308GTSi: what triggers the fuel pump relay?

Well, nothing on mine. I put a ingnition switched +12V to the relay, so when I turn the key the fuel pump runs and I can start the engine, runs fine, ignition on both banks but when the engine runs and I remove the extra wire it stalls again.
Fuelpump is normally triggered when starting and then when the engine runs it is detected and the fuel pump receives current, if the engine stalls the pump should stop. How is the pump switched on, by what? In a general K-jetronic article it is said from the coils.
I don't know where to look elsewhere, please help!

first drive in 3 years: http://home.tiscali.nl/308gto/f1.mpg
more: http://home.tiscali.nl/308gto/f2.mpg
www.ferrari288.com

 

Bert -- Your particular K-Jet system doesn't use a "tach" signal for the fuel pump control. It uses three things:

1. There's a safety switch (item 72 on your OM schematic) on the airflow meter. It has two wires -- ZB (violet/white) and N (black). The logic is that this switch should be closed when the airflow metering plate is at rest (i.e., engine not running), and it should be open when the airflow plate deflects during engine running. First, just try unplugging this switch and see if the engine will run:

If it does run = you have a bad safety switch item 72
If it doesn't run = go to step 2 (and replug the safety switch back in)

2. Relay F (item 90 on your OM schematic) is a Bosch 0332204101 relay (the OM has an error and shows this as Bosch 0332015006 relay, but that's wrong). Try swapping this ...101 relay F with one of the other ...101 relays. (They call this F relay the "Start electro-valve control relay", which is one of its functions, but it also controls the fuel pump relay N based on what the safety switch is doing)

and finally,

3. Not sure where you're putting the +12V to make it work -- i.e., are you putting the +12V directly to the fuel pump or are you putting the +12V to close the ...113 relay N. If the former, try swapping the ...113 N relay for one of the other ...113 relays.

Try some of those things and give a shout back.

 

attached is a simplified chunk of the schematic from 1981 which shows how it works.

However, in 1980, there may not be an airflow sensor switch. It's a blue plug a little under the back end of the air filter box....is there one?

In this circuit, the engine start relay is picking where the 12V for the fuel pump relay is coming from - the fuse box or the ignition switch. The engine start relay is controlled by the air flow/safety switch.

Pulling out the blue plug means the easy path is picked...fuse box direct to the fuel pump relay. That bypasses any problems with the ignition switch, cold start injection fuse or contact issue inside the engine start relay - but the fuel pump will run all the time when there is power on the fusebox.
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rereading what I said with a lower scotch level, I see it's badly worded. Good thing there is a pic.

The engine start relay is always in the fuel pump relay circuit, so a bad contact inside the relay can always stop the fuel pump relay from closing.

Put another way, do what steve said

 

now youse guys seem to know wat ur takin about, my 308 got this fuel prob when i stop the engine try to start it it turns over ok but wont start so i unplug the fuel pump relay then plug it back in and it starts ok also have noticed the fuse terminals for f/pump look as if they have been getting hot can you guys shed any light on this cheers phil in oz

 

1. There's a safety switch (item 72 on your OM schematic) on the airflow meter. It has two wires -- ZB (violet/white) and N (black). The logic is that this switch should be closed when the airflow metering plate is at rest (i.e., engine not running), and it should be open when the airflow plate deflects during engine running. First, just try unplugging this switch and see if the engine will run:

If it does run = you have a bad safety switch item 72
If it doesn't run = go to step 2 (and replug the safety switch back in)

steve i have just done this and the engine ran do you think this could be my relay problem cheers phil

 

Bert -- I forgot to mention one other (fairly simple) test. With everything plugged in for normal operation, put that extra +12V source you have onto the large P (beige) wire at the bottom of fuse #3 -- if it works OK, then either the LH fuseblock itself is bad or the large R (red) wire at the top of fuse #3 is not at +12V (and it should always be at +12V -- even with the key "off").

phil -- I don't like your report that just removing and reinstalling the fuel pump relay N seems to makes a difference (especially if the female contacts inside the N relay socket look OKish -- i.e., not frazzled) -- but it wouldn't hurt to try a different ...113 relay in that position. Also you might just be shaking/vibrating relay F enough during that process that it helps relay F. Consequently, also try is swapping a different ...101 relay into the relay F position.
Since your unplugging the safety switch 72 seemed to make a difference, you should probably try to make a resistance measurement of just the switch itself when unplugged -- i.e., it should be a low resistance (maybe a few ohms maximum) when the engine is off and open (infinite resistance) when the engine is running. However, this switch controls relay F so a flaky relay F could be the real problem rather than this switch.
With regard to the fuse terminals for the fuel pump looking "burned", this is a common problem on all of the high-current circuits on the 308 fuseblocks. You need to either try soldering the riveted connections at the fuse terminals of the fuseblock (both frontside and backside) so the electrical connections are not just dependent on the mechanical forces of the rivets squeezing things together (but this might be very difficult since the parts are now heavily oxidized from the heat), or get a new fuseblock.

Good hunting guys...

 

Thanks a lot 91TR and Wolftalk, great explanations, with the written stuff from 91TR and the drawing from Wolftalk I could understand how it works, printed this thread and took it to the car. I removed the plug from the fueldistributer but it didn't make any difference, removed the airfilter and hand operated the airflow plate and I heard a relay clicking (ignition on of course) so that was in order. I thought it could only be the start relay then being bad, I couldn't find in my documentation which one it was so I followed the wire that should trigger the pump relay to see were it was going, and guess what? It was cut and connected to a black wire that dissapeared behind the dash, and another black wire returned there and was connected to the other end leading to, what then should be, the starter relay. And with ignition on and the plug from the fuel distributer removed, that one had +12! The 2 black wires were going to, as you may have guessed already, the alarm system module. The alarm was in good order I thought and the immobilizer (spell?) was function I thought because I had ignition and I could crank the starter. Appearently not all was good then, I removed the wires to the alarm and reconnected the wire from start relay to pump relay and all was well, good! I will pay attention to the alarm later, I only have no anti theft on the fuelpump now, not a big deal.
Thanks again guys, I searched all the "308 not start" threads and couldn't find this info, that drawing extracted from the general wiring diagram is very helpfull, much easier to understand.

 

Glad you got it sorted out Bert, but I think I'm learning, that whenever someone asks about an electrical problem, the first thing I should do is ask "do you have an alarm system or any other wiring modifications"

 

Indeed, the original F electrical system is not as bad as everyone thinks, another false accusation (spell? I've been drinking to celebrate my F revival) about F electrical wiring omitted. After 3 years of not running, all the standard F electronics hadn't suffered, like fuel distributer, marelli modules, everything. These 308's are well developed and well build cars!

 

Steve i have all new relays fitted this problem only happens every so often the fact that the engine runs with the air flow sensor unpluged i think maybe i will replace air flow senor switch and see what happens i the next couple of weeks cheers phil

 

Sounds good phil -- let us know how it works out.

 

Fuel/rly problem update as the terminals in fuse box for the fuel pump fuse looked as if they had been getting a little hot i have disconnected the red wire top of f/pump fuse and the beige wire bott of f/pump fuse and fitted a 8 amp inline fuse, drove car today with no problems will keep my fingers crossed see what happens therefore i thank you steve for your input cheers phil

 

I have a similar problem with my 308 GTSI. Engine starts and idles smooth, however, when I touch the trottle it dies, but will start right up again then problem repeats itself. It does appear to be ok when the engine has warmed up. I thought I had the problem solved but it has shown its ugly face again. Appreaciate any help that I can get. Thanks