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Discussion Starter · #1 ·
Looking to ohm out the injectors but can't find any definitive ohm readings online for my truck. Where should a 1989 Dodge 318 tbi injector ohm be? Some where saying between 2 and 3 ohms and others where saying 1 to 1.5 ohms which one is actually correct?
 

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You can still have a bad injector even if it passes the resistance check. Do you have a fault code 26?:

If you measure both injectors, are they close to each-other? The resistance will vary quite a bit with temperature
The checks in the chart below call for a temp of 68℉ (20℃). I would say between 10Ω - 16Ω passes.
The PCM self-tests the injectors by looking for the inductive (electromagnetic) spike after the injector fires. In this way, the PCM can tell a coil is a coil. The resistance doesn't mean much.

Electrically an injector can pass with flying colors, but if it drips or dribbles it can cause driveability concerns.
A 32 year-old injector may have wear or corrosion issues. If replacing, always use OEM parts.


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Discussion Starter · #3 ·
You can still have a bad injector even if it passes the resistance check. Do you have a fault code 26?:

If you measure both injectors, are they close to each-other? The resistance will vary quite a bit with temperature
The checks in the chart below call for a temp of 68℉ (20℃). I would say between 10Ω - 16Ω passes.
The PCM self-tests the injectors by looking for the inductive (electromagnetic) spike after the injector fires. In this way, the PCM can tell a coil is a coil. The resistance doesn't mean much.

Electrically an injector can pass with flying colors, but if it drips or dribbles it can cause driveability concerns.
A 32 year-old injector may have wear or corrosion issues. If replacing, always use OEM parts.


View attachment 84456

View attachment 84458
No, I don't have a fault code 26 that was the first thing I checked and Yes the injectors read within 0.1 ohms of each other. I'm getting 2.5 ohms on the left and 2.6 ohms on the right. They are Low impedance injectors according to what I found low impedance injectors are only suppose to be between 1 and 4 ohms. Please correct me if I'm wrong. The truck slowly just died over the course of a month and wouldn't start back up by itself I've replaced the fuel lines, bad fuel pump and filter, TPS sensor, fuel pressure regulator, completely new ignition system Distributior, wires, plugs, coil and it still will not start checking the pickup coil as the Distributor I got was a Reman as well as the MAP Sensor before I buy Another set of injectors. I also have checked for spark and injector pulse I have both. The smec is out putting 9v to the injectors.
 

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Discussion Starter · #4 ·
No, I don't have a fault code 26 that was the first thing I checked and Yes the injectors read within 0.1 ohms of each other. I'm getting 2.5 ohms on the left and 2.6 ohms on the right. They are Low impedance injectors according to what I found low impedance injectors are only suppose to be between 1 and 4 ohms. Please correct me if I'm wrong. The truck slowly just died over the course of a month and wouldn't start back up by itself I've replaced the fuel lines, bad fuel pump and filter, TPS sensor, fuel pressure regulator, completely new ignition system Distributior, wires, plugs, coil and it still will not start checking the pickup coil as the Distributor I got was a Reman as well as the MAP Sensor before I buy Another set of injectors. I also have checked for spark and injector pulse I have both. The smec is out putting 9v to the injectors.
I have no fault codes
 

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I have always read that low-impedance injectors are supposed to be 2-3 ohms.
 

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Discussion Starter · #6 ·
I have always read that low-impedance injectors are supposed to be 2-3 ohms.
Ok so my source was correct I've gone though and tested every sensor, vacuum operated valves and tested the pickup coil and MAP and they all came back good as far as voltages I think I'm just going to buy a set of injectors like you had said because everything else is checking out ok.
 

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Before you throw parts at it, diagnose further.
Do you have spark?
Do you have compression?
Are the valve and ignition timing correct?
Does it start if you spray starting fluid into the throttle body while cranking?
 

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Discussion Starter · #8 ·
Before you throw parts at it, diagnose further.
Do you have spark?
Do you have compression?
Are the valve and ignition timing correct?
Does it start if you spray starting fluid into the throttle body while cranking?
I have spark and 14.5psi of fuel pressure and it starts right up on starting fluid and runs perfect. then dies out after it runs out of starting fluid. Working on getting a timing light. Haven't checked compression.
 

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Discussion Starter · #9 ·
I have spark and 14.5psi of fuel pressure and it starts right up on starting fluid and runs perfect. then dies out after it runs out of starting fluid. Working on getting a timing light. Haven't checked compression.
If I continue to spray starting fluid or gas in the Throttle body it continues to run perfect.
 

