Rough Idle, Bad fuel mileage

[ikeman]

I have '93 GMC, 4.3l, with 130K miles. It is idling a little rough and my gas mileage has gone done about 75 miles per a tank full. I notice the engine also detonates when it is turned off. There is no service engine light nor is it displaying any code.

 

I did a general tune up. I've replaced the plugs, wires, distributor cap and rotor (Plugs and wires are AC Delco and the distributor cap and rotor are Borg Wargner). The local GM dealer just did a fuel injector flush. I still have the rough idle.

 

The dealer put the 'computer' on it and they told they can't find anything wrong with it - everyting is operating within specs. I had my shade tree mechanic look at it and he can't figure what is wrong with it either.

 

I've been told because it's a 6 cyclinder it's to idle a little rough, but they can't explain the deminished fuel mileage. I'm the orginal owner of the truck, drive it everyday and there is definelty something not right.

 

Anybody got any ideas on where to look.

 

 

Thanks,

Ikeman

[redvett]

I have '93 GMC, 4.3l, with 130K miles.  It is idling a little rough and my gas mileage has gone done about 75 miles per a tank full.  I notice the engine also detonates when it is turned off.  There is no service engine light nor is it displaying any code.

 

I did a general tune up.  I've replaced the plugs, wires, distributor cap and rotor (Plugs and wires are AC Delco and the distributor cap and rotor are Borg Wargner).  The local GM dealer just did a fuel injector flush.  I still have the rough idle.

 

The dealer put the 'computer' on it and they told they can't find anything wrong with it - everyting is operating within specs.  I had my shade tree mechanic look at it and he can't figure what is wrong with it either. 

 

I've been told because it's a 6 cyclinder it's to idle a little rough, but they can't explain the deminished fuel mileage.  I'm the orginal owner of the truck, drive it everyday and there is definelty something not right.

 

Anybody got any ideas on where to look.

 

I would start with a leakdown test, check fuel pressure, and check  out the TPS sensor, MAP sensor and probably depending on mileage change the O2 sensor.

OBD 1 doesnt have the ability to tell the problems that OBD 2 has.

 

 

Thanks,

Ikeman

 

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[snoman]

I have '93 GMC, 4.3l, with 130K miles.  It is idling a little rough and my gas mileage has gone done about 75 miles per a tank full.  I notice the engine also detonates when it is turned off.  There is no service engine light nor is it displaying any code.

 

I did a general tune up.  I've replaced the plugs, wires, distributor cap and rotor (Plugs and wires are AC Delco and the distributor cap and rotor are Borg Wargner).  The local GM dealer just did a fuel injector flush.  I still have the rough idle.

 

The dealer put the 'computer' on it and they told they can't find anything wrong with it - everyting is operating within specs.  I had my shade tree mechanic look at it and he can't figure what is wrong with it either. 

 

I've been told because it's a 6 cyclinder it's to idle a little rough, but they can't explain the deminished fuel mileage.  I'm the orginal owner of the truck, drive it everyday and there is definelty something not right.

 

Anybody got any ideas on where to look.

 

I would start with a leakdown test, check fuel pressure, and check  out the TPS sensor, MAP sensor and probably depending on mileage change the O2 sensor.

OBD 1 doesnt have the ability to tell the problems that OBD 2 has.

 

 

Thanks,

Ikeman

 

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MAP first as I do not think TPS could cause that but a bad MAP or ECM sure could and if the O2 sensors is not fouled already, it will be soon and need replacing anyway but do not replace it until you get a handle on the rest of it.