P300 Multiple Misfires

Mitsubishi Mirage Technica 1998 Automatic 1.8L. When I purchased this car from its previous owner, I immediately had to fix a few things to get it running smoothly. Got the spark plugs replaced, wheels aligned. A while aftee that the car overheated on me, the temperature gauge wasn’t working correctly unbeknownst to me so I had to get the head to a machine shop and all that. The misfiring problem started after the overheat fix. So far I have replaced ignition coils and ignition cables. Also used a Seafoam Fuel Injector cleaner on it. Spark plugs are still the same. It still misfires. There’s no smoke, no coolant leak, etc. It’s consuming a lot more gas than it used to. The misfires occur idling, when trying to maintain speed, when accelerating from low speeds - this in particular the engine struggles to get enough power for a few seconds. I’m thinking TPS sensor, or a compression leak or a clogged fuel filter. To be honest I have no idea and I’m tired of taking it to the shop and not getting the problem solved. Any ideas?

Multiple misfires are usually caused by a fuel supply problems. Fuel pressure should be properly check as well as fuel regulator.

Did you get the thermostat in correctly? If the car doesn’t warm up quickly, it could indicate the t-stat failed or is in backwards. Is the coolant temp sensor reading correctly? If the engine thinks it is too ool, it will dump lots of extra fuel in.

Did you remove and replace the head or did a shop do it?

What are the cylinder compression numbers?

If all of this occurred after you had the cylinder head removed and decked… When they reinstalled the head…they more than likely have the T belt off one tooth… It needs to be perfect and there are ways to go back and check the mechanical timing of the engine.

This must be done before you continue to try and solve this issue…

Check the accuracy of the T belt job…


I’ll see to it and get back to you

Will check this out I hope you are right!

So today my mechanic isn’t working and I don’t know what I’m dealing with, not wanting to make it worse with my ignorance I still gave it another look. When I accelerate it starts fine but then it loses power and starts misfiring. I also noticed there’s smoke coming out of the header area by the battery. I will check everything all of you suggested but just wanted to add that, which I missed before.

What kind of smoke . . . ?

Engine oil burning off on the hot exhaust manifold, producing smoke . . . ?

Or an actual exhaust leak, due to a cracked exhaust manifold, missing/broken hardware, etc. ?

I used the word “exhaust manifold” because I doubt your vehicle actually has header pipes, but I have to admit I’m not familiar with a Mitsubishi Mirage Technica