USA Fiat 124 Spider 2 liter engine dies - fuel starvation?

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Yunko
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USA Fiat 124 Spider 2 liter engine dies - fuel starvation?

Post by Yunko »

I have a 72 Fiat 124 Spider with a 2.0 litre engine.

I am running a 34AFD carb, mechanical fuel pump, and replaced the fuel sending unit.
I have blown out the fuel lines and replaced 80 percent of the rubber fuel lines and I am still experiencing fuel starvation or vapor lock.

Always when the engine is at running temperature and I have driven 8 - 10 miles it just dies on me. I have gone to an electric fuel pump (Facet) 3-5 psi and put an in line fuel pressure guage on the car. Pressure gauge reads 4psi and drove the car 10-15 miles in 109 degree temperature and when I got home checked the pressure guage and it was fluctuating between 0 and 1/2 psi. I know the electric pump is a temporary fix and don't want that.

Can't figure why car does not run with a mechanical fuel pump.
Guy Croft
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Post by Guy Croft »

First please do an essential test.

Drive the car with the mechanical pump only connected - on a safe, quiet road - till it dies on you as described - and then take off the air cleaner and remove the carb top cover and confirm that the float chamber is actually empty. If it is empty hook up the Facet pump to get you home. If it's not, the likelihood is that the mech pump is not to blame.

Examine the layout and how it's disassembled before leaving so you know what tools to take, on some carbs the choke mechanism & levers etc get in the way of that strip and you mustn't let anything fall in the carb barrels.

Please advise the result of that test.

GC
sumplug
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Post by sumplug »

Two things spring to mind here.
One, is the tank pickup is getting blocked, due to something floating in the tank, or/and the tank is not venting properly.
Where is the electric pump fitted? Engine bay fitment will cause problems.

Andy.
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Post by leifa »

sumplug wrote:Two things spring to mind here.
One, is the tank pickup is getting blocked, due to something floating in the tank, or/and the tank is not venting properly.
Where is the electric pump fitted? Engine bay fitment will cause problems.

Andy.
I would guess venting problems. Try driving without the filler cap and see if the problem is gone. An other way to diagnose is to unscrew the filler cap when the fuel pressure is gone, and try to hear if air gets sucked into the fuel tank. If this is the problem then take a look at your fuel tank. It has probally shrunk. To correct this use pressurised air and a blow gun and blow carefully trough the filler hole, sealing of with paper around the blow gun. This should restore your fuel tank to its original volume.
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Yunko
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Post by Yunko »

GC,

After testing the car running the mech pump the same situation happened. Removed top of carb and there was fuel in the bowl. Connected electric pump and drove home. Couple things to mention is the carb is new but was never adjusted in any way, however, I was experiencing the same problem with the old carb on the car. Awaiting your advice on what to do next.
Guy Croft
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Post by Guy Croft »

OK, not straightforward.

Possible scenario as suggested by other members is tank vent misbehaving. Maybe it will allow either pump to suck enough fuel to go, say 10 miles and then effectively block further fuel delivery by creating vacuum in the fuel tank. I'm guessing here but the fact that the electric pump can then get you home may be simply that by swapping the fuel line over the vacuum is released.

However:

If there is fuel in the carb when the motor stops it cannot have stalled due to fuel delivery per-se. The carb float chamber is vented to atmosphere (or should be, make sure it is not sealed off by the air filter etc) so the car should keep going - even with a defective pump or feed line/tank until the engine stalls at which time the float chamber will be totally bone-dry. You have a conversion carb, you do need to check that the carb vent is clear.

I am wondering whether this is actually a faulty ignition coil (or power pack if Marelli electronic). I know that when a power pack or coil is defective it will cut the spark, then after cooling down a bit it works again, eventually it packs up altogether. I think I might be for pulling off an HT lead and cranking the engine to see if there is a healthy spark when it stalls. No spark and you've got the answer. A two person job that one really. That intermittent coil/amp unit fault by the way is almost impossible to detect with diagnostic equipment, and I only know about because I ran TCs for years and experienced it myself.

Other suggestions welcome, but no wild guesses please, experienced observations only - and read thru the issues already mentioned carefully before posting please.

GC
Last edited by Guy Croft on July 5th, 2007, 2:41 pm, edited 1 time in total.
sumplug
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Post by sumplug »

One way to test if its electrical. Does the ignition lights come on the dash when it dies? If so, its an electrical problem.
The Weber 34 ADF has a fuel cut off solenoid on the carb housing, which cuts the fuel when the ignition is turned off. This maybe faulty, but i doubt it as the chamber has fuel in it. Also check for vacuum leaks around the carb.
How far are the fuel lines from the exhaust manifold, and has the manifold got a heat shield attached?

Andy.
Yunko
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Post by Yunko »

Ran electrical fuel pump today and it died after 11 miles. Checked float bowl and there was gas in it. Before it died the pump started to tick loud just like when I first srart it up in the morning. It would get quiet and all went well then it would start ticking loud as if it was really working hard.

