Fuel Injectors

mechwarrior1977 · May 1, 2010

I have 1998 GMC K2500 with 5.7 Vortec. 198k miles on the original engine (and no,it uses very little oil).Just replaced all filters,plugs,wires,cap,and rotor button.Still idles rough and actually stalled backing out of parking space today at pretty much idle speed.Thinking it's fuel injectors.Need to do fuel pressure check later (at work now).But my main question is,looking online at fuel injectors at auto parts retailer.I plugged in my vehicle and engine.It gave me option of Central Multiport fuel injector kit (which was only $115),or a Central Sequential Multiport Fuel Injector kit ($563).How do I identify what I have?Will make decision when I do fuel system pressure check.Oh yeah,no codes,weird....but it's been more faithful and easier to figure out than my ex wife!

rodram · May 1, 2010

.. these trucks certainly are more faithful than an ex-wife... I hear ya

.. if you have the original equipment fuel injectors on this engine then you have the SCPI Sequential Central Port Injection system... standard on the 4.3L, 5L, and 5.7L Vortec from 96-99. These can be problematic as the poppet valves to control the fuel flow are located at the tip of each injector and these can build up deposits... and then either plug up, stick open, or otherwise just not spray properly.... a good injector cleaning can usually get them working again, unless they are really gummed up... when these are acting up you usually get a P0300 (?) Random Misfire DTC on your obd2.

... the MFI (Multiport Fuel Injection) is a GM replacement injector system that can resolve this issue of sticky/faulty SCPI injectors... the spray control is actually inside the spider housing and the injectors just spray, they don't actually control the on-off function of the injectors... you have to replace the entire spider (gets a new fuel pressure regulator) and the 8 injectors as the MFI spider and the old injectors are not compatible.... and of course the MFI injectors will not work with the old SCPI spider... I hear that the conversion work is not difficult, it just takes a couple hours and a bit of patience.... check to see what you are getting with that $115 kit ... it does sound like a low price ... gmpartsdirect.com has them on line as well with a picture of the parts that come with the kit... theirs is $350 plus shipping/handling process fee.

.. I had seriously considered the MFI conversion for my truck, but could not find the parts here (... in Canada) for anything that resembled a reasonable price.. ($800+ at a dealer... and not much cheaper at NAPA) so I cleaned the SCPI injectors with a good injector cleaner added to the tank... and thankfully that has worked for me..... some people on this forum swear by Seafoam as a cleaner, but you can find your favourite snake oil for this...

.. check your fuel pump pressure first before doing any other radical parts removal .... the fuel pressure spec for these Vortecs is 61 to 66 psi ... some say the injectors will still work at a little less ( down to about 58 psi) but if your fuel pump is getting down to that then you know it is setting you up to totally crap out on you one day... if you replace the pump then get a new in-tank filter sock and a new external wiring harness .... and don't settle for less than an ACDelco pump or a Delphi pump (... I don't always push OE GM parts, but for a fuel pump they are the best and most reliable.... (a failing fuel pump usually will not set any DTC codes)

... no oil consumption here either on my 5.7L

mechwarrior1977 · May 9, 2010

Well,I finally got enough time off to have it checked out.ECM was not throwing a single code and fuel pressure was fine.Mechanic thinks I just have trash/water in the tank being that it's 12 years old and tank's never been dropped.I change the fuel filter regularly,but I know,it's on the downstream side of the fuel pump intake.Couldn't find any seafoam,but am still looking.I've read where some guys swear by it.But seems to be running fine now.I'm not going to sweat it.Should be getting a nice new 2WD soon to play with and leave my 4WD in the driveway for when I need it.Thanks for the help.