Alfa Romeo Owners Club of Australia Forum

Technical => 160 Series (90, 75, 164 Sedans) => Topic started by: bteoh on October 08, 2018, 11:22:50 PM

Title: Alfa 75 TS fuel cut off
Post by: bteoh on October 08, 2018, 11:22:50 PM
Hi,
Was hoping someone here could help diagnose my problem. My 75 TS starts and idles, but after a few seconds, the fuel pump shuts down. I checked the pink/white wire connector under the rear seat that connects to the fuel pump - it supplies 12v but after a few seconds , the power turns off.
It will start again without problems, but dies after a few seconds. I swapped the fuel pump relay in the engine bay but that didn't help. Would a failing crank angle sensor cause these symptoms? Other areas that I may need to check are the TPS , airflow meter and possibly ECU? But was hoping someone may point me in the right direction with the above symptoms.
Thanks
Title: Re: Alfa 75 TS fuel cut off
Post by: Citroënbender on October 09, 2018, 12:08:06 AM
Is it an early Motronic or similar, with ignition amplifier module?

The easiest fix if you're handy and originality isn't a big concern, is to power the fuel pump relay using a Peel brand LPG relay. You'll need to splice in a tach feed from the coil low tension negative terminal.
Title: Re: Alfa 75 TS fuel cut off
Post by: Colin Edwards on October 09, 2018, 08:35:26 AM
Hi bteoh,

The symptoms you describe suggests three possibiliities:
# The air flow meter contact that ultimately controls the fuel pump relay is not functional
# The combination relay control signal from the air flow is not reaching the pump relay
# The combination relay is not processing the signal from the air flow meter

A contact in the AFM closes when the AFM detects air flow consistent with an idling engine.  Once the engine starts and idles, this contact must close.  This signal confirms to the fuel pump relay the engine has started and idling.  If the engine does not start or does not idle their is no need for the fuel pump to operate.  The air flow dependant contact ensures a stalled engine disables the fuel pump - very important!!

With the ignition on (NOT in the "start" position) and the engine not running, you should see 12v at terminal 88A of the combination relay and 12V at the AFM contact - terminal 39.  The AFM contact can be closed by simulating air flow - move the vane slightly.  The AFM contact should close and 12v be seen at terminal 36.  12v should now also be seen at terminal 86B on the combination relay.  This signal should energise the "pump run" half of the combination relay and the fuel pump should then power up.

If your not seeing 12V at terminal 36 with the AFM contact closed the AFM the contact is worn or dirty and needs attention.  It can be cleaned by wetting thin carboard with contact cleaner and wiping it between the two contacts - tread gently!  DO NOT USE AN ABRASIVE OF ANY SORT!!!  The wiper arm that actuates the AFM contact prevents these contacts from closing unless air flow reaches a critical level.  The contacts can be "adjusted".  Again tread very gently!  The AFM typically has 7 connections.  The two closest to the outer edge of the case are numbered 36 and 39.  If your AFM does NOT feature terminals 36 and 39 please ignore this post!!

If you are seeing 12V at terminal 36 on the AFM but not at terminal 86B on the combination relay you have a busted wire or dodgy connection. 

If you are seeing 12V at terminal 86B on the combination relay but not at terminal 86D you have a dodgy combination relay.

This part of the EFI system is 100% binary.  The signals are either high or low / 12V or 0V / on or off.  No messy analogue voltages to worry about. 

The above assumes the system is the Bosch L Jetronic, although identical principals apply to similar systems. 
   
