Running Issues - advice needed - UPDATE:

Just a brief update on my last post about the 355 and its rich running issues, Thanks to all who chimed in - appreciate all you knowledge and pointers.

Right, have fitted a replacement exhaust valve and took the car out for a test drive yesterday. Now, I have never driven a 355 with a working bypass valve so didn't really know what to expect or how it might change the cars behaviour. Have to say, performance seems a bit "flat" and docile after an unrestricted exhaust. Car's a lot quieter as you'd expect relatively speaking - so the neighbours and wife will be happy - but I can't say that I can tell if the by-pass is opening or not !.

Any pointers apart from the noise level ?. Do you have to really floor the throttle to get it to open or will it open on a more linear acceleration ?. Did both during the drive and there seemed a bit of a difference but could be imagining it.

On the mixture front - no dark exhaust pipes !. None of the rich running symptoms showed up during the drive which is really encouraging. No lazy throttle response on the downchange - just a nice crisp "blip". It was a relatively short drive - half an hour or so - but have to say was really pleased with the result.

Any further thoughts from the gurus much appreciated - but tentatively say it looks like a result !.

Laurence.

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Yep I fitted it myself but I did check to see if it worked OK prior to putting it on the car. Which it did - works very well on a Mityvac !

Thanks for the info from the Workshop Manual - that's very interesting as the main probs I am (was ?) getting with the intermittent misfire/rich condition was bang on that 2500-3000 rpm mark (usually following a deceleration).

I have no idea of the significance of that but that is one hell of a coincidence !

Cheers .

 

Thanks for the replies gents.

Gavion - I think the problem such as it is, is that after driving her without the bypass valve for 4 years, the car just seems well, "tame". An open throated 355 is really addictive as we all know and although it still sounds nice, I suppose I was expecting more when/if the valve is now opening as it should. I think I could a detect a greater urgency in the engine when the valve opens - but I might be imagining it that's the problem.

Yelcab - this is getting really interesting now as you are describing what I think has been happening to mine to a tee - I have driven the vehicle twice now with the replacement valve in situ and encountered no rich running or light missing as yet but they have both been relatively short trips (less than 50 miles). Could you describe what you mean by a "standing wave" please ?.

I am also running test pipes on the car.

Regards

 

As a post script to this thread Guys - I think I can definitively say now that the running issues which have afflicted the 355 since got her have now been sorted !.

Now, a statement like that is normally the kiss of death, but having driven her for 200 miles today, I have a degree of confidence.

The problem was I think, caused by the vacuum system at the back of the car (main culprit - vacuum tank). I thought I had fixed the hole in this tank a few years back, but seemingly not.

Found the problem whilst looking into the operation of the air pump, which I had got working, but sussed that the secondary air valve wasn't opening. A quick rework of the vacuum lines by-passing the vacuum tank and hey presto - one working secondary air valve!. The pump is a LOT quieter in operation now too so if your air pump has got noisier - check out the secondary !.

The driveability of my car has improved massively - its smoother, faster, there's no miss, and the throttle response is much better - so chuffed ! All the probs I was having as described earlier have - seemingly - disappeared.

So to sum up: if you feel your car has started to run richer than it should at idle, suddenly go rich on a light/trailing throttle, really not like being under 2500rpm or so, start to hiccup/slight misfire on steady throttle - might be worth having a look at your vacuum system, could be the culprit.

Best regards