Puzzling fuel system symptoms '86 spider

[espresso veloce]

I drove my spider down to Nashville a few days ago, which is a 375 round trip. I had no problems driving down, but when I finished my business and started home, There were a couple of brief hesitations while I was going down the street, getting ready to climb on the interstate. It was as if someone had switched off my fuel supply for an instant--like flicking a light switch. I got on the interstate and drove home, with no problems for the remainder of the day.

The next morning, I started up the spider and drove a couple hundred feet to the end of my driveway, then as I pulled out into the street, the engine again acted like its fuel supply was being cut off. I ended up stopping in the middle of the road for a few seconds, while the engine struggled for fuel, but then it was fine. Just the same, I backed up and drove the car back down the driveway and parked it for the day.

This morning, I changed out the fuel filter (I had an extra) and I checked and cleaned the AAC, as well as looked for loose or dried-out hoses. I started up the engine and it seemed, at least until the engine warmed up, like there was a "stutter" in the fuel supply, a mild throbbing when I tried to hold the engine at a steady idle. It seemed to fade away after several minutes.

Any suggestions as to what would cause this sort of throbbing on the fuel supply? Is this an obvious symptom? My instinct is to suspect one of the fuel pumps, but there are so many sensors that it's just hard to say. I'm not sure I'm ready to get stranded at the side of the road, so I'd like to catch this before it goes completely.

Tim

[jarrington]

Quote:

Originally Posted by espresso veloce I drove my spider down to Nashville a few days ago, which is a 375 round trip. I had no problems driving down, but when I finished my business and started home, There were a couple of brief hesitations while I was going down the street, getting ready to climb on the interstate. It was as if someone had switched off my fuel supply for an instant--like flicking a light switch. I got on the interstate and drove home, with no problems for the remainder of the day. The next morning, I started up the spider and drove a couple hundred feet to the end of my driveway, then as I pulled out into the street, the engine again acted like its fuel supply was being cut off. I ended up stopping in the middle of the road for a few seconds, while the engine struggled for fuel, but then it was fine. Just the same, I backed up and drove the car back down the driveway and parked it for the day. This morning, I changed out the fuel filter (I had an extra) and I checked and cleaned the AAC, as well as looked for loose or dried-out hoses. I started up the engine and it seemed, at least until the engine warmed up, like there was a "stutter" in the fuel supply, a mild throbbing when I tried to hold the engine at a steady idle. It seemed to fade away after several minutes. Any suggestions as to what would cause this sort of throbbing on the fuel supply? Is this an obvious symptom? My instinct is to suspect one of the fuel pumps, but there are so many sensors that it's just hard to say. I'm not sure I'm ready to get stranded at the side of the road, so I'd like to catch this before it goes completely. Tim

[espresso veloce]

I'll take a look at that, Jason, thanks for the suggestion.

Right now, the car is running like a champ. I guess I'll have to drive it for a few days and see what happens. So far, I've checked several things, but none of them appeared to have a problem.

Tim

[jarrington]

See if the problem gets worse as your fuel level drops. By the time my car got down to 1/2 tank or so it was pretty bad.

-Jason

[espresso veloce]

Okay, now I'm really stymied. Jumped in the spider today. Drove to work. it was fine. Drove to the gym. It was fine. Drove back from the gym. It was fine. Drove to a restaurant, it was fine. Drove to Target. It was fine. Left Target and sat idleing for 5 minutes while I made a quick phone call. Couldn't get the rpms over 2,000, no matter how hard I hit the pedal. Went like this for 15 minutes. Decided to try pulling out of the parking lot, and was limping along until all of a sudden I have full RPMs and power. It lasted through second and third gear, then was back to no power. I limped 12 miles home like this. When I got home, I pulled up to the barn, and decided to pump the pedal a few times, and suddenly the engine cleared right up, was running fine.

Okay, if this was my Harley, I'd say that one of the cylinders wasn't firing, but it sure sounded like all four were going when it was at idle. I don't know. This is blowing my mind. So, what exactly does the accelerator pedal do? I suddenly doubt this might be a fuel pump problem. It was hot today, but this was the end of the day.

Okey Dokey, who's got great Alfa intuition? I really could use a clue.

Tim

[rgsspider]

Admittedly I am a complete novice at this but could it be a gunked up fuel injector? Maybe a bottle of fuel injector cleaner would do the trick?

[espresso veloce]

I think one question that I need answered is: How well does a 2.0 Alfa engine run on 3 cylinders? Does my description of the symptoms match an engine running on just 3 cylinders? If the answer is yes, then I need to figure out which cylinder is getting fouled up.

