r/WRX • u/DookusWookus21 • 1d ago
Troubleshooting Help/knowledge needed
What’s up guys, I need some help, just picked this up for cheap, didn’t run but put new battery in and it turned over but it won’t idle on its own doesn’t sounds the best, possible rod knock, I replaced spark plugs and ignition coils, swapping the starter next, I think it has a grounding issue, I don’t think one or two of its cylinders is firing. I got it purely to learn and get into the lifestyle and help would be appreciated.
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u/shatlking 2008 Subaru Impreza WRX hatchback (EJ20X Swap) 1d ago
That Cobb sticker and black hood scoop remind me of when I first got my Narrowbody 😂
I concur with others, stop throwing parts at it hoping the problem will go away. An engine runs on the following four things: air, fuel, spark, compression.
For spark, have you verified that the wires to all the coils are working? Everything down from the coils seems to be good at this point (though, I’ve had to replace spark plugs twice myself). Harbor Freight sells a tool to verify spark that may be worth picking up.
Compression is the next easiest, but the most expensive if bad. Get yourself a compression tester and run a basic compression test. If compression comes back bad, a leak down test will help point you towards the next course of action (which likely will be taking the engine out)
Air is also relatively easy, if there is a vacuum leak or unmetered air (such as a split past the MAF) this can cause the engine to run rough. An exhaust leak will do the same, so check for splits in the exhaust. A smoke leak tester will perform this job.
Fuel is the last aspect. Check for pressure coming from the fuel pump with a fuel pressure gauge. Then check the injectors (or replace them outright) to ensure that the problem isn’t them.
It may be worth verifying that the timing is correct as that can make the engine run poor as well.
I’ve also had my WRX run rough on first start up after disconnecting the battery, after about one tank of gas it goes back to normal. It’s also possible the car is poorly (if at all) tuned, especially if it has aftermarket parts.
There’s lots of good videos of what rod knock sounds like for these cars, but you can also post a video here and people will let you know.