#4 Fuel Injector Not Firing-Tried Many Things, Can't Figure It Out-

[meeko]

I have a 90 240sx with the KA swap. She ran great for 6 months after swap and randomly about 2 weeks ago it started missing. I diagnosed the prob to the #4 cyl. I checked the compression, spark, and they're both good. I thought it might be the fuel injector, so i bought a new one and still it changed nothing. I'm guessing it is in the wiring??? The ecu is throwing code 34, knock sensor. Anybody have this kind of problem or have any ideas on where to start looking for the answer??? Thanks

[UNVMY240]

Have you even checked the injector pulse with a noid light yet? The injector gets its signal from the ecu so if you are not getting a signal at the injector check resistance from injector connector to ecu. Also was it an Autozone injector or one from the dealer? Either way I have seen faulty injectors out of the box. It is an electric part.

[OutToWinPAHC]

Yeah it sounds like the ECU is not gating the injector open. I would check that, but the knock sensor is important to the fuel management. Check it for loose connection, and whatnot but I might want to try replacing that first.

[240FeVeR]

I would think that the knock sensor code is a result of the cylinder not operating properly, not the other way around.

When you have a problem like this, I wouldn't go out buying new parts unless I can be absolutely sure that the injector needed to be replaced. It's very simple to do.....take one of the other injectors and move it to cylinder 4 and see if that fixes #4.

[meeko]

Thanks for he advice, Ive never been much of an electonic guy (hah) how would one go about checking the pulse on the injector?? Thanks I did swap around the injectors, and the original four are working so i am going to take the new one back to autozone...

[elpiar]

Did you figure out the problem?