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. . . I also have checked for spark and injector pulse I have both. The smec is out putting 9v to the injectors. . . .
Why did you swap in low impedance injectors? You may have caused the driver circuits in the SMEC (single module engine controller) to fail. Using ohm's law with OEM equipped injectors, divide 9 volt power source by 13 ohms resistance gives about 0.69 amps current through the drivers. If you use low impedance injector with 2.4 ohms resistance you get 9 volt power divided by 2.4 ohms resistance and you get 3.75 amps through the circuit. That excessive current flow may have slowly damaged the injector drivers. The SMEC is no longer able to pulse the injectors but you can get the engine to run by manually adding fuel into the throttle body.
 

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Discussion Starter · #11 ·
Ok, thank you for that information the reason behind wanting to replace the injectors was because I can start the engine on starting fluid and then keep it running by pouring gas into the throttle body. I was just trying to make sure that it was the injectors by ohm the injectors that are in the truck right now and couldn't find any info on the injector ohms again thank you for your help in this matter. The fuel pressure is at 14.5psi when running and the list of new part for the fuel system are the pump, lines, regulator, and filter as I found that all of that had gone bad at the same time and then when it wouldn't start is when I posted this to begin with.
As well as the entire Ignition system was replaced due to the bearing in the distributor going bad so I had decided to TDC the engine and replace the Distributor, coil, wires and spark plugs and checked the brass brushing in the engine. As well as the timing. Had a friend who was a Dodge mechanic help me with making sure the timing was good. But he had moved out of the state and I was having problems figuring out the rest on my own. I also went over testing all of the sensors and wiring and found no problems with it. So I was getting stumped.
 

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Discussion Starter · #12 ·
AllenC those injectors were TBI factory injectors that came in the truck I haven't changed them. My engine only has Two injectors. I'm just going through trying to rule out parts so far I have an instance where my noid light is flashing dim when chanking the engine, but once it's started it flashes brightly. Please note the I'm using a 12v noid light set. Can you recall anything related to that scenario. I've gone through and tested the following with read outs:
TPS 0.8v to About 5v
Pickup coil no/off 0.05v to 5v
MAP 0.5v to 4.5v
New Temp sensor, fuel pump,filter,regulator and lines. Ignition coil, Distributor, wires and plugs.
The fuel system and Ignition system where replaced previously to the current problem because they each died or went bad over the course of a year.
I have 14.5 psi fuel pressure at the TBI and Spark and when I start it on starting fluid it starts right up then dies out when it runs out of starting fluid. But I can keep it running that way which rules out timing being the problem. So I think that the only other thing to test is the smec grounds and the injector wiring from the smec to the injectors. Any other ideas are welcome. Also what voltage are the injectors supposed to get when starting the engine vs it running.
 

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Injectors run on the same voltage at all times. What changes is the duration of fuel flow.
 
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. . . . I have 14.5 psi fuel pressure at the TBI and Spark and when I start it on starting fluid it starts right up then dies out when it runs out of starting fluid. But I can keep it running that way which rules out timing being the problem. . . .
Your test proves that ignition timing is correct and spark is present. Valves are operating properly. You have correct fuel pressure at 14.5 psi so the electric fuel pump is performing as designed and the fuel filter is not plugged. So the issue lies with fuel delivery: the fuel injectors are not pulsing due to failure of the driver circuits in the electronic engine controller or there is a wiring problem on the injector control circuits between the engine controller and the throttle body.

. . . . AllenC those injectors were TBI factory injectors that came in the truck I haven't changed them. My engine only has Two injectors. . . . .
So a previous owner changed the fuel injectors from original issue and probably made a difficult situation worse. As I outlined in post #10 the resistance of the fuel injectors is too low and allowing excess electrical current to flow in the circuit. This can permanently damage the driver circuits in the engine controller. You are correct in that you have dual fuel injectors in the throttle body. Each injector has its separate power and ground from the engine controller.

You indicated usage of a noid light. What were you checking? Spark or fuel injector pulse?

. . . So I think that the only other thing to test is the smec grounds and the injector wiring from the smec to the injectors. Any other ideas are welcome. Also what voltage are the injectors supposed to get when starting the engine vs it running. . . .
You do not need to check any other sensors on the engine. Check power and grounds to the fuel injectors. Attached is a pinout for the 1989 V8 engine controller and the location of the 4 pin electrical connector at the throttle body.

It is possible that there is logic built into the engine controller such that it is sensing the excessively high electrical current flow in the injector circuits and disabling the circuits to prevent failure. Electronic fuel injection was in its infancy in 1989 so I do not know if engineering design would have incorporated such a safeguard. Test for injector pulse and if present then you need to install injectors with the correct resistance. To test disconnect the 4 pin connector at the throttle body.

