I have a bit of a project peuegot 205 , a rough guide to the engine is thus.
2.0 iron block bottom end, 1.9 gti head and cam, 4 branch mnanifold, dizzy/coil ignition and bike carbs from a gsxr.
Anyway the issue I have is it starts and idles fine except for a popping noise from inside the engine. I think Ive tracked it to pot1 as when it happens pot 1 has a brighter flash down the gunson colour tune. Im struggling to work out what it is. The head has just been rebuilt so is known good in all aspects, compression test shows up nothing untoward, oil pressure is spot on, coolant is dead level, fuel/air is right at idle and it only makes the noise at idle.
Ive got a quick vid of it, first from the exhaust and then from the gunson so you can see it defiunatley up the engine end and you can see the brighter flashes. Video isnt great quality due to being from a phone.
www.pgacnortheast.co.uk/pop.mp4
anyone any ideas whats going on?
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How's the ignition timing set up? If it's still tuned for the bike engine it might not be right for the Pug engine. It might be a bit advanced and could do with a bit of retarding. Also worth checking the fueling on each of the carbs, one might be a bit richer than the others.
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Test for air leaks in the inlet manifold, Use a real time scope and monitor, via an induction loop, the HT on that pot, I'd be looking for random HT pulses, it almost sounds like the exhaust valve sticking open. Make a sound recording of the exhaust note and send it to me at Peter@3DAssociates.co.uk and I will use some time domain analysis to see if it points the finger. Regards Peter
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I have managed to transfer the MP4's sound track to MP3 and done some analysis on that and I think the exhaust valve is sticking. This causes a weak mixture and a denonation in the pot and head/manifold, thus the sharp crack/Pop. If you can supply an MP3 sound file recorded with a stand alone mike and a laptop I'll have another go at it. Use 44K plus sample rate. Regards Peter
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The exhaust note recording is in saturation and very difficult to analyse make a reording further away from the rear of the car, The more I listen and time expand this popping the more I think the valve is not closing. The detination is quite acute. Regards Peter
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wow thanks for the help, I will try and get a better recording but I have limited recording equipment and space in the garage. If it is an exhaust port staying open then why would it only do it at random and also why would it fire back out of the carb? It does literally come out of the carb as I have checked. It just seems to reverbarate through the exhaust
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ignition is retarded, it seems to run better retarded.
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You had not mentioned it firing back out of the carb before. Are you sure it is doing this. Test using a thin piece of cotton rag and hold it over the carb inlet allow the rag a little slack and observe the movement of the cotton diapham it should be neutral or sucked in not popped out. Regards Peter
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Ok make a new recording but move to about 6 feet away from and to the side of the exhaust. Regards Peter
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I will thanks. Ye its definatley 100% coming back out of the carb on pot 1.
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well I went out to try and record it, it started and was doing the same then by the time I looked for a sound recorder on my phone it seemed to right itself and it now idles smooth, well it did until it cut out and now it wont start again. I think its possibly fouled the plugs up or its having difficulty getting enough fuel out the tank as its been stood a while with not much in it.
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If it is just quitely chuffing out of the carb and no flames I suspect the the ehaust valve is still cracked open then the inlet valve opens. When you have it running a gain make a recoring od both the exhaust and the carb noise. Regards Peter
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Sounds like No.1 carb is running too lean to me at idle and causing the random missfire. Possible air leak from carb to head... vacuum is high at idle and sucks in air
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found out why it died anyway, the pump packed in which isnt good as its practically brand new. Getting it exchanged though and now wondering if the pump had anything to do with the fault. No1 pot is slightly higher as car was at an angle so possible any air or debris from pump was floating up that way.
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Are you running a blind pump or a pressure reg and return system. Regards Peter
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That fits in, if the colortune gave a bright white flash it would be indicative of a weak mixture. That would burn so slowly that it would ignite fuel in the manifold/carb causing the popping noise.
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Yes that fits but you can hear it in the exhaust and the detination is very very acute. When the engine is running ok the exhaust note does not have a cyclic pattern like a lean pot would have. I also assume this only happens ad idle. What head have you put on it and is it oil filled hydrualic cam followers or adjustable tappets I would think the latter. Regards Peter
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The other problem here is that if the inlet is chuffing the next induction stroke will be weak and catching that is difficult with some complex diagnostic gear. Regards Peter
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I would have thought that a lean pot would give a random exhaust pattern not cyclic ... a lean mixture + entirely random air turbulence found in any engine results in random fluctuations in burning velocity and cylinder pressure. A mechanical valve fault would be more cyclic. The cylinder running lean burns so slowly that its similar to the ignition timing being severely retarded on that cylinder...in effect the mixture contues to burn well after tdc and into the exhaust stroke and that (could) explain the popping in the exhaust.
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the fuel pump is a solid state 5 psi self regulating pump capable of 120 litres per hour, fuel reg is adjustable 0.5-5.5 psi and it does have a fuel return system via the carbs.
head is 2 valves per cylinder with fixed shim and bucket system.
