Blazer 4.3 1995-1996 issues when warmed up

Hi there!!!I'm AlexanderAnd im from Kazakhstan The situation is as follows:The car is a 1996 Chevrolet Blazer 4.3 4WD.As it turns out, the VIN indicates it’s from 1995, but the serial number on the ECU and the engine says it’s 1996. I bought it in October 2024, and until mid-December, the only issue was sluggish acceleration on 4th speed at 80km and 1500rpm when i need to accelerate it was so slooow, which I suspected was due to ignition problems. However, in mid-December, another problem appeared. When the engine is cold or when it’s warmed up but the fans haven’t kicked in yet (the previous owner installed electric fans), the car runs fine — no jerking or shaking. But as soon as the temperature reaches the point where the fans kick in, the engine power drops dramatically, and it starts jerking while driving at around 80 km/h. When stopped, the engine idles roughly, the tachometer needle jumps erratically, and the engine shakes badly. Interestingly, the engine temperature stays stable at 70-75°C when warmed up. It only rises higher in traffic jams, on uphill climbs, or during long, hard driving. The previous owner doesn’t remember which thermostat was installed, and I haven’t checked yet. When the issues first appeared, I went to check the ignition. What’s strange is that on the right bank, the even cylinders have a good spark that matches the timing mark, but on the left bank, the odd cylinders don’t spark as well. Also, the distributor gear has wear, as well as vertical and axial play. We couldn’t fix the gear wear, but the vertical play was removed, and the axial play was reduced slightly. Additionally, the distributor cap was replaced with a better one, as mine had two suspicious spots that looked like arc burns. After this, the car seemed to run better. However, when I drove it hard out of excitement, the power dropped again when the engine got hot, and the jerking returned. The question is: why does this happen specifically when the engine is hot? Where should I start looking? Could the worn distributor gear cause such issues due to the axial play? At the same time, I’m confused because the play shouldn’t depend on temperature. However, the problems start only when the engine is hot — but today, it was acting up even on the first cold start. Also, when pressing the brake pedal, there’s a hissing sound in the cabin, but only at the moment of pressing. When pressing the brake pedal several times quickly, the engine stalls.

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