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Discussion Starter #1
Tried starting my stored 3.0 last week, and not enough petrol in tank, backfired big time. Now got fresh fuel, starts and then dies. AFM moves freely, plenum hasn't blown off, all pipes still look good (replaced everyone anyway), wiggled all connectors etc, did run really nice last time I started it about 3mths ago. Being UK car no emissions stuff (cat etc). Any ideas?
Thanks
 

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Used to happen a lot on my GTV6, but the plenum would pop off, I always had to pull plugs and clean them prior to getting it to restart. Just my thoughts.
 

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Cracks in the rubber air duct from air flow meter to engine? Does the AFM move freely off the stop, I had one a long time ago that moved freely, except right off the closed stop.
 

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Double check the plenum couplers. This happened to me when my distributor failed and although it looked ok, some of the plenum couplers were leaking air after the backfire. Took a while to sort out all the air leaks after the "big backfire".
 

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Discussion Starter #5
Thanks guys. Took accordion off, looks good, wacked plenum with rubber mallet, now runs rough. Battery on trickle charge as hasn't been used for awhile. Maybe plenum did move, will loosen couplers tomorrow and wack again. Replaced plenum couplers awhile ago, so they should be ok. A wise old Alfa mechanic told me long time ago not to overtighten the couplers, oops!!
 

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"Tried starting my stored 3.0 last week, and not enough petrol in tank, backfired big time"

Did you have your foot on the gas pedal? You cannot open the throttle when starting the GTV6s and the Milanos when doing a cold start. You will get what you did.

Once it starts running, then ok.
 

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No, didn't think you would but sometimes stuff happens. We've had our 89 Milano since new, and yup, one day, pop goes the weasel. Brain fade, lol. I don't know about low fuel being a cause of that certain phenom.
 

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Worth doing valve timing check while you’re head scratching, in case the belt jumped a notch?
My son’s gtv6 bent a valve or two after a backfire.
 

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When I drove a Milano with L-Jet I deliberately left the couplings from the plenum to the runners a little loose so that the plenum acted as a relief if I had a backfire. It saved other things from damage. At that time, in addition to being an engineer I also coached at a high school. One day after school I went to start the Milano and it backfired.I opened the hood, did a visual check and replaced the plenum. When I restarted the car there was a loud cheer from a crowd of kids who had been watching the whole thing. They probably thought that it was pretty cool.
This does not happen with Megasquirt, it is an L-Jet thing.
 

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Discussion Starter #11
Battery fully charged and still running rough. CSI working as revs drop after a minute of starting. Will get my timing template out tomorrow and check, will remove plugs to turn to TDC and check and recheck all hoses again. Thanks Ed, do know about the runners being a bit loose, as mentioned cryptically before, and yes maybe foot did go on accelerator pedal a bit Del, but NOT on the gas pedal 😂
 

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Ah, ok. We over here just say gas pedal or go pedal. Was raised on British cars at first, Minis, MGAs, and Austin Healeys, pressing on the gas pedal sometimes did not cause the car to accelerate, lol.
 

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Discussion Starter #13
Checked timing today with template, and spot on. Spark plugs could do with changing (valve guide seals need doing), but run ok before so assuming these aren't main culprit, will get some more anyway. Wondering if Ive pulled some crap into fuel filter. All FI hoses have been replaced and all air hoses, cant see any splits. Any ideas guys?
 

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Knowing it DID run ok before the backfire, and knowing that minor work on the plenum/big air intake seemed to improve conditions, I would still be chasing an air leak. Maybe take the plenum off and reseat/retighten just to be sure the cause of the issue isn't an air leak there? It's not much work and you can see a lot more with it off than on.
 

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Use an unlit propane torch to find an air leak with the engine running. Just waving it around in certain areas will locate most air leaks, as the engine revs up a little. Not dangerous at all. Did this with my LS when the check engine light would come on every once in a while. Was curious so did this, and found a hidden cruise control vacuum hose pulled off. Reconnected that and it's been fine ever since.
 

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Discussion Starter #16
Put 6 new plugs in, took plenum off, checked all couplers still runs really rough, thinking of getting some Normfest spy dry to check for leaks. Running out of ideas!
 

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Have you checked the static distributor timing? Is the roughness enough to kill it? A full leak test sounds like a good idea to me.
 

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Some brake cleaner also works wonders to find vacuum leaks. Just spray a bit on suspected parts and the idle will change. Not as safe as the propane burner trick, but everyone who works on Alfas has a can of brake cleaner right?

Does it only idle rough, or can you rev it up and is it still rough?

Also I dont know about your storage conditions, but in some places 3 months is plenty enough for rodents and stuff to chew at wiring. So an extra good look around never hurts.

Also do not fall in the trap that because it was running right before that certain things can be ticked off your checklist.
Especially since you had a backfire that mightve knocked some things loose that were working before.
 

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Discussion Starter #19
Felt my ears burning from another post. Changed fuel filter and checked thermos time switch (cross terminals 32.5ohm, top to gnd 0.7ohm and bottom connector to gnd 32.6ohm), coolant temp 2.7K across terminals so all good. Still rough. Will now take cam covers off and check cam marks, although template is pretty accurate. In no hurry as not the only one keeping it in storage (in dry garage below house) whilst kids grow up (nearly finished uni) and take all my money. What damage can be done to AFM/Throttle body by backfire?
 

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The AFM vane can be bent by the force of a backfire. If that happens, the vane can then rub on the housing giving erratic movement.
 
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