Technical Fuel Injected Engine Only Runs on 3 Cylinders

[Oliver01]

Hi everyone, I’m stuck on an issue with my engine.

It will only run on any combination of 3 cylinders. If I connect the remaining wire to any last injector, the engine won’t start. If I connect it while the engine is running, it immediately shuts off/stalls

The injectors are brand new, and the car started fine before I replaced them. I’ve checked the resistance of all 4 injectors, and they’re identical. I’ve also gone through the power supplies, ground connections, most of the wiring, relays, and the ECU, but I can’t figure out what’s causing this.

Has anyone dealt with something similar? Could it be an issue with the new injectors themselves, or am I overlooking something else? Any suggestions or guidance would be a huge help.

Thanks in advance!

 

[Zardo]

Are you saying this happens to any of the wires 1-4, no matter what cylinder, if you connect three, the last one „bites the dust“?

Are those OEM injectors?

If not, do they draw more current than the original ones?

 

[Oliver01]

Are you saying this happens to any of the wires 1-4, no matter what cylinder, if you connect three, the last one „bites the dust“?

Are those OEM injectors?

If not, do they draw more current than the original ones?

Yes, if I unplug any of the four injectors, the car runs on the other three cylinders. It doesn’t matter which one I unplug. The injectors are aftermarket; I didn’t check if they draw more current, but they were listed as a direct replacement.

 

[Zardo]

If you still have the old injectors, you could compare their resistance with the new ones.

I don‘t have any other idea for the moment.

Edit: actually, did the car run on all four cylinders with the old ones?

 

[judderbar]

Weird fault.

https://www.mirafiori.com/faq/content/81_82_COMPLETE.pdf

For some reason each injector has its own constant 12 volt feed wire all the way from the relay connection. And then each injector is grounded by the ECU.

Try adding an extra ground connection directly to the battery from the ECU ground

 

[LudekKucera]

If you still have the old injectors, you could compare their resistance with the new ones.

I don‘t have any other idea for the moment.

Edit: actually, did the car run on all four cylinders with the old ones?

I have compared the resistance of the old and new injectors: old 2.7 ohms vs new 3 ohms. The car ran on all four with the old ones. I also tried to connect the disconnected injector plug into the old injector while engine running on 3 cylinders. The rpm's dropped a little bit, but the engine kept running, so I assume that the new injectors draw more current that the old ones. While checking the possible causes I found other fault - I have a problem with alternator - it is not charging and the car runs on battery with about 12.2 volts. First I will fix the alternator to ensure that I have the correct voltage and current supply to the ECU and than I will continue.....
Thanks to everyone and a lot of happy miles in the New Year to everyone, I will keep you posted about the problem...
Oliver and Ludek

 

[Zardo]

If the new injectors have slightly more resistance, then they likely would not draw more current.

old: I = U / R = 12.2 / 2.7 = 4.52 A
new: I = U / R = 12.2 / 3 = 4.07 A

Of course, these values are only indicative as every coil will initialy magnetically oppose a change of magnetic field (self-inductance, Lenz's law).

However, connecting 4 injectors will consume more power and drop the battery voltage more (in case of a faulty alternator) than connecting three injectors.

Let's assume the case with an engine idling at 1000 RPM.

One injection per cylinder every 2nd revolution.

4 * 0.5 * 1000 = 2000 injections per minute.

Now for three cylinders:

3 * 0.5 * 1000 = 1500 injections per minute.

The electric energy needed is therefore 75 % when running on 3 cylinders instead of 4.

Possibly, this might just drop the battery voltage enough for the ECU to give up (in case of an old, weak battery which is mostly discharged).

If the engine ran fine on 4 cylinders with the old injectors, then you've worked on it and now it doesn't run on 4 cylinders anymore, this could indeed be explained simply by the battery discharging itself. You could prove this theory by reinstalling the old injectors... or simply switch to a new, fully charged battery. And repair the alternator, of course ;-)

 

[LudekKucera]

If the new injectors have slightly more resistance, then they likely would not draw more current.

old: I = U / R = 12.2 / 2.7 = 4.52 A
new: I = U / R = 12.2 / 3 = 4.07 A

Of course, these values are only indicative as every coil will initialy magnetically oppose a change of magnetic field (self-inductance, Lenz's law).

However, connecting 4 injectors will consume more power and drop the battery voltage more (in case of a faulty alternator) than connecting three injectors.

Let's assume the case with an engine idling at 1000 RPM.

One injection per cylinder every 2nd revolution.

4 * 0.5 * 1000 = 2000 injections per minute.

Now for three cylinders:

3 * 0.5 * 1000 = 1500 injections per minute.

The electric energy needed is therefore 75 % when running on 3 cylinders instead of 4.

Possibly, this might just drop the battery voltage enough for the ECU to give up (in case of an old, weak battery which is mostly discharged).

Thanks, the battery is old, so I will get a new battery and make sure the alternator generates power.
I will get done after New Year and see if there is any change.
Ludek

 

[LudekKucera]

Thanks, the battery is old, so I will get a new battery and make sure the alternator generates power.
I will get done after New Year and see if there is any change.
Ludek

The car is a project with my son and was not running, we stripped it down and now are starting to rebuild it, we got the engine running, but the wiring was a mess with a lot of " extra wires" etc. I just wanted to get it running before a paint job, so not all electrical wiring is connected, the dashboard is out etc

 

[LudekKucera]

The car is a project with my son and was not running, we stripped it down and now are starting to rebuild it, we got the engine running, but the wiring was a mess with a lot of " extra wires" etc. I just wanted to get it running before a paint job, so not all electrical wiring is connected, the dashboard is out etc

I have solved the problem. After I checked the fi wiring harness for any shorts or wire breaks and measured all inputs according to the bosch diagnosis manual, the only thing left was the new injectors. Even though they had the same resistance 2.7 ohms, O decided to change them for the old ones.
That solved the problem. I guess Italian car with German FI does not like Chinese aftermarket injectors.
The injectors that did not work in 1980 Fiat Spider 2000 CS0 are DEFUS fuel injector 0280150121

 

[s130]

I sympathise with you in that these types of not expected problems with new components should not be happening.

Thankfully you kept the old injectors. I keep old components so one always has something to revert to in troubled times.

Next question is why the new Chinese injectors cause such a problem. I can only think of resistance and more importantly? inductance values.

Injectors are no more that a solenoid. Solenoids have resistance (static DC ohms value) and Inductance values. In a varying voltage environment at a frequency then these resistance and inductance values create a Impedance (where impedance in simple terms is the equivalent of resistance but varies with frequency). Could be that these Chinese injectors have a lower impedance than the original ones.

 

[Zardo]

The maximum peak current is defined by the resistance and the voltage applied to the injector. How fast the maximum current is reached depends on the impedance of the injector. So overall current (the area below the current-clamp curve) depends on both resistance and impedance.



Would be interesting to verify with adequate equipment (current clamp and oszilloscope).

 

[LudekKucera]

Thanks for the info. I have only measured the resistance and it was identical with the old injectors. Unfortunately I have no equipment to test the difference, nor I have the knowledge. I am just happy that the engine runs. Thanks again.
Ludek