Question: High Resistance on OEM Fuel Injector.

[Jin1976]

My mechanic friend found that almost all fuel injectors in my car are around 2.5 ohms. He said due to this the plunger in the injector are fully open even at lower RPM. That would explain why my car is still running rich even after cleaning the injectors? I've been debating with my lecturer colleague about how the plunger in the injectors became fully opened when its resistance is high. Can somebody explain to me how this mechanism works?

 

[Daedalus]

It's a solenoid. It is normally closed, and opens under current. I don't see how having higher resistance would make it stay open longer. Are you certain the injectors are OEM? Unusual to see them all out of spec but so close in measurement.

 

[Jin1976]

A good injectors would have resistance between 1.5 to 2.5 ohms. Mine is to the higher limit. Maybe the high resistance would cause the plunger to open a bit longer hence rich fuel. The injectors are OEM and has been on the car for 15 years. The car has about 90k miles on it.

 

[Daedalus]

Wait, I just looked at the manual on prime. It says resistance should be 5-7 ohms. I was thinking they were spec'd at 1 ohm. Where did you get 1.5-2.5?
A resistance increase won't make the injectors close slower--the magnetic field only opens the injector. Perhaps the return springs are weak? Verify the spec and measured numbers. Sorry if you posted this previously--how do you know it's running rich?

 

[Jin1976]

If you check the manual on page 11-90 is says there to measure resistance between the 2 terminals of the injector and to replace if they are not between 1.5 to 2.5 ohms. The exhaust gas smells of fuel even when the car is hot.

Wait, I just looked at the manual on prime. It says resistance should be 5-7 ohms. I was thinking they were spec'd at 1 ohm. Where did you get 1.5-2.5?
A resistance increase won't make the injectors close slower--the magnetic field only opens the injector. Perhaps the return springs are weak? Verify the spec and measured numbers. Sorry if you posted this previously--how do you know it's running rich?

 

[Daedalus]

Ah. I was looking at 11-94, which measures them in series with another set of resistors. I wouldn't worry about being at the high end of the range.
Make sure the O2 sensors and coolant temp sensor are working right. Fuel pressure OK?

 

[Jin1976]

Haven't check the fuel pressure yet.

 

[drew]

You need to slow down your mechanic friend a bit. He is adjusting things that should not be adjusted and trying to out guess the computer.

Make sure your INPUTS (fuel pressure, temperature are correct before you start worrying about your OUTPUTS (injectors).

Your computer is running a program the best it can and it responds to inputs, makes decisions and sends commands to output devices.

Consider what is *more likely* before going off on a some obscure, beyond rare, cause. You and your mechanic need to go over the theory of EEC before you continue diagnosis.

Things that make an engine run rich
1. cold engine -- bad thermo sensor or stuck thermostat
2. bad o2 sensors
3. high fuel pressure
4. (and now) eff'd adjustments on your intake system.

Start MEASURING and RECORDING your inputs before you MODIFY YOUR OUTPUTS.

Drew

 

[BadCarma]

almost all the injectors I have tested (ALOT) were 2.5 on the nose.its very normal for our car

 

[Jin1976]

Thanks for the input Drew. How do I measure the fuel pressure and what is the correct spec and what should the temperature of the engine be? What page on the manual can I refer to?

Thanks to Drew and Badcarma in advance.

You need to slow down your mechanic friend a bit. He is adjusting things that should not be adjusted and trying to out guess the computer.

Make sure your INPUTS (fuel pressure, temperature are correct before you start worrying about your OUTPUTS (injectors).

Your computer is running a program the best it can and it responds to inputs, makes decisions and sends commands to output devices.

Consider what is *more likely* before going off on a some obscure, beyond rare, cause. You and your mechanic need to go over the theory of EEC before you continue diagnosis.

Things that make an engine run rich
1. cold engine -- bad thermo sensor or stuck thermostat
2. bad o2 sensors
3. high fuel pressure
4. (and now) eff'd adjustments on your intake system.

Start MEASURING and RECORDING your inputs before you MODIFY YOUR OUTPUTS.

Drew

 

[BadCarma]

Jin,as far as fuel pressure go to page 264 in the fuel section of the online manual

 

[Jin1976]

Bringing out from the dead. I just got the temperature sensor. I will install it when I get my coolant hoses next week. If incase the thermostat need replacing how much it would normally cost to get one? And on point no.4 (eff'd adjustment) what is eff'd?

Thank you in advance.

Things that make an engine run rich
1. cold engine -- bad thermo sensor or stuck thermostat
2. bad o2 sensors
3. high fuel pressure
4. (and now) eff'd adjustments on your intake system.

Start MEASURING and RECORDING your inputs before you MODIFY YOUR OUTPUTS.

Drew

 

[drew]

And on point no.4 (eff'd adjustment) what is eff'd?

See reference in the UrbanDictionary:

http://www.urbandictionary.com/define.php?term=eff

 

[Hugh]

How do I measure the fuel pressure and what is the correct spec and what should the temperature of the engine be? What page on the manual can I refer to?

With this very simple and useful mod.

The correct fuel pressure is discussed in the service manual on page 11-88.
Normal coolant temps are between 84 and 90 degrees Celcius as show on page 3-4

 

[Jin1976]

Thanks Hugh and Drew. That eff'd meaning in that dictionary doesn't sound so good.