Pop Pop

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M0T

M0T

Soldato
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When I start my car up from cold it runs like a dog (i.e. it will pull away but the revs wont rise and it will suddenly lose power).

Whilst it does this I can hear a metallic popping from the exhaust, then after 10-15 seconds it rights itself and works fine until the next time it is cold.

Car is an Alfa 156 V6 and it has no fault codes logged, any ideas?
 
Popping could be fuel combusting in the exhaust after the piston didn't fire.

Entertaining question is why?

On my 146 TS it was the relay which powered the coils and ECU, the relay and the holder were corroded, but needed to pass 32 amps for the coils alone (at low RPM). Result was a hunting idle due to sensors running below voltage (supplied from the ECU), the symptoms you described, and ultimately not enough power to run the ECU.

You need to get a workshop manual, and trace supplies for sensors, fuel pump, fuel injectors, coils, and the ECU back to the battery, measuring the voltage drop under load across each joint/plug/relay.

If it's anything like mine, the Coils and ECU will share a supply out of one relay next to the fuel pump relay, and the sensors will be supplied by the ECU, so again the same supply.
 
Just thinking about the explanation of fuel combusting in the exhaust - surely that couldnt happen when it's cold?
 
on my old car, a pug106 started popping at full throttle i couldent think what it was then i changed spark plugs and it was fine from that day forward, dont know if it will be that on urs.
 
Plugs are 2 years old and have done about 5,000.

When you say electrical and its an Alfa, I say let it pop - I'm not wasting my time with this!
 
Not if its only happening for 10 seconds!

Get it checked out at the next service. If you're anywhere near Exeter I can point you in the direction of a superb Alfa specialist who would probably have a look without charging
 
my friends 156 2.0 TS does this, without the sound from the exhaust though. reseting the ECU (via the OBDII port) cured it for 6 months, then it came back, reset again and it was gone again.
 
iaind said:
Just thinking about the explanation of fuel combusting in the exhaust - surely that couldnt happen when it's cold?
Click to expand...

fRostiE said:
Popping could be unburnt fuel - but i thought this only happened when a car had been driven hard so the exhaust was hot enough to make the fuel combust
Click to expand...

One charge not firing means fuel/air mix in the zorst. Next charge firing will expell hot, possibly still burning, gasses into this. POP!





Stop being lazy and have a cursory poke around. The relay I suspect won't be far from the battery.
 
You know that poking around with the relays of an Alfa is like jumping into a bullpen and sticking a lighter under the meanest looking ones dangly bits.

Asking for trouble, there is a reason most of the electrical components are called 'black boxes of death'.
 
Could be a valve sticking open/broken valve spring.

Means the engine is firing with a valve open, hear it through the exhaust..

Thats old school tho, havent seen it on a modern car.
 
Car conked out at the bottom of a hill today after a popping session and wouldn't restart. Error code for MAF disconnect, new MAF ordered :(
 
Mine had a fat pile of MAF errors with my relay. Has anyone done anything to make sure the current MAF has enough power etc?

It really should be capable of running without a MAF in limp home mode. Though a hot day is about the worst for limp home mode.
 
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The MAF is a 2 year old ebay special - the connector doesn't even fit on it properly so I'll replace that anyway.

I had a look at the relays and there wasn't any obvious sign of problems but I pulled them all and cleaned them and the connectors up along with the underbonnet fuses.

Couldn't really be bothered to do much more because the footie was on.
 
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