View Full Version : injector problem

01-14-2007, 05:47 PM
I just got through putting a set of 40lb injectors in my 87 GN and when I turned it over it showed hardly no pressure on the fuel gauge and would not crank,yet the pump IS working.... It got to the point where I could hear the motor having a hard time turning over and eventually not at all.. so i pulled the plugs off and fuel went everywhere (when i turned it over without plugs) .. I just want to say that my car has been down for a while do to a head gasket and I have had the motor apart doing a lot of other things.... My guess is that the injectors are staying open letting all the fuel right into the intake.... I know they worked because i pulled them out of my buddy's car and they worked fine(about 3 weeks ago)..
I'm thinking i can pull them off and try to blow air through them and see if it goes through.. if it does, that means there bad right? if so, can i fix them....
Any info at this point... Thanks!! Just hope its not something on the electrical side

01-15-2007, 10:43 AM
OK, does the chip match the injectors?

01-15-2007, 11:57 AM
OK, does the chip match the injectors?
Yes, it does... but i have 2 other ships and i will try them.... btw i did take them back out and tap on them and put back in .... little better but, still a problem... one thing i was thinking about was the pressure being too high ....
it was set at 40 with the old and still is....

01-16-2007, 02:55 PM
They can stick, although I usually see them stick "shut." And this generally only happens when they sit for a LONG time and the fuel 'caramelizes' as I like to call it. You can check them by putting some fuel in the top and 'ticking' it with a 12V source across the coil and you should see some fuel being shot out (just do the 'ticking' away from the injector so you don't cause a small fire :flame:

If they are staying open from an electrical standpoint it could be drivers fried in ECM or simply bad wiring somewhere... check this by measuring the ECM side of the injector plug with a DMM. The ECM grounds the one side of the injector coil and the other end of the connector is supplied with 12V - so if you measure the voltage across the injector connector (ooo that rhymes :what: ) without the injector plugged in and the voltage is 12V 'all the time' with ign on, then there is an electrical problem. If the ground is 'floating' (which it is when the ECMs injector driver is OFF) then you shouldn't have any voltage across the connector pins. To check ECM driver, try measuring the resistance (with ECM power off or Bat disconnected) from the "negative" leg of the injector to a good ground. If the resistance is high/infinite, the injector driver isn't shorted closed (good) OR your ECM ground is not such a good ground. If you measure continuity from the ECM pin to ground, then the driver is shorted closed. I don't remember if the stock ECM drivers are BJTs or FETs... I know FETs usually fail in the "ON" or "shorted" position but I'm guessing GM used BJTs as drivers.

BTW, 40psi FP is NOT high by any means. The injector coil returns are designed to handle much more pressure than that, as evidenced by the boost reference where the FP increases much higher than 40PSI!

LMK if you need any more help!

01-19-2007, 01:08 PM
Hey, Thanks phil.. I got a 12 v source and made my own little injector cleaner
and worked with them till i could not blow air through them anymore (power off) and now they work fine...

01-19-2007, 03:02 PM