Can a Faulty Double relay damage the ECU?

[kimu]

I am stuck in a the middle of Africa with a 1982 Fiat Spider with no source of readily available spare parts. Brought with me a spare D-relay, ECU and AFM. All pretested and working before we left Canada.

Local guys painted the car (removed wires in the engine bay) and left it in a mess. Up until last week, the car would start but would not run. Spark and Fuel pump works as designed but car would not fire. The cold start injector was working (sprays fuel) and there was voltage to the injectors.

When troubleshooting step by step as outlined in the FI diagnostic manual, , two pins on the double relay got shorted - Step 12 - 88y and 85. Now there is no power to the fuel pump - no signal from ECU to energize the relay (even with the AFM flap manually open). Installed the spare relay - same issue.

At this point, I am tempted to fit the second spare ECU but a bit concerned that a faulty relay may render the spare ECU useless - double jeopardy??

FWIW, I have tested the 3 diodes, energized the coils and corresponding contacts, checked the resistor in circuit on both the relays all appear to be ok.

One more thing to note and this has totally baffled me; the wire from the coil (-ve) to the ECU pin 1 is a shielded wire (black insulation with yellow inner) an the outside wire going to pin number 5 of the ECU which is grounded. The core wire goes to Pin 1 of the ECU as its control signal. There is NO WAY that this car could have even started with the coil grounded. In fact the coil was getting super hot to touch. I have since disconnected the outer wire to pin 5. I have 12 v on both terminals of the coil in start and run positions.

So will a possibly faulty double relay kill the one and only Bosch ECU available on this continent?

Thanks in advance.

[spider2081]

I don't think a double relay failure can cause the ECU to fail.

I believe shorting pins 88y and 85 of the dual relay connector would blow the fuel injection in line fuse. This fuse powers the fuel pump and the Aux air regulator. Pin 88y is "hot all the time" power through this fuse to the dual relay's fuel pump relay contact. Pin 85 connects to pin 28 of the ECU and pin 28 connects to pins 17 & 18 in the ECU. When the ECU is plugged in they connect to ground by a ring terminal under one of the two intake plenum bolts closest to the firewall. It is possible that the printed circuit land in the ECU burned open before the 16 amp fuse failed. So I would check the 16 amp in line fuse located behind the fuse panel tucked up in the wire harnesses. Also test the ECU pins 28, 17 and 18 are still connected together. Maybe remove the cover and do a visual inspection for damaged printed circuit lands.
It is not uncommon for people not familiar with these cars to leave the ground wires off the intake plenum. The back 2 bolts holding the plenum to the intake manifold have grounds for the fuel injection system.

Hope this helps

[kimu]

Thank you spider2081.

The fuse is ok. All the grounds on the ECU connectors are showing to be good. There are no signs of any burning within the two PCBs in the ECU.

Will do the checks mentioned again - to be sure..

Any thoughts on the shielded wire from the coil to Pin 1 of ECU? It is really baffling.

[spider2081]

Any thoughts on the shielded wire from the coil to Pin 1 of ECU? It is really baffling.

I have seen a black protective sleeve covering a yellow shielded wire so I think what you have is how the car left the factory in that respect. At the coil connection only the center conductor was connected to the coils D or - terminal and the shielding was not connected to anything. So if you have the coils end of the wires center conductor connected to pin 1 of the ECU and the shield just cut back about 1 centimeter or greater that should work.

It is a common practice for noise shielding of wires to connect a wires shield at one end only. This prevents a condition called "ground looping" or "electrical ground loop". Electrical ground loop by definition is when 2 ground points develop a difference of potential allowing a current to flow between them. Usually this practice is used to eliminate noise in audio systems.

If you are using a digital volt meter select AC and measure the AC voltage at the D or - terminal of the coil. I would look for a reading of 1-2 volts AC while cranking and 2-4 volts at idle. The AC voltage reading should increase as RPM increase. THis is a crude test of the output of the electronic control modules pulsing the coil to make a spark.