Title: Re: Alfa 75 TS fuel cut off
Post by: bazzbazz on October 09, 2018, 09:13:33 AM
Just for my own curiousity, would this mean if the AFM was unplugged then the same problem would occur?
Title: Re: Alfa 75 TS fuel cut off
Post by: Colin Edwards on October 09, 2018, 01:31:07 PM
Hi bazzbazz,

Possibly.  However, hopefully Bosch built in a "sanity check" where if the analogue / potentiometer area of the AFM went open circuit or out of spec, creation of igniter pulses was disabled.  Simple to implement and would prevent the engine from trying to run on a damaging overly rich or lean mixture.  A theory i'm not going to explore!
Title: Re: Alfa 75 TS fuel cut off
Post by: bteoh on October 09, 2018, 02:13:33 PM
Hi Colin,
Thanks for the detailed reply. The 75 TS runs a Motronic 4.1 and doesn't have the combination relays like the L Jetronic. I was wondering why the ECU would cut fuel and the usual suspects were the AFM , TPS or Crank Angle sensor. However, if the CAS was to fail, that would mean the car wouldn't start? However, in my case, it always starts but fuel cuts off after a few seconds. So, I think you might be right in suggesting the AFM being the possible culprit? As BazzBazz mentioned, would it run ok or longer if I was to disconnect the AFM connector?
Title: Re: Alfa 75 TS fuel cut off
Post by: GTVeloce on October 09, 2018, 02:19:10 PM
The 75 TS uses Motronic not L Jet and as such is quite different. There is no combination relay like the V6 cars have and the AFM has 5 terminals not 7. The car will start and run even with the AFM disconnected albeit fairly rough.

A stalled engine is controlled via the CAS that send the signal to the ECU.

I am not quite sure why your car is starting and suddenly stalling but I think you are on the right path. If you don't already have the attached diagram you will find it very useful to diagnose problems.

The second attachment is the pin out list for the ECU. I have never had an ECU fail yet but have had almost everything else fail at some point. The last one that had me stumped was the pulley key was damaged and meant the pulley was out of alignment in relation to the crank. The CAS was working correctly but the timing was still off.

Hopefully yours is something easier and best to start from the beginning and work your way through the list. I'd start with the full fuel electrical system first just to ensure there isn't an issue there even though I feel it is more likely a sensor that is sending a poor signal to the ECU resulting in the ECU killing the fuel. Again, you could test that by seeing if the lambda probe heater (also an output from the fuel pump relay) is also losing power when the fuel pump does. I would also disconnect the lambda probe heater and test to see if it is shorting and resulting in the relay shorting.

Good luck!

If you need other pages let me know and I can attach them.
Title: Re: Alfa 75 TS fuel cut off
Post by: GTVeloce on October 09, 2018, 02:21:32 PM
Second page of the wiring diagram.
Title: Re: Alfa 75 TS fuel cut off
Post by: Colin Edwards on October 09, 2018, 03:15:10 PM
Hi bteoh,
Maybe time to invest in a Fault Code reader.  However likely culprit will be the CAS.  As well as being responsible for ignition the CAS also provides crankshaft rotation speed - rpm.  Does the tacho reveal idle rpm at any stage during starting / momentary idling?

The CAS maybe only just be ok to provide an ignition reference point but not up to providing a higher frequency output.  At an idle speed of say 800 rpm the CAS should be producing something like 800 pulses per second.  The high frequency signal is used by the ECU to generate an engine speed / rpm value. 

A couple of missing teeth on the CAS disk produce a defined loss of CAS output.  This regular loss of output every engine revolution is the ignition "window".  If the CAS is ok at these lower frequencies but not ok at higher frequencies the ECU may not "know" the engine has reached a particular rpm - started!

I'm not sure however if the ECU needs air flow info AND engine rpm info to decide if the engine has in fact started.  A Fault Code Reader should confirm this.
Title: Re: Alfa 75 TS fuel cut off
Post by: bazzbazz on October 09, 2018, 06:57:24 PM
Errr, just what would he plug the Fault Code Reader into? Unless I am mistaken 75s don't have diagnostic ports?  ???

