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Discussion Starter #1
Hi guys

I have a gt 3.2 V6 with a misfires on cylinder 1,2,3. So fare i tried changing the lampda probe, and cam.pos. sensor.
still got the missfire, the spark plugs are only 4000 KM.

now i need some help with figuring out what can be the problem???

BR Mads
DK
 

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Is the missfire at any engine speed or just at tick over or lower engine speeds.?
It would be worth doing a compression test to rule out a mechanical issue.
 

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Did it just suddenly start, or was it after some work had been done to the engine, perhaps after a cambelt change?

It could be a timing issue. I had that once, after a cambelt change. Car would idle a bit unevenly, like a race car, and it would throw up misfires, usually under half throttle while the engine was cold. The mechanic initially did not want to reset the cams using the markings machined into the back ends, until I forced him to do it. Ran sweet as a nut again after that was done, and the mechanic admitted that I had taught him something.
 

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Discussion Starter #4
I had an exhaust leak in the exhaust header, for 2 days, based on sound. (turns out to be a loose lampda sensor).
then the missfire happend while driving after 20 min accelerating out of a light.
When the car is driving above 4000 rpm and 2nd gear and up, the beeping stops so i expect the missfire to stop.

I changed the lampda sensor as i thought that was the problem, but no. the same with the cam sensor.
 

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Can you hear an intermittent electrical ticking/sparking noise in the engine bay? I had this recently and it was two coil packs shorting out on the rear bank. Replaced both and no more problems.
 

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Take the plenum off, compression test it. If compression test is OK, then check the belt alignment.
 

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I would start with the basics, i.e. spark plugs, MAF, vacuum leaks etc.

Eric The Car Guy has a couple of videos on YouTube on diagnosing misfires.
Check out this one.


It's quite long, but he explains the common reasons for misfires and how to diagnose.
Good luck :)
 

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Compression test.

If you happen to have a decent garage nearby, they may be able to put a clamp meter on the starter lead - you'll spot low compression cylinders as they draw no current on the compression stroke.

If compression test is good, is the ECU actually switching the coil packs to ground? Are the injectors firing ? You can test this in Multiecuscan. Could be a wiring problem.
 

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Does it run better when you raise the rpm?
If so, my money is on a vacuum leak.
If the missfire goes when you lift the revs this can also point to a valve, usually an exhaust valve not seating or starting to burn out.
To check if its sucking in air from around the inlet then spray some brake cleaner around the suspect area, if it sucks the solvent in then the revs will rise.
 

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The problem is that it takes a pretty good ear to spot a high speed missfire. You can have an engine running on 5 that still makes OK power at speed. Even harder with an 8 or 12. I once drove my V8 Land-Rover for about 30 miles with a plug lead disconnected. It seemed a bit down on power and a bit rough, but that was all. Only opened the bonnet to check the oil....
 

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I've had a perished intake flex pipe and a few coils starting to fail with resulting in intermittently misfiring at low RPM. Mid to Higher RPM generally had little misfire.

Fixing 2 coils solved bit of misfiring, then got worse, fixing the flex pipe solved a quite a bit misfiring, fixing the last of the failing coils solved the last bit of misfiring. I fixed a total of 4 coils over the last 4 months
 

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Discussion Starter #16
OK, update after a Holiday.

checked compression today....

cylinder psi

1. 145
2. 55
3. 145
4. 200
5. 75
6. 175

so, head-gasket, valve tightness, piston rings?

is there anyway i can check for any of above, before remooving the Heads?

I like to fix my car by my self in a diy garage and i need to be prepered as i need to move the car the same day. so:)
 

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If you do a 'wet' test, squirt some oil into the cylinders and then redo the test, if its piston rings then it will improve your readings, but my money is on exhaust valves starting to burn out, Im not familiar with the v6s layout but are the 2 worst readings on the same bank?
With the head off you can check if the valves are sealing by pooring a bit of petrol into the combustion chamber and see if it runs out through the valves.

Heads off, valves replace and or lapped in and rebuild isnt a job you can do in a day.
 

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You're low on the middle cylinders on opposite banks. A bit odd, unless it has running a bit crappily on 5, and now that it is running really crappily on 4 you're noticing it.

Unlikely to be both HGs at the same time unless it has been building up for a while. Ditto valves - the 2 banks are under the control of different lambdas etc.

Agree that you won't fix this in a day. Best outcome - take the heads off, get them to a machine shop, new valves etc. Day to get them off, several days in the shop, day to get them on. Worst outcome - it's rings/bores, engine out, new pistons + liners. I've done it with the engine in, but it is a lot easier to take it out.
 

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Bare minimum you should do a full top end rebuild. Don't just skim the heads & replace the gaskets. Those valves need to come out, new stem seals, re-cut the seats, grind the valves back in again.

Middle cylinder rear bank could have been on low-ish compression for years and now the front bank has caught up.

For what its worth I would 100% take the engine/gearbox out to do this work, then put the subframe back on so the car is mobile.
 

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Discussion Starter #20
Garage and parking space booked for next week, Parking space for a lot longer:-(, now only waiting for spares.
Will make an appointment with a Head/valve workshop if I conclude the heads need rebuild. Witch I STRONGLY suspect now.

I will try to make a photo montage as I have a hard time finding detailed pictures and guides online.
I have the Alfa workshop manual, but they also talk about removing aircon and oil hoses.

Any special advice when pulling the heads
 
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