Was able to dirve it home the next two miles after I put the carb top back on but the pump would get loud then quite then loud.

Fuel lines are on the opposite side of the headers. Metal in line fuel filter in the engine bay. I did remove the gas cap when there was no pressure but I did not hear any air being sucked into the filler neck.

John
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Post by sumplug »

This was happening on my Fiat 131. It would go for a distance then conk out. Leave it for a few minutes, and it would be fine again. When i removed the sender unit, wrapped around the pick-up pipe gauze, was a piece of cotton fabric/thread. This would only happen on a 1/4 tank. Fill it up, and it ran sweetly.
You have not said if the dash lights come on when it dies. It could still be electrical.

Andy.
Yunko
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Post by Yunko »

The only light that comes on is the alternator light and that is only because the ignition is in the on position. Believe me, the dash lights on the 124 spider are normally so dim I wouldn't see them come on in the day time. I will conk out at 1/4 or full tank, does not matter.

My fuel sending unit is new, although when I replaced it, the mesh web around the old one was totally gone. Looks like it had been gone for some time.

Was not able to check spark on coil. Will do that this weekend when I have a buddy in the car with me.

Without the electrical pump on, I didn't realize how hard that pump had to work to get gas to the carb. It was really laboring before it conked out.

Other than the main and return fuel lines that go from the sending unit to the carb there are four (4) additional lines that come from the tank. One looks to be a larger vent line going to the fuel filler neck. Three of them go from the tank to a canister mounted in the trunk next to the filler neck, and there is one more that goes from the canister into a plastic valve then directly to the front of the engine bay and is connected to the fuel vapor canister. Actually, the last line I am talking about just vents into the atmosphere. The vapor canister has not been there for 15 years. I am not running any emissions on my car whatsoever. I do have a fuel vapor canister and know where the in hose goes but where does the out hose go, carb, or intake manifold? Not sure this would solve the problem as I have driving 15 years without any problem.
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Post by Guy Croft »

John, hi

the original emissions control system is pretty complicated, there are many pages to this, I have a copy for the 2lliter Brava which is probably the same layout. I'd have to photocopy and mail it, there may be someone stateside who can do that. There are all sorts of hoses/lines and in-line check valves and compensators etc etc - any of which could cause a problem.

Irrespective of whether this turns out to be a fuel delivery problem I would be tempted to overhaul the fuel lines entirely:
Run one feed line from the tank pickup to the mechanical pump only, and one return line from the carb back to the tank, retain the tank vent to atmosphere that normally is connected to the charcoal canister and strip out/blank off everything else. That will at least rule out a failure in any of the OE system and guarantee that the pump can get and deliver fuel.

If your system has the thermostatic valve in the air cleaner check that it's functioning properly and not starving air.

Good luck with the ignition test.

GC
sumplug
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Post by sumplug »

All you need is one or two venting pipes to atmosphere. Any others, just blank off.
I think your tank needs to be dropped and cleaned out as the pump is struggling to get fuel up to the carb. But check those pipes first to see they are clear.

Andy.
Yunko
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Post by Yunko »

Drove home today ignoring the stop and go traffic. I drove on the freeway with the gas cap off and the fuel pump was as quiet as could be. After 8 or 9 miles the fuel pump started ticking. Another mile or so it became louder, and at the 11 mile mark started to choke for gas. I was lucky and just made it home. I will replace all the fuel lines, and even if it is not fuel related it is a good idea. I will post a picture of my tank with the fuel or vent lines so you will have an idea of what is there. I found a new tank on e-Bay for my year and noticed it only had the feed line and return line from the sender to the carb and only the larger pipe for the vent line to the filler neck. It eliminated the other lines and canister I have in the trunk. Just a thought, even though it is a new carb, could the air and fuel mixture screws need adjusting? Also I have a brass nipple just like the ones the feed line and return lines go to on the carb and it is just sucking air. No instructions or idea what line connects to that if one does at all. Seems to me it should have a hose to it or it should be plugged off. I will post a picture of that as well. Thanks so far GC and Andy. I am sure we will figure this problem out.
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Post by mdburchette »

The original 72 model had the line going from the charcoal canister to the intake manifold. Thought you'd like to know. This problem is very perplexing. I felt sure the problem would be solved once you loosened the fuel cap. Good luck!
Yunko
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Post by Yunko »

Now this is strange‚¦.Actually, I am very upset unless this was done for a purpose but it sure doesn't make any sense to me. I was inspecting my fuel lines going to and from the carb and as I was squeezing the fuel lines I felt something hard inside the fuel return line about 1 inch from where it connects to the carb, and come to find out that someone put a carb jet inside the line. Now I have had my car worked on by two different mechanics and neither of them said anything about putting a carburetor jet inside the fuel return line. Was this a trick of the trade to try and cure the fuel starvation problem I have been having or did someone sabotage my car. I am dumbfounded. Is this a common practice or was someone playing a bad joke on me :?:
I know I never put that there.
John
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