More than one way......

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • dsavary
    Junior Member
    • Apr 2007
    • 3

    More than one way......

    ........to skin a cat.

    I had a 95 Olds 88 in today with a 3.8 L engine with the complaint of an intermittent misfire and MIL.A code P1200 was stored in memory .The scan tool listed this as a "injector circuit failure". I could find no listing anywhere for a P1200 ,but this is one of the 1995 models that is a kind of hybrid OBD2,so that is not surprising.

    I wanted to current ramp all of the injectors at the same time for comparison,but could not find a good(read easy)common point to put my current probe.And as far as doing each injector individually,all of the harnesses were taped up to about a 1/4 inch of the injector connector.Way to much work for an old guy.
    The injectors and connectors are easy to get to on this 3.8 so I thought I would look at the voltage signal on each injector instead of using the current probe.By back probing the neg side of the injector circuit and really zooming on on the portion of the voltage pattern where the inj. is grounded,I was able to see this.



    Look familiar.What you are looking at is the voltage drop on the active inj. circuit.As the current flow rises so does the voltage drop and will give you a nice current ramp type of wave.You can even see the "pintle hump".Notice the voltage setting.This is a very low scale to be working with under the hood and most scopes won,t filter at this scale,so be careful of what you may be seeing in the wave.This technique may not work at all in some instances.

    Anyway 5 of the inj. looked identical in amplitude but #4 looked like this.



    Not much of a difference in the ground offset,but enough to make me look closer.I thought I would put an ohm meter on the injector.When I started to remove the connector ,it came right off.These connectors have the wire release clips and this should not happen.Ok,it was not plugged in good,no problem.When I went to plug it back on it would not latch.A look inside the injector revealed a bent terminal that would not let the connector seat.Straightening the terminal eliminated the added resistance and intermittent connection and cured the problem.
    Attached Files
Working...