91 Q45 electrical dropout

[Desmoquattro]

Here's a fun one -

My Q has worked fine up until recently - it's been intermittently dying and then hard starting. What happens is the engine will stall, then be very difficult to restart. When it restarts, it is in fail safe mode (3k limit, engine light on).

At first I though MAF or something common like that. But some further playing around (and after a new MAF) revealed that when it dies, the running lights shut off. And they will remain off when it is difficult to start. The alarm system also stops functioning. You can turn on the main beams, and the starter will crank just fine, it just doesn't seem to get any spark/fuel.

When the engine stalls, the computer throws a "Low Battery Charge" warning, even though the battery is strong and has lots of cranking power.

So I'm looking for an electrical culprit but I have no clue how to proceed. Obviously it's something in the system that controls the running lights and alarm system (probably the ignition as well) but independent of the starter and main beams. The relays and fuses look fine, and a burnt fuse link wouldn't cause an intermittent problem.

Ideas? There is no rhyme or reason to the dropout. It happens when cold, hot, at rest, driving down the road, pretty much totally random.

[Q451990]

I would clip a cord with a lighter plug end and hook it to a multimeter, then monitor the voltage at the cigarette lighter. You might get a clue as to what's going on monitoring the voltage. It's entirely possible that you have a voltage regulation problem with your alternator that's intermittant.

Heath

[Skibane]

If it was an alternator voltage regulator problem, it's hard to imagine how the battery voltage would drop enough to kill the engine, yet still have plenty of power to spin the starter.

Des, you mentioned that none of the fuses are blown, but one of them may not be making good contact with its fuseholder. So, you might try pulling the main fuses - one by one - and sure that both blades on each fuse are clean and making good electrical contact. Ditto for the ignition relay. I like to use Iso-HEET fuel system de-icer as an electrical contact cleaner - It's almost pure isopropyl alcohol, which is excellent for removing oxidization on metal.

ETA: Looking at my Y33 Power Supply Routing diagram (and assuming that it's similar to the G50), the ignition relay looks like it controls everything that's acting up on your vehicle - Which makes it a prime suspect.
Modified by Skibane at 11:24 PM 11/21/2009

[Q45tech]

State Votech/trade schools/colleges are excellent ways to learn electronic technology and troubleshooting.Half of an automotive technology 2 year course in now pure electronics.A year of theory and a year of practice.

Diagnostics are the weak link in most old hand mechanics.

A quality volt ohm ampere meter and a portable digital storage oscilloscope is all one needs.

One must memorize the hundreds of common waveform shapes so that you immediately spot any defect.

So many common dc motors. alternators, solenoids, sensors, positional potentiometers [variable resistor] ....................things all covered.

[Desmoquattro]

More information -

The failsafe mode is not related to the initial problem. Some research revealed that it automatically engages when the starter motor is turned continuously for more than a few seconds (which is exactly what is happening, when the problem pops up).

Now it is no longer intermittent, it simply refuses to start and the running lights/alarm do not work. The starter still cranks and everything else seems to work fine. Power functions, main lights, interior lights, doors, locks, windows, etc are all working, the only things that do not work are the running lights and the alarm.

I checked the ignition relays, and the ignition coil relay. Ignition relay one is not related, disconnecting it disables other systems. Ignition coil relay is fine, and is clicking on-off as it should. HOWEVER, ignition relay 2 (as per FSM) has NO effect. Disconnecting it, replacing it, it doesn't matter - the car behaves exactly the same. Nothing else shuts off, and nothing improves. So the ign relay 2 is likely the correct circuit, but the relay itself is not to blame (I swapped it with two other relays to no effect).

The circuit of ignition relay 2 seems to be related to the ignition of the motor. So the question is, what else is connected to that circuit that could cause problems?

My other theory is that the alarm system is malfunctioning and cutting the ignition, but I think this is wrong because the alarm is supposed to cut the starter function, not the ignition.

[Infinitiguy19]

Check the Anti-theft section of the service manual in the EL part of the FSM, only 1990-1993 Q45's. Too many tests need to be done on you part which we (Internet people) wouldn't have any idea where your at.

[Desmoquattro]

Here's where I'm at with the anti-theft -

Disconnecting AF relay 2 (located behind the ECU/ECCS, along with the ECCS and coil relays) disables the starter. This seems right, because that relay is in the starter circuit. AF relay 1 (in the engine bay) is related to the lights and horn, disconnecting it changes nothing in my current situation.

I'd like to access the AF control unit for more testing but it will require disassembling the heater box under the dash to get at it, so I haven't gone there yet. I'm trying to exhaust the other possibilities first.

According to the EL troubleshooting and the circuit diagrams the AF system controls the starter - which is working fine. There is no mention of a spark ignition kill circuit, only a starter kill circuit.

Other info -

The horn works.

The fuel pump primes.

Ignition relay 1 and 2 are located under the driver's dash next to the fuse panel.

It would seem to me that this is related to the ignition (key) system somehow. After all, what turns on the running lights? Only the key does that, there is no switch to turn them on-off manually.

I like to approach things logically, but when it comes to electrics that is sometimes impossible...

[Q45tech]

The alarm system only cuts the voltage to starter solenoid nothing else.The multiple folded schematics at end of FSM are detailed and all their is.

One must mentally be able to visualize exactly how the ecu to engine works.

Few realize that a ignition coil only creates high voltage the moment the primary voltage is removed [turned off].

ECU internal problems are checked by ecu substitution AFTER all inputs to ecu are verified.............as a coil or injector short can destroy the driver transistors insude ecu.

[Desmoquattro]

Here's where I'm at:

I fiddled with it today and hit upon something. It started ok and ran for some time. I left it running and proceeded to fiddle with every electrical connector I could lay my hands on, looking for a loose connection. Nothing disturbed it.

Then after several minutes, without touching anything, it stalled. I restarted it and it ran rough, then stalled.

So I got to thinking, what about the battery?

I checked the charge on the battery. WAY too low, less than 12V. Then I started it long enough to measure charging output. Again, too low - fluctuating between 13 and 13.7 at idle, and NOT increasing with revs. I checked the alternator a year ago and idle charge was over 14.5V then, and it would spike with engine revs.

SO the first thing is I've picked up a new battery; I knew the old one was getting worn out, but I WRONGLY assumed it was fine because it was cranking. Going by voltage alone it shouldn't have had enough to start the engine at all.

I'm leaving the battery on a charger overnight before I install and test the alternator again. First I'll check belt tension and ensure there is no slip, and check the connections for corrosion. If that's ok then it's time for a new alt.

This makes sense to me as I have similar issues with my Ducati - if the battery runs down (which it will, because the charging system is inadequate on 916s) it causes all sorts of weird manifestations, including stalling, misfires and lots of gremlins. That's exactly what I'm looking at here, so I think I'm on the right track now. Voltage is dropping faster than it can be replenished and it starves the major electrical systems, causing stalling, misfires and hard starting.

Make sense?

[Q45tech]

Remember the battery must provide a voltage [to create an electromagnet] to alternator BEFORE the alternator starts working

[Desmoquattro]

NOPE. That ain't the problem.

Brand new battery with a full charge did absolutely nothing. It wouldn't run at all, regardless of what the alternator was doing. It's still cutting the light circuit randomly and stalling.

I'm calling in my electrical engineering uncle to help us diagnose the undiagnosable.