ECU #3 Injector Troubleshooting

[76was124]

I figured out why my 82 was running so rough.....no combustion in #3 cylinder. I think the answer is a bad ECU, but before I go through that expense, I thought I would run by you all the troubleshooting steps I used to suspect the ECU.

Below is with regard to #3 cylinder

1. Spark Good
2. Compression Good
3. No Fuel (only on #3) so I can rule out fuel rail, regulator, double relay etc. its only the #3 FI system that is suspect....
4. 12 volts at the Fuel injector (with ignition on)
5. Test Light across harness side of FI connector (#32 wire) and 12 Volts inconclusive (lights, but doesn't flicker at all)
6. Good continuity on #32 wire between ECU and fuel injector
7. No short to ground on #32 when ECU and Injector unplugged
8. 3 ohms measured across fuel injector terminals at the FI.
9. Measured 3 ohms (FI) at ECU harness connector (on harness with ECU disconnected) between #32 and #29 (#29 is tied back to the same contact on the dual relay as the other side of #3 injector (aka#40)...so wiring to FI apears good.
10. Used an analog volt meter across the two terminals on FI harness connector and got steady voltage? (tried it on #1 FI and got needle bounce as expected (both were done with engine running although it was a little scary testing #1 FI as I was then running on 2 cylinders for a very short time!)
11. Put 12 volts momentarily directly across #3 FI terminals with jumper wires and heard solenoid fire crisply.

So I can see only two possibilities (unless I have both problems below):

A. A clogged FI screen? (But had the screens replaced and the FI cleaned last summer) and #10 troubleshooting above points to ECU.

B. ECU is bad, but doesn't the #10 troubleshooting indicate the injector (incorrectly) would be on all the time?

I know voltage and impedance tests can get a little weird with blown electronics, so I am leading towards the ECU thinking maybe I'm getting a very high impedance measurement of voltage when I do the voltage test (item #10 above).

Is there any impedance tests I can do actually on the ECU terminals? What terminal does the ECU uses as it's common in order to pull #32 to ground? I would think a diode test or impedance check compared to the good circuits on pins, 15,33, & 14 would give me a good indication if the circuit on #32 is blown?

Thanks in advance, also other than EBAY, any suggestions for buying an ECU that is known good?

Wiring on printed page9 (PDF page 11) is available below thanks to Mr. Artigue
http://www.artigue.com/fiatcontent/Wiring_1980_1982.pdf

[spider2081]

I think that all the injectors fire at the same time. The signal to all the injectors is paralleled inside the ECU and comes out separate pins. The ECU output is a ground that lasts between 3-9 milli seconds. The power to the injectors comes from the dual relay. injectors 1 & 2 share a relay terminal and injectors 3 & 4 share another. The injectors inject 1/2 the needed fuel each revolution of the crankshaft. So the ECU output switches to ground for 0.003-0.009 seconds. I don't think you meter can react that fast with engine running.

I would try and swap connectors for injectors 2 and 3 and see what happens.

Actually I would suspect the connector on #3 more than anything else at this point. Were the injector hoses replaced when the injectors were cleaned??

If you open the ECU you might be able to see how the injector pins are jumped together inside.

[76was124]

I don't think you meter can react that fast with engine running.

I would try and swap connectors for injectors 2 and 3 and see what happens.

Actually I would suspect the connector on #3 more than anything else at this point. Were the injector hoses replaced when the injectors were cleaned??

The meter I used isn't digital, picture old VU meters on stereos, I think it is responsive enough as it saw #1 injector blip when firing.

Yes replaced all rubber fuel hoses.

Good idea on swapping to see if the problem follows the #3 connector....that would rule out an injector problem.

Thanks for the suggestions!

[76was124]

Found some interesting reference info for Bosch D-Jetronic, which I know is different than the Fiat L-Jetronic version, but I assume the schematic would probably be similar on the output stage (injector firing circuitry) since they use the same injectors. Details at: http://members.rennlist.com/pbanders/ecu1.jpg

It appears only difference between the output stage firing #2 and #3, is they have separate current limiting resistors. Since they are fired from the same output transistor and all my wiring and injectors are good, it must be a blown resistor, or more likely a bad solder joint on the resistor.

