CEL codes and rough running HELP I'm stumped!
12-08-2014, 07:39 PM
#15
It's a stretch, but one of those brand new plugs might be bad ? The way I would check for a bad plug (short of pulling them one by one and testing them) Is to clip my timing light on each wire and see if it flashes.
If the plug's no good, the timing light won't flash.
Admittedly. this has only identified a bad plug once in a lot of years, but it's worth a shot, just in case.
If the plug's no good, the timing light won't flash.
Admittedly. this has only identified a bad plug once in a lot of years, but it's worth a shot, just in case.
12-08-2014, 07:50 PM
#16
Junior Member
Thread Starter
Yeah. I'll try tomorrow pm. On my way to 2nd Job now. On a sidebar. A couple of years ago we had an Xterra that did a very simular thing. It turned out to be a bad fuel pressure regulator. Any thoughts on that?
12-08-2014, 08:46 PM
#17
Fuel pressure is usually the first thing I check on an EFI system that isn't working right - they're very sensitive that way, so it's worth exploring.
As for the regulator the way it works is that at times when you need lots of pressure to give a really good spray (because there's lots of air rushing past), it will be closed. That's also the time when you have very little vacuum.
When your foot is off the gas, either idling or using the engine to slow it down, you need an easier spray cause the air's not moving nearly as fast. The motor is also pulling against closed throttle plates creating a lot of vacuum.
At that point the higher vacuum opens the regulator, which drops the amount of pressure in the fuel rail (returns excess to the tank) and you get a gentler spray, more synched with the reduced airflow that the injector is spraying in to. Follow that ?
3 things can go wrong with the regulator. 1 is the diaphragm inside starts leaking, dumping fuel into the intake via the vacuum line. 2 is the thing seizes up, either open, closed or somewhere in between. 3 is you don't get any vacuum to it at all, in which case it's blasting fuel out of the injectors as if you were at wide open throttle when you're trying to idle.
All that shouldn't really give you a miss though, although you did mention that you didn't see any difference in idle when you unplugged the regulator, and you should.
A fuel pressure gauge is the only way to really sort out fuel pressure issues or the lack of them. You should be in the low 40's psi on your truck with the vacuum unhooked (or KOEO), and drop 5 to 8 psi at high vac. (Operating range is 30 to 45, but she just don't even run at 30) If you can't borrow or loan-a-tool one, you can usually pick one up for under $60 and they really are invaluable if you own a fuel injected vehicle. You should just have one anyway.
Maybe someone will buy you one for Christmas ?
As for the regulator the way it works is that at times when you need lots of pressure to give a really good spray (because there's lots of air rushing past), it will be closed. That's also the time when you have very little vacuum.
When your foot is off the gas, either idling or using the engine to slow it down, you need an easier spray cause the air's not moving nearly as fast. The motor is also pulling against closed throttle plates creating a lot of vacuum.
At that point the higher vacuum opens the regulator, which drops the amount of pressure in the fuel rail (returns excess to the tank) and you get a gentler spray, more synched with the reduced airflow that the injector is spraying in to. Follow that ?
3 things can go wrong with the regulator. 1 is the diaphragm inside starts leaking, dumping fuel into the intake via the vacuum line. 2 is the thing seizes up, either open, closed or somewhere in between. 3 is you don't get any vacuum to it at all, in which case it's blasting fuel out of the injectors as if you were at wide open throttle when you're trying to idle.
All that shouldn't really give you a miss though, although you did mention that you didn't see any difference in idle when you unplugged the regulator, and you should.
A fuel pressure gauge is the only way to really sort out fuel pressure issues or the lack of them. You should be in the low 40's psi on your truck with the vacuum unhooked (or KOEO), and drop 5 to 8 psi at high vac. (Operating range is 30 to 45, but she just don't even run at 30) If you can't borrow or loan-a-tool one, you can usually pick one up for under $60 and they really are invaluable if you own a fuel injected vehicle. You should just have one anyway.
Maybe someone will buy you one for Christmas ?
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