At least not any that you can plug a generic code reader into?
Title: Re: Alfa 75 TS fuel cut off
Post by: Citroënbender on October 09, 2018, 07:06:12 PM
Motronics usually have a flasher "code" output ability.
Title: Re: Alfa 75 TS fuel cut off
Post by: bazzbazz on October 09, 2018, 08:27:33 PM
And where would one get a suitable reader from to use on it?
Title: Re: Alfa 75 TS fuel cut off
Post by: bteoh on October 09, 2018, 10:31:40 PM
Thanks guys,
I have a multiecuscan software that I will plug it into and check tomorrow. It doesn't have a listing for my 75 TS but has one for the 164 TS ( Same engine ). Hopefully it may throw up a fault code that I could check. The 75TS has the same diagnostic plug as the 164, located under the passenger dash.
Will keep you updated on what I find tomorrow.
Cheers
Title: Re: Alfa 75 TS fuel cut off
Post by: bteoh on October 09, 2018, 10:33:49 PM
GTVeloce,
Thanks for that 😀👍🏻



Quote from: GTVeloce on October 09, 2018, 02:19:10 PM
The 75 TS uses Motronic not L Jet and as such is quite different. There is no combination relay like the V6 cars have and the AFM has 5 terminals not 7. The car will start and run even with the AFM disconnected albeit fairly rough.

A stalled engine is controlled via the CAS that send the signal to the ECU.

I am not quite sure why your car is starting and suddenly stalling but I think you are on the right path. If you don't already have the attached diagram you will find it very useful to diagnose problems.

The second attachment is the pin out list for the ECU. I have never had an ECU fail yet but have had almost everything else fail at some point. The last one that had me stumped was the pulley key was damaged and meant the pulley was out of alignment in relation to the crank. The CAS was working correctly but the timing was still off.

Hopefully yours is something easier and best to start from the beginning and work your way through the list. I'd start with the full fuel electrical system first just to ensure there isn't an issue there even though I feel it is more likely a sensor that is sending a poor signal to the ECU resulting in the ECU killing the fuel. Again, you could test that by seeing if the lambda probe heater (also an output from the fuel pump relay) is also losing power when the fuel pump does. I would also disconnect the lambda probe heater and test to see if it is shorting and resulting in the relay shorting.

Good luck!

If you need other pages let me know and I can attach them.
Title: Re: Alfa 75 TS fuel cut off
Post by: simmi1983 on October 10, 2018, 12:26:10 AM
My CAS was buggered and was doing similar things.

The fuel pump will only operate if it sees a signal from CAS.

We are you located? Maybe someone here could help you swapping some parts around. Ive got all soare EFI stuff but am located in Brisbane.

Luke
Title: Re: Alfa 75 TS fuel cut off
Post by: bteoh 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???
Title: Re: Alfa 75 TS fuel cut off
Post by: Citroënbender 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 you've 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).
Title: Re: Alfa 75 TS fuel cut off
Post by: bazzbazz on October 11, 2018, 12:10:35 AM
Do 75s have fuel cut off switches, in case of impact/rollover?
Title: Re: Alfa 75 TS fuel cut off
Post by: Henry Goodman 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.
Title: Re: Alfa 75 TS fuel cut off
Post by: bteoh 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?
Title: Re: Alfa 75 TS fuel cut off
Post by: bazzbazz on October 11, 2018, 05:30:08 PM
Is the power cut off or the earth cut off?
Title: Re: Alfa 75 TS fuel cut off
Post by: simmi1983 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
Title: Re: Alfa 75 TS fuel cut off
Post by: Colin Edwards 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?
Title: Re: Alfa 75 TS fuel cut off
Post by: bteoh 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 didn't have any Bosch markings.
With the spare ECU connected, it still died after 10seconds or so.
Colin, the engine doesn't die at exactly the same sequence. Sometimes 10 seconds and sometimes up to 20 seconds.
I tried connecting the other AFM but the engine wouldn't 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 can't see why it is failing now?
Title: Re: Alfa 75 TS fuel cut off
Post by: bazzbazz 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.
Title: Re: Alfa 75 TS fuel cut off
Post by: bonno 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
Title: Re: Alfa 75 TS fuel cut off
Post by: GTVeloce 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.
Title: Re: Alfa 75 TS fuel cut off
Post by: simmi1983 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.

