Mechanical mystery

"Chairman Kaga" (mike-mckinnon)
11/21/2014 at 16:06 • Filed to: None

I asked the Alfa guys and got some suggestions, but why not see if anyone here has some magical insight?

My '82 GTV6 runs great. Except when it doesn't. I'll be tooling along, glorious noise and heavy steering, when suddenly the car loses power. It's as though it drops three or four cylinders. It doesn't die, it just goes limp. A few seconds later, it's as though nothing happened.

The other night as I was turning across traffic to get to my neighborhood it went tits up. With cars coming at me. I meekly trundled across the road, barely making it across. The car rattled and banged all the way to my garage, sounding as though it was suffering catastrophic misfire, where it promptly died at idle. I popped the hood, fired it (right) back up, and it was fine.

If it was the coil, it would have flat died. If it was losing electricity at all, including a bad ground manifesting itself, it would have died. If the timing belt jumped a tooth, it would be FUBAR. It's really like it's just dropping spark to multiple cylinders, but only for a moment, aside from this last time.

So. Bad plug wires? Weird that there would be multiple bad ones that somehow simultaneously short, then simultaneously come back to life.

Could it be the AFM? It has Bosch L-Jet ignition, which is finicky when it comes to electricity. Maybe a bad ECU? They're prone to oxidation. A gimped O2 sensor? All suggestions from the Alfa guys.

Again, just wondering if you lot had any other ideas.

DISCUSSION (24)

505Turbeaux > Chairman Kaga
11/21/2014 at 16:13

those are all reasonable, but I would also say fuel delivery could be an issue too. Fuel filter, or wonky wiring to your fuel pump (or a dirty fuse) could be the culprit too

Will with a W8 races an E30 > Chairman Kaga
11/21/2014 at 16:13

Try the simple things yet? Clogged fuel filter, pump giving up, shit in the fuel tank clogging the screen, bad connection in the injector harness, clogged injectors...

BoulderZ > Chairman Kaga
11/21/2014 at 16:15

I have no idea what your Alfa's ignition system is like, but the symptoms are exactly what we saw in a 60s Datsun roadster on a group drive. In that case it was tracking inside the distributor cap. We pulled the cap/rotor and saw black carbon tracking making all sorts of connections that should happened. Wiped it out and all was well again. Could easily not be that in your case, but if you do have a distributor system, that's a quick easy check. Hope it's quick/easy/cheap, whatever it is.

You can tell a Finn but you can't tell him much > Chairman Kaga
11/21/2014 at 16:19

Sounds kind of like fuel starvation. Does it happen during certain conditions (accelerating, cornering, steady state cruising) or does it seem to be random?

4muddyfeet - bare knuckle with an EZ30 > Chairman Kaga
11/21/2014 at 16:20

Had a similar problem a few years ago with my Legacy. Turned out to be silicon impurities in a fuel batch from a multi-chain fuel station near me. You haven't used a different fuel station recently? If not I can only think fuel filter/pipes, or lambda sensor

Svend > Chairman Kaga
11/21/2014 at 16:44

Don't shoot me down straight away but a guy I know had something very similar happen to his car, he changed the fuel filter and started using a premium fuel and found the problem stopped straight away and he gets better mileage now and works out cheaper to use the more expensive fuel compared to using more of the cheaper generic fuel.

Give it a go, a fuel filter costs very little and adding a couple of dollars to your fuel bill now could save you more in the future.

Chairman Kaga > 4muddyfeet - bare knuckle with an EZ30
11/21/2014 at 16:45

Fuel filter is practically new. Some techron might not hurt though.

Chairman Kaga > Svend
11/21/2014 at 16:46

I just replaced mine not even 1,000 miles ago. I do have a spare though. Maybe swap em and see if it help? I don't think it's dangerous to put the first one on the shelf, then drop it back in later.

Chairman Kaga > You can tell a Finn but you can't tell him much
11/21/2014 at 16:46

Random. Totally random.

Chairman Kaga > BoulderZ
11/21/2014 at 16:48

Has a dizzy, no points. The rotor is new but the cap is not. I cleaned it all not that long ago but it's on the list for inspection.

Maybe a short in the coil wire?

4muddyfeet - bare knuckle with an EZ30 > Chairman Kaga
11/21/2014 at 16:49

Ah well best of luck. Love the GTV6

Chairman Kaga > Will with a W8 races an E30
11/21/2014 at 16:51

Those are mostly down the list as they invo;ve more work. I had the injectors sonically cleaned a couple of years ago. The fuel filter is less than 1,000 miles old. I'm leaning toward bad electrics. Maybe a fritzy coil wire? Like the plug wires, I doubt it's a batch of injector leads all shorting then coming back simultaneously, and they are all energized via the same combo-relay, so if that's the problem then the car would probably just die. But a shorting coil wire that's delivering not enough voltage to the dizzy COULD be creating symptoms like this, right? And a short could come and go.

