Low economy at citi???

[javi2001]

Ok Thanks all, some clarification:

There is no catalityc converter. Exhaust system is same used with previous engine.
There are no error codes, nor Check Engine light
Engine use 95 octane just becuse provides a bit extra power. There is also 91, no 87, 89.
Knock sensor is in place.

That's why I guess problem could be excesive wear at inyectors and they are leaking fuel to intake manifold. Is it posible? at least diesel engines do so...

[chrono4]

It's possible that they leak down, but I wouldn't imagine that they are leaking down much, if at all if it took 3 hours for the pressure to drop.

I scanned through, but don't remember, have you checked any of the plugs for a reading?

[SR_Crewchief]

Javi2001,

It's a common misconception that higher octane produces more power. Octane is a value used to indicate how easy it is too initiate combustion, the lower the value the easier it is to ignite. Unless your having predetination problems at a lower octane level, don't use the 95.

Depending on the method used to increase the octane, the fuel could be causing you an issue. Specificly, if it is ethenol, and your fuel system hasn't been modified for it, your lines and seals could be drying out and failing. Seals like the o-rings in the injectors as well as the diaphram in the pressure regulator.

Hopefully you have a good manual that has detailed procedures for checking various sensors for function as well as troubleshooting. I'd start with the HEGO(O2 sensor) and work my way through things like the MAP, IAT, and ECT. Also check retention of fuel pressure(leak down), if it drops too quickly most likely either the pressure regulator is failing, or, 1 or more injectors are not closing properly.

If the engine checks out start looking for causes of mechanical drag. Are the brakes releasing correctly? What's the condition of the transmission and differential? Tire pressure? etc etc etc

[javi2001]

Originally Posted by SR_Crewchief

Javi2001,

Also check retention of fuel pressure(leak down), if it drops too quickly ...

How fast is too quickly???

Hummm that's sound interesting, it seems to me I have to perfor a full sensor checking

[SR_Crewchief]

Honestly, I don't know off the top of my head. I'm at work and don't have a manual handy. My best general advise is to order a Haynes or Chiltons manual from the States as a reference source.

It sounds like the engine running fairly well. You mention that the mileage suddenly dropped. Since your not getting codes I'd suspect either a redical change in driving habits, mechanical drag increase, or fuel theft. From your discriptions drag is the most likely cause. I'd do a full inspection of the suspension and brakes for wear and proper operation. Also a flush and fill of the gearboxes (transmission, differential(s), transfer case if 4x4). Are you driving with the tailgate down on an empty bed? Carrying exessive weight? Oversized shell on the bed?

For that matter, do you have A/C? If so is the compressor trying to lock up? Same for power steering.

Basicly, if the engine is running correctly, look for sources of additional load demand.

[javi2001]

Ok thanks for the advise, in 2 weeks I'm going to repair front suspension, I'll check brakes also, anyway in december I'm planing install a rebuilt engine, let see what happend after that...