Title: Re: Alfa 75 TS fuel cut off
Post by: simmi1983 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.
Title: Re: Alfa 75 TS fuel cut off
Post by: simmi1983 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 ?
Title: Re: Alfa 75 TS fuel cut off
Post by: bteoh on October 13, 2018, 02:18:53 AM
Thanks guys for all the good advice.
Will have a go this weekend and keep you updated.
Cheers
Title: Re: Alfa 75 TS fuel cut off
Post by: bazzbazz on October 13, 2018, 11:27:26 AM
Just one last point, when you measured the voltage going to the pump I assume you measured the voltage between the 12v pin and the earth pin at the pump plug, and got 8V.

Try measuring between the 12v pin on the plug and the chassis of the car. If you still get 8V it's a power supply problem, if you get 12V it's an earth problem.
Title: Re: Alfa 75 TS fuel cut off
Post by: bteoh on October 13, 2018, 03:31:42 PM
Hi guys, good progress. Found the cut-off problem. It was a bad connector behind the instrument cluster in the dashboard. The fuel pump wire ( Pink/white ) was not making good contact. This cured my cut out problem and the car is running fine now.
However, I am still getting poor voltage at the fuel pump - only 9.5 volts (Measured from fuel pump connector under the rear seat to chassis ). At the fuel pump relay , the pink/ white wire only measures 10.5 volts. Same voltage with the pink / white wire on the driver's side engine bay before it goes through the firewall.
Will try swapping relays later to see if that is the cause?
Am glad the car is running again and thanks for all the good advice  :)
Title: Re: Alfa 75 TS fuel cut off
Post by: GTVeloce on October 15, 2018, 12:28:24 PM
That wire carries a lot of current AND it is not a well designed part of the system. If you look at the diagram, the fuel pump relay (terminal 30) is fed by terminal 86 of the aux motronic relay which in turn is fed by a green black wire that runs from the brown wire of your ignition switch. Therefore the current has to flow from the battery (probably in the boot) to the starter; to the ignition switch, then to the relay before going all the way (via the fusebox) to the fuel pump. Most of the way is with fairly thin, old wire. I had issues with my green black wire and replaced it completely (from the ignition to the relay - S12D) however, I believe the system should have another relay somewhere close to the fuel pump (probably under the rear seat) that feeds 12V direct from the battery to the fuel pump and uses the pink white wire as the switch. All the other components (except the lambda heater) that run off the four relays are fed with a strong 12V source so why not the fuel pump?!?
Title: Re: Alfa 75 TS fuel cut off
Post by: ALF750 on October 27, 2018, 02:57:13 PM
just saw this - glad it is now working bteoh.   My 5c worth is to run a dedicated heavier wire direct from some good power source to the fuel pump along the door sill under the carpet.   Activate the pump supply via a relay with the pink/white wire behind the dash or fusebox.   My TS has been good since I have done this (should not have tempted fate......:).   Downside is now I can hear my pump running at warp 9 from about 20 metres away!  No idea what the fuel pressure is...
Title: Re: Alfa 75 TS fuel cut off
Post by: bteoh on October 30, 2018, 04:43:33 PM
Thanks,
It will be on my To-Do list in the near future. Car seems to run ok now but 12 volts at the fuel pump would be ideal :)
Title: Re: Alfa 75 TS fuel cut off
Post by: GTVeloce on October 31, 2018, 03:10:43 PM
I measured mine the other day and had similar results to you. 13.8V at the battery: 13.5V at one of the hot wires leading to the relays: 11V at the feed wire for the fuel pump: 10V at the connector to the fuel pump (under rear seat). And that is with new, thicker wire running from the fuel pump relay to the fuse box and then to the pump connector.

Will be installing a relay under the rear seat soon and see what effect it has on performance if any.