1989 Nissan 240sx KA24E Stock: Cold Idle misfire/nofire

[xs04298]

Background:

Bad idle since they day I put the engine in, cured after replacing the following. Injectors replaced, O2, CTS sensor, IACV cleaned, vacuum lines checked many times, ECU throwing no codes, new fuel lines and filter (new pump about 2 years ago).

What its doing now (after a month of it running good).

When the car is cold after sitting overnight, the problem is at its worst, ignition on, starter cranks, after a few revolutions (a few more than it used to take) it catches fire and runs up to its normal 1000rpm start, then a few seconds later it acts like its starving for gas/air, and idles down to the point where it will stall out if I don’t gas it up quite vigorously, It doesn’t act like its "missing" like it did before, it seems much along the lines of a carbureted engine that someone left the choke on, or running out of gas, more of that sensation.

After 2-3 minutes of giving it throttle it will start to pick up speed, and idle a little rough like at around 700. After ~half hour of driving it will be back to its normal smooth idle. Slight "pinging" heard under hard acceleration that I have never heard in 2 years from this engine until this very problem arose, goes away after warmed up.

Starting it up during the heat of the day, after its naturally warmed up by the sun, it still doesn’t start right up and run perfect, but its significantly better than when its dead cold.

Starts essentially normal when its "warm" after running for a while.

The problem is extremely repeatable, it does the same thing every day (when starting up cold) and hasn't gotten any worse or better in a month no matter what system I check. Other than this the engine feels more responsive and more "powerful" than ever with the new sensors, unfortunately me and the shop have fun out of routes to take to investigate why this problem started, or how to cure it.

Terribly sorry this turned out to be so long, I'm trying to be as descriptive as possible to help everyone understand the issue fully.

Thank you all for any possible advice, it is greatly appreciated.

[MaximA32]

Have you checked your MAF? Disconnect the MAF and see if it runs any different. If not, there are a few other things we could try but I would start there.

[xs04298]

MAF disconnected used to make it run horrible, now if i do it during its "warming up" phase it just stalls right out. I'd say the symptoms are simular, but the unpluged maf makes it "miss" and stumble more than what its doing now.

[MaximA32]

I'd replace the MAF. As I said, you should be able to find one no problem on the classfieds.

[xs04298]

Okay I'll look around and see if we have any at the shop, if not i'll look into one. I have a voltmeter, is there any way to test it to see if its functioning?

Thank you for your help by the way, i'm really just running out of places to look and this is the first lead ive gotten

[MaximA32]

So I just ran this problem through a diagnostic program we have at the shop and it says this problem is widespread. There is a TSB out for it and the only way to resolve the issue is to replace the ECM if you have exhausted all other options and have checked all idle speed and engine control according to service manual specifications.

[xs04298]

So I just ran this problem through a diagnostic program we have at the shop and it says this problem is widespread. There is a TSB out for it and the only way to resolve the issue is to replace the ECM if you have exhausted all other options and have checked all idle speed and engine control according to service manual specifications.

seems unlikley the ecu would go bad overnight, but stranger things have happend

Drove the car for 45k miles on this engine and it just started now, leads me to believe its some kind of mechanical issue. However, it has been disocvered that the ECU in my car is the wrong one for the engine, its an 88 pre update ecu and harness, so its for the low compression engine without the air flow sensor, so the ECU is reading all the correct things it think it should be reading, but its likely not optimal.

But with that said, still doesnt make sense for that to bet he issue, since it worked fine before.

The only other possible thing i can think of is the FPR, it was on the fuel rail i used to get the injectors to stop leaking, is it possible its not letting fuel flow through on startup, causing air buildup through the rail making it starve for fuel untill it gets the air out through the injecotrs? its a reach but it just seems so much like its starving for fuel, no idea how that system works though

[MaximA32]

Possibly but without having a reading of the fuel pressure in front me there's no way to be certain. Also, my apologies for the ECM stuff, I clicked on the wrong thread and posted. My bad yo. lol

[xs04298]

Possibly but without having a reading of the fuel pressure in front me there's no way to be certain. Also, my apologies for the ECM stuff, I clicked on the wrong thread and posted. My bad yo. lol

ohhhhhhhhhhhhhhhhhkay, thought that seemd a bit off thewall

okay, heart attack over...fuel pressure gauge, wonder if i can borrow one from a parts store or something, do we know when it should have pressure on the "return" line?

[MaximA32]

You only read pressure from the fuel rail. You should have a consistent reading, no fluctuations.

Also, I re-read your original post and that TSB I was speaking of, DOES apply to this case as it's not a mis-fire but an idle speed problem. I would try cleaning out our IAC-V and see if that helps. There is a tutorial on how to do it at the top of this forum.

[xs04298]

IACV replaced in summer 2005, recleaned last january, really helps get rid of "missfire/stumble", which im not necessarily saying its not doing now, it runs very rough, even pauses (ceases to fire for multiple strokes at a time) and then catches again, or even stalls flat out from lack of fire, perhaps my first post was misleading to that? Its a very differnt feeling from the normal KAE bad idle, more of a starvation sensation i havnt seen since working on carb engines.

[xs04298]

Tried another maf, no change at all.

I just cant figure it out what its doing, It's so hard to describe, almost makes me want to take a video of it doing it

[616angelito1]

I have the sam eproblem too!!I cant figure out what it is though...

[the converted]

My maxima had a cold misfire that went away after it was warmed up. It ended up being one of the coils so that might be a place for you to try. Can't be to hard to scrounge up a coil to borrow.