Also, Full info on D-Jetronic at: http://members.rennlist.com/pbanders/ecu1.jpg

[juvius]

just pm'd you. you can use this dme i have for trouble shooting if you'd like...

[76was124]

just pm'd you. you can use this dme i have for trouble shooting if you'd like...

Wow, that's very generous, but I think I'll get it figured out today whether it's the ecu or not, and if it is, I'll need to purchase a replacement then anyway.
Thanks!

[azruss]

as stated above, the first place i would check would be the electrical connector to the injector. these get old and brittle and the wire can break going into the connector.

[76was124]

as stated above, the first place i would check would be the electrical connector to the injector. these get old and brittle and the wire can break going into the connector.

Agreed, but if it was the connector, would I still see the 3 ohm coil resistance of the fuel injector when I do an ohms check from the ECU end of the wiring harness (assuming that is its supposed to be 3 ohms?)

I tried swapping #2 and #3 connectors at the FI, but the wires are too short to reach.

Against my better judgement, I'm now opening the ECU up to see why I don't get a resistance measurement between terminals #32 and #33 on the ECU since they both fire off the same transistor just through different resistors.

[spider2081]

Let us know what you find.

I don't remember any current limiting resistors in the ECU used in the Fiat. I recall years ago thinking the injectors would fire in time with the intake and was surprised to find 4 + pins all going to the same printed circuit land in the ECU. It was after that I read up and found they are all paralleled in the ECU and fire at the same time. your pins 14,15, 32,33 should all read close to zero ohms between them and high resistance to ground.

[76was124]

Against my better judgement, I'm now opening the ECU up to see why I don't get a resistance measurement between terminals #32 and #33 on the ECU since they both fire off the same transistor just through different resistors.

Okay, figured out the mistake in my troubleshooting. I had the ECU connector pinout wrong. Pin 1 in the top row and Pin 19 in the bottom row are at the same end of the connector. The pin counting order doesn't rap around from top row to bottom row. That's why Pin #32 and Pin 33 on the ECU wasn't showing they were connected. #32,33,14 &15 are all in common, zero ohms as you guys previously mentioned. Odd that they all are tied together, but there is a toggle/flipflop of the two + 12v side feeding the dual relay. That's how injectors 1 & 4 fire as a pair separate from #2 and #3 which fire 180 degrees out as a pair as well.

Therefore, ECU is fine so as suspected by spider2081 & azruss, I need to double check the connector and wires at the fuel injector again even though it measured okay to the injector coil from the ECU.

If not that's not right, then next step is to pull the injector.

Too bad it's not direct injection or I would pull #3 plug, switch the ignition to get the fuel pump going and externally power the #3 iith jumpers to see if I can some fuel in the cylinder..

[76was124]

Using a spare FI connector with some lead wires I was able to test the #3 connector on #2 injector, and visa versa. Looks like the problem is staying with the #3 injector. So I will pull it out for inspection.

[spider2081]

Great to hear you are making progress.
I thought I could check my injectors out of the car. I put about a 1 foot hose on put in some fuel and connected it to a 12 source. The injector clicked and I blew in the hose. Fuel came out so I thought it was ok. I sent the injectors out for cleaning and was told that two of them needed to be replaced. The shop that cleans them does not sell injectors.

Let us know what you find

[76was124]

I pulled the injectors, nothing obvious about #3, but figure I should replace it based on troubleshooting.

Do I need to replace all 4? ($$) or just the defective one? All other cylinders seem to be firing fine and the entire fuel rail was serviced and tested 2 years ago; all new rubber parts installed.

[spider2081]

I use: http://www.cruzinperformance.com/fuelinj.html for cleaning and testing. about $20 per injector. US postal about $9 each way so it costs about $100 to know all 4 are operating good. I think that includes new seals.
I would send the 4 out and see.
If you have the rail off and #3 injector off the hose and you blow air in is the rail clear to the injector???

[76was124]

Success (sort of)
Put in a new injector on #3 and all cylinders now running so the rest of the fixing/tuning can continue.

Looks like vacuum advance is not working, and have an annoying miss every few revolutions even at idle.

So weekend work ahead.