Injector problem

[Jim Wright]

Gotta 1989 2.9 ranger. Having injector problems. Have 12 volts at injector connector. Have pulse. When I check voltage at injector when cranking voltage drops to 3 volts. Heck of a voltage drop. Checked resistance between pcm and injector connector. All good. Checked lnjector pulse by back probing injector ground pins at pcm and only 3 volts. Switched out pcm with known good pcm. Same thing only 3 volts. Crazy stuff. Hopefully someone else has experienced this problem and traced it down. Thanks Jim

 

[Shran]

Grounding issue somewhere?

 

[Curious Hound]

I agree. Check the grounds for your pcm.

 

[franklin2]

Which wire has 3 volts? The common power supply red wire or the other two wires going to the computer? This engine is batch fired, and the injectors are grouped 3 together on one circuit, 3 together on the other circuit.

 

[Uncle Gump]

I don't play with this stuff full time any longer... so I'm a bit rusty perhaps.

But injectors are supplied 12 volts and ground side switched at the ECM. The majority of that 12 volts gets dropped across the injector when active so the switched ground side should only have enough voltage to complete its path to ground.

 

[Jim Wright]

Which wire has 3 volts? The common power supply red wire or the other two wires going to the computer? This engine is batch fired, and the injectors are grouped 3 together on one circuit, 3 together on the other circuit.

If I hook jumper between hot side of injector connector and ground side of connector I have 12 volts key on no start. Voltage drops to 3 volts when cranking engine. Seems to be the same at all injectors. Also checked pulse power at pcm pin 58 and 59
Just over three volts when cranking at those pins. Weird.

 

[Jim Wright]

I don't play with this stuff full time any longer... so I'm a bit rusty perhaps.

But injectors are supplied 12 volts and ground side switched at the ECM. The majority of that 12 volts gets dropped across the injector when active so the switched ground side should only have enough voltage to complete its path to ground.

The voltage drops when connector is disconnected from injector. So now I am tracing grounds. Would a bad shielded groun
cause this problem
Thanks. Jiim

 

[Curious Hound]

Not sure what you are calling a shielded ground. Normally, if you have a shielded cable (several conductors wrapped by a braided shield), the shield would be attached to ground. I’m not sure there are any shielded cables involved in this system.

Anyway, I would be checking to make sure the ground wires for your pcm have good, clean, tight ground connections.

 

[2011Supercab]

Is there a problem with the engine running, or are you just playing around with a voltmeter and think you've found a problem?

The 12v + is always hot, the 12v - is only for a micro second while cranking and running, There is no real way to check the voltage using the 2 injector wires while running or cranking.

 

[franklin2]

If I hook jumper between hot side of injector connector and ground side of connector I have 12 volts key on no start. Voltage drops to 3 volts when cranking engine. Seems to be the same at all injectors. Also checked pulse power at pcm pin 58 and 59
Just over three volts when cranking at those pins. Weird.

I would expect that. I am surprised something didn't start smoking. You are shorting the injector out with the jumper, and then when the engine starts turning, the computer starts firing the injectors. Firing the injectors means it's grounding the injectors on the "ground side". So when the computer tries to fire the injectors, it is shorting out the 12v supply because you have jumped around the injector. I would not short the injectors out anymore, hopefully you haven't damaged anything.

 

[Eddo Rogue]

Which wire has 3 volts? The common power supply red wire or the other two wires going to the computer? This engine is batch fired, and the injectors are grouped 3 together on one circuit, 3 together on the other circuit.

The one with a bad ground. And yes exactly that is why the ground wires making solid contact are so important.

 

[Uncle Gump]

Is there a problem with the engine running, or are you just playing around with a voltmeter and think you've found a problem?

I'm with you here... just what are you trying to fix?

 

[franklin2]

The one with a bad ground. And yes exactly that is why the ground wires making solid contact are so important.

The injectors are not grounded. That may be where you are getting sidetracked. Any ground they get is coming from the computer, and it will not be a complete 0v ground, it will be a little bit above ground. But still enough to fire the injector.

 

[Eddo Rogue]

The injectors are not grounded. That may be where you are getting sidetracked. Any ground they get is coming from the computer, and it will not be a complete 0v ground, it will be a little bit above ground. But still enough to fire the injector.

You might be right, but there's something going on.

Maybe weak or brittle wire/connectors?

 

[Jim Wright]

Is there a problem with the engine running, or are you just playing around with a voltmeter and think you've found a problem?

The 12v + is always hot, the 12v - is only for a micro second while cranking and running, There is no real way to check the voltage using the 2 injector wires while running or cranking.
Thanks for the comeback greatly appreciated. Gotta a no start. Spray gas into intake starts and runs till fuel runs out. here's what I have done. Pulled upper intake
and removed fuel rail checked fuel flow by cranking engine over. Very weak flow pattern. Removed injectors and bench tested with carb spray and checked resistance on all injectors. Good flow pattern when bench tested.checked fuel pressure at fuel rail between 45 and 50 lbs no noticeable drop with engine cranking. I am pretty sure it's a ground problem. Wiring diagram shows pins 59 and 58 are injectors grounds at pcm. With injectors disconnected so no load on circuit I checked voltage at those pins and still shows very low voltage when cranking. it is getting the pip signal from the distributor to pcm just not enough juice to injectors. I really appreciate you guys for helping me out here. Jim