jamesaz

My 1998 Chevrolet Blazer is apparently possessed by demons, 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

UghChevy

Well James it does sound like you have a serious problem on your hand. Based off of my Diesel Mechanic abilities, I will do what I can to at least point you in the correct direction.

~Oil leak under the car: That will definitely be a good starting place to get that fixed. Epically if it is causing the sensor to get messed up, it could be causing a short in the wiring if enough oil gets built up to eat away the wires.

~Fuel gage mysteriously flips to empty: With the Fuel sender unit in the gas tank it is basically a mini potentiometer that is looking at resistance, the reason it could be freaking out like that could be due to a bad coil in the sending unit itself.
The way to test that would be to take it out of the tank and take an Ohm Meter to it and look for a smooth transition of numbers a nice even flow sort of speak.

~Occasional "Freak-out"
-Engine sputtering: That could be bad gas, or a clogged injector, garbage in the fuel lines or a bad fuel filter.
A way to tackle it would be to replace the fuel filter, and add some injector cleaner additive/treatment to the gas tank (use as directed on the bottle all are different)
-Dash lights dimming: That could be an intermittent short like a loose wire connection to either the back of the dimmer switch or the dashboard itself.
Not much advice to tackle that other than to follow a million wires to try and find a loose connection possibly.
-RPMs Dropping: That could be related to the engine sputtering.
Try and fix the sputtering and see if it still continues.
-Oil Pressure dropping: That could be caused to a bad sending unit in the engine to the gauge, or it could be low on oil.
A way to check the problem would be to plumb in a Mechanical Oil PSI gauge in the oil passage and monitor the Mechanical gauge as well as the Oil PSI in the car itself. But first you can just check the oil and make sure to use the recommended oil for your climate and the engine itself and see if by simply changing it or adding more will cure the problem.

Now I am not sure if all of that will actually fix it but it might help point you in the right direction to start looking, I don’t know if it is much help but I hope it is :-)

Rotten101

I have another suggestion.
My 97 Astro with a 4.3L Vortec V6 was doing almost exactly the same things. Except for the fuel guage and the oil leak. Same codes, same troubles. Felt like the tranny was slipping etc... It turned out to be the catalytic converter having disintegrated inside and wasn't flowing properly. It made a vibrating noise just before it started giving us troubles and every mechanic I took it to had a different opinion on what it was. First it was a tuning problem, ergo we installed plugs, wires, rotor and cap etc... drove itaway still did it.Then took it to another mechanic he figured it was the tranny...??? What? How does that make any sense? With a code of P0108? Needless to say... I got my vehicle out of his hands right away. Then took it to my original dealer. They said I needed four sensors and a new intake manifold. Plus a tune up! Which was just done a week before!!! So I went to my local parts store, bought my owncode reader. Found out that it was the map sensor but it also had something to do with the catalyst sensor. I clicked rightaway. I went and bought the cheapest replacement catalytic converter I could get. $140Put it in myself had my welder friend weld it for me. Voila! Didn't even need a map sensor. The code has stopped and hasn't returned. The vehicle drives almost like new with a total of 270000km on it. I surmise that it could have all been caused by the back pressure caused bythe catalytic converter or something. I will warn you, however, that although this is what worked for me... I am not a mechanic. I also agree with the fuel guage problem being in your tank sending unit. I haverigs and I have run into that problem alot. It's really a cheap part that probably has nothing to do with the other stuff. Likely the leak is just that, a leak. All of your other symtoms sound just like mine were and all seemed to be related to the catalytic converter. Once that was fixed they went away. I also had to replace the alternator about two weeks later but I am not sure if it was related. It ran fine in between.

techboy07

well, for starters, oil ussually doesnt just "leak". there has to be a reason for it. on your year of vehicle, its possible to be any seal or gasket on there. first thing you need to do is check to see if you PCV valve or lines are pluged. next, as for the "freakouts", i would recomend a fuel injector flush, and a tune up. use good quality parts too, no "NAPA" or "Auto Zone" parts. it will save you alot of un-needed maintinence. depending on youre climate, you could be getting moisture under your distributor cap, causing the engine to stall and in turn making your lights dim and oil guage drop slightly. and for the fuel sender, its normal. youre lucky you have made it this far without having this problem. its VERY common. just to warn you, your fuel pump may be on its way out to. thats very common too. hope this info helped.

rutler101

These other diagnosis are very possible. Just one thing i wanted to add. This very well could be a bad ground causing these multiple problems. Everytime i saw a Voltage High on a vehicle in the shop it always came down to a ground or short to ground problem. I have also seen this happen with a bad altenator generating too much electricity. just a thought good luck.

ampchevy88

common engine oil leak, from the remote oil filter housing lines if you have a 4wd.
bad ground, a common issue for intemittant lights dimming and gauges fluctuating.
egr valve carbon buildup, acommon issue for sputtering.