No fuel injector signal on two injectors

[Bdstone]

Hi,

 

New to this forum and this is my first post.  Looks like ther are some really knowedgable people on this forum.

 

I have a 1987 GL 10 turbo 4WD with multi point injection.  I did a valve job and had the car running good for a couple of days.  Then I had gas flowing out the tail pipe with the engine off. Found the injector connector problem and fixed it. Put on all new connecters at the injecters.

 

Problem is I do not get a ground signal to two of the injecters.  I gave it to my mechanic and he thinks it is the ECU.  I tried a used one and another that was supposed to be rebuilt and still had the same problem.

 

I have the factory manuals but can not find what tells the ECU when to fire the pairs of injectors.  

 

I doubt that three ECU's could all have the same problem.

 

Check continuity on all the injecter wires back to the ECU. Even open the harness all the way from the engine to the ECU and found nothing.

 

Could it be crank position sensor ?

 

Stumped on this one.

 

Bruce

 

 

[NorthWet]

IIRC, the injectors are all gang-fired:  If 2 cylinders are working, the basic function of the ECU is working.  It looks like on my 88 XT manual that the 4 injector grounds get merged into 2 lines for a bit and then back out into 4 lines where they still remain electrically paired.  Assuming that your 87 is the later-style system (hot-wire MAF instead of flapper-MAF) your wiring should be similar.

 

You say that you have the set of factory manuals?  Checking the wiring diagram for the fuel injector in Section 2 manual might help.  My manual has the schematic in section 2-7, page 27, under the heading of "Fuel Injector and Resistor".  Your manual is different year, different model, but should be close to that.

 

If I had to guess, I would say that the section of harness where the paired injectors share a single wire (assuming harnesses are similar) would be a place to look for damaged wire or pulled-loose connector/splice.

[Bdstone]

So do all 4 injectors fire at once or are they fired in pairs?

[naru]

All 4 at once.

Control wires exit the ECU in pairs though.

Crank position sensor tells the ECU when to fire them.

If the other pair of injectors are OK so is the crank position sensor.

 

Since 3 ECUs have an identical problem,I suspect a poor connection between the wiring harness connector and the ECUs or a faulty wiring harness/resistor pack(despite the positive continuity test-wire in question may not support any real current flow).

 

I would look for the ground signal directly at the ECU by backprobing the connector.

This would eliminate the wiring(or not).

Edited October 22, 2013 by naru

[MilesFox]

From what i understand is the injectors are live all the time, and ground through the resistor to the ecu. If the resistor failed, it would prohibit a signal. If i remember right there are 2 resistors. There is a ceramic resistor in an aluminum shroud mounted on the passenger side strut.

[ivans imports]

Timing belt wrong ? or ground for injectors damaged ecu mabe does it have the injector resistor on ps firewall ? damaged resistor pack

[jono]

3 plug ECU or 4 plug ?

 

1987 was a tricky year for some of us. I have a 1987 EA82T that was actually built in 9 , 1985 so it is 1985 stuff.

 

Another 87 wagon was made late 86 for the 87MY so it was an 1987 model.

 

85/86 did not use resistors on injectors did they ?

Isn't there a flow chart to follow to test each injector wiring ?