Dave51

And if there's no power to the injectors at key off, then that's probably how many injectors have a problem.

Dave51

No, it means one of them is stuck open.

Dave51

And I think it's more likely that if the drivers are bad the injectors wouldn't fire at all, and again, getting them noid lights might be able to get a better understanding of what's going on.

That said, we can still test with the multimeter.

Noah911

But you do not need to prove the ECU cable has been disconnected whenever you disconnect it. It is a given.

The important thing here is with the ignition key off, the drivers circuit of the PCM is supposed to be in an open loop configuration. As such, it would display OL when testing resistance with the key off.

His testing showed a low resistance and not OL.

Of course unplugging the PCM will result in OL... BUT, only if the wiring of the driving ground feeder circuit is proper. If the wiring itself is what is shorted to ground it would be a nullifying factor to the first test he did showing low resistance on the ground feeder circuit when it should have been in open loop.

It verifies and differentiates the reason.. of the first abnormal test result.

Noah911

I would say a good next test is done with a test light.

If the test light stays lit then you know it has a completed circuit. Specifically, the ground circuit which should be NO (Normally Open) when the key is off.. it may be abnormal and is instead NC (Normally Closed) when the ignition key is in the off position.

One test light lead on the (+) battery post. The other test light lead clipped to the ground feeder circuit wire at the fuel injector. Testing of the ground feeder circuit...

Noah911

WHOA.... HOLD ON

This is true? That changes everything and would make me way wrong...

(edited to add):

I believed what you wrote above... I just missed seeing it until I went back to look closer at the diagram you provided. I completely missed it being a Renix Jeep in the beginning. I tend to stay more reserved answering many Renix Jeep questions. I would not have known the difference with their plus side control for the injectors


There it is in black & white from the manual. Each injector is connected to a permanent ground and energized when connected to battery voltage through the ECU. I would agree to test for voltage is the way to go...

Hopefully, the spare ECU will work for you.

Jordan Double

Ok well today I’m going over to get the other ecu and if it fixes it thank god if not then I’ll probably voltage test some injectors to see if any are bad, I wouldn’t think they are sense they are all brand new 4 holes

Noah911

It seems to me it probably might be a problem of the ECU. It is similar to how a ground powered circuit would be. Except, it is the other battery power 'plus' side of the injectors circuit that has the work being done on it to turn on and off.

I am not sure? Maybe the same type of testing applies to the plus side in the same similar way? It all depends on how it is switched on and off. Maybe the PCM internally breaks the plus side circuit the same as it would be doing on the ground side, to give the same results? I mean, it has to open and close the power side somehow right... It is possible it might just be able to apply it though.

I would be interested in a repeat test done in the same way after the replacement PCM gets installed, hopefully to fix the problem.

Dave51

Actually, the voltage test should tell you if the ECU is bad.

BTW what injectors did you get?

Jordan Double

I will repeat the test with the new ecu once I get it today after school

Jordan Double

Fuel Injectors 0280155710 0280155700 for Jeep, Ford, Lincoln, Mercury(Set of 6) those are the injectors I bought, form what I could tell all these yellow ones were the same so I got the same bed that were brand new not referbished in my price range

Noah911

Cool thanks. I really hope it is as how I was questioning it to be.. similar to how a ground feeder circuit does the switching between open and closed. In particular, because you already have the spare ECU to swap in and this could mean it was the reason for your problem.

Jordan Double

Yeah I do too, I read a bunch of that manual that was posted earlier and it seems that’s how it works I could be not interpreting it right but I think so. We’ll see when I swap the ecu I should be back with actual results weather that it is fixed or not by around 6 or 7

Jordan Double

Well I picked up the ecu and am in route to install, just out of curiosity does the ecu houseing need to be grounded on its mount or isolated or does it not matter

Jordan Double

Well I just hooked up the new ecu and it fired right up let’s hope it keeps doing good, I’m gunna keep starting and stopping it and test for if injectors stick open and if not then I’m gunna change some oil and finally do jeep things with my Jeep. This is my first jeep and first car actually it’s been an adventure but I’m loveing it