88 2.8L s-10 EATING GAS

[wyatt_earb]

I've got an 88 S-10 4x4 blazer with a 2.8L thats eating gas. I'm getting around 10 mpg and I was getting 20 mpg.

It has r-15 245 tires on it and had a recent tune up, plugs wires etc...
The cat has been hollowed out, about a year ago and I've always kept up on oil changes and tune ups.

The gas tank leaked, which I thought it was the reason for the bad gas mileage, but after fixing the leaks it still eats gas.

The EGR, O2 sensor, and thermostat have all been recently replaced, within 1.5 years.

Soo just recently:
I changed the plugs wires cap rotor, again!, the problem still exsist. so now I've been told that it could be the MAP sensor and/or the idle sensor..... not sure on this. ANY ADVICE FROM ANYONE????

I'm also currently runnin a can of seafoam through a tank of 93 octane. And a friend of mine told me to run a bottle of tranny fluid through it to clean out the motor, but this sounded kinda redneckish to me.

SOMEONE HAS TO BE ABLE TO HELP ME ON THIS....PLEASE!!!

[silicon212]

You didn't indicate whether the MIL (Malfunction Indicator Lamp, aka check engine, service engine soon light) is on? If so, can you obtain diagnostic trouble codes (DTC) from it? When you turn the key from the off or lock position to run, the light should 'bounce' on, off and then on again. If it does not, this could indicate an ECM and/or ROM CALPAK/MEMCAL issue. If you are able to obtain a DTC and it's a Code 12 - the ECM and MEMCAL should be running OK. If the ECM tests OK -

My first guess would be a plugged air filter (especially with a Code 45 DTC) and my second guess would be an EGO sensor (oxygen, lambda et al) issue, especially if the engine is running rich. It doesn't matter if it's recent, an engine running overly rich can cause the EGO sensor to go 'tango uniform' in short order.

PS - hollowing out a cat on anything newer than 1977 (the old bead cats) won't yield either a performance or economy gain - contrary to popular opinion. In fact, many of the engine's onboard systems are designed around it and removing it (or hollowing it out) can actually hurt. In fact, GM's first incarnation of what would become the C3 system that you have onboard now was called C4 - for Computer Controlled Catalytic Converter (C3 is Computer Command Control). You are wasting your money with 93 octane, and with the SeaFoam treatment. The problem could be a leaky injector, but that would show up with an MIL and a DTC 45 (and a dead EGO sensor).

Another possibility could be the coolant temperature sensor (CTS).

[wyatt_earb]

The check engine light isn't on. Could the problem just be that I need to put another catalytic converter on it? I took it to a shop and they said it'd be a waste of time to hook the computer up to it b.c the check engine light isn't on. Just this last weekend I changed the plugs, wires, cap, rotor, fuel, and air filter. And the O2 sensor isn't even a year old. I'm really stumped on this one, it runs great and sounds fine, just eats gas.....

[silicon212]

Originally Posted by wyatt_earb

The check engine light isn't on. Could the problem just be that I need to put another catalytic converter on it? I took it to a shop and they said it'd be a waste of time to hook the computer up to it b.c the check engine light isn't on. Just this last weekend I changed the plugs, wires, cap, rotor, fuel, and air filter. And the O2 sensor isn't even a year old. I'm really stumped on this one, it runs great and sounds fine, just eats gas.....

There are some trouble codes that could be set without lighting up the MIL - you can still pull codes.

I'd check the CTS and replace the EGO.

If your cat was plugged, that would definitely hurt economy, but it'd also hurt performance and your engine will always be on the verge of overheating.

[wyatt_earb]

Going to switch the MAP sensor out, I'll see how that goes for now.

[liloldbeater]

I had the same problem recently with my 1989 4.3 jimmy and it was the coolent temp sensor for the computer, was always giving a cold signal which made it super rich all the time. It was $5 at auto zone.

[wyatt_earb]

Off work today, so I'll dick with it today. I have an 87 2.8 s10, so could I just take the map sensor from that and see if that makes a difference?

[silicon212]

IT ISN'T THE MAP SENSOR. What you're doing is tantamount to replacing the motherboard, CPU and power supply on a computer that's not powering on because the main breaker for the house electricity is off.

Don't continue wasting your time with it.

Check the Coolant Temperature Sensor. It should be on the thermostat housing (or near it) and it should have a yellow and black wire on it.

[wyatt_earb]

Took it to the auto parts store and they ran their free diagnosis system on it and it came back "low voltage" to the map sensor. But he said that could be many different scenarios leading to that. Advised me to take it to a dealership and have them hook it up to a better diagnosis system. Silicon I'm just going to take your advice and replace the coolant sensor, it was only 8$, and see where it goes from there.

[wyatt_earb]

Changed the coolant temp sensor and it still seems to be eating gas. Going to take it and have it ran on the diagnosis machine again and see if the same codes pop up.

[wyatt_earb]

Diagnosis came back and didnt come up with anything and it's still eating gas.
Exhaust smells rich and I'm guessing that you can't manually adjust a throttle body they way you can a carb. Running out of options here, any ideas??????

[BlazerLT]

Yes, I know what you need to do.

You need to get a timing gun, remove the timing wire from the connector under the glove box (brown and black wire), and time the engine to zero.

Your base timing might be off quite a bit and could be retarded and rich.

The next thing would be to replace the thermostat.

Ever zero'd the timing?

[wyatt_earb]

Never zeroed the timing, but I have replaced the thermostat.

[BlazerLT]

What temperature range of thermostat did you install?

I would reset the timing like I described earlier. Usually will be the problem.

So you said that there was a code stored for the MAP sensor? Did you ever solve that?

[wyatt_earb]

Changed the coolant temp sensor and the code went away. The code was " low voltage to map sensor" so the guy told me to change the coolant temp sensor and the code went away.

I believe I put a 160 degree thermostat in it, but it was eating gas before this. Not seeing why the timing would need resets, seems responsive or backfire, etc...

But I did notice the gas tank is still leaking, very lightly though. It's nothing like it was, infact it doesnt even drip to the ground, the frame is just moist with gas. I'm going to a self serve junk yard thats full of cars, so I'll hopefully pick up a tank there, along with a map sensor.

Are the s-10 trucks and blazers the same tanks? I figure they are, but never know. Also do most of the tanks from the 80s match up, 4.3s, 2.5, 2.8? And are the maps sensors from 2.8s all the same from the 80s era?

If anyone has any other advice it'd be greatly appreciated.