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Im working on a 95 Sonoma 4.3 with the TBI and I can't figure out this EGR issue. So when the truck starts up and gets warm, it will cut out, buck, surge when accelerating. Also, if I keep a stead speed of 15 mph, its just sputtering and bucking. The moment I give more gas it clears up and runs fine. I know its and egr issue but I cant figure out why. It has the linear style egr, not the vacuum operated one. If i pull out the 5 pin connector out of it, it doesn't have the issue anymore. Plug it back in and the issue returns. Same thing happens when I disconnect the o2 sensor. Also, I noticed that if I take out the o2 sensor or disconnect the cat, the problem goes away. I checked the exhaust back pressure and there was no resistance. However, the truck had a gutted cat and the muffler was rusted back I went ahead and welded in a new cat and muffler. Still has the issue. Also when I first was working on the truck, both exhaust manifolds were cracked so I replaced them with new ones. The EGR was already replaced why the original owner, i checked it for carbon build up or a sticking pintle but it checked out good. No carbon obstructions in the intake. I swapped out a good working EGR vavle just to see if that was the issue, but still had the issue with the know good EGR. I replaced the o2 sensor, MAP sensor, and coolant sensor. Still has the issue. I dont have an OBD 1 scanner but I was able to borrow one of my neighbor's scanners and I noticed that when the issue happened, the commanded and actual EGR positions did NOT match. From what I recall, the would get of to a difference of 100 steps at some points. So anyways, I dont know what else to check or do. Could it be ECU related? Any help would be greatly appreciated! Thanks!
Sounds like the problem is happening at closed loop (when ecu is monitoring O2 sensor activity). When you unplug O2 sensor or give gas, you are forcing ecu to jump to open loop.
Sounds like the problem is happening at closed loop (when ecu is monitoring O2 sensor activity). When you unplug O2 sensor or give gas, you are forcing ecu to jump to open loop.
Have you seen fuel trim number?
Have you observe O2 sensor voltage activity?
Thanks for replying!
Yeah that's makes sense, I thought it was happening in closed loop because when I first start it up and it's cold, the issue isn't there but is there where it warms up.
As far as fuel trims and o2 voltage, I have not checked that. I need to get my hands on a OBD 1 scanner to get the values but I will report back on that
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