Also a common issue with the fuel pump not running is a bad ground in the trunk. It and the tail light ground are usually made at one of the mounting studs for the drivers side tail light. Many relocate the ground to a paint free spot and use a machine screw and nut for a more positive ground.

Lastly the green black wire from the dual relay crosses under the dash to a single bullet connector behind the fuse panel. This connector sometimes gets disconnected or becomes corroded and needs cleaning.

[kimu]

Spider2081

You nailed it! THANK YOU.

Pin 28 on the ECU has a hairline break and therefore no continuity between it and pins 16 and 17 (18 is not ground). Would have never seen it if you had not pointed it out.

Now back to troubleshooting the ORIGINAL problem - why the car starts and runs for 2 seconds and shuts off. Cold start valve sprays for 8 seconds as required, fuel is pump is on, AFM flap triggers a voltage at the fuel pump etc. All sensors check out ok. Will restart the troubleshooting process again next week.

<Have not quite figured out how to post a pic on this forum as yet>

Much appreciated.

~K

[spider2081]

(18 is not ground)

Yes you are correct. I guess my aging eyes misread pin 16. Good thing you picked that up.

Have you removed a spark plug after the car stalls to see if it appears wet with fuel or fuel starved???

Also if you join the www.mirafiori.com web site they have a library available to members only. Membership is free. There are a few Fuel Injection manuals, and electrical troubleshooting manuals posted in their library under "124"

Hope thiis helps.

[kimu]

Got all the troubleshooting manuals so makes life a lot easier for sure.

Found out that there is a short circuit between the shielding wire and the core cable <ECU Pin 1 to Coil - terminal>. For now, I have cut off the shielded wire going to PiN 5 of ECU but will likely replace the wire entirely with a single core leaving off off grounding wire to PIN 5. The coil was grounding and getting super hot as a result. The resistance of the coils is withing limits and I have spark.

I have 2 AFMs. One gives me an always on fuel pump, the other behave as its is supposed to that is, comes on with the AFM flap movement and yet both AFM resistance checks are within stated values. Another head-scratcher of a problem. Oh what fun.

Will devote the time this weekend.

~K

[spider2081]

The square black cover is glued to the AFM with a silicone type glue I use a sharp pick bent at right angel to cut through the glue. Then lift of the plastic cover This allows visual inspection and ease of moving the flap. Once finished I re-glue the cover on.

[kimu]

John,

I have done my final troubleshooting checks before I return back to Canada in a day or two. This is what I have found that can perhaps lead to some indication of the problem.

Referencing the FI Diagnostic Manual Check 12 "Check Voltage Input to Fuel Pump Relay of the Relay Set"
Test light between 88Y and 85:
Result
a) WITH ECU connected -Test light comes on without the key in the ignition (HOT AT ALL TIMES)
b) WITHOUT ECU Connected, Test light DOES NOT come on with the Ignition switch in START of RUN positions.

Check 13 "Check Input Voltage to Control Relay of the Relay Set"
Connect light between terminal 88z and 85
Result
a) Light comes on without the key in the ignitiion (HOT AT ALL TIMES)

Points to Double Relay BUT the known working spare is also exhibiting the same problem.

All grounds to ECU are good. Ground to Fuel pump is fine at it comes on at the care is switch one/AFM flap moment.
The THERMO TIME SWITCH is ok ad I get decent spray from the COLD START INJECTOR for 8 seconds.
The TEMP SENSOR on the Coolant -Tee is measuring withing SPEC
AFM resistance checks are withing range
*** There is power to the FI injectors when checked with a test light at Pins 14,15,32,33 withe Ignition switch in Start/Run Positions****

Can logically explain but I am wondering if it could be the Ignition Switch?

Thank you

[spider2081]

terminal 85 at the dual relay is ground for the relay set. It gets its ground path through the ECU. So for tests using terminal 85 to work the ECU must be plugged in.
Terminals 88z and 88y are "hot all the time" inputs to the relay. They should have battery voltage on them as long as the battery is connected in the car. The tests you have shown here are testing relay inputs and not relay function or operation.