Alternator question

I'd be inclined to have the alternator checked it should supply more than enough power to run lights and the aircon fans without starving the ignition. Try lights heater fan and heated rear window and see if that causes the problem. Derek

Thanks, I will.

I had a similar problem with a Ford Laser, it turned out to be a badly corroded connector/very bad electrical connection to the AC pump clutch. Caused the clutch to cycle on and off fairly quickly giving the engine the feeling of a misfire.

This is a very definite misfire, but I was suspecting something in the AC taking more current than it should. I think there's only that clutch and the fans and a solenoid under the dash somewhere.

so turning the other kit on didn't replicate the problem then? I had a thought about the fans when the brushes are all but worn away on leccy motors they do draw more current than they should before getting to the expiry stage I would still check the alternator first tho simply because its easier to do

Derek

No, it has to be lights and AC. Any other combination of loads doesn't do it. When the belts were loose the AC alone would make it misfire or stall, but lights alone were ok.

I'm struggling with this, there has to be some sort of electrical interference happening when the lights and AC are on which is then feeding back into the ignition circuits causing the misfire. But what?

The battery should be able to cope with the power drawn from the lights and AC if the alternator is topping it up.

Can you check the condition of the battery - lights on and see if they go dim in a few seconds.

Try disconnecting, connecting AC fan, clutch, headlamp until the misfire stops - that will narrow it down - hopefully.

Also check all the charging circuit wiring - corroded connectors that can cope with partial load but not full load. You might need a multimeter to check voltage on each side of the connectors.

Then start looking for voltage drops across the light and AC switches.

Since I found the alt clamp slipping and it improved markedly (even seems to have more HP than it did with no lights or AC on), it only really happens at night now and I'm not that clever electrically and thought it was solved and money is a bit tight ATM I haven't hunted too deep. Because the belt needs to be very tight to not slip, it seems like there is something imposing an abnormal load rather than a bad connection starving the ignition. Maybe the ignition system itself? I have a meter and a manual but not that good at translating it. Would it be a voltage drop to look for? Surely there is ~13.6 throughout the main wiring? Do you mean an amp drop?

jg Hi,

May I suggest you also check your alternator's bearings? An alternator belt which requires very frequent tensioning MAY be due to bearings starting to go bad. This problem also increases the load on the engine, increases fuel consumption and decreases performance.

Take care Pantelis

And most of the modern alternator pulleys don't have a key to the shaft and some of them fall apart, make sure the nut is tight on the shaft. Also check earth connection on ignition module under the coil, you might have two unrelated faults.

Martin

Too right - they are made out of old biscuit tins. I had a pulley come loose on my V6 Calibra, it nearly ate through the alternator shaft before it was so wobbly it threw the belt off. To get the alternator off you need to remove the flaming exhaust system and access it from underneath, so it was a 240 mile RAC relay recovery. I simply couldn't believe that some twit thinks it is OK to do away with keyways holding a pulley on a shaft, and its not British engineering either, it is an Opel in disguise.

What is the world coming to....

Steve

Sorry for laughing at that, you must have been a bit pissed off. Have you still got the Calibra? I have some NOS driveshafts which I think may be off those, can give you the numbers if you want.

Martin

Thanks everyone for suggestions. The bearings seem ok. 20 years of life had partly mangled the steering pump clamp system and the alt clamp bolt had a washer grown countersunk which parted the slide bar when tightened, so what is basically a bad arrangement (with a belt off another belt) had everything working against it. I found the belt spec has changed to a narrower one, which I suspected might be an attempt at addressing slipping. That's why I asked if it was a common problem, but it sounds like it isn't.

It wasn't so bad, the fuel saved just about paid for the RAC membership, and I only joined 2 months before it happened.

Yep, still got it. Its my daily commuter, cheap, economical, and practical. Only thing it really needs is a 75% lighter flywheel - the standard one must be off a Massey Ferguson. - and the air con fixing, but hey this is England, who needs aircon !!

Steve

Its not uncommon to see a corroded connector act as a resistor and drop the voltage through it.

The reason I was looking for a volts drop is that it seems reasonable to expect a lower volts is affecting the ignition circuit somehow - though how is a mystery as it should be isolated from the AC and lighting circuits.

Can you get the misfire with the vehicle stationary? Then go through the disconnecting an item at a time until the misfire stops.

My gut feel is that the AC clutch circuit is causing the problems.

No, only doesn't do it below medium load and revs.

Yes that's mine too, or there is a solenoid in the dash to work a flap for AC air flow, but I can't find it.