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1989 Dodge 318 injector ohm

9K views 37 replies 6 participants last post by  Bob Lincoln 
#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?
 
#2 ·
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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#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.


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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.
 
#5 ·
I have always read that low-impedance injectors are supposed to be 2-3 ohms.
 
#6 ·
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.
 
#7 ·
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?
 
#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.
 
#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.
 
#14 ·
. . . . 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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#13 ·
Injectors run on the same voltage at all times. What changes is the duration of fuel flow.
 
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#15 ·
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.
 
#18 ·
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.
 
#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.
 
#20 ·
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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#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?
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#22 ·
. . . .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.
 
#24 ·
Could you measure the injector resistance on your truck and post the results here?
Temperature will affect resistance.

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#27 ·
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.

 
#28 ·
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...............
 
#30 ·
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.
 
#31 ·
So here are all of my notes on this truck It will not start from cold. But if you drip gas down the throttle body to get it going it will run. When cold if you push the throttle down even a little bit it stalls out. Once it's warmed up it will run fine and if you shut it off once warm and restart it. It will start up just fine. Any guesses?
Got it to at least start and stay running at this point. Had it running for 3 hours once I dribbled some gas down it.

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#35 ·
Ok, thank you. For that information and ended up having a set of bad injectors hence the no start as well as no power to them shorted wire both have been fixed and it sprays fuel into the TB and has Compression as well as Spark. So the coolant temp sensor has been replaced and is reading 5 ohms on the 200K ohms scale at roughly 40°F. Also the TB temp sensor was just put in today and it ohms to 8.8 ohms on the 200K scale at 68°F tested before I put it on the truck the old one was reading 22 ohms at 40°F on the 200k scale and no change to the condition.
 
#38 ·
These readings indicate a fault if they are accurate.
Coolant temp sensor is normally a very steep curve, but at 40F should be on the order of 20K to 15K ohms. At 70F, they are usually down to 1K ohms or so, and at normal operating temperature about 600 ohms.
A temp sensor that reads such low resistance would appear to the computer as if the engine were fully warm, and would set it leaner than it should be for 40F. Or, if as low as a few ohms, perhaps be interpreted as a short and store a code.
 
#37 ·
. . . The injectors were replaced with part number SMP TJ22 injectors as well as the fuel pressure regulator with SMP PR188 I sent the links for the forum to review the video's to give an idea of what is going on. . . .
I reviewed the links which show cranking but no start. I noticed that the throttle plates are completely closed. Try cranking cold engine again but open the throttle to a fast idle position. Does engine start?
 
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