sluggish performence

[kb3jhp]

I have a 98 gmc Sonoma with the 4.3 VIN w. It has 100000miles and is and auto. My problem is it has very poor performance at times. It accelerates slowly from stop to about 40 on light to mid throttle if you floor it it runs fine. It seems to run first gear out longer before shifting like if you were towing. Some times it will run great and other times it just falls on its face. Here is a list of what I have done. no codes

Complete tune up including
Plugs-ACDelco
Wires-ACDelco
Cap-ACDelco
Rotor-ACDelco
Coil-ACDelco old one was bad
Fuel filter-ACDelco
Maf sensor

my fuel pressure is 62 when key is first turned on the pump stops running it holds 62 then you here the regulater click it then drops to 60 and holds for at least 5min if truck is started at idle it is 55 and goes to 58 if it is reved

[old_master]

Have the oxygen sensors been replaced? There are three on that vehicle and recommended replacement is at 100,000 miles.

[kb3jhp]

No not yet waiting for sale. but would they make it run fine one day and bad the next it is like 100% one day and 50 the next it hard to even maintain speed on the highway. If there is a little hill it wants to down shift all the time and unlock the converter when it’s running bad. And if it’s running good it will accelerate in fourth gear with the converter locked up on the same hill

[taillight]

Yes they can. If you put it on a scan tool with live data read the O2 sensors.

[kb3jhp]

Originally Posted by taillight

Yes they can. If you put it on a scan tool with live data read the O2 sensors.

what should i look for i have a mac mentour scaner so i can read them

[old_master]

With the engine at operating temperature, holding steady at 1500 RPM, Bank 1 sensor 1 and bank 2 sensor 1, (both upstream sensors), should fluctuate rather rapidly from about .2 to .8 volts. Bank 1 sensor 3, (post catalyst), should remain fairly constant around .4volts.

[kb3jhp]

checked them they are working good it just runs like crap its like I am driving a geo metro with 4 fat people and 500 dollars of food in the back

[sward774]

i kinda have the same deal with my 98 s 10 with the 4.3 ive been thinking about replacing the throttle body sensor, I had a buddy who did that with his 5.3l in his 2001 chev and it seemed to get ride of the low end sluggishness, has anyone else herd of doing that??

[old_master]

You gave great details in your first post. Provided all of the parts you replaced are good, no K&N air filter is installed, no SES light on, and your fuel pressure is as you stated: With 100,000 miles on the original oxygen sensors, it's time to replace them. It might just cure the problem, even if it doesn't, they still should be replaced.

[kb3jhp]

thats what i will try next i love the truck but when it runs bad i hate driving it. i just cant beleave the difference in power and it not haveing any codes it dangers at times dont no if it going to get up and go or just fall on its face the truck is a reg cab short bed with 3.73s it should run stong also sward774
what do you mean throttle body sensor do you mean the TPS sensor