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Discussion Starter · #21 ·
So I found a short at the Z1 circuit splice and fixed that. This is a before picture. Now have 11v to 11.9v roughly to the injectors and my ECU is plusing used a noid light and a test light. But the injectors still won't fire. That would mean I have bad injectors right?
Electrical wiring Electrical supply Cable Wire Electronic device
Electrical wiring Electrical supply Cable Wire Electronic device
 

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. . . .So I found a short at the Z1 circuit splice and fixed that. This is a before picture. Now have 11v to 11.9v roughly to the injectors and my ECU is plusing used a noid light and a test light. But the injectors still won't fire. That would mean I have bad injectors right? . . .
That Z1 circuit is direct system voltage and is supplied by the ASD relay when engine is running. The dual throttle body injectors are ground side switched by the PCM (powertrain control module). How are you measuring the voltage to the injectors? The crankshaft has to be turning for the PCM to close the ASD load side contacts and provide power to the fuel injectors. If the crankshaft is NOT turning then there should be 0 volts at the injectors.I think you have the wrong injectors for the throttle body application.

The low impedance injectors are allowing excessive current flow in the circuit to the PCM. The logic in the PCM is detecting this and disabling the fuel injector driver circuits to prevent permanent damage to the electronic circuitry. Only sure way to know if this theory is correct is to find OEM or like kind throttle body injectors and measure the resistance. I would suspect a correct throttle body injector would have resistance in the 10 - 15 ohm range. This falls in line with the injector resistance chart ImiperialCrown presented in post #2. In post #3 you indicated the existing injector resistance is about 2.5 - 2;6 ohms which would allow excessive current to flow in the injector control circuitry.
 

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1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
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I have the same truck. Watching closely, sorry I'm of no help.
Could you measure the injector resistance on your truck and post the results here?
Temperature will affect resistance.

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Discussion Starter · #25 ·
Ok, ImperialCrown so my injector ohms are 2.5 ohms on both
 

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Could you measure the injector resistance on your truck and post the results here?
Temperature will affect resistance.

View attachment 85613
Truck is at my father's and I'm working overtime with toddler and baby at home, I'd be happy to do this when I can get to my truck, have my own stumbling issue you guys have tried to help me with that I haven't been able to go play with for a while.

Might be a couple weeks yet before I go back to my folks. 😒
 

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1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
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A 'stumble' may be from an internal EGR back-pressure transducer diaphragm spring rusted out. This causes the EGR to come on too early (just off idle). You may or may not have an EGR solenoid.
The transducer halves unsnap and sometimes all that is left behind of the spring is rust particles and an orange stain.
The back-pressure half (spring-side) is connected to the exhaust which has lots of acids, combustion by-products and moisture.
The replacement transducers went to stainless steel springs which didn't corrode.

 

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A 'stumble' may be from an internal EGR back-pressure transducer diaphragm spring rusted out. This causes the EGR to come on too early (just off idle). You may or may not have an EGR solenoid.
The transducer halves unsnap and sometimes all that is left behind of the spring is rust particles and an orange stain.
The back-pressure half (spring-side) is connected to the exhaust which has lots of acids, combustion by-products and moisture.
The replacement transducers went to stainless steel springs which didn't corrode.

Sorry for the hijack OP.

Stumbling is less accurate, have my own thread up its mostly a slightly rough idle, most often with extremely light brake pedal pressure applied.

I beleiev you have made some suggestions there I've just yet to get to it. I'm planning a 440 swap for the truck..... Eventually...............
 

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. . . Could you measure the injector resistance on your truck and post the results here? Temperature will affect resistance. . . . .
I was finally able to disengage the electrical connector for the throttle body fuel injection on my 1991 Dakota with 5.2 liter V8. The fuel injectors for a 1991 5.2 V8 are the same specification as 1989 5.2 V8. I used a digital volt-ohm meter and found one injector had 3.2 - 3.3 ohm resistance. The other had 1.1 - 1.3 ohm resistance. I cleaned the pins in the connector and repeated measurement numerous times with the same results. Overnight outside temperature was about 30 deg F so I do not think the engine metal had warmed that much when I performed the measurement this morning. My fuel injectors are original and the engine exhibits no problems with starting and running. I used an alternate, analog volt-ohm meter and confirmed my readings so the discrepancy is not due to a meter issue. So my theory I expressed in post #22 about excessive current flow in the injector control circuit is incorrect. The throttle body injection circuitry was designed with these low impedance injectors.

But the chart ImperialCrown presented in post #2 shows impedance in the range of 10 - 15 ohms. But notice that the engines listed were for model years 1996 - 2000. Research that I reviewed indicated that manufacturers first used fuel injectors through the early 1990s with low impedance. That would be the era of throttle body injection and then the start of port injection. Low impedance injectors take more electrical current to operate. With port inejction and the presence of 4, 6 or 8 injectors, injector design changed and impedance increased. This decreased the overall electrical power consumption necessary to operate the fuel injectors.

So I believe that chart in post #2 is valid for later model engines with thinner, pencil type injectors and NOT valid for the fatter, throttle body injectors used in 1988 - 1991. So I am thinking that the injectors curently in his 1989 Dodge 5.2 V8 are probably satisfactory. There is another issue that is not allowing the injectors to spray into the throttle body.

Image below is one that I found on a Dodge Ram forum. Problem presented was that the throttle body injectors were not spraying fuel. Someone posted an image of the engine wiring schematic and mentioned to check a certain connector for corrosion. Any corrosion in the power feed wire to the injectors would reduce electrical current flow and keep a low impedance injector from opening and closing properly. See red arrow.

Product Rectangle Font Schematic Line
 

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The difference between 3 ohms and 1 ohm is significant. Lower impedance means more current draw, which the ECM may not be able to supply. Even if it can, the rise and fall times will be different between the two, so fuel delivery will be different.
When I see lower than normal resistance readings on solenoids, fans, motors, I think immediately of the most likely cause that the thin insulation over the wire in the windings is breaking down and the windings are shorting out. This can happen with age.
I had a cooling fan that was drawing so much current at turn-on, it would overwhelm the alternator and the voltmeter would snap down to about 10 volts, then snap back up as the fan passed the turn-on stage and current settled down to steady-state. I measured with a DC clamp-on ammeter from work, and it was 36 amps (on a 40A fuse) at the turn-on spike, and 13 amps steady-state. The engine would often cut out for an instant when this happened. The fan's motor windings measured only 0.6 ohms. I bought a junkyard fan that measured 2.4 ohms and installed it. Current spike was reduced to 13 amps, and 4.5 amps steady-state, and no more trouble with the car.
I'd replace the injector that has the 1 ohm reading.
 
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