My 1998 Chevrolet Blazer is apparently possessed the devil, and I'm wondering if you guys might have any insights that would help me
figure this crazy thing out.

(This will be a longish message, but only because I'm trying to get all the details in.)

Here are the symptoms (which may be one problem, or several unrelated problems):

- Oil leak under the engine (may be related?)
- Fuel gauge mysteriously flips to empty (with Low Fuel light), then kicks back to normal
- Occasional "freakouts", which consists of....
o Engine sputtering, getting ready to stall
o Dash lights dimming
o RPMs dropping
o Oil pressure dropping
These freakouts usually happen when idling, but I've also noticed it running rough even when driving at normal street speeds.

Some backstory....

We had recently noticed some odd behavior at high speeds (the tach was bouncing a bit, surging forward and then letting up). Check engine light came on at one point. Took it to Checker, and their diagnostic tool said it was a slipping transmission (there was also a code for the MAP sensor, but we hypothesized that the transmission was the *real* problem). Took it to the transmission place, and they fixed (if I recall correctly) the pump and the torque converter.

Got it back from the transmission place, drove it around, and it worked great (couldn't recreate the original problem) -- until I was pulling onto our street and it started acting rough. Check engine light came on. Took it to Checker again, and it was the MAP sensor code again.

So, today, I went ahead and replaced the MAP sensor. The actual sensor portion of the old one was covered in oil, and it looked like it was starting to disintegrate. Definitely needed to be replaced.

Took it for a test drive, and everything seemed to be awesome (engine running more efficiently, for one thing), until I was at a stop light and the engine started one of the freakouts described above. Check Engine light came on again. Argh.

Drove it over to Checker to get the codes again. They came up with...

P0108: "Manifold Absolute Pressure/Barometric Pressure Circuit High Input"

...the same code we were getting before, but this time there were two others...

P0101: "Mass or Volume Air Flow (MAF) Circuit Malfunction"
P0404: "Exhaust Gas Recirculation Circuit Range/Performance"

...so it sounds like it definitely wasn't as simple as replacing the MAP sensor (though that probably needed to be done anyway).

Now, since all this stuff happened right after we got it back from the shop, it's temping to assume that the transmission place messed something up, but I don't think that's the case because we've actually had these problems (fuel flip, freakouts, etc.) at various times in the past -- just not as much recently. They've been on-and-off for the past few years.

The reason I include the oil leak is that we had actually brought it in to the dealership a couple years ago to have them diagnose it. I don't remember their exact explanation, though I believe it included the words "manifold" and "cracked," and I recall they wanted a heap of money (which we didn't have) to fix it. I didn't really trust the guy I was talking too, though, so I don't know if that was accurate information, and we took the classic automotive strategy of ignoring it and hoping it would go away.

So, that's where we stand now -- after putting lots of money and time into it, the Blazer actually runs *worse* now than it has in the past several months. We don't have the cash to just take it to a mechanic and ask them to fix it, so I'm probably going to have to tackle it myself (if possible).

(Oh, and it's due for emissions testing at the end of the month. Of course.)

Any ideas??

Thanks!
James

 

Sounds like you may have a wiring problem that is affecting all of those sensors... It could be something as simple as a faulty engine ground.

When was the last time a tune up was done on the vehicle (plugs/wires/cap/rotor)?

Some other easy maintenance that can be completed would be to remove the throttle body and clean it completely (especially the IAC - idle air control valve). Remove and clean the MAF sensor (be careful with the delicate wires). Remove and clean the EGR valve (new gasket is pretty much required). You'll have to use some sensor safe cleaner on these items. There is MAF sensor specific cleaners that do a better job of removing the crud that builds up on the fine wires reducing the risk of damaging the sensor while cleaning it. For the EGR valve, just use the same throttle body cleaner that you used on the TB and possibly use an old tooth brush to clean it. Before you toss the EGR valve back on, attempt to start the truck with it off so that it'll blow all of the junk out of the EGR supply tube.

As far as your oil leak... Well, if you have something broken that is leaking the oil out, then you pretty much have to replace the component or deal with the spot on the driveway... It could be something as simple as a leaking stand-pipe for the oil pressure sending unit or loose oil pan bolts. I personally went through loose pan bolts on my '00 Bravada. I had 9 loose bolts on the oil pan and I was scared that it was a leaking rear main seal. Just figured I'd try tightening them up and the leak stopped dead in its tracks.

 

My first thoughts were electrical, and Kyle has done an excellent job (as usual) of covering that thought. Could be a piched wiring harness, could be a bad bad ground strap, could be an abraded wire shorting to ground. Electrical gremlins are a real pain to trace.

My other thought was a vacuum leak. I know that sounds strange, BUT a friend of mine had a perfectly functioning mini-van that he brought in to have a simple oil change. When he got the van back, he couldn't even drive it away from the shop, it barely ran. He stated the van "freaked out" with the dash lights flickering, the guages jumping, etc. They got it back to shop (under human push power) and "diagnosed" a catastrophic transmission failure. He didn't buy it since it ran perfectly fine before the oil change. A little more poking around revealed that one of the oil techinicians had "accidently" disconnected a vacuum line and tucked it out of his way. He forgot to re-connect it. Once they found the line and re-connected it, the van was back to normal.

Could be nothing, could be something. Good Luck.

 

Good call on the vacuum leak! These MAF controlled engines do not deal too well with unmetered air entering the engine. Just for haha's, make sure that the valve cover vent line is connected to the back of the throttlebody intake hat (plastic part on top of the throttle body).

 

Get your alternator tested

 

I think grounding may be a contributing factor. Good luck!