Author Topic: Alfa 75 TS fuel cut off  (Read 1487 times)

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bteoh

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Re: Alfa 75 TS fuel cut off
« Reply #15 on: October 10, 2018, 09:12:42 PM »
Thanks simmi83,
Unfortunately I am in Perth but thanks for the offer all the same.
Update :- I swapped the CAS with a working one from my other 75 3.0 V6. I originally thought that was the problem as the wiring on the CAS was quite frayed. Anyway, tried it and the symptoms are still the same - fuel cuts off after about 10-20 seconds.
Checked and cleaned both the connectors on the AFM, TPS but still no luck.
Not sure what is causing the ECU to shut off fuel???

CitroŽnbender

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Re: Alfa 75 TS fuel cut off
« Reply #16 on: October 10, 2018, 09:23:21 PM »
The ECU usually supplies the negative side of the relay coil, as it stops working after a few minutes and youíve apparently ruled out the crank sensor, you might have a minor issue with the ECU; dry joint or poor overall grounding (of the case or neg ECU feed).

bazzbazz

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Re: Alfa 75 TS fuel cut off
« Reply #17 on: October 11, 2018, 12:10:35 AM »
Do 75s have fuel cut off switches, in case of impact/rollover?
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Henry Goodman

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Re: Alfa 75 TS fuel cut off
« Reply #18 on: October 11, 2018, 11:15:00 AM »
Have you tried swapping out the fuel pump itself? These fuel pumps have limited life spans and are cheap and easy to replace. If it were me, I'd want to rule this out before going down the rabbit warren of ECU related causes.  I've been down this road before with my TS. I'd also endorse Simmi's advice given his first hand knowledge of TS.

bteoh

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Re: Alfa 75 TS fuel cut off
« Reply #19 on: October 11, 2018, 05:00:22 PM »
BazzBazz, I am pretty sure it doesn't have a fuel cutoff switch like the GTV6s do.
Henry Goodman, I have hooked up a tester on the fuel pump connector and definitely see the power being cut off after a few seconds to the fuel pump. I can't see any changes to hooking up another fuel pump? The current fuel pump was changed about 2 years ago with a new Bosch pump.
It is either the wiring from CAS or AFM or a dodgy ECU, AFM maybe?

bazzbazz

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Re: Alfa 75 TS fuel cut off
« Reply #20 on: October 11, 2018, 05:30:08 PM »
Is the power cut off or the earth cut off?
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simmi1983

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Re: Alfa 75 TS fuel cut off
« Reply #21 on: October 11, 2018, 08:16:31 PM »
Baz baz if the eart or power supply werent connected the car wouldnt start or run.

Do you have a full 12v at the pump when the car is running?

As far as i know the only components that are involved in running the fuel pump are :

Igntion switch
Fuel pump relay
CAS
Motronic relay.
ECU.

 The fuel pump relay is powered by ignition.
When the CAS  can see the engine rotating it sends a signal to the ECU via the motronic relay which then activates the contacts in the fuel pump relay, sending powet to the fuel pump.

My way of thinking is, the only components that can switch off the fuel pump are listed above.

Ive heard something about the fuel door on the AFM having a micro switch , but these cars still run with the AFM disconnected . Ive never explored that fully but i dont think so. If you can get hold of one you should try for the hell of it.
Swap your relays around but be careful as the motonic relay has a diode in it.

As previously mentioned the only other thing is the tone wheel on the harmonic balancer. These can come loose and bounce around muffling the signal to the CAS. Unlikely but check anyway.

Good luck.

Luke

Colin Edwards

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Re: Alfa 75 TS fuel cut off
« Reply #22 on: October 11, 2018, 11:54:07 PM »
Hi bteoh,
You said initially the engine only ran for a few seconds.  Later post said 10 - 20 seconds.  The true duration of the running is critical to diagnosing the fault. 
The fuel pump stopping will stop the engine however the engine stopping will also stop the fuel pump!!  Difficult to determine  what happens first but it is possible.  However you first need to ACCURATELY measure how long the engine runs before it dies.  If the time progressively reduces you may simply have a low battery not being charged by the alternator.  If the battery voltage gets low enough the ECU will call it a day and drop the fuel pump relay.  The battery may then recover enough to start the engine for the next cycle.  Remember the battery starts the engine - the alternator keeps it running!
If you can start the engine ten times and the duration of each successive run is virtually identical, its a fair chance the ECU logic is killing the engine not progressively reducing battery voltage.
Is the alternator a goer?  When the engine runs for this short period does it sound "normal" - no misfire?  Will the engine rev ok?  Do the engine and tacho confirm what each other is doing?
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bteoh

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Re: Alfa 75 TS fuel cut off
« Reply #23 on: October 12, 2018, 08:13:28 PM »
Update :-  A friend loaned me a working ECU and a new AFM ( might be an aftermarket AFM which didnít have any Bosch markings.
With the spare ECU connected, it still died after 10seconds or so.
Colin, the engine doesnít die at exactly the same sequence. Sometimes 10 seconds and sometimes up to 20 seconds.
I tried connecting the other AFM but the engine wouldnít even start.
I tested the voltage at the connection under the rear seat to the fuel pump. I was only getting 8 volts.
I was just wondering, if the ECU was also getting 8 volts, it may just shut down? The battery is fine and although less than 2 years old, I took it back to Autobarn this morning and they load tested it and said it was fine. When the engine was running, I was getting about 13.5volts at the battery terminals - that would mean the alternator was charging ok?

