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Discussion Starter #1
Hi
I have a 92 164L that will no longer start. Cranks fine, no fire. Diagnosis so far:-

Battery power applied directly to fuel pump = start OK.
Check wiring relay to pump - continuity OK.
Pump relay OK - (clicks with external battery power).
Switched relay with another one - no start.
Motronic relay OK - clicks at turn on.
12V to relay OK - switched by Motronic relay.
Manually ground pump relay (ECU connection) = start OK.
Replace ECU - no start.
Motronic and pump relays are the right way around.

The ignition switch was changed and this condition happend shortly after but not immediately... Old switch was refitted but didn't help. New switch is now installed again.

This was as far as I got, weekend is coming up so another debug session is planned. From the work so far, it looks (to me) like either the connection between ECU and relay is bad (not very convinced about this) or the ECU is not happy with an input condition and refuses to energise the pump relay.

I have looked thru other postings and 2 things come up - coolant temp sensor and connector, and crank posn sensor and connector. Will look into those items.

Are there any other necessary conditions for the pump to be energised or, put it another way, what else would prevent the ECU energising the pump?

Thanks in advance.
Jon
 

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G'Day Jon,

Pretty thorough.

This:
Manually ground pump relay (ECU connection) = start OK.
Proves this:
From the work so far, it looks (to me) like either the connection between ECU and relay is bad (not very convinced about this) or the ECU is not happy with an input condition and refuses to energise the pump relay.
These:
Battery power applied directly to fuel pump = start OK.

Manually ground pump relay (ECU connection) = start OK.
Prove the CAS (crank angle sensor) is ok.



Now, the 164 is still pretty new to me so I might be wrong but I don't think the CTS (coolant temp sensor) will prevent the engine starting so my guess goes with the wiring to the fuel pump relay. However, there might be something like an inertia switch that I'm not aware of.

Check that none of the connectors has been pushed out of the relay base.
 

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Did you pull codes and get a 1243 Code for fuel pump relay control final stage failure?

Your thorough troubleshooting so far sounds like that is the case. I think you have to verify continuity of gray-black wire going from fuel pump relay S12a pin socket 85 (ground) back to S11 motronic ECU pin 20 (ground). Be sure socket 85 is locked flush with surface in fuel pump relay socket and is not broken. That was my recent problem with my speedometer and was very hard to see down inside connector.

Guess you need to verify same condition in ECU harness connector for pin 20, too if gray-black wire checks good for continuity.

Big puzzle not covered in manual is what exactly sets pin 20 in ECU to ground to energize fuel pump relay. CLEAR ONLY IF KNOWN aka C.O.I.K. fallacy.
 

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Automatic? Also check the start inhibitor switch H16 and relay I62. Check connector S25 for both auto and manual.

I think the ECU requires CAS (Crank Angle Sensor) signal to get fuel pump going. It is a safety feature. I don't think a bad CTS or CTS connection will disable fuel pump.

Here's one way to test continuity between ECU and fuel pump relay: Disconnect ECU connector, measure resistance between pin 20 and pin 33 at the connector. Then pull fuel pump relay and measure the resistance between terminal 85 and 86 (the relay coil) of the relay. There should be very minimal difference between the resistance.
 

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If he monitors fuel pressure when starting (must "tee" into line with gauge), then he will most likely see low to zero fuel pressure from the pump not being energized. This can be verified (if needed) by tying voltmeter to power leads of fuel pump. No voltage ==> no fuel pressure and no start. He says if he powers the fuel pump directly, the car will start. A start inhibitor will inhibit the starter engagement, no? His starter engages and spins the engine ("cranks fine"). Because it only requires powering the fuel pump to make it start, he is missing only fuel pressure. The relay is good because if he powers it, then the fuel pump starts and the engine starts. Steve's pointer to the relay actuation wiring seems quite well directed. If the crank angle sensor were broken, the engine wouldn't run. The ECU _must_ be getting the CAS info, else it wouldn't make spark. The ECU fuel pump output _might_ not be active, but if it were the ECU alone, one would expect that swapping ECUs would correct the problem. Therefore the harness is most suspect. I'd look for a broken wire or backed-out pin, as Steve seems to suggest.

