How do I test for grounded injectors on a 1991 Ranger 4.0 OHV. My truck won't start, have fire and fuel,,,, but after trying to start it if I pull a spark plug it's soaked,,, I am thinking an injector might be grounded and just pouring fuel.

 

Turn on the ignition and measure the voltage to each wire of the injectors. Both wires should show 12vdc. If one is 12v, or lower, and the other is 0vdc, that injector is shorted to ground.

However, all injector grounds are tied together on each bank, so if one shows a short, they all should on that bank. jd

 

check ignition module. u may have fuel, but it may be shutting the fuel off. ive had fords, chevys and a dodge all do this to me

Matt

 

You could get a visual indication of what is going on with the injectors, by plugging a "noid" light into the suspect injector/s wiring harness.

They are avalable at most auto parts stores. Some stores may have them available for a refundable depsit, on their "Loan-A-Tool" program, so you won't have to buy them.

A steady glow means the injector is constantly grounded & squirting. Maybe a short in the ground lead to the computer. Maybe a faulty computer grounding circuit.
Maybe the computer is confused & getting a corrupt signal from the ignition module, as fordboy has suggested.

A flickering noid means it's getting a ground pulse, no light means it's not getting a computer controlled ground pulse.

Just another option for consideration.

 

Jim, I figure this is a good opportunity to get you to help me get this one. This is for my education, and I'm always wanting to get to know this sytem better. I've run across it on a couple of older threads, but was in too much of a hurry to ask.
I know the engine in question is an oder 91, but on the V6 injection systems, and please explain if and how they've changed to present models, exactly how are the injector pulses controlled by the ECU(PCM?). From what I remember, at KOEO, they have 12V supplied to them but with zero current. This is why we detect 12V on both connector leads?. So they have voltage, but no current, so the injector is 'open' or 'closed'? And the ECU( or is it the PCM- I'm a bit confused on if it's the same module with different acronyms or if one is a slave to the other) pulses the injector by grounding one of the leads, initiating an electric current which opens? closes? the injector. What I remember about the old TBI, is that the PCM increases the the frequencey of the pulses to increas fuel flow.

You mentioned that the ground leads to the injectors on each bank are ganged together. Would'nt it be the power feeds that are ganged together with each individual ground leads being on their own 'switch' controlled by the PCM? I'm just wondering that if an injector is 'grounded' with KOEO, that we'd detect a current through that individual injector and this is why we'd see a voltage drop between the leads of that injector(which I'm sure has a resistance).

So, following this logic , a 'grounded injector' would be in the open position and flooding fuel through it when the fuel rail is pressured up?

Hope it makes for good discussion .

Thanks in advance

Fred

 

ECU = Electronic(Engine) Control Unit, or ECM = Electronic Control Module,
PCM=Powertrain Control Module basically all the same thing, a computer.
Injector control varies with the status of the engine, cold/warm/hot. Cold it uses look-up tables, as it warms and the sensors come into play, it uses sensor inputs to adjust to conditions. Injector timing also varies depending on the engine/system, but usually it is controlled using ignition timing.
A fuel injector is nothing more than a solenoid. Current, the pintle opens, no current spring pushes the pintle closed. There are other types of injectors, but basically the operate the same way.
Yes, the power source is also ganged together.
This is what happens in "sequential fuel injection" with each injector firing independently of the others. The 91 4.0 does not have this.
This would be true if it had sequential fi.