. A cracked connector, get another. O Rily's has a great selection of connectors and they don't cost an arm and a leg!

The trouble code stored in the ECM can be cleared from memory by pulling the neg. cable for 10 to 30 seconds, and it will reset. After clearing the memory (even if the part was replaced prior to you getting the vehicle if not cleared from memory will remain in the ECM) you can start the engine and let it warm up and see if the check engine light comes on again. Then go to the diagnostic check with the ALDL and get the code from that. Or simply do this even if the light doesn't come on after clearing the memory.

If it goes back to a code 33, that indicates a problem with the MAP sensor for sure. However, simply replacing the MAP sensor may not resolve the problem. Too often parts and sensors are yanked out and replaced only to find the problem still exists. Check connections, wiring, and such first before going at it with the "Shotgun Approach" by pulling parts and sensors and replacing things until the problem goes away. That way you don't really find the problem at it's source and you spend more than you need to.

Ok, I yacked long enough....

Give me a hollar if you need more assistance. I surely don't know it all, but together with the assistance for other forum members, we'll get this problem licked!

Wade

 

Alright... I went out there... By myself this time! And read it again. This time I had my full attention directed on it. It flashed that code 12 three times like you said, but then it kept on flashing code 12 over and over until I turned off the key. Does that mean there is no code? Like I said, the check engine light hasn't been on. I would've noticed that... I think it might be the fuel pump. I went through a rough time lately, and I was always running on empty. I heard that's bad for the in-tank pumps, and that's what these Blazers use. When I press the gas, it's fine, but when I let it idle by itself it shudders every now and then. It acts like it's kinda low. Is there a way to test the fuel pump?

 

Well then, the code 12 is normal. That tells us that the ECM has no recorded trouble codes stored in memory. You're good there as far as any emissions trouble codes, thus no trouble there....

Fuel pump....ah, well first off have someone turn the key on, but not start the engine while you are right up next to the tank by the left rear wheel. Listen for for a "whirrling" sound to know if the pump is going. This sounds kinda stupid in a way, but it does let you know if it's getting the voltage to the pump, that it's turning, and at least is delivering fuel. Now as to testing the fuel pump further, that involves checking the fuel pressure (you'll need a fuel pressure gauge and adapters to fit your TBI fuel inlet and you will have several things to do that are usually not easily done by a new home mechanic. Many things go with a pressure check that are just a bit tricky if you have never done anything like this before. If you have no trouble getting the enging to run well past the rough idle, chances are your fuel pump is doing it's thing well. If the fuel pump is week or on it's way out, it should be working badly through all phases of running, from idle to near full throttle. (usually....)

Another thing you might do is check the EGR valve. That is easy by simply pressing GENTLY on the diaphram of the EGR and if it moves easily, you're good. There may be some built up carbon on the inside of the unit. You can pull it and clean the the system. DO NOT use solvents to clean it. Use a wire brush, scrapers, and such. Solvents will melt the diaphram and you will have trashed the ERG valve. Be sure to clean it dry and to knock out any dust and debris that is on or near the fitting. You don't want that gunk going into the valve and killing the diaphram! Be sure to use a new gasket. They don't cost that much and using an old one that may peel apart when you do your inspection/cleaning will lead to more problems by leaking!

If the EGR is pugged up it will make the engine run rough. Idle poorly, and generally make your whole engine act up! If the valve opens too much, it will cause a rough idle. If it's always open it might not idle at all! If there are no vacuum leaks found, check that EGR valve and if dirty, clean it. If the diaphram is stuck or won't move, replace the EGR valve.

If you must replace that valve, be sure to clean the mounting surface well and use a new gasket when mounting the replacement. Try to keep as good a seal there as possible. Leakage will not help you in getting the system right!

Hope that gives you more on what to look at with this problem. As for my poor old '92, I'm fighting nearly the same thing. Tracing tons of vacuum leaks, filthy parts, the works! Idle is good, but I'm getting a surging at times at cruise speeds. That's usually vacumm and EGR related for the most part. Finding the time is what's killing me here! That and money too!!!

Later,
Wade