Help! I've been tidying up the car and fitting a few extras (radio and the like). I noticed that the battery loses its charge "fairly" quickly, so bought a new one. That lost its charge over a few days to (I'm not driving the car at the moment, and am trying out different things like the radio and amp, so I thought it might drain the battery a bit more than usual - no problem) I connected a battery tender (CTEK) to keep everything topped up. I've just been in the garage and by chance my arm brushed over one of the Mass Air Flow sensors. They are both HOT! The plugs have 12V on one of the pins (heater wire I presume). Strangely enough, all the other pins have a small signal voltage on them as well. All of this is happening and being measured with ignition off! Both are heating to the same amount - considering that the electronics are divided LH / RH this soesn't seem to be a stray short circuit problem. In the course of installing an immobiliser, the only thing I've touched which is remotely near to these circuits are the wires coming from the passenger footwell fuses 14 and 18 which are the Motronic power supplies. These now pass through two relays which are only closed when the key is in the immobiliser. Only thing I did in the engine bay was to give it a good jetwash and clean up. hhhheeellllppp!
Have been continuing the diagnostics... Both relays in the footwell for injection system LH and RH are warm and operating (without ignition being on). They are providing the 12V to the MAF heater element. If I pull the relays, the MAF's cool down so they are getting their 12V from the right source. These relays (d and l) are operated when the motronic units connect pin 36 to earth. This must be due to some command they receive. What can be causing them to think they should start heating the MAF elements?
I'll start with the easy stuff until the experts chime in here: 1. Have you let the ECU's reset properly after changing the battery? i.e, when power is reconnected, start the car and let it idle for 10 to 15 minutes (or until engine temp goes up to the point the fans kick in) without touching the gas, any electronic controls, etc. 2. Replace (or swap from another location) the d & l relays.
I'm in a bit of a hurry, have to leave for a while, but I will add that I think there is a process where the "hotwire" in the MAF sensor is supposed to be heated after shutting off the engine, in order to clean any deposits that are building up on the wire, but this is only supposed to happen for a short time. Perhaps the relay is sticking on? I'll check the book when I get back. You aren't leaving the key in the ignition switch, are you?
I had swapped over the relays for the same type from somewhere else on the board. No difference. I haven't done the ECU reset yet. I guess you're right that I should eliminate that too. That's very interesting because that would affect LH & RH together if it can actually cause the problem. I've put my hand on the relays when turning the key on and off and they definitely "click" when I turn the key or or return it to zero, so the circuitry to operate them on and off seems to be in place.
I've jiggled the ignition switch about all over the place and removed the key and also left it in. All seems to be working there. Relays go boinngg when I turn key on or off. Very interesting the bit about the burn-off heat cycle. It seems VERY much like what is happening - i.e. JUST the MAF's getting warm with no other symptoms or whirring noises and also on battery power only with ign off. I'm off to bed now to dream of ice cold MAF's, but don't let that stop ya all working the problem while I sleep! Drew
Perhaps you should dis-connect (cut the wires or whatever) to the immobiliser and/or radio and see if that fixes the problem. If it does, then you know you got power for either from somewhere you shouldnt have.
OK - the workshop manual says " The ECU (meaning the Motronic) keeps the hot wire clear of any residue deposits not captured by the air filter. In particular, about 4 seconds after the engine has been shut down, it actuates a high current flow through the hot wire causing an increase in temperature up to 1200 degrees Celsius (normal hot wire temperature is about 155 degrees Celsius). This takes place only if, during operation, the engine temperature exceeds 40 degrees Celsius and speed exceeds 2000 rpm. The control lasts for about 1.2 seconds." So perhaps the fact that your immobilizer is tied into fuse 14 and fuse 18 (which are the fuses for the Motronics) is confusing the Motronics about engine shutdown, and causing them to hold onto the hot wire cleaning program. This would cause the MAF's to be hot to the touch, and would cause the battery to run down. I'm afraid the wiring diagram is very complicated in this area, so I'm not exactly sure which wires to test, but if you're getting power to the MAF more than 10 seconds after the engine is shut off, then something isn't right, and I don't see anywhere in the diagram that indicates that there is a timer relay involved with the hot wire. There is a timer for the light around the ignition switch, but apparently the timer for the MAF is integral in the Motronic. I'm surprised that the MAF could survive for very long with the hot wire running at 1200 degrees Celsius. That's hot!
Many theft deterrent systems (not sure if this would include an immobilser) have a backup battery to keep the system functional if a thief disconnects the car battery. If it has been wired into the same circuit as your ECU's or MAF's this may be presenting a +12 volt condition even with the ignition off. It might explain why your battery is draining so quickly if certain components believe the car is running even when the ignition has been turned off.
Well, out of bed and finished in gym, so I'll meander down to the garage and try out some of your ideas. The MAF's weren't cooking, and you could hold your hand on them, but very nicely warm. Perhaps more akin to normal operating wire temperature, but without cold air flowing continuously through them. (I hope, anyway!) I'll be back!
Well, I've found the problem! Don't know quite how to solve it yet! It seems normally that..... When you turn the ignition on, the MAF's start heating and the Motronic powers up. When you turn the ignition off, the Motronic stops and tells the MAF's to stop too. But ......... I had put my immobiliser in the Motronic power supply, so when it is ARMED, the Motronics don't get the power they normally would from Fuses 14 and 18. So..... IF I don't put the immobiliser to "SAFE", and I turn the IGN key (like to listen to the radio in the garage) then the MAF's start heating, but the Motronic doesn't power up. When I turn off the IGN after having listened to the radio, the MAF's never get the signal from the Motronic to stop heating. As the Motronic was never "ON", it never gets an "ON to OFF" signal. If I ASSUME that the immobiliser key goes in first before I turn the IGN key, then everything works fine. As the immobiliser only auto arms itself 30 secs after the ign is turned off, that gives enough time for the Motronics to get their "ON to OFF" signal. However, as we all know ASSUME makes an ASS out of U and ME. So I've got to figure out some other wire which I can cut into to disable the engine electronics (legal and insurance requirement in Germany) Not knowing what pin does what on the Motronics doesn't help. Has anyone ever turned up a pin allocation for the Ferrari 2.7 Motronic? (Not the Workshop Manual as that only traces the wires to the Motronic plug but doesn't indicate what pin does what) Thanks for the support guys! It helps to know you're not on your own! Drew
Have now just finished rewiring the immobiliser to interrupt the ignition plus (15) to the motronics. Lost a day as I had to take out the footwell relay box to do the soldering etc. All seems ok now. Cheers guys! Just hope the MAF's are still ok, but I guess if they were still capable of heating up that means the wire hasn't vaporised! Drew
Makes me glad that I don't have an immobilizer. Infact, I can't remember the last time that I locked the car!! Good job with the fix!
All put back into place now. No smell of burning PVC when I turned the power back on either! Now to press on with the refresh. (see separate thread!) Image Unavailable, Please Login
