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Discussion Starter · #1 ·
This problem is intermittent and therefore difficult to diagnose or, worse yet, expect until it happens. Sometimes (it doesn't seem to matter the weather conditions or ambient temperature) my 1978 Spider doesn't have enough power to rev to or beyond 3,000 RPM without shuddering uncontrollably. This shuddering gets so bad that I push in the clutch, downshift, and as a result the car will die. This has always happened around town and in all gears. This problem seems to arise after the car has been sitting overnight, but it could also happen while I have been driving it for a period of time and the car is hot.

I haven't had any trouble in the last week but this problem arose again last night and am not sure what to do. Does anyone have any ideas? Thanks in advance!
 

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I would suspect an issue with fuel delivery. Perhaps the pump is not putting out enough pressure (need to check the pressure), or something is clogging the system (use Techron first to try an clean it). Another cause could be that something with the distributor assembly is loose, such as the bracket that holds it. These type of issues are not that easy to diagnose over the BB, but you could start with what I said, and certainly search for threads covering these topics. Hopefully, others much more knowledgeable than me will also chime in...

Best regards,
 

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I'm not claiming more knowledge! Basically your engine needs a few things to run right. It must be in decent mechanical condition (rings/valves/compression). We can rule that out as something wrong there wouldn't tend to come & go.

Then it needs to mix fuel & air and ignite it at the right time. Here's where the problem lies - a fault in either of those systems (or both) could explain the trouble.

What is the condition of the air & fuel filters? Does it seem to happen if the fuel tank is below 1/2 full? Does it happen when the engine is fully warmed up or even while it is still cool? Do you have SPICA FI or carbs? How old is the distributor cap, rotor and the spark plug wires? How old is the coil? And what color is your car? (that has nothing to do with the problem but Click & Clack always ask that on Car Talk to stall for time...)
 

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Discussion Starter · #4 ·
Thanks, Zunige. I put Techron in a couple of nights ago hoping it would help. The car ran great that night and I thought that the issue was solved; however, the next morning I was having the same problem again. I agree that it probably has something to do with fuel delivery, but why would the problem be intermittent? Also, how would I check the fuel pressue?

Thanks.
 

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Discussion Starter · #5 ·
I put in a new air filter about a month ago, but haven't checked the fuel filter. The problem arises seems to arise more often when the fuel tank is full or when it is about 1/4 full. However, this problem has also occurred when the tank is 1/2 full and 3/4 full. Also, the problem can arise when the engine is cold, warming up, and hot. The problem seems to be more prevalent when the engine is cold and warming up. The Spider has SPIKA fuel injection. I've replaced the the distributor cap, rotor and spark plug wires within the past month.

And finally, the Spider is red with tan interior.

Thanks for all of your thoughts...
 

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Try this: when the car is running right, make note of how warm the coil feels. Then see if the coil is really hot when it acts up. If so, consider replacing the coil.

But it does sound like a fuel delivery problem. I hear that red cars with tan interiors are especially prone to that...
 

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Assuming that the car runs normally at least part of the time, my first thought went to fuel filters and the possibility of crud in the tank, as others have mentioned. So, to eliminate that possibility -- and because it sounds like it's time --I'd change the fuel filters.

However, the ignition system seems a more likely possibility. While fuel supply issues can cause the car to stumble, stall, or not rev past a certain range, the "shuddering uncontrollably" sounds more like an electrical fault.

I'd go back through the ignition system and check it out carefully, considering that one of the recently changed parts might be the problem. Then I'd look for a loose wire or a bare wire that is shorting (ignition switch through distributor and coil, everything in the ignition system with a wire to it). I'd also check the fuse block, spin the fuses (if you have that type) and generally make sure that all are held securely.
 

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I'd go back through the ignition system and check it out carefully, considering that one of the recently changed parts might be the problem. Then I'd look for a loose wire or a bare wire that is shorting (ignition switch through distributor and coil, everything in the ignition system with a wire to it).
I'll second that. I've just spent a frustrating few weeks trying to track down a similar problem which was partly carb set up but also a loose condenser on the side of the distributor. This was shaking the connection inside and partially shorting above 3000 rpm. I only discovered the problem when finally the screw fell out and the engine died completely.
 

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Dpo,
does the tach remain normal or does it jump back and forth from normal rpm down towards zero quickly during the engine shake. If so, it surely indicates loss of ignition pulses. If it remains fairly steady it tends to indicate fuel supply problems. I had this happen on one of my other cars and it turned out to be a wire inside the distributor that was broken due to repeated flexing between the side and the vac advance disc.
 

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Dpo, does the tach remain normal or does it jump back and forth from normal rpm down towards zero quickly during the engine shake.
A useful guide if you have an electronic tach but my 1968 is cable driven. I think they made the change in 79/80 so this may not apply to Dpo's car.
 

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I had a similar problem just a couple months ago.
I had replaced fuel filters, rotor, cap, plugs, points and capacitor.
I drove it a couple hundred miles and suddenly had the stuttering and lack of revs.
I think 2500 rpm was around my limit. It turned out to be a faulty ignition capacitor.
Good luck, intermittent problems can be extremely frustrating.
BTW, Mine is Brown and Tan.
 

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Rev to or beyond 3000 rpm? so it idles fine at 1000 to 1500? Could be as simple as failing motor mounts. Mine went on my 79 Spider and it sure makes the car vibrate!
 
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