What could cause my 4.3l automatic to run rich?

Currently has trouble codes:
P0175 System Too Rich
P0300 Random/Multiple Cylinder Misfire Detected

It runs smooth, do not feel missing, just did tuneup. To start it when it is not cold I have to hold gas pedal down. Starts right up when cold motor and cold morning. Idle is a little rough. Seams to have no power, have to kick it down a gear to get up small hill/grade.


History:
POS when I got it, would die randomly when hot, changed ICM. The changed fuel pump which fixed that.

 

P0175 - Fuel Trim System Rich Bank 2
P030x - Random/Multiple Cylinder Misfire Detected

Since it is only on bank 2 (passenger side), I would look around that side of the motor. Do you have any exhaust leaks on that side? How many miles are on the truck? Have the O2 sensors ever been changed? Do you have access to a scan tool capable of displaying live data?

 

Has 184,xxx miles. I highly doubt o2s have been changed. I have a scanner cable and obdwiz that can capture data, I can take it for ride tomorrow an scan it and post data if that helps.

I am not sure if there is an exhaust leak(don't hear or see one but haven't checked). How does that affect it?(Curious)

Could a cat converter going bad/plugging up cause it to run rich?

 

An exhaust leak can pull outside oxygen into the exhaust and make the O2 sensors read lean. The PCM would respond by cranking up the short term fuel trim for that bank to richen up the mix. Over time this would increase the long term fuel trim and set the code.

If the cat were the problem, it should show on both banks, not just one. What is the LTFT for bank 1 & 2? How close are they?

 

Ok, thanks for the knowledge on exhaust.

I will have to get back to you on that. Will try to post the numbers tonight or in morning. I think the ltft was off a bit between the two.

 

Ideally, the LTFT's will be very close to zero. If the LTFT1 is at or near zero, then that really narrows down the problem to the passenger side and you have to start looking at those sensors which only deal with that side. Namely, the O2 sensor. If you can watch the sensor output with your scantool, you will be looking for an abnormally high bias on the signal. The output should switch back and forth across 500mV, dipping down to ~100mV and up to ~900mV.

As a diagnostic step before replacing anything, you could try swapping the sensors and seeing if the problem moves from the passenger side to the driver side.

But given that you don't know when or if the O2 sensors have changed, you may just want to replace both the upstream sensors. I recommend AC Delco sensors for these trucks.

 

Ok, i will try that and let you know. Thanks.

 

i recently did work on my 4.3l as well and mine is the cpi. i had the same issue on mine. i replaced alot of parts which on the other hand i have an extra spider injector for sale if any one is interested, the map sensor another words the tps was one of the issues with idling and running problems with starting from a stopping point, my fuel pump fixed some of my issue and the o2 which helped with running rich. your able to reset the codes on the older vehicles with a simple paper clip and jumping one terminal to another. also i found out my blazer still ran crappy so i checked the fuel lines and filter and nothing clogged so i checked inside the plentum which to my suprise the lines for in and out were really old and cracked. if your having an issue still check that, its a simple fix and will save you gas. you could also check the vaccumm lines. i hope this helps in some way

 

Screen shot from last nights scan while idling in driveway:

http://carolinabowfishing.com/misc/codes.gif

 

Get it up to operating temp & then look at the same data. Maybe mix it up a bit by driving down the road as well. Right there, both sides are near identical and pretty close to zero. Certainly not enough to set a code.