Michael
 

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A start inhibitor will inhibit the starter engagement, no? His starter engages and spins the engine ("cranks fine").
Yes, the start inhibitor should inhibit the starter motor also. But we can't be sure that the circuit was not modified (like the switch been bypass due to previous no start). Through the automatic gear select relay I62, another ground path is provided to the ECU pin 28 through connector G154 pin 4. Although I think this is more for providing a smoother gear shift for automatic and not the cause for fuel pump relay not getting the ground signal, it does not hurt to check. Connector S25 might be more important.

I think Jon has narrowed down the problem to ECU pin 20 not grounding so fuel pump relay not engaging. It sounds like his fuel pressure and CAS is fine since the car runs if he grounds terminal 85 of the fuel pump relay. It could be just a poor (ground?) connection somewhere.
 

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Discussion Starter #7
Update from Jon

Guys
Many thanks for the quick and detailed responses. Lots of things to try here this weekend.

Follow up to one query - it is manual (standard) transmission. Also should have added, US model => 3L, V6.

Sort of looking forward to the hunt - will keep you posted.

Jon
 

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Discussion Starter #8
Further observations

So, spent a rather frustrating day under the hood trying to fix this no start issue.

Focus this time was checking the wiring btw fuel pump relay and ECU. According to the manual, the wire is grey/black and this I found at the relay connector. Again, according to the manual, this wire should go straight back to the ECU, no connectors. I could not get continuity back to the ECU connector so I thought I had it solved. However, some other checks on that ECU connector did not work out either (power and ground locations). So, I took the ECU connector apart and could not find a grey/black wire.

It's extremely difficult to trace the wiring once it disappears into the loom.

Anybody have any clues? Is the manual wrong - perhaps there's a connector and colour change for this wire?

Thanks again

Jon
 

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I have a harness out of a salvage car let me see if I can trace wire for you later today.

See picture, gray-black wire is one solid wire from pin socket 85 in fuel pump relay S12a holder to pin socket 20 in ECU S11 connector. Pin socket 20 is in bottom (shorter) row cable end of ECU connecter second terminal socket in from cable end.

Note: Top row is pin sockets 1-18 counting from cable end. Lower shorter row is 19-35 counting from cable end.
 

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Bump, see my picture and edit info my last post of pin 20 location for gray-black wire.

Also, if wire checks good I would try a NOID wafer in one of injector connectors and crank engine to see if you really are getting a flashing trigger signal from computer.
 

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Discussion Starter #11
Steve
Many thanks for taking the time to get the picture.

Working from memory and cross referencing the manual (p607), I have the fuel pump relay S12a as the one on the left (as seen from looking into the engine bay from the front of the car). Again from memory and looking at the location of the coil in your picture, it looks like you have the red probe on S12b (Motronic relay). Maybe, your pictured set up has the relay sockets swapped on the bracket - I seem to remember s12a socket was grey so maybe not an issue.

Is there anything between the relay S12a pin 85?? (grey-black wire) and ECU connector - any intermediate connectors or is it a straight run?

Thanks
Jon
 

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Below is a picture when I jumped the relay to power the fuel pump without engine running.

Yes, the two relays socket position can be swapped so don't rely on the position. Check the wires color underneath. The wiring diagram does not show anything between S12a #85 to ECU #20 (the gry-blk wire).
 

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Bob
Thanks for the picture and reply.

I asked about the directness of the wiring as I could not see a grey/black wire at the ECU connector (I removed the connector cover), also had no continuity...

I'll take my camera out to the car at the next session - might be able to capture something useful for discussion - didn't think of doing that before.

Jon
 

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reread my post above or here: http://www.alfabb.com/bb/forums/showpost.php?p=395187&postcount=9

Gray black wire is one piece wire from relay to ECU. If you don't have a ohm reading between those two points you need to repair wire.

Gray relay socket holder is for fuel pump relay. I have three cars and one of them has sockets reversed in car so you always go by wiring colors.
 
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