Jerking While Accelerating? - Alfa Romeo Bulletin Board & Forums
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post #1 of 23 (permalink) Old 12-27-2018, 08:10 AM Thread Starter
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Jerking While Accelerating?

Tried to take my '82 Spider out yesterday and while it started up fine once underway it began jerking while accelerating and shifting. My first thought was water got into the gas tank, but after googling a bit (I am a rank noob when it comes to mechanical stuff) I think it might be moisture under the distributor cap. The car has been parked outside with a car cover on it while my garage is getting sorted, and there's been a bit of rain in NorCal over the past several weeks and a fair bit of condensation on the cover even when it doesn't rain. Anyone have a similar problem or think this might be it? If so I assume its as easy as marking and disconnecting the spark plug wires, removing the cap, and drying it out then putting everything back together (and finding somewhere warm and dry to park it for the rest of the winter!).

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post #2 of 23 (permalink) Old 12-27-2018, 08:21 AM
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Your theory has merit. You need not remove the spark plug wires - just release the two clips and the cap comes off the distributor. Wipe the inside dry - a squirt of WD40 might help (the WD supposedly stands for Water Displacement). Also clean the spark plug wells - debris & moisture can collect there.

Another possibility is an intake air leak. Our cars are very intolerant of intake air or vacuum leaks. Make sure all the air duct's connections are secure. I suggest you remove the large black duct from the Air Flow Meter (AFM - on top of the air filter housing) and inspect the accordion section closely for splits. These splits can open & close as the engine moves on its motor mounts and really mess with the running. All air entering the engine must pass through the AFM so the computer knows how much fuel to inject. Such leaks are called 'false air' since they go unmetered.

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post #3 of 23 (permalink) Old 12-27-2018, 11:29 AM Thread Starter
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Thanks @ghnl. Unfortunately not the distributor cap and no air leaks that I could detect either (all the ducts and filters were recently replaced; fuel filter too). Took me a while to figure out how to get at the distributor cap clip (had to remove the radiator overflow to get at it), but once I popped it off it was bone dry. Started up fine again but less than a half block in she started kicking and bucking again, and barely made it back up a modest grade. Seems like this one is probably beyond my pay grade :-) so unless someone has another idea its off to the mechanic she goes.

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post #4 of 23 (permalink) Old 12-27-2018, 01:00 PM
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Fuel filter was replaced? IIRC, there is a special hose there - it is formed in sort of a U shape. If that hose is replaced with a piece of regular fuel hose it can kink and shut off fuel flow. Since the U shaped hose is NLA the key is to replace it with a long enough hose that it doesn't need to make a sharp bend (so it won't get kinked).

Also check for tank venting. As fuel is pumped out air has to come in or a vacuum develops in the tank. In the compartment just forwards of the trunk is the vapor recovery tank and a one-way valve & air inlet valve. Either valve can get gummed up and prevent proper venting of the tank. A quick test is to remove the gas cap when the engine is misbehaving. If there a rush of air and the engine then behaves, the tank venting needs service. The valves can be cleaned with some squirts of carb cleaner. Make note of the correct orientation of the one-way valve so you can re-install it correctly.
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- -~ 1981 GTV-6 ~
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post #5 of 23 (permalink) Old 12-27-2018, 02:34 PM
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Could also be a fuel starvation issue. Bad in-tank pump or bad stepped hose can give these problems as fuel sloshes around while moving.

What is the fuel level in the tank?
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post #6 of 23 (permalink) Old 12-27-2018, 02:45 PM Thread Starter
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Thanks again @ghnl. The filter hose looks fine and isn't kinked (APC in Orange, CA did the work so I did not expect to find anything there). I did remove the gas cap and no rush of air. I saw the vapor recovery tank but haven't had time to try to fiddle with it yet. I may not get this fixed on my own but its still been fun and worthwhile learning a bit about how it works and getting my hands a little dirty along the way. :-)

Tank is about half full @sloboy89. That is, if you believe the gauge.

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post #7 of 23 (permalink) Old 12-27-2018, 03:00 PM
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Quote:
Originally Posted by eatmydust View Post
Thanks again @ghnl. The filter hose looks fine and isn't kinked (APC in Orange, CA did the work so I did not expect to find anything there). I did remove the gas cap and no rush of air. I saw the vapor recovery tank but haven't had time to try to fiddle with it yet. I may not get this fixed on my own but its still been fun and worthwhile learning a bit about how it works and getting my hands a little dirty along the way. :-)

Tank is about half full @sloboy89. That is, if you believe the gauge.
Try filling the tank and see if that solves the problem. I had a similar condition that turned out to be a bad in-tank pump.

