Vapor lock? - Alfa Romeo Bulletin Board & Forums
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post #1 of 18 (permalink) Old 04-25-2016, 07:43 AM Thread Starter
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Vapor lock?

My GTV6 is with my mechanic. I was actually just driving it up to him to have the thing given a thorough going-over, as it's been sitting for a while.

However, this was the first time I'd driven it for more than 20 minutes in a stretch. I'd experienced some hesitation under throttle before, which I chalked up to bad plugs (they were in fact done) and timing. Possibly gas. I changed the plugs, drained the gas, checked and rechecked the timing (including advance), and hit the road.

After about 15 miles of driving the car began missing. Then bucking. Then stalling.

I pulled off the highway to a frontage road and got stuck at a light. The car died. After some panicked cranking, it came back to life, grumbling mightily, and would only stay running if I rode the throttle. Then it died again as soon as I lifted to make the U-turn to get to the shop. Then again as I crossed the street to pull in. Then it just wouldn't start at all.

My mechanic, who's an old-school Alfa pro, didn't see anything like a missing vacuum line or spurting gas or oil that would give him concern. It's gotta be internal. He's going to give the fuel delivery system a thorough check, then move to the ignition.

It feels like vapor lock, but in my experience, it takes a good long while for the fuel temp to cool down enough to restart. My car did it almost instantly the first few times it stalled. He thought it was strange that the issue got progressively worse the more I drove it.

It wasn't a particularly hot day - mid 70s. Dry air. The engine temp and oil pressure were all normal (or normal according to the car's stock gauges).

Funnily enough, when he tried to start it to move it into the garage, it fired right up.

Bottom line, this one is probably going to be pretty expensive as the testing and diagnosis is an extensive process. I can't wait to explain it to the wife! It's days like that when I just wish I had a Miata...

Any thoughts, though?

as good as a car can be... briefly.
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post #2 of 18 (permalink) Old 04-25-2016, 08:37 AM
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Vapor lock in unlikely. That is a term left over from the days of carburetors & mechanical fuel pumps on the engine block. If it got hot enough, fuel would vaporize in the fuel pump such that it would fail to pump gas. Our cars have electric fuel pumps located far away from hot things plus the fuel pressure regulator works by sending unneeded fuel back to the tank so the fuel is constantly flowing.

Anyway, with that off my chest, the engine needs three things to run properly: compression, fuel of about the right mixture and spark at about the right time. Assuming no internal derangements, that leaves fuel or spark (or both) as suspect. (one other thing - a clogged catalytic converter can allow exhaust gases to pass when cold but clog up when warmed up).

Observe the tach when the engine starts missing. The tach works off ignition. If there is an ignition fault the tach needle will drop then the engine misbehaves. If there is a fuel problem, the tach will read as the engine dies.
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post #3 of 18 (permalink) Old 04-25-2016, 08:41 AM Thread Starter
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So I replaced the ignition coil with an MSD Blaster II recently. The old one was overheating after a few minutes which would cause the car to simply die. No sputtering, no drama - just shut off.
I wonder if I didn't futz something with adapting the stock wiring, with the factory ballast resistor, to the newer, simpler hardware?
I'll have him check that first.
But if memory serves, the tach remained active as the engine choked to death.

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post #4 of 18 (permalink) Old 04-25-2016, 10:02 AM
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First, let me just say that I really feel for you with this constant drizzle of drivability issues you have. You must feel rather snake-bit at times. It seems a little unfair that my ugly '82 beater that I abuse in various ways is a picture of dependability.

If I remember right, in one of your recent threads, on over rich running, you seemed to determine that the CSI was the culprit. Did you straighten that out?

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post #5 of 18 (permalink) Old 04-25-2016, 10:11 AM Thread Starter
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Yep. New injector, and I confirmed it does NOT do its thing if the engine is warm.

Yeah, I wonder if the reason the PO was so willing to let the thing go for so few dollars wasn't because the car was snakebit. I feel like it's fix one issue, rejoice, realize something else has broken in the interim, cry, repeat.

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post #6 of 18 (permalink) Old 04-25-2016, 12:12 PM
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It's hard for me to remember exactly what you've checked so far (seems kind of like you've been over everything a couple of times), but fwiw if I were in your shoes I guess I'd start with teeing a fuel pressure gauge in and verifying that it's within spec during all running conditions.

