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Posted by: BMartin914 Apr 12 2007, 07:29 PM

I have a 74 2.0 w/ d-jet that is only firing 2 of the 4 injectors.

I have already:

-swapped connectors on each side, problem moves with connectors
-swapped trigger points, problem remains unchanged
-checked continuity throughout system (injectors, trigger points, etc.)
-case ground terminals brand new, female ground connectors have been cleaned

Any suggestions (ideas) as to what may be causing this condition? I feel like I have been through most if not all of the appropriate troubleshooting procedures and still can't seem to put my finger on the problem. I have got to be missing something small...

Posted by: 911quest Apr 12 2007, 07:38 PM

On the two that are inop. have you checked for voltage check it across the connector and each wire seperatly

Posted by: r_towle Apr 12 2007, 07:45 PM

suspect the wiring harness, then the relay board, then the computer.

For the wiring harness, put a flashlight bulb on the connector (rig it up)
turn car on, move throttle body...see if you can get it to light up.
Check the lightbulb on the known good ones.
If it lights, its an ignition problem.

If not, you may have a broken wire or two inside the 35 year old harness, it happens.

Rich

Posted by: john rogers Apr 12 2007, 08:26 PM

Injector point, replace them with new only.

Posted by: swl Apr 12 2007, 09:59 PM

I agree with John. Trigger points are about the only thing I can think of that would effect 2 injectors - which 2 are not working?

You can check the trigger points and harness by pulling the connector off the ecu and using an ohm meter across 12 - 21 and 21 - 22. Spin the distributor and you should see the points opening and closing.

If that proves good try pins 3,4,5 and 6 to ground. These are the runs to the 4 injectors. Should be be low resistance (coil of the injector - I measured about 3 ohms)

Posted by: Dave_Darling Apr 12 2007, 10:23 PM

As the others have asked: Which two injectors?

The trigger points pair them up diagonally. I think the grounds are paired left and right.

How are those grounds, anyway?

--DD

Posted by: boxstr Apr 12 2007, 10:26 PM

Does'nt that year have the injector ballast resistors? If yes, check the wires to the resistors, could be broken.
CCLIN914NATION

Posted by: Jeff Bowlsby Apr 12 2007, 10:26 PM

Which two injectors...its important

If cyl 1-2 or 3-4 are not working then it may be grounds, injector pairs on each side of the engine share a common ground in the harness

If cyl 1-4, or 2-3 (diagonal cylinders) are out, then its trigger points because those are the two injector groups they control.

I suppose it could also be an ECU problem, but those seldom fail. Bad injector coils...maybe? Injectors simply plugged and need cleaning? A kink in the fuel line serving one set of injectors?

Posted by: BMartin914 Apr 12 2007, 11:02 PM

Injectors are diagonally-opposed. Either 1 and 4 or 2 and 3 depending on which direction the connector on the trigger points is facing (21,12,22 or 22,12,21).

Posted by: TROJANMAN Apr 12 2007, 11:05 PM

ben,
didn't you have similar problems a year ago?

Posted by: BMartin914 Apr 13 2007, 08:15 AM

No.

Posted by: jasons Apr 13 2007, 08:32 AM

If its the diagonal pairs, its got to be your trigger points. The contacts may look good, but the little dudes that ride on the dizzy shaft wear out. When they wear out, the contacts don't open and close.

Posted by: TROJANMAN Apr 13 2007, 09:29 AM

what about the boss?
I'll be bringing a car in next week

Posted by: BMartin914 Apr 13 2007, 01:47 PM

He's helping too.

I will look forward to seeing you then.

Posted by: pbanders Apr 13 2007, 01:56 PM

If you've swapped in known good trigger points, and checked the injectors and harness by measuring the resistance to ground of each injector at the ECU plug, then your ECU is bad. There are two output driver circuits in the ECU that each drive two injectors, most likely, one of yours is dead, probably one or both of the two Ge power transistors is out.

Oh, just thought of one more possibility - check you trigger contact point circuit at the ECU plug. You might have a wiring fault to the TC's.

Posted by: swl Apr 13 2007, 09:32 PM

My bet is now squarely on the trigger points themselves. One side is not closing. The ECU is getting the signal for one pair when it is connected one way down 12. When he flips it around the other way it is getting the signal down 22. That pretty much confirms the harness and the ECU.

Posted by: BMartin914 Apr 13 2007, 10:34 PM

The trigger points, injectors and ecu are all fine. I had to remind myself to spin the dizzy and operate the throttle at the same time. Obviously in a stationary position the system is only operating 2 injectors at a time.

The car still has a poor running condition that I *believe* to be a faulty MSD 6AL. For some reason it is causing the car to run like crap (will not idle and misses like crazy). Eliminate it and the car runs fine.

Thanks for all of the input guys.