Slow starting, stumbling when cold, backfiring

[anothernord]

So I just recently encountered a few problems with my OB:

Already checked:
MAF
PCV
Plugs, wires, coil

1. Starting, whether its cold or hot is strange; sometimes it will crank and crank then sputter then start, sometimes it will start with a couple cranks, and sometimes it starts right away. It doesn't seem temperature dependent, and it seems to be related to fuel, because if I prime the fuel pump a couple times, in starts a little easier.

2. For the first 3-4 gear changes after starting in the cold and driving along, the car will go full-lean and fall on its face as soon as I press the gas down after changing a gear. I'm kinda stumped on this one. It goes completely away once operating temp has been reached.

3. Any time I am in gear and coasting (engine braking), or while coming on the gas after shifting, I'll get some nasty (and sometimes hilarious) backfiring. This is only when the engine is at operating temp.

I'm pretty sure this is related to fueling: Injector O-rings? I put in my 535cc STi sidefeeds a few months ago, and the O-rings looked fine at the time, and I lubed them up before installation, but I'm very suspicious of them. Fuel pump? Fuel filter? Bad injectors or IAC?

Any help would be appreciated.

[Huffer]

Could check your engine temp sensor, it sounds like a sensor issue rather than a mechanical one.

[TGX4776]

Mine backfires as well on throttle off

[anothernord]

I checked the sensor with my OBD scanner, it shows the correct temperature just fine. It matches outside temperature fine, and it reads 194 degrees at operating temperature.

[ouch1011]

What are your fuel trims at idle? My car has the same problem and I'm pretty sure its engine mechanical problems causing the fuel trims to go way negative at idle. And the PCM uses the same fuel maps at idle and right off idle, so for me, something makes it run way rich at idle only, so it leans out, and then when taking off from a stop or getting on the gas, it runs way lean for a short time until it switches to a different fuel table. Its worse when cold as well, it'll fall on its face and pop out the intake.

All started after the head gaskets failed and the engine overheated... a lot, and is accompanied by a valvetrain like ticking noise and rough idle. I've got a EJ257 in the garage waiting to get rebuild and put in.

Your problem could also be a leaking injector. If it leaks down with the engine off, the engine will run way rich on startup and may sputter or run rough. On hard decel, if its still dripping in fuel with the throttle closed, the fuel might make it all the way into the exhaust and light off in there, causing a backfire. And if its dripping in at idle, it would run the idle fuel trims way lean, and then could cause a stumble on accel until it switches fuel tables like I mentioned before.

[anothernord]

Well, LTFT's are at around 3% once the car is warmed up, but I haven't check the either of them when the engine is cold. I'm willing to bet it's an injector-related issue. I check the fuel trims when cold, and if they're ok, I'll swap my stock injectors in, which I know are good. If that makes a difference, I'll try new O-rings on the STi injectors, and if that doesn't solve it, I'll see if the injectors themselves are at fault. I'm hoping is just the O-rigns.

[jey]

How old is your fuel filter?

[Grafton]

sounds like a fuel issue, try swapping the injectors like you said, also make sure you don't have any, I had a bad o-ring on #4 injector and it was really hard to start unless i "primed" the fuel system

[anothernord]

How old is your fuel filter?

No more than 25k on it. I'll check anyway, though.

[anothernord]

I went to try out my stock injectors, but was missing one of the rubber caps. Instead, I took out all my STi injectors, carefully inspected and cleaned the O-rings, which looked perfect, then re-lubed them and put them back in.

I also replaced the fuel filter, cold cranking still takes forever, but at operating temp, it starts fine now. Not sure whether or not I actually fixed anything. I was able to reduce the backfiring by reducing my tip-in enrichment, but it still bogs, goes very lean and nearly dies when its warming up. I'm sort of thinking that one of the injectors is bad. Is there any way to test them?

[anothernord]

Well, I finally got around to putting in the stock injectors. I think that solved the problem.

One thing I noticed when reinstalling the stockers was that they were MUCH harder to push into place than the yellows were. My theory is that the yellow injectors' o-rings are just a bit smaller, and leak slowly when the engine is cold. When it warms up, they would expand and solve the problem. So, it looks like new o-rings are in order.