i have a 1988 volvo 740 turbo wagon and it misfires under boost. ive replaced the entire ignition system, distributor, cap, wires, lugs, ignition box, lately what ive tryed to do to fix it is a colder plug and all that did was make it run worse and misfire at idle heres a video

 

Any codes? Have you adjusted the valves? What the compression? That old could be an injector that's not spraying correctly - difficult to measure/check that - but possible.

 

the compression is 160 ive recently cleaned out and had my injectors balanced. and no i dont have a check engine light. i just find it weird that when i changed out the heat 6 plugs for heat 8 it made it worse and now it misfires at idle

 

How about an intake manifold gasket leak? Or an air leak near one cylinder runner (injector seal)

 

yeah that all looks good um just checked the tps and it should have 3 wires to it and 2 of the 3 are going to one pin while the other is just ground i think somthing is jank here

 

tps won't cause a misfire under load, it just tells the idle motor when the car is supposed to be idling.

 

ok what do we check next, i mean my buddy has a leak down tester for a turbo system so i can check for vacuumleaks like that

 

If it's misfiring at idle you can disconnect the injectors one at a time and note if the idle speed changes more with one cylinder than another to possibly isolate the problem cylinder. The iac/idle motor/auto air valve whatever you want to call it should try to keep the idle speed constant - but it usually takes a second to kick in and stabilize the idle, or you can disconnect it (if it will still idle ) to be able to check the idle drop per cylinder without the idle motor trying to intervene.

Check for vacuum leaks with a can of carb cleaner - Spray with the nozzle at suspected areas and if the engine ingests carb cleaner through a vacuum leak the engine speed will change! Sure you can use a smoke tester, but a can of carb cleaner is faster and cheaper.

 

So I can do that, I had to take my buddy home but before I did that I replaced the fuel pressure regulator and put the colder plugs back in. At first it misfires under load again but no ruff idle then over the span of the drive the misfire under boost got better till by the time I got to his out it completely stopped misfiring and ran great and just roasts the tires 🤷‍♂️