What I can't figure out is why pumping the gas pedal hard cleared it up. Does that cause the injectors to get more pressure or something? It seems to me, that if it was a fouled plug, after 12 miles of driving, it would be a lost cause--at least that's the way it always was on my Harley.

In any case, I'm still driving my spider. It's running beautifully this morning. I feel like I won't get close to the answer if I don't experience the problem in all of its nuances. I'm going to order new wires, get some plugs, and new hose, and start updating what appears to be all original parts.

Tim

[Russ Bellinis]

Has it always happened in hot weather? Sounds like you might be getting a vapor lock.

[Tifosi]

Quote:

Originally Posted by espresso veloce What I can't figure out is why pumping the gas pedal hard cleared it up. Does that cause the injectors to get more pressure or something?

[espresso veloce]

I've got to admit, we're having a heat wave right now, with the temp hovering in the high 90's. And come to think of it, the problem has come up both times after the heat of the day has passed and things cooled off just a little.

Russ, can you describe the vapor lock condition a little more, as it pertains to Alfas? What's the best way to address it?

[espresso veloce]

Tifosi, those are some good thoughts. It's not the fuel filter. I put a new one in over the weekend, and I checked the old one. It wasn't clogged at all, and fuel was flowing fine through it.

I was thinking of low pump pressure, but that doesn't explain how it keeps coming back, unless it was an electrical issue. I have doubts about it being electrical, because when I sat in my barn last night and started hitting the accelerator pedal, the car wasn't moving and suddenly everything cleared right up.

I will check the tank breather valve. I have to admit, vapor lock seems to ring with me, on at least an intuitive level. I pulled 3 out of 4 plugs when it was giving me fits and all were dry, and I'm betting the one under the air plenum would have been dry too, if I had pulled it. There was no trouble starting, so it seems like I was getting fuel and spark to all cylinders, but maybe it only seems that way because I've never heard the engine on 3 cylinders.

What sorts of causes are there for vapor lock?

Tim

[Tifosi]

A few would be: Hot road under fuel tank that's painted black, (that used to be a real Spica issue IIRC, to the point where tanks were repainted silver as a fix. Can't see why it may not also apply to the Bosch system), fuel boiling or atomizing in the pumps (turbulence making bubbles), breather system for tank partially/fully clogged, hot engine boiling fuel in the rail or feed line, pixies, imps and those nasty gremlins.

I'd lean more toward pixie or imp as the gremlins tend to break stuff outright in an effort to get you killed, where-as the other two tend to just be nusances or pesky for sport.

For giggles and something else to try next time it does it and you have time, tools and inclination, wait for it to run goofy then while it's still doing it pinch off the regulator return line with some pliers (protect the line with cardboard or something so you don't cut/gouge it) and see if it improves.

If it does, you could be looking at a pressure or volume thing.

Pressure would be pumps and lines or regulator proper, (thus giving you cause to check the pressure properly), while volume would be more relative to tank breather, filters and restrictions, (though pumps could just be pushing slow too).

Query:

When you changed the filter, did you also change the filter sock on the in tank pump?

It too can get clogged, or worse yet, wad up and block flow. (which will magically clear itself up after you shut down the engine and the pumps stop running long enough for the sock to 're-settle')

While in there you should check the short rubber line that goes from the in tank pump to the rest of the in tank junk for tight fit and no cracks. (it'll cause really ignorant stuff to happen from about 1/2 a tank or less in the cell but can be just fine from 3/4 tank to full if it's faulty)

[espresso veloce]

It sounds like I really need to check my fuel pressure coming through the system to either isolate it, or knock it out of consideration. I don't have the proper equipment to do that--yet. I need some sort of inline gauge, right?

My guess would be imp. I think only an imp would make me drive home 12 miles with no more than 2k revs on the engine, and then completely cure the problem once I was parked at home. Gotta love 'em.

What is the most common cause of vapor lock? Tank breather?

Tim

[Tifosi]

Tank breather/ventilation or something boiling fuel are the general causes.

When I was going through simular issues on mine I permanantly fitted a pressure gauge into the system so I never have to wonder again, nor is having a gauge laying around on the shelf doing nothing a concern. (certain tools I don't mind a 'once in a lifetime' use, but gauges I don't like sitting around as they generally fail before you need them again)

If you're interested, see this post for a description and part # for what I did and this post for a pic of it in the bay.

[jarrington]

If you're really hurting for a fuel pressure gauge I have a full-on, honest-to-goodness Bosch Jetronic fuel pressure testing kit out in the garage. I've never used it but have no reason to believe it doesn't work. If you need it just pay the shipping, then send it back when you're done.

-Jason