95 C1500 4.3 automatic, about 100k miles hesitating in first & second gear.
About the last week of May I posted a much longer version of this listing a ton of questions. Got 118 views and one pm. Maybe I was in the wrong section.
Because it is OBDI, and my scanner won't work, I short the A and B jumpers to read codes. I don't really get a lot of codes but the ones I was getting were primarily in the emissions area. So I replaced the EGR valve, the EGR solenoid, the MAP sensor, the IAC, the Oxy sensor, fuel filter, and all other filters.
The problem WAS that when it got hot it would hesitate and stumble. I put in a 160 degree thermostat, a temp switch, an engine coolant sensor that feeds the ECU, two new knock sensors, and a new water pump. I also put in a new radiator because the old one had 3 bad holes in it.That hardly helped at all. By the way, at one time or another the OBDI said I had problems with all of the above emissions sensors. I also changed every vacuum hose on the top of the engine relative to emissions.
The problem persisted and finally I began getting codes that suggested the wiring to the ECU was bad, or I needed to replace the ECU.
Everyone at parts shops told me I needed a OEM #16196395. This is a plug and play computer, preprogrammed at the factory but when I checked mine out it called for an OEM #1619742. This computer is supposed to be flashed at the factory and again in the vehicle after it is installed, and has a Powertrain Control Module.
When I talked to the manager at Autozone he called the manager at Cardone while I stood there. The guy said it absolutely did not have to be flashed, just install and go. So I bought it, installed it according to directions, and it fired right up.
Shortly after I began having the hesitating problems and a couple times it went into "limp" mode. It gave me codes saying the distributor wiring was bad or the distributor was.
I checked the wiring and it was fine. I replaced the distributor with a new one, not rebuilt. Also a new cap and rotor. It took me forever to get it timed right. I was always 180 degrees off. Finally, an old timer who worked for GM before he retired told me that engine, for 2 years, has two timing marks that have to be lined up correctly. When one is at zero degrees at TDC, the second one should be about 60 degrees to the right of the marker. You can reach under and feel it. Of course, if you don't have the #1 cylinder at TDC on the compression stroke you will be 180 off, in which case you can turn the crank around until the SECOND timing mark comes up. Put the flat part of the dist cap pointing to the firewall, and the rotor at the #1 cyl position on the distributor cap and you should be there.
I did all this, it started right up, and I was ONE degree away from being zero degrees at TDC. I hooked everything up for a road test. Nine miles and it was perfect, then it started the hesitation again, primarily in low and second gears. Again, I have gone up to 5 degrees retarded to 5 degrees advanced.
I know I've thrown some of these parts at it trying to solve it, but it is a truck I will eventually give to my granddaughter, and I want it as perfect as can be.
Help me guys. Do you think it needs to be flashed now? Rebuild the TBI with new gaskets and O rings? (It sprays perfect 360 degree cones out of the injectors.) Any suggestions will be welcome.