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1.7 16v misfire - does it exist

 
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The Wombat
Alfa Sprint


Joined: 31 Aug 2012
Posts: 168
Location: Deepest darkest Huntingdonshire

PostPosted: Sun Aug 03, 2014 7:53 pm    Post subject: 1.7 16v misfire - does it exist Reply with quote

Had some chaps come and view the red 16v today. All polite and friendly but they didn't want it because it had a misfire. Not a problem, not every car suits everyone.

I don't, however, think there is a misfire. Car was fine on emissions for its MOT, runs as a 16v boxer should, runs like the others I have, and drives like it should. Has been the same since I bought it 18 months or so ago from Alex.

I was asked (in so many words) why I hadn't done anything about this, but the answer is simple, if you don't think there is a misfire, why would you do anything?

However, I don't want to miss a trick here, and wondered if anyone had any experience of 16v misfires and how they would present or manifest themselves.

The car idles in a stable way from cold. Very slight throttle shows a slight imbalance which I believe is throttle body adjustment, but no missing or hesitating, then at wider throttle openings, revs increase as one would expect, no missing, vibration etc.

Not worried about the lack of a sale as the interest was somewhat unexpected and the car has a home here, but any information or thoughts on the misfire would be very helpful.

I could investigate by pulling off plug leads, swapping plugs, compression testing etc, but I can't see the symptoms that would take me down that path.

Thoughts very appreciated.
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Bobkelso
Alfa Sprint


Joined: 09 Aug 2011
Posts: 190
Location: Milan - Italy

PostPosted: Sun Aug 03, 2014 10:37 pm    Post subject: Reply with quote

Hi Wombat,
for me the tests are the same for all boxer:

when the engine reach temperature, and you stay on the driver seat,
did you have vibration at the body of the car (or under your feet)

1) at idle with gear box disengaged

2) running, when accelerating

If not, I think you cannot have more than very few misfires.
(ps: perfectly 0 misfires I think is impossible, may be
only today cars with completely different ignition system
are near to 0 but not at 0)

also:

3) engine at temperature, engine bay open, motor at idle
900 rpm and you cannot see the block move side-way->
no misfires (at idle) (you have also video on youtube
about people putting a glass with water on
the boxer engine at idle to see it doesn't move)

4) (sorry very few scientific if you doesn't measure
the sound spectrum and use only ears) when running,
if accelerating there are misfires, the engine will be at least "rough"
(something less than vibrations), and the sound
will be less harmonious and more like a motorbike engine,
because sound spectrum is enlarged also to uneven multiples frequency
of the first harmonic (more rumor and less music, apparently the sound will
seam more "bad sport car" or "sport motorbike",
something young people could like,
but in practice is a bit of more rumor, the fingerprint
of boxer engines (and expecially with standard simmetrical
exaust) is a more "round" sound

My 8v when was ok didn't move side-way at idle also
at 450-550 rpm but I think it was a better than average
situation(non only it had not misfires but that
time it had been carbs balanced very well).

However a simple test for cables may be you already know is see
in the engine bay at night with a light rain (or you can do moisture
with some hand water mister /nebulizer), at idle or revving the engine
by hand on the trottle leverages.

If there are some dispersions from the 4 plug cables or from the cable from the coil
you will see orange or blu sparkles outsides the cables..but you must do the test
in almost perfect darkness or you hardly could see sparkles also if they are there Very Happy
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The Wombat
Alfa Sprint


Joined: 31 Aug 2012
Posts: 168
Location: Deepest darkest Huntingdonshire

PostPosted: Mon Aug 04, 2014 7:40 am    Post subject: Reply with quote

Thanks Bob

That makes sense.

I've just been out and checked per what you suggest below and it passes with flying colours. I will post a couple of video clips shortly of my morning cup of coffee on the plenum.

Interested in peoples thoughts when they see the vids.
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The Wombat
Alfa Sprint


Joined: 31 Aug 2012
Posts: 168
Location: Deepest darkest Huntingdonshire

PostPosted: Mon Aug 04, 2014 8:32 am    Post subject: Reply with quote

Here is the car!!