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I have had vehicles with good fuel pressure because the fuel was standing still in the lines. As soon as the fuel began flowing, the pressure dropped.
I then performed a fuel pump volume test where I would watch the pump fuel fill a clear soda bottle. It slowed to a trickle and was riddled with bubbles. You can also observe fuel color which should basically run clear. Use caution when handling raw and open fuel containers.
The problem was inside the tank with the pump drawing air in the suction side before the pump.
If I pinched off the hose up front, the pressure would gradually rise to spec.
Does the pump run quiet? Keep an open mind that this may not be an electrical problem.
 

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Discussion Starter · #16 ·
Your test proves that ignition timing is correct and spark is present. Valves are operating properly. You have correct fuel pressure at 14.5 psi so the electric fuel pump is performing as designed and the fuel filter is not plugged. So the issue lies with fuel delivery: the fuel injectors are not pulsing due to failure of the driver circuits in the electronic engine controller or there is a wiring problem on the injector control circuits between the engine controller and the throttle body.



So a previous owner changed the fuel injectors from original issue and probably made a difficult situation worse. As I outlined in post #10 the resistance of the fuel injectors is too low and allowing excess electrical current to flow in the circuit. This can permanently damage the driver circuits in the engine controller. You are correct in that you have dual fuel injectors in the throttle body. Each injector has its separate power and ground from the engine controller.

You indicated usage of a noid light. What were you checking? Spark or fuel injector pulse?



You do not need to check any other sensors on the engine. Check power and grounds to the fuel injectors. Attached is a pinout for the 1989 V8 engine controller and the location of the 4 pin electrical connector at the throttle body.

It is possible that there is logic built into the engine controller such that it is sensing the excessively high electrical current flow in the injector circuits and disabling the circuits to prevent failure. Electronic fuel injection was in its infancy in 1989 so I do not know if engineering design would have incorporated such a safeguard. Test for injector pulse and if present then you need to install injectors with the correct resistance. To test disconnect the 4 pin connector at the throttle body.

View attachment 84519 View attachment 84520
AllenC I was checking injector pulse. I have a dim flash when cranking and a bright flash when temporarily started with starting fluid.
 

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. . . . I was checking injector pulse. I have a dim flash when cranking and a bright flash when temporarily started with starting fluid. . . . .
Did you remove the electrical cap on each fuel injector and attach the noid light to the 2 prong receptacle and test?

During START mode the injectors are pulsed 8 times per 1 crankshaft revolution. In RUN mode the injectors are pulsed 4 times per 1 crankshaft resolution. I am thinking in START mode there are more interruptions / pulses of the electrical current flow to the injectors and as a result you get a pulsing illumination that is dimmer than when in RUN mode. So the fuel injector driver circuits within the electronic engine controller must be good and functioning correctly.

In my post #14 I mentioned that there could be logic in the engine controller such that if excessive current flow is detected in the injector circuits, the circuits are disabled. With the electrical connector separated from the injector, the noid light would NOT draw excessive electrical current and the engine controller would allow the circuitry logic to pulse the injector circuit. With injectors connected to their respective circuits, there is excessive electrical current flow and the engine controller is disabling the circuitry.

I would suggest that you need to test each injector with electrical connections in place. You will have to back probe the appropriate wire at the 4 pin connector at the throttle body. Use a test light with an LED bulb; no incandescent bulb. An incandescent bulb can cause an excessive electrical current draw and cause problems. LED bulb only draws a fraction of an amp electrical current and is safe to use on electronic engine controller circuits. That engine controller pinout diagram provided in post #14 gives wire colors. Hopefully it is correct and matches what is on your engine.
 

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Cranking draws down battery voltage and that might also account for the dim flashes.

Now that you've established that you have flashes with engine running it may be time to go back to the fuel flow test suggested above to see if you have a weak pump or sucking air.
 

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Discussion Starter · #19 ·
Built a 9v and 12v injectors pulse tool for pulsing injectors on the truck and found the spray pattern is good and found out that the dimmed flashing is do to it fluctuating between 0.8v and 2v when cranking so I'm going through tracing the injector curcuit wires from the ECU to the injectors and I'm going to test the wiring to see if they shorted to themselves by ohming the wires. Just posting it here in case someone has the same problem.
 

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How are you measuring the injector voltage - analog or digital multimeter, or oscilloscope? Unless you use a scope, the voltage may be changing faster than the meter can respond, and you will get an inaccurate reading. At idle, injector firing in my 4-cylinder is 55ms, and a typical multimeter needs 250ms or more to respond. So before it can acquire the full high-side voltage, it's falling again, and that will throw off the reading.
There are good handheld scopes out there for cars that are not too expensive.
 
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