knights89

Good Evening Enthusiasts,

Hoping someone can shed some light on my situation. 1991 S10 Blazer 4.3 TBI. About a year ago check engine light popped up as the engine seemed to be bogging down at idle. Code reader showed P0172. I checked all vacuum lines, no leaks or breaks. Cleaned the TB injectors, no change. I noticed the check engine light would go off after a while and the engine would run well, then the light would pop up again. I drive 50 - 60 miles a day - the light would go on and off a couple of times but I would not notice a difference in the performance, only at idle. I did notice that I might get about 230-240 miles from a tank of gas, but sometimes only 120 - 140 miles. Brought it to the shop I use - they cleaned the injectors, and adjusted the timing, but it kept throwing the code. They suggested replacing the computer. No change. Replaced the computer again (thinking it might have been defective) and replaced the O2 sensor, still no change. They said it must be the TBI - purchased rebuilt ones twice - still no change. A month ago went to my local GMC dealer - one of the mechanics at the shop I use said he knew a mechanic there that was supposedly an S10 guru. Requested him, after a couple of days he told me I needed to replace the distributor. Did that - still no change. So - I have replaced the computer 4 times, TBI 2 times, distributor 1 time, O2 sensor 2 times, oh and the EGR valve - I still have the issue. Anybody have an idea what to try next?

Irish_alley

kind of confused. you mention 91 that should be an OBDI system, the code you posted is from an OBDII system. but then im not too familiar with the s10 systems but i was pretty sure gm didnt utilize the OBDII till 96ish

since im pretty sure this is a tbi system and from what i know they all work kind of the same. how does it idle? have you cleaned your grounds?

other sensors that can cause a rich condition are the coolant temp sensor (C.T.S.), this is the one on the intake vs the one in the head
and MAP sensor


Troubleshooting sensors and how to test

knights89

Hi Enthusiasts! apologize for not responding - I had a medical procedure - I was out of commission for a while.

Thank you Irish_alley for your response. You are correct - I gave the incorrect code. I remembered it was the O2 too rich - The correct code (just checked) is 45. Oxygen O2 sensor – Rich Mixture. I checked grounds - all OK - I tightened down to be safe. It idles good, but when the check engine light appears, it idles rough. Took your advice and changed the CTS, and cleaned the MAP sensor. I did not see the light for two days, but it appeared last night. Checked the code and again its 45.