Luke,
You mentioned the relays for the fuel pump and motronic are located in the engine bay and that the motronic relay has a diode in it? Anyway, I checked the four relays close to the left fender near the battery and they are all the same. I believe the original had the silver looking relays but mine are all black Bosch relays. The car had been running fine for many years like that so I canít see why it is failing now?

bazzbazz

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Re: Alfa 75 TS fuel cut off
« Reply #24 on: October 12, 2018, 08:48:54 PM »
Well the supply to the Pump Should be 12v (Battery Voltage) so replace pump relay with new one. If that doesn't fix it back track from the pump to the Pump Relay for any faulty wiring or shorts.
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bonno

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Re: Alfa 75 TS fuel cut off
« Reply #25 on: October 12, 2018, 09:10:13 PM »
Per bazzbazz comments the voltage drop to your fuel pump connection (12 to 8V) is higher than the 5% acceptable limit defined by Electrical standards. I suggests your may have bad connections or some other wiring issue (corroded, loose, burned or broken connectors) that maybe causing the problem. Additionally for checking fuel pump relay and ECU intergrity (bias voltage) for the operation of fuel pump find the following Youtube link.
 https://www.youtube.com/watch?v=McnXLcJNVfI
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GTVeloce

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Re: Alfa 75 TS fuel cut off
« Reply #26 on: October 12, 2018, 10:01:06 PM »
8V is getting very low and the Motronic does have the ability to reduce itself (I think it retards the ignition) until it will eventually just cut out the engine. You will be unlikely to get a full 12V at the fuel pump even if everything is perfect due to the very long run of cable, size of cable etc. 11V would be more likely but 8 is definitely too low.

Can I strongly suggest you concentrate on the four relays. They can tell you almost everything. Ideally the moronic relay should have a diode in it however, that is just to protect the ECU from a surge going backwards through the relay. The car will work perfectly fine with four identical relays.

Check everything you can think of at those four relays. For example, see how many volts you are getting while the engine is running on the feed to the coils or similar. That will help to determine if the issue is a general power supply issue or perhaps more focussed on the fuel pump side of things. Disconnect the lambda heater to ensure it is not shorting out (it is fed from the same relay as the fuel pump). Check the quality of the cable running from the ignition switch to terminal 86 of the aux moronic relay (S12D). If that wire starts to degrade you will have all sorts of problems. In one car I had to run a complete new wire to replace it and it solved all sorts of problems I was having (that looked much like fuel pump problems - I had even changed the fuel pump, all wiring and relay to no avail).

Check the stiffness of all cables going into the four relays. If any are stiff, they could be a sign they are burning out inside resulting in reduced current flow. Oh, and away from that area, check the ground wire is sound, clean and tight. I wouldn't worry too much about the secondary fuel pump. Many a TS has run ok without it being connected/operatable.

The fuel pump wiring (if you wish to check all connections) is as follows:
From terminal 87 of the relay to a junction (white 8 way IIRC) which can be found close to the pedal box/clutch master. From there it goes to fuse 13 in the main fuse box. From there it goes all the way to a connecter under the rear seat and from there to the pump (and I think it is daisy chained to the secondary pump in the tank).

But start with the relays and determine the problem is definitely after the fuel pump relay and not before.

simmi1983

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Re: Alfa 75 TS fuel cut off
« Reply #27 on: October 12, 2018, 11:17:09 PM »
8v isnt enough to stop the pump from keeping the engine going at idle but is a good indicator that there's a connection going on there. Maybe a bad connection is also affecting current flow.

Bonno and Gt veloce are onto it.
Check output voltage at the fuel pump relay (pink/white) if you have anything under 12v try another relay. If you have 12v the relay is good. Run a wire from pink and white on the relay to +ve of fuel pump if it fixes it theres a bad connection somewhere,  if not something else is stopping the engine which is stopping the pump -not the reverse.

But seeing 8v is a good indicator.


simmi1983

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Re: Alfa 75 TS fuel cut off
« Reply #28 on: October 12, 2018, 11:20:14 PM »
Check input voltage to fuel pump relay too, pretty sure its gets 12v from the motronic relay.

simmi1983

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Re: Alfa 75 TS fuel cut off
« Reply #29 on: October 12, 2018, 11:25:15 PM »
If all electrical checks come up with nothing..maybe we are overlooking something really obvious- a blocked fuel filter isnt stopping the engine is it ?