If by chance you can't afford LSD, buy yourself a color TV. - Godard

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post #7 of 18 (permalink) Old 04-25-2016, 03:37 PM
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Maybe you have a problem with your fuel tank vent being blocked. Easy test - if you hear a rush of air into the tank when you remove the fuel cap after driving for a while...you probably have a blockage. A vacuum in the tank will probably affect fuel delivery, although the injected system is less familiar to me - On my 4cyl car, the tank even started to buckle/shrink with the increased flexing and created a small split, so the vacuum can get pretty strong. The hissing you hear could be the tank trying desperately to suck air back in any way it can.
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post #8 of 18 (permalink) Old 04-25-2016, 04:00 PM
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After building me Radio Shack Bosch Double Relay I was able to take the plastic cap off the working one? Well the right relay #2 that powers the fuel injectors was Pretty Brown the copper in the winding's of the transformer of the relay were BAD, and even though it worked I feel it was compromised. Hot weather would certainly KILL it maybe 8V to the injectors. Voltage drop NO fuel. Your chasing Ghosts try me solution $25.00 buck and a little soldering and wiring.

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post #9 of 18 (permalink) Old 04-25-2016, 06:04 PM
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Hey Alfasrule! Here's the final wiring diagram I made from your schematic.

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If by chance you can't afford LSD, buy yourself a color TV. - Godard

1982 GTV6
1973 GTV2000
1971 Karmann Ghia Vert
1982 Land Cruiser
1988 Land Cruiser
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post #10 of 18 (permalink) Old 04-25-2016, 06:41 PM
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Chairman -- I once had a non-alfa which exhibited similar symptoms. Turned out it was sludge in the fuel tank. The sludge settled to the bottom -- the car would run all day in the service bay. Take it out for a drive and after a while the sludge got sloshed around and things got ugly. Ended up having the tank hot tanked. One of the things found in the tank during cleaning was evidence of a prior sealing job peeling off. The same vehicle had rust and gunk in the fuel hard lines.
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post #11 of 18 (permalink) Old 04-26-2016, 08:51 AM Thread Starter
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We're checking voltage thru the combo-relay and also the fuel tank. Mine does seem to have excessive pressure, but it's not negative pressure (collapsing tank).
When I drained the tank there was nothing in the screen or filter to indicate sludging but I'll have it scoped, regardless. Who knows! Could even be varnish in the lines that causing a gradual drop in fuel pressure?

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post #12 of 18 (permalink) Old 04-26-2016, 03:46 PM
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My old Milano would have the same issue on hot days and the task of removing the fuel cap and screwing back in place solved the problem each time. The fuel level was pretty low each time too. My current alfetta sedan also likes the cap opened every now and then on hot days or it wont start but it runs on carbs. Just saying sometimes its just something easy but I'm assuming you have already done the cap thingy. good luck getting it worked out.

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post #13 of 18 (permalink) Old 04-26-2016, 07:20 PM
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IF removing and replacing the cap 'fixes' it for you as it did for the last poster, then it is almost certainly another pointer to a blocked tank breather. if the tank seems pressurised positively to you rather than negatively, (why do you say that, does the pressure blow into your face as you remove the cap? I found it hard to tell which way the air was going) I still smell the same rat. That shouldn't happen to a significant extent with a working breather system either.

The breather valve is easy to find and clean, so is easy and cheap to eliminate it as an issue. If you haven't already found a solution, follow the thin plastic/rubber breather tube from the tank - the valve is a small plastic T-shaped thing under the plastic cover above your rear seat back. At least that's where mine was.
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post #14 of 18 (permalink) Old 04-26-2016, 08:06 PM
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There are two parts to the breather - the little plastic valve which lets air into the system and a metal one way valve connected to the oil separator in the engine bay which relieves pressure. You need to remove the rear seat and rear hatch/boot cover to get to all the plumbing for the breather. There is also a filter/strainer in the fuel tank which is easy to overlook - you need to remove the large fuel fitting to get to it.

Having read about your ongoing sagas I'd guess it is more likely to be an electrical problem than anything else. Bad/dry solder joints tend to fail at temperature - bad wires with cracked cores can cause all sorts of issues and not be obvious. But I would also never expect to find a stray tool in the inlet manifold and that it would jam a valve open - so guessing with your car isn't going to work. You seem to have replaced most everything and electrical gremlins can be hard to find without a methodical approach and a bit of luck. Hope you get it sorted out.
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post #15 of 18 (permalink) Old 04-27-2016, 08:00 AM Thread Starter
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We're exploring the electrical issues most thoroughly. The combo-relay is a likely suspect, although it's new, as is the fuel pump. Maybe it's overheating? Losing voltage somehow? Otherwise nothing has turned up. It's not the tank itself. The injectors check out. The coil and distributor are OK. AFM is fine. Etc.

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