Rich

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post #8 of 23 (permalink) Old 12-27-2018, 03:37 PM
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Rich has a good idea. A failed in-tank pump or faulty stepped hose will often reveal itself with running problems when the fuel level is below 1/2 full. Attached is a photo of the stepped hose. Be sure you are sitting down when you check the price of a new one.

A no-cost test you can do is to remove the vacuum hose from the Fuel Pressure Regulator (FPR - see arrow pointing at it). There should be no evidence of gas on the vacuum side (sniff the end of the hose). If present the FPR is likely faulty.
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post #9 of 23 (permalink) Old 12-27-2018, 07:27 PM
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Pull off that big air intake hose and check it for cracks, as the engine rocks a little a small crack will open up and introduce extra air causing it to run lean.

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post #10 of 23 (permalink) Old 12-28-2018, 06:39 AM
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I had the similar (water in gas , wet wires, ect) symptoms. There was a small crack in the big intake hose, changed it , runs great !

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post #11 of 23 (permalink) Old 12-28-2018, 07:56 AM
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Originally Posted by eatmydust View Post
Thanks @ghnl. Unfortunately not the distributor cap and no air leaks that I could detect either (all the ducts and filters were recently replaced).
Just because the crossover intake air ducts we're "recently replaced" does not guarantee there are no air leaks created when the engine twists on it's motor mounts under acceleration. Actually, the fact that those were "changed" or "adjusted" just prior to the problem being noticed tends to indicate the fault may lie there. It is not uncommon for one of the large hose clamps to create an air leak just by being slightly too tight or too loose, and I have heard rumors that some of the new crossover tubes are a little bit shorter in length and can be a source of connection issues. All that being said, don't be too quick to cross off the possibility of an air leak as the reason for your performance irregularities during acceleration.

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post #12 of 23 (permalink) Old 12-28-2018, 10:36 AM
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Another vote for a loose or cracked/split air duct. Here's another anecdote: we bought our GTV6 (also L-jetronic FI) in Texas. On the drive home to North Carolina I stopped to fill up the gas tank and about 10 miles later the engine started to buck & skip. I feared I had bought a tank of bad gas. I nursed it to a safe place to stop. With the hood open I couldn't see anything amiss and the engine was idling fine. Poking around I discovered the intake air duct was barely connected to the AFM. With the engine idling it was touching but when trying to accelerate the engine would rock and pull the duct away from the AFM. Then, when coasting, it'd settle back and rest against the AFM and run OK.

- - Eric
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- -~ 1981 GTV-6 ~
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post #13 of 23 (permalink) Old 12-28-2018, 11:43 AM Thread Starter
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Thanks all. I did check the air duct and the connections were all tight and there were no visible cracks or gaps that I could detect. The vent was also still very pliable, not brittle like you get with the hoses that have been on for a while. Still it is possible there is a hairline there somewhere that I couldn't see.

It just seems like there should be a connection between the moisture (rain/car cover condensation) and the skipping, since that is when the problem started to appear. But should be ain't is.

The in-tank pump failure would be consistent as well, so I had it towed to the mechanic yesterday evening so he can take a look, as replacing that would be beyond my tools and capabilities. I hope you all are right and its just an air vent issue I missed, but I will check back in and let you all know once I get a diagnosis.
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post #14 of 23 (permalink) Old 12-28-2018, 12:21 PM
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although my 1st guess (as others) would be the big air hose, it could also be a loose or shorting wire somewhere on the intake side, exasperated as the engine moves under acceleration.

Or, even a loose battery cable...that can happen!

Anyway, let's wait and see what your mechanic comes up with...it'll be interesting.

Dom - Alfa Spider 1990 S4 - formerly: Alfa 101 Sprint, 2600 Sprint, Montreal - family classics: Jensen Interceptor II, '58 Hooper RR Silver Cloud I, Shadow II, '60 Corvette.
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post #15 of 23 (permalink) Old 12-28-2018, 12:46 PM
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I had a similar issue with my 86. The bucking was mostly off idle. I had already gone through whole intake system, replacing hoses and checking for leaks. I figured no way was it a vacuum leak. Thought of every possibility like you are. I finally took a stethoscope and listened everywhere...... small hose on the bottom of plenum was the culprit. That stethoscope is now hung proudly on the garage wall, my go to Alfa tool......
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