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Discussion Starter #1
I recently experienced a problem starting my 1990 alfa quad. The starter cranked OK but the car wouldn't start. so either no spark or no fuel, right? I checked that I was getting spark with a timing light and when I disconnected the fuel line from the injector manifold and cranked it no fuel came out. I could hear that the fuek pump relay was working when starting (clicks on) and the fuse was OK so I decided to change both pumps and filters. Even with new pumps it still wouldn't start. Then I finally checked the voltage at the fuel pumps - only 0.07V when cranking - at both pumps. The battery is fine - there was plenty of amperage to turn over and I even tried jumping it for extra amps but still no luck. I haven't traced out all of the wiring but it is all as new (original owner -33k miles). This problem came up all of a sudden. One week it ran fine the next it wouldn't start. Does anyone have any suggestions?
 

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I don't know the Motronic system too well but in the L-jet system, the fuel pump power is controlled by a relay. The relay gets a signal from the coil that the ignition system is firing then it powers on the pumps. So, if you are certain there is spark, I suggest you check the relay (guessing it is located next to the computer behind the right side seat) and double check any fuses (L-jet has an in-line fuse next to the computer for the fuel pumps). Sometimes a reluctant relay can be jolted into working by giving it a rap with a screwdiver handle.

Also, the L-jet doesn't wake up if the voltage drops below about 10.3 Volts. And that is possible during cranking - the engine will sound like it is cranking over OK but if there ain't enough juice left for the computer = no go.

If anyone with more knowledge of the Motronic system chimes in, listen to them as I am mostly guessing & assuming...
 

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Discussion Starter #3
I thought about the relay. I wasn't sure how to check it. A prervious thread discussed that it needs to be installed when testing but I don't know what the correct voltages should be. I did check to see that the coil in the relay wasn't shorted. I also installed the relay back in with the metal cover off and could see the plate move (with an audible click) when the engine was started. there are several other relays also associated with the ECU, if one of those malfuncted would it shut off the fuel pumps? Also frustrating is the wire color guide in the shop manual - the wires actually installed are not the color that the manual indicates -except for red and black. Both fuel pumps have pink/white power wires but I didn't see a pink/white wire at the relay.
 

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Trained (ex)Professional, , 1953-2018 RIP,
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The Motronic fuel pump circuit is far more complicated than the L-jet version so let's take this one test at a time. Please refer to the relay locations pasted below courtesy of fellow BBer John M;

Looking at the relays next to the ECU here is what they are in order from left to right as you look at them with the ECU below and the relays above so to speak.
The first relay is the Main/Auxiliary Relay.....0060805422
The second relay labeled S12B in the manual is the Motronic Relay with Diode.....0060807340
The third relay is the VVT Relay....0060805422
The fourth relay labeled S12A in the manual is the Fuel Pump Motronic Relay....0060805422
So the VVT and S12A fuel pump relays can be swapped with the Main/Auxiliary. But the S12B motronic relay with Diode is a different part number.

On to the test. With the ignition switch on, check for battery voltage at fuel pump relay terminal #30 (wiring diagram says it's a green/black stripe wire). Is there voltage?
 

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Discussion Starter #5
I didn't see the posted wiring diagram but I did check the voltage of the far right relay of the #30 terminal (green/black) and it is reading 12.05V in run or start. I have been thinking that the far left relay was the fuel pump relay since the fuse is directly behind it - but the wire colors didn't match up. What's the next step?
 

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Trained (ex)Professional, , 1953-2018 RIP,
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Good! Voltage at terminal #30 rules out a lot of things (I just hope that the relay we're working on is the fuel pump relay :eek: ).

Next test. Disconnect the wiring connector from the fuel pump relay. Fashion a jumper wire and connect terminals 30 & 87 in the connector. Turn on the ignition. Do the fuel pumps run?
 

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Discussion Starter #7
It must be the right relay because when I jumpered #30 and #87 and hit the key I could hear both pumps! I did notice that there are 2 #87 terminals and nothing was attached to the central terminal. Is that odd? Anyway, I hope that a successful jumper is good news. What's next?
 

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Trained (ex)Professional, , 1953-2018 RIP,
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Well, jumping out the relay is good news in that it eliminates the fuel pumps and the fuel pump wiring as being the problem.
At this point, like Tifosi, I'm leaning toward the fuel pump relay. It was previously mentioned that the metal plate in the relay would move with the key in the start position. This is good as it would indicate that the fuel pump relay control circuit is in good order. This means then that the 30/87 contacts in the relay could be dirty/burned.
One last test to confirm that the relay is the problem. With relay connector terminals 30 & 87 jumped, start the engine. Test for battery voltage at terminal #86. Then test for ground at terminal #85. If yes to both, replace/service the relay.
 

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Discussion Starter #11
With #30 and #87 jumpered I checked the voltage at #86. It read 11.5V. with the meter at the 200 ohm setting the #85 contact read 33 ohms. The voltage between the two read -12.5V. I guess it's looking like a relay problem after all. Also, with #30 and #87 jumpered, the engine started right up! I could try swapping either the VVT relay or the main/aux. relay with the fuel pump relay to see if the pumps come on. I know that the main/aux relay works because that's the one I saw the plate moving (at the time I thought that one was the fuel pump relay). Can these relays be bought at an auto parts store or do you have to order them through a catalog?
 

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1966-2013
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They can be had through most parts stores.

Just bring the old one with you and they'll be able to get the exact thing, or cross reference the number stamped on the top for a suitable other brand replacement.

As you've got an 'open' 87 terminal, you could even get away with one that's got an 87b in that location. (the 87 ~ 87b type is a bit more common at the stores as people use them to wire up trailer brake and running lights)

Should run around the 10-15$ range for an actual Bosch part.

Oh, if you've got AC, either one of the two relays for that on the right front fender would be the one to swap in to test with. They're the exact same type.
 

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Discussion Starter #13
I took off the metal cover on the relay. Everything looked ok so I just cleaned up the contacts a little. I put it back in but it still wouldn't start. I then swapped the main/aux relay with the fuel pump relay. The car started right up and I ran it for about 15 minutes, then restarted -no problem. It seems odd that it will still work in 1 location and not the other. I do feel that replacement is probably the best choice.

Thanks for all the help and Happy Thanksgiving!

alfaquadinpa
 
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