Loss of Power & High Reving engine before shifting

[drseuss620]

I have a 2000 GMC Sonoma 2x4 with the V6 4.3L Engine. Approx 180k miles.

Within the last 30 days I have noticed a significant loss in power on the freeway and some intermittent shifting issue in between gears. I immediately assumed transmission woes and took it to a local shop.

The owner checked the fluid, smelled it, then took the truck for a test drive. When he came back, he suggested that the fuel filter might be plugged because it sounded like the truck was starving for fuel and consequently caused the engine to rev higher before the transmission could shift into the next gear.

I was happy to learn that this might not be transmission issues and a relatively cheap fix... only when they replaced the filter, they found the new filter didn't help and the old filter didn't appear to be plugged after all.

There is no check engine light, no error codes, nothing... Now the mechanics are scratching their heads trying to figure out what else it could be without billing me for too much labor. Everything they could think of would cause the check engine light to come on... The only thing they could think of would be possibly the Catalytic Converter.

Does anybody have any other suggestions? At the end of last year my fuel pump died and they had to put a whole new assembly in... at the time they changed the plugs, wires, wiring harness, and all that.

Your help would be appreciated.

Dennis

 

[lphernan]

Dennis:

You're going to like my story but if the tranny shop didn't find it on your's you may not be so lucky. My truck starting doing exactly as you described. I took mine to a local tranny shop as well. After the test drive the mechanic came back and told me it wasn't my tranny, it was my mechanical engine fan. As I had planned on putting an electric fan anyway, and already had the parts for it, I went ahead and converted. Sure enough, problem solved.

Hope this helps.

louie

 

[drseuss620]

Hi Louie,

thanks for your reply... Turns out it was the Catalytic converters... Apparently one of them completely disintegrated and plugged up the second. Once they were replaced, I had full power back and improved fuel efficiency.

Cheaper than a transmission, but not as cheap as a new fuel filter.

Maybe I can get a few more years out of it before I buy something new.

Dennis

 

[drwet]

I'm glad it wasn't too major. I'm curious. How did they figure out it was the catayltic convertor?

 

[drseuss620]

They removed the O2 sensor and did a back pressure test. Once the test showed there was a problem, they decided this was probably the cause and cut open the catalytic converters. Sure enough, one of them had started disintegrating. According to the mechanic that year of GMC doesn't have the sensor for this problem, otherwise a check engine light would have come on.

Funny thing, one of the guys told me that there was probably a vibration noise I might have noticed... There had been one but I had realized then I hadn't heard it since about the time I started losing engine power.

Runs like a champ now.

 

[sidemoney]

Hello im new to this forum. I just purchased an 03 Sonoma a few days ago. Happy with the truck except im having that same problem. From 1st to 2nd gear is a hard shift. This truck has new converters but it still shifts hard. I also have a temp guage and fuel guage that has a mind of there. Any help for these problems would be appreciated.