Chairman Kaga > 505Turbeaux
11/21/2014 at 16:52

Fritzy coil wiring, maybe? I was farting around that general area when I was installing the headlight relays. Which come to think about it was when this issue first manifested. But it happened once or twice then poofed away. Lately it's been much more frequent. Burnt wire, getting more burned every time it shorts?

Chairman Kaga > 4muddyfeet - bare knuckle with an EZ30
11/21/2014 at 16:53

And lambda sensor is always a possibility. The car was running rich all of last year, so it could be sooted up. I'll pull it and see what's what.

505Turbeaux > Chairman Kaga
11/21/2014 at 16:55

that is a good possibility right there too. Italian wiring might as well be just a big fuse!

Svend > Chairman Kaga
11/21/2014 at 16:56

For the cost of a filter (which you have a spare anyway) and running a tank or two of premium fuel through won't do the engine any harm. As I say it worked for the guy I know and he's more than happy, he and the garage can't really justify why it did, maybe it was all the crap that goes into generic fuel but it did.

punkgoose17 > Chairman Kaga
11/21/2014 at 17:07

This sounds like their is something in the gas tank that intermittently clogs the out line.

It reminds me of the story of the last Jensen off the production line. It was for the owner of the company and an upset employee shoved a note in the gas tank that said, "bye yank." I cannot find the stories on it now to save my own life.

Chairman Kaga > 505Turbeaux
11/21/2014 at 17:12

I was gonna say one big bomb... but fuse works.

BoulderZ > Chairman Kaga
11/21/2014 at 17:26

Very possible, and would also allow for intermittent due to heating (e.g. fine when cool, starts shorting when warm/hot). Do you have another coil and wires you can sub to test? There's a famous (maybe apocryphal) story about a camaro (I think it was) that could tell if it's owner bought chocolate ice cream or rocky road at the store. Short version: took longer for the owner to walk to the back of the store for rocky road whereas chocolate was in a case up front. Time difference allowed the car to cool/not cool sufficiently for the starter relay to function. Maybe you have a similarly temp sensitive thing going on?

RallyWrench > Chairman Kaga
11/21/2014 at 17:38

I'd call this an electrical mystery.

Does this only happen after the car has been running for a while, when it's hot, or will it do it when cold as well?

I've seen weak coils drop output & cause similar symptoms in L-jet, Motronic, and VW Digifant cars when they get heat soaked, but I'd expect it to do the same when re-fired in that case. That can be misleading because if you simply pull a wire you'll see spark & assume it's ok, but if you scope it you'll find it's too weak to fire properly. Carbon tracking in the dizzy cap can also cause spark to drop, if that's what's happening.

The ECM is certainly possible if perhaps it's dropping the coil trigger (terminal 1 on the coil) or doesn't like the RPM signal; I don't know if the Alfa version uses a crank sensor or a Hall sensor in the distributor, but those can both cause running issues if there's any electrical interference or resistance issues. In any case, this isn't a common failure.

I'd put a fuel pressure gauge on it first to make sure it's not a weak pump. Sometimes when the key is cycled it's enough to jog them back to life until the pump motor heats up again & slows down. As for the AFM, it's a simple rheostat, and is isolated enough from the engine that it's likely not affected by temperature too much. Usually when AFMs go, they cause jerky throttle response or flat spots under acceleration, not dead misfires. They're easily tested with a meter, it should show a smooth increase & decrease in resistance with no spikes or drops as you sweep the door. I'd take a close look at the coolant temp sensor as well, if it goes OL when warm, it'll tell the control to fuel the car as if it's cold, which can overwhelm the ignition & cause rich running & misfires.

This might not be helpful, but there are several possibilities here, all of which lead to more questions about test results.

Good luck!

You can tell a Finn but you can't tell him much > Chairman Kaga
11/21/2014 at 17:42

Do you run premium or regular? Could be ethanol wasting your fuel system. That can take a while to start giving problems and take forever to clear up. The ethanol loosens everything and you end up with crap flying around and clogging filters and carb jets forever. It would screw with injectors too.

Chairman Kaga > BoulderZ
11/21/2014 at 19:29

Maybe? In that it doesn't seem to occur until after I've been driving for a bit.

The coil wire is pretty generic. Might be a good place to start after checking all electrical connections.

Chairman Kaga > You can tell a Finn but you can't tell him much
11/21/2014 at 19:32

Yeah. Yeah, I considered that. Short of pulling the tank and fuel lines, what's the best way to test this theory? I'd cut the filter open but it has a heavy duty aluminum chassis and getting through one without setting it on fire is a real challenge. I know. I've tried.

You can tell a Finn but you can't tell him much > Chairman Kaga
11/22/2014 at 11:17

That's a good question. I've mostly seen it on boats, so they are usually carbed and have water separating filters. The carbs get all nasty from varnish getting loose and the water separators fill up with water and sludge.