My brother has a 2003 Blazer with the 4.3L I believe. He called me over because he was having trouble and need some advice. He said that the truck hesitated and stuttered over 60 km/h, and barely made it to 100 km/h. First thing that I did was pull the dip stick and it was bone dry and HOT. Added over 3 liters to it, then took it for a test drive. As he said, at low speeds and rpms, it seemed ok, after you hit 60 km/h, shakes and shutters like crazy and barely gets up to 90 or 100 km/h. Would of pulled the plugs to inspect and check compression, but the motor was so hot and it was getting late so will check further in the morning. Need some advice on how to proceed. Those plugs look like they are in a real tough spot to access as well??

Just to note as well, he stated that his fuel mileage has been terrible after this started.

The secret to the plugs is jack it up and take the front wheels off, they're more accessible then.

Tks for the tip!

Another thing to note.....he said that there was a strange smell, my sense of smell is terrible so I could not pinpoint it for you, maybe running rich which would explain the poor fuel economy?? Just something to note.

Any check engine light? If so, what are the codes?

Did the engine overheat?

He says that it did not overheat at all....which is surprising based on the amount of oil left in the block. There is no check engine light on.

Lack of oil won't necessarily raise the water temps much, but I imagine the bearing surfaces got a bit hot. I'd say give it an oil change then you've got the right idea with a compression check for a starting point.

Took it for a test drive today and was fine until it warmed up, once warm she started stuttering again. Cold was fine.

how long has it been since the last tune up?

because a bad miss would explain bad gas milage, the shuter at high speeds, and it all could start when somthing got hot such as a pick up coil or plug break down

After I saw how long he waited for an oil change, I am going to assume he has never done a tune up. Will do plugs and wires today, along with a fuel filter and pcv valve and see what happens.

If it runs fine when cold, but has problems once it warms up, the problem is likely with a sensor or other electronic device. You would need a decent scan tool to see what mode the PCM is operating in (open loop or closed loop) to see if it is one of the sensors causing the problems, but I have also seen coils & ignition control modules cause issues once they are hot. They cool relatively quickly. You could have both the coil and ICM tested if the autoparts stores in your area still remember how.