Video footage at tick over at working temperature. Engine is rock steady, rpm is a little lower at 700ish. Not a useful sign, but rev counter is rock steady at that idle. No hunting up and down or anything similar.

http://i1109.photobucket.com/albums/h440/wildtry/Mobile%20Uploads/th_IMG_1224_zpsbe4a2e8f.mp4

And now footage with a little more revs applied

http://i1109.photobucket.com/albums/h440/wildtry/Mobile%20Uploads/th_IMG_1225_zpsad07dcd7.mp4

I know it is difficult to diagnose things from pictures and video clips, but from a basic perspective, and having done Bob's suggested tests, is this engine behavior suggestive of mis-fires?
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Bobkelso
Alfa Sprint


Joined: 09 Aug 2011
Posts: 190
Location: Milan - Italy

PostPosted: Mon Aug 04, 2014 8:11 pm    Post subject: Reply with quote

I'd like the definition "cup of coffe test" Laughing

- it seams to me the idle test is excellent
(I don't see misfires AND valves are probably perfect,
usually any valve problem is more evident at low rpm);
this cup of coffee test it is a good presentation because
to me it say heads are mechanical ok..

- the revving test seams to me not as perfect as the idle one
but it is very good (actually i'd like my car running that way);
May be there is very few imbalance and slightly rough sound,
for this that person was thinking about misfires?
(or simply the mp4 quality is too low too appreciate real sound)

If you have a spare HT coil you can try it to see if sound
revving is better (in the case your coil is failing only
when revving, i.e. getting hot) or equal.
If equal you are probably misfire free at every rpm.

To do a better than this (very good) revving test
could be time consuming and a scrupulousness work,
as you already say probably leverages and throttle alignment
is not at 100%, is a common 'problem' with 8v double carbs version,
is difficult to get 100% alignment, many regulations involved,
so you get one single slight vibration at starting accelerating
like in the video and some very light rough revving
(and when 100% aligned, to do still better you need a 0 miles engine
and a thick oil, so the mechanical rumor is at his minimun, and a standard air intake filter,
your air filter instead seams quite open sound/sport one,
may be is only this that makes some 'rumor' Very Happy )

Instead/before touching leverages, you can first verify simple things to get more possible ronded sound,
like no air leaks in induction or in exaust, and some clean up at fuel injector electrical contacts
(I know you are quite skilled, so sorry if this is trivial ).

Ok, let's see if some one more expert give some more opinion.

Ps.: I'd like the look of this red - big brakes 16v Shocked
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The Wombat
Alfa Sprint


Joined: 31 Aug 2012
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Location: Deepest darkest Huntingdonshire

PostPosted: Mon Aug 04, 2014 9:42 pm    Post subject: Reply with quote

Thanks for the feedback Bob. This all sounds good to me.

I do know there is a slight throttle body imbalance as I attempted to adjust a while back but my set of vacuum gauges were not accurate enough. I remember doing something similar on a 4 cylinder Honda a long time ago, trying to balance the carbs, and found that the tubes of mercury were the best way to do it!!

Sound wise, the car has the later non-symmetrical manifold, which from experience is a slightly harsher noise that the symmetrical manifold. The sound quality isn't great on the video clip though.

As you say, the car is a GM big brake conversion, with 75 V6 master cylinder, and late model EU 33 rear disks. The braking is more confident than standard.

Interested in any other perspectives on mis-fires that might be out there
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The Wombat
Alfa Sprint


Joined: 31 Aug 2012
Posts: 168
Location: Deepest darkest Huntingdonshire

PostPosted: Sat Aug 09, 2014 1:10 pm    Post subject: Reply with quote

Well, having done a few more assessments on this fabled misfire, and checked the engine under load, based on that and the above, I am still firmly of the belief that there is no misfire.

I know the engines sound a little offbeat due to the flat 4 configuration, so perhaps the knowledgeable person who was bought down to review the car perhaps does not have the knowledge in relation to Alfa flat 4 engines.

A bit of a win/win I guess. Potential buyer doesn't end up with a car they don't understand and will worry about, and it stays with me Very Happy Very Happy
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BigAl
P4


Joined: 06 May 2003
Posts: 2990
Location: U.K Surrey

PostPosted: Sat Aug 09, 2014 10:14 pm    Post subject: Reply with quote

When I had a standard engine setup I balanced my throttle bodies by making sure the throttle stops were the same, by using feeler gauges on the inside of the throttle bodies so that (1 and 3) were the same as (2 and 4).
Then I used a syncrometer when the engine was running and got (1 and 3) to measure the same as each other and then (2 and 4) to measure the same as each other. then adjust the throttle stops so both sides measure the same as each other, as in (1 and 3), which should be the same = (2 and 4) which should be the same .
When I tried this on Paul.H car, it would not idle with the plenum chamber off though.
If you make any adjustments to the drivers side throttle body you may have to move the TPS (throttle position sensor) so you get the same click as before, which is a click as soon as you move the throttle.
You could try adjusting around the driver side throttle body by leaving that throttle stop and adjust the other.
Don't forget to adjust the balance between throttle bodies so they open at the same time.
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