Question for the mechanics-92 GMC Suburban.

[jmebonner]

I have a 92 GMC suburban w/ 98k 4x4 automatic I'm getting ready to sell. It's in VERY good shape for the year, only one problem. When I really get into the gas - like floored, or it kicks down to passing gear on a hill, It makes a short noise, like a 1-2 second purr, like If you purse your lips and roll your tongue and breathe out real hard at the same time (lol, I know you get that kind of stuff all the time, but that's the best way to describe it.) And then the Service engine soon light comes on. It clears when you turn it off and back on again. There's no difficulty shifting at any time, before or after the problem. Nothing. Seems to have no effect at all side from the light. Any ideas? If it's something minor, I'll just sell it like that and tell the buyer. If it's major I'll get it fixed first.

Thanks!

[electric]

Service engine soon light means your engine is burning
to rich and the oxygen sensor needs to be replace

in my opinion

for your non believers disconnect the wire to your oxygen
sensor and see how far you get [on your exhaust pipe]

[RedFury]

I'd have to agree with Electric.

Now, you can confirm this by shorting out two of the connectors on the diagnostic port under the dash to the right of the steering column and turn the key on. the service engine light will blink out the code for the offending signal caller ( O2 sensor, coolant sensor, MAP and MAF sensors, etc ). Look up the code in a Chiltons manual, or call your local shop and ask them what that code points to. If it calls for a faulty or failing O2 sensor, then you probably need a new one. They get partially plugged up after a while, and should be replaced periodically.

Now, here's what's happening. When you get on the gas, you are allowing more Air into the engine than fuel, the O2 sensor senses this and richens the fuel mixture to compensate. If it isn't reading the Oxygen levels at a fast enough rate, then you will have a lag in the response time. So, when you tromp on the accelerator, the engine is fuel starved for a moment, which is most likely what is causing the noise.


Or, I could just be talking out of my rear end, but that's for you to decide

[pickel]

Check your EGR valve( take it off and see if it clogged with carbon and the diaphram is working properly ) and all vacumn lines. Get some fuel injector cleaner and try a tankful of "Premium" gas along with about a pint of automatic transmission fluid ( breaks up the carbon ) and see what happens before any major work.

[RedFury]

Originally posted by electric

for your non believers disconnect the wire to your oxygen
sensor and see how far you get [on your exhaust pipe]

Not as far, but the Computer will put the O2 sensor signal to the default and you will definetely lose some of your gas mileage.

Same thing goes for pulling the lock out solenoid on the torque converter plug. The converter won't lock up, so mileage will also suffer....won't hurt the tranny, just won't be as efficient. ( this is a work around for a sticky solenoid on some front wheel drive GMs with high mileage trannies that stay in gear even with the lever in park ).

[truckpuller]

If this noise you are discribing sounds somethime like a jet plane taking off possibility of a partially plugged catyalitic convertor causing a restriction in your exhaust flow by having to much back pressure which can screw with the oxygen sensor which in turn can turn your check engine light on. Best thing to do is have someone run a scanner on vehicle. This was just a thought Good Luck.

[jmebonner]

Thanks fellas. RedFury, can you elaborate as to how I should go about shorting the diagnostic port? I could probably try it late tomorrow.

Thanks!

[RedFury]

Sure, just let me run around here with my head cut off trying to find the book...AAHHHH!!!!
code number: 13- Oxygen sensor or it circuit
Short the A and B terminal with a paper clip , then turn the key "on" and count the flashes of the "check engine" light.

This connector should be right under the dash by your knees.

The codes will flash 3 times each. Write down the numbers and check Here to find out what they mean.

[pickel]

One other thing you might want try. Disconnect the negative battery terminal for about a minute. This will reset the computer and clear any faults.

[sao95]

if it was the o2 sensor there would be light jolt backwards/lag, that could be felt as well as heard