chaseincats

Good call on watching the tach needle. It is a fuel problem, as the needle behaves itself haha. I will pull the injectors in the coming week and see if they are all firing at the same rate.

Interesting - It did run really well yesterday but granted I didn't drive it, just idled it until it got to temperature so I could get readings with the fuel pressure gauge. so maybe not?

I don't remember which make/model it is, but there is one of those clear plastic filters between the tank and pump. I checked it yesterday and looked fine.

I believe its a few years old

Good to know this exists. This was a problem that just cropped up while driving so it has to be something mechanical rather than aging ecu related I'd think.

It was definitely running worse than it had in the past, and the rough hot-start idle was new. That said, it was running great today and didn't even have the hot start issue so I'm not sure what's going on. I will take the rental gauge I have to my friend's place tomorrow and test it on his z to see if it reads 36 at idle or if it says 32 which would mean the gauge is just off.

I haven't since its just a hose gauge from oreilly's but I did start the car this time and let it run to temperature and watched the gauge as the car warmed up and at a variety of different rpms. The car never went above 32 when idling at any heat range if that helps.

Update: the gauge is saying 32psi idling. When I tap the gas and hold it, it will go up to 38 but drop back down to 32. Isn't idle PSI supposed to be 36? If I unplug the vacuum line to the pressure regulator it will sit at 40psi when idling. Gas is not coming out of the pressure regulator with the hose unplugged.

@Zed Head Fuel pressure looks good - 38 at cranking.

coincidentally I just got off the phone with oreillys to confirm they had a fuel pressure test kit - will get back to you with an answer on that tonight

It's weird this would just start all of a sudden though. The car started running really lean on the freeway out of the blue, I had to get off the freeway and richen it a tooth on the AFM because I was concerned about potential engine damage if I didn't (it read 18 on my AirFuel gauge all of a sudden and started to misfire). Cylinder 3's spark plug looked very rich compared to the others.

Hi guys, I'm running lean all of a sudden and not sure why. It is worst when hot-starting with a very lumpy idle that stabilizes after a minute or so but it is weak throughout the rev range (unless flooring the pedal). The idle stabilizes the longer it sits but is definitely misfiring (or not firing) when hot started. The idle is very lumpy but also smells very rich. New plugs with ~2 hours run time on them. Injectors about 2 years old. Any idea on the below plug images?

Looks like we have something mechanical/unrelated causing all of this - I'll make a separate thread EDIT: As a heads up for those reading this thread to tune your cars, the problem ended up being unrelated to the tuning and was instead an issue with cylinder 1's injector connector. The thread where this was solved is titled "Sudden Running Lean Issue" if this happens to you.

Update: I picked up Costco's Interstate battery (1624505 this one) for $120 and it works great.

I remember the days when batteries came with a 10 year warranty

Sold - group 24 it is

Is the head thread pitch/thread length identical for all s30 heads? If they are different, then my guess is that would be the cause. Regarding NGK plug part numbers I found the bpr6 to be 7133 and the bpr7 to be 5534. Just putting this in here in case people look for those NGK part numbers in the future.

So go for a group 24 instead of 24f? I didn't know there was a difference, I'll grab one, thanks.

It seems that plug doesn't fit my head. Amazon and O'reilly's site says its not compatible with the car. Does that make sense to anyone?

Interstate MT24 has the positive terminal under the inspection flap. Having it the other way around makes sense, but my wires wont reach.

Hey gang, So it's time for a new battery - my Interstate MT-24 from 2018 has thrown in the towel. Should I just get another one of those or is there a commonly agreed upon better one to go with, without breaking the bank?

Yep to the right plugs or yep to it being pre-gapped to the right spec (or both haha)?

so, these would be what I'm looking for? The -11 means that it is pre-gapped so I just pop them in, right?

The engine is absolutely running leaner which adds heat. The TPS on a stock car basically keeps the car in WOT configuration at almost all pedal pressure we discovered earlier on in this thread, and since we bent that pin out a bit, the car will be in cruise mode longer (highway speed). So maybe a 7 would be a good test in this case?

So if I'm understanding this right. When running leaner, it's better to use a BP5 plug since it will absorb cylinder heat better than a BP6?