The more Im thinking about it the more Im convinced Peter is right on the exhaust valve theory. Reason being when it righted itself after 5 minutes running it ties in with the fact its an alloy head with steel valves, hence the clearences increase when warm so the valve overlap becomes less prominent and the popping stops.
As soon as the new pump arrives I'll get it started up again and if it still does it I will try and get an MP3 recording with the car out the garage for a clearer noise.
Thanks for all the input so far, I kind of expected a lack of input since its such a specific application.
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I assume the head has either steel or silted brass valve guides. When you say overlap do you mean the inlet to exhaust overlatp as this does not happen on the compression stroke but the end of the exhaust stroke. Can you borrow a scope a microphone, a knock sensor and an HT industion clamp, you may have to analyse the timing relationship between the detination and the spark and ideally the rotational position of the crank but I do not recall 205's have this available as it was a dizzy job. Where do you live. Regards Peter
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My instinct is to look at the fueling first, presume your running sidedraft bike carbs which are very difficult to set up.
If it runs better after 5 mins that would tend to confirm the mixture is weak and too close to flammability limits for stable running ...fuel would vapourise and burn more easily the hotter the engine gets. I presume you have checked the valve clearances on no. 1 are close to 0.2mm inlet and 0.4 mm exhaust if it''s the standard XU engine head.
If the clearances are ok you could place a piece of tin near the throat of no. 1 carb to choke it slightly and spray the carb/head gasket area with wd 40 to confirm it's running too weak. Don't get too close or you could lose your eyebrows or worse!
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peter yes its dizzy ignition although I plan on mappable when funds allow. Im in middlesbrough
Dieselhead yes its standard xu and all clearances are fine, Ive sent the fuel pump back today so hopefully I will have a replacement by end of the week and I can continue the quest to solve it.
It is very strange though as it had run before without this issue and nothing was changed. Im suspecting the fuel pump failure to be the route cause of this at the moment as pot 1 is furthest from the fuel feed and it is possible with a lazy pump before total failure that pot 1 simply wasnt getting enough fuel as you suggested. I'll keep this thread updated when the pump arrives.
Thanks
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Yes bit much of a coincidence the pump failing but the colour tune did not seem to imply if was running week and detination was quite severe. Lets see what the new pump brings. Regards Peter
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finally back onto this, I got side tracked building a new garage. the new fuel pump arrived and was duly fitted, no difference at all. So Ive had the full inlet side off and double checked and replaced things so there is 100% no air leaks on the intake. Also checked the exhaust has no restrictions on the pot. Finally I got hold of some different feeler gauges to recheck clearance, seems like pot 1 exhaust valve is a bit tight, its .305mm and should be .4mm. Will this be enough to cause the issues? Dont want to strip the cam out and replace the shim if its not.
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That's 12 thou instead of 16 thou well close call is that cold or hot. Measure both to see if the clearance is closing when heated or opening. Is the pop just the same as I thought it was going to be. You say you had the head rebuilt, what did you have done about the lip on the valves, refaces and eats cut or what. Make me a new recording at a lowever level so it is not in saturation, one at the front and one at the rear. As you have gathered I've been here before. Regards Peter
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that measurmenet was cold, I cant run it long enough to take a warm measurement unfortunatley. I will have it out of the garage tomorrow so I will grab some sound recordings while its out which should be of better quality than the last time. I know that the clearances on these get larger when warmed up so in theory it should stop when warm. I just couldnt run it long enough in the garage as I started to choke to death.
The valve seats where fine when it weas stripped down so they werent recut just lapped in with a coarse paste then again with a fine paste. A friend has kindly done a leak down test and found nothing wrong on that side of things either.
he's going to have all the timing checked over as he has better equipment than me and from here I can try and set the idle fuel then record the noise (if its still there). I just dont know if its worth the effort of replacing that shim beforehand?
I have a load of spare shims so n doubt will have one that will open it up .1mm
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The use of the dixxy rather counts out a random spark form a coil back so that is no surprise. Does it still go away then relly warm and can you listen to the the four iintake port with a stethorscope or a piece of pipe and comapare the breathing. The swirling noise should be very similair if they are fueling well. Not listening mode. If you cract the thottle open do all pots respond well and if you run up at 4000 rpm for 10 secs and let go does it return to straight awy to an even sweet tick over. Regards Peter
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I assume form the video you are using Rubber couplings to the carbs, are they firm enough or can the carb resonate very easily shaking bike carbs ar low rpm is not normal, try some tie wraps around the rubber to stiffen it up as a test. Regards Peter
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the rubbers are extremely firm, the carbs are right up against the manifold as well so they definatley support the carb and dont flex inwards etc with vacuum.
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hard to say how well it revs up as the main jets were wrong previously so it 'borked' when the throttle was cracked open. After the car was left to idle for while it would rev as long as it was donw gradually and when it did it sounded sweet as a nut, it did return to idle nicely but coughed a large cloud of fuel back out of the carbs. I do have a very quick vid from how it ran befoire so you can see the cloud, although on the vid it appears it blows out when revving, I think the sound is slightly off time.
www.pgacnortheast.co.uk/cough.3gp
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