Porsche Enthusiasts Club Forum

Hi everyone,
Just got my 944s back from the garage. To cut a long story short a few weeks back the engine backfired and then refused to start. Two garages later it turned out to be a small vacuum hose that had blown off the manifold. So I have had that replaced and the airflow meter tinkered with because the emissions were way too high. Car runs really well until I got it home. Turned the engine off for a minute and then started it again and guess what? The engine backfired and blew the airbox off again. All the timing has been checked twice so I am at a bit of a quandary as to what is going on. Let the engine cool for an hour and stated just fine. This only happens when the engine is hot and on ignition, never when driving. However, I do think this trouble coincided with me filling up with shell v power for the first time (i think).
If this is going to be an intermittent thing i was wondering if an induction kit may be a good idea to save the original air box.

Any thoughts?

It hasn't dropped a valve has it? Did it pass a compression test?

I'm not sure. I didn't think to ask but the car does seem to run well and idle very smoothly.

Cheers Tony

Mine ran for 6 months with a stuck inlet valve & I didn't notice except for a slight loss of power. The balance shafts mask quite a lot. Just an idea & easy enough to do.

Backfires are normally damaged inlet valves or very weak mixture. Quick enough to check weak mixture by getting a garage to use an exhaust analyser CO should be around 2%. Might be something stupid like a cracked or dodgy plug. Or possibly another vacuum leak which would also cause weak mixture & may only be apparent at certain revs/temperature etc.

It's not expensive to replace all the small vacuum hoses with a silicon kit. There around £20 & it will take you an hour or two. Looks a lot better when you've done as well. Quite a few AFMs on ebay some for a 10 to £60

Thanks for the replies, I'll have a look at the hoses first as that sounds a cheaper option. The mechanics did the emissions and checked them so I presume that side is ok. I'll see how it gets on over the next week or so. The strangest thing is it only does it when the engine is hot. Tried turning it over in the garage a couple of times last night and it started and idled well!

Are backfires dangerous? The reason I ask is that one of the mechanics told me that 911s do it all the time and they have escape valves in the afm and air box. So I was wondering if an induction kit would perform a similar service?

Thanks for the help and once I’ve finished paying the garage bills I'll join the club!

Cheers Tony

If it's an inlet valve it will get worse until you can't start or drive the car. It may contact the piston & wreck the engine. You shouldn't ignore it. A compression test should only cost around £25 as it takes as long as it does to take the spark plugs out. If it's running lean it will pass on emissions so don't rely on that. As Jim says a CO meter will tell you whats going on.
Sounds like you need to make friends with a good enthusiast mechanic. I couldn't run mine on specialist prices. I just had my head swapped. New water pump fitted. All front seals & belts & rollers done. Also new door check straps for less than £400. (Parts supplied obviously.) With cars of this value it's hard to justify 2K services. Car goes in Tuesday for a full service & exhaust to repair. Bill will be £150. Theres a credit crunch on. Many have already sold there Porsche. Get cheeky & ask for a discount. Shop around!

might be an idea to join the club and get along to the meets, the guys there tend to know someone or someone who knows someone or know something that will really help with problems, lot of people have allsorts of guages and testers

this forum is of course full of people who really know the 944,

joining the club would mean you can ring the tech advisors and say " I am a tipec member and .........................."

Really is worth it in the long run, plus you get the discounts like the AA and buying bits you have found you need!!!! Always useful.

dont be afraid to shop around for bits, mail order may add a day or two but can save pounds
and always ring a few people and give it the "well so and so are doing them for xxxx can you match or beat that?"
before you settle for a price look at the sort of offers you can get from people like Jon itchell who