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76C10Stepside · 08-03-2014, 05:25 PM

I could use some help troubleshooting a problem with my '89 S10 4.3 with model 220 throttle body injection. Engine has been running a little lean for the last year, idles a little funny. Suddenly started running very poorly, but no trouble codes. Rebuilt the TBI. It ran a lot better, but would stall suddently, or not want to start after being run. Several hours later, it starts right up, like it was flooded, but there is no strong gas smell. At idle, there is enough gas being sprayed to coat the butterfly valves, does not look like a lot to me. What does a normal spray pattern look like at idle?

Just replaced the fuel filter (gas looked clean). It's still not running right. Idles too fast, 2000 rpm when started cold, revs go up and down for awhile, then down to 1500 for awhile, then 1000, and finally 750, but is not idling smoothly.

Followed Step 10 in "Troubleshooting your TBI Fuel Injection System" (http://www.73-87chevytrucks.com/tech...TBISystems.pdf) for when engine is revving up and down. I don't hear any sucking sounds, no loose vacuum lines. Again, no trouble codes. With key on, I hear a "clacking sound that I don't remember ever hearing before. When I pull the Idle Air Control (IAC) plug, the clacking stops, so it was the IAC (is that normal?). Then remove the jumper from ALDL connector (key still on), turn off for at least 15 seconds, and restart the engine. The engine refused to start. I sort of got it started by pumping the gas pedal, but it would not run. Not sure what to make of this. Plugged IAC back in, but engine still won't start/run. Again, no strong gas smell, but acts like it's flooded.

Another weird thing that started happening today is the oil pressure reading is very low at idle. The "oil can" even started flashing for a bit. Engine has a fresh oil/filter change and is topped up. This truck has the digital dash with the led bar readouts, and has been replaced once. Sometimes it acts up a little, but turning off and back on makes it work right again. This oil pressure thing kept up for numerous on/off while testing.

The only other thing is one of the rubber insulator things that go between the injector and the plug is missing, pretty sure it was missing when I got the truck, does not seem to affect running.

Not sure what to do next. Suggestions?

08-03-2014, 05:25 PM	#1
76C10Stepside Registered User Join Date: Feb 2012 Location: Olympia, WA Posts: 300	89 S10 4.3 Need help troubleshooting TBI/IAC Idle issue I could use some help troubleshooting a problem with my '89 S10 4.3 with model 220 throttle body injection. Engine has been running a little lean for the last year, idles a little funny. Suddenly started running very poorly, but no trouble codes. Rebuilt the TBI. It ran a lot better, but would stall suddently, or not want to start after being run. Several hours later, it starts right up, like it was flooded, but there is no strong gas smell. At idle, there is enough gas being sprayed to coat the butterfly valves, does not look like a lot to me. What does a normal spray pattern look like at idle? Just replaced the fuel filter (gas looked clean). It's still not running right. Idles too fast, 2000 rpm when started cold, revs go up and down for awhile, then down to 1500 for awhile, then 1000, and finally 750, but is not idling smoothly. Followed Step 10 in "Troubleshooting your TBI Fuel Injection System" (http://www.73-87chevytrucks.com/tech...TBISystems.pdf) for when engine is revving up and down. I don't hear any sucking sounds, no loose vacuum lines. Again, no trouble codes. With key on, I hear a "clacking sound that I don't remember ever hearing before. When I pull the Idle Air Control (IAC) plug, the clacking stops, so it was the IAC (is that normal?). Then remove the jumper from ALDL connector (key still on), turn off for at least 15 seconds, and restart the engine. The engine refused to start. I sort of got it started by pumping the gas pedal, but it would not run. Not sure what to make of this. Plugged IAC back in, but engine still won't start/run. Again, no strong gas smell, but acts like it's flooded. Another weird thing that started happening today is the oil pressure reading is very low at idle. The "oil can" even started flashing for a bit. Engine has a fresh oil/filter change and is topped up. This truck has the digital dash with the led bar readouts, and has been replaced once. Sometimes it acts up a little, but turning off and back on makes it work right again. This oil pressure thing kept up for numerous on/off while testing. The only other thing is one of the rubber insulator things that go between the injector and the plug is missing, pretty sure it was missing when I got the truck, does not seem to affect running. Not sure what to do next. Suggestions? Last edited by 76C10Stepside; 08-03-2014 at 05:32 PM.