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Popping from the engine.

C

chrisrush82

PCGB Member
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Ok slowly getting there with the Turbo, one problem im having that i really cant seem to cure is:
when driving along the car runs smoothly and is great. but when the foot it taken off the accleterator pedal or speed slows down i get a multipule popping noise from underneath or engine, i have changed the spark plugs i have hada new exhaust on it ive put a new coil and distributor on it. and it still dose it,
one question is this normal?
dose anyone else have this problem?
or coiuld anybody give me some other advice on what it could be?

thanks chris


 
Might be daft this, but isn't it unburnt fuel in igniting in the exhaust?? When lifting off the engine starves of air/ is over fueled temporarily and the fuel passes through the cyclinder and into the exhaust where it combusts.
It could also be indicative of a leaky exhaust (if its new it may well not be sealed fully?), sucking air in and allowing said combustion. I'm far from knowledgable on the matter though, someone should be a long to confirm/deny
 
thanks guys ive had the exhaust checked out again and they say there are no leaks where the new one has been put on,
it was doing it before i had the new exhaust fitted i thought that was the problem and a new one would fix it but it hasent obviously.
Some ideas i ve had to fix it are a put some injector through it to see if the injectors are blocked or something and B go and have it tuned properly.
 
Yes I think giving the engine a run through with a dose of Redex Injector Cleaner is worth doing, I recommend the deluxe kit. You need to run the tank well down before you add it, do some driving, then top up with fresh fuel.
When the injectors get a bit dirty they can "dribble" a little, and thats the source of the fuel that gets getting into the exhaust and igniting on engine overun.
Regards Big Bob
 
If it's a turbo wouldn't it have K-Jetronic continuous fuel injection? If this is the case injector dribble may not be to blame. There was an overfuelling thread earlier where the control pressure was to blame.
 
Absolutely correct Mr B the CIS fuels continuously, pooling behind the inlet valve when it is closed.

We need three things for a fire, fuel, oxygen and an igniton source. Igniton is the hot gas, so it is either fuel or oxy. See if the mixture is going too lean on the overrun. Then the unburnt fuel accumulates. Check plug colour and if they are a bleached very light grey clour then you are probably set up a wee bit too lean.
 
Thanks for that 924nutter, I have not owned a 924 but I have been learning about cars and their systems for just under 50 years now, and its good to know that my diagnostic knowledge is not totally flawed.
Regards Big Bob
 
924nutter, do you think if one of the injectors was releasing at a lower pressure then the raised fuel flowrate through it would cause the pooling? I was told in college that flow and pressure are linked so that if one is high the other is low and vice versa, K-Jet is a really good system in my opinion and i'm always trying to understand it better.
 
There is a check valve in the injector which is set slightly higher that the check valve on the pump outlet. If the injector was leaking significantly, that cylinder would have a sooted-up plug as it would always be running richer than the rest. Take the plugs out and have a look. It is a peice of cake on the turbo, except for no2, but still way easier than the N/A as the plugs are on the exhaust side of the engine. Have you checked the plate stop in the metering unit? Perhaps it is not allowing the metering arm to return fully and delivering too much fuel.


 
Hi guys thanks for all the advise ive run injector cleaner through it fully and it hasnt made a difference ive had the exhaust checked and thats not leaking at all. i have ordered a new set of Plugs as i have no record of when mine were last changed!!!!! and i have owned it 5 years!!!!
so they will be here tuesday hopefully.

Is it easy to check theplate stop in the metering head? im not sure what this look like or how to get to it?

 
Ok adding to that last post i have now changed the plugs and they havent made any difference at all so i have beeked it in with Autostrasse in coggeshal essex for them to have a nose over and see what the problem is i have never had it tuned properly so it could be that i guess but everything will be checked over
 
Just had a quick check under the car took the shield off and found a crack in the sump would that cause enough of a gap to suck air into the system?
http://www.facebook.com/album.php?aid=16923&id=556138168&saved#/photo.php?pid=2566515&id=556138168

 
Ok New thing following up the Sump has already been welded up so no problem there the oil is leaking from the seal around the Oil pump so could do with a new one of those but its not drastic.

I had the Cam cover of today in the hope of finding that the cambelt was a tooth out and causeing the poping problem but no luck there it was all correctly positioned. so its definetly comming down to the injectors or the fuel management system, im a bit reluctant to remove the injectors as they seem to be the original ones and hve proberbly never been removed before is this a hard task to do?
 
They unscrew from the head once the pipe has been disconnected. Use two spanners to undo the pipe union, one to turn, one to oppose.
 
Years ago I had a problem with my series 2 Turbo. It had some of the same symtoms that are identified in this thread however with mine the car stopped altogether. It happened again this week but without the stopping. I remembered the advice given those years ago by our 924 Turbo guru, 'The Nutter' and checked the ecu unit located in front of the radio. The multipin plug had worked loose and wasn't making full connection.

I assume that 'the Nutter' will explain this better for you.
 
Thanks for that i just checked the Plug and wiggled it around when the engine was running but it dosent seem to make a difference i guess it could be the computer on the way out?
 
Having thought about this for a long time, check the vacuum hose to the ecu, and the throttle positioning mechanism, thats that large thing that looks like the advance/retard mechanism for a distributor. If I understand its function correctly, in the U.S., it is used to prevent the throttle from snapping shut and thus prevent pullution from unburnt hydrocarbons, by trying to maintain the correct stoichiometric ratio, gradually closing the butterfly; the mixture tends to go lean when the throttle snaps shut. Any air leaks in this mechanism, which as far as I can tell is fitted but not used on U.K. models, will allow air to be introduced. While I think about it check the wastegate is not letting air in by leaking slightly.
 
Thanks another thing to try! i will get this sorted eventully i hope i cant really think of much else it can be i shall try those things too hopefully if the weather is good tomorrow ill have a check.
 
Just thinking about that the popping seems to come from the wastegate area and when it was last replaced it was a secondhandone then so this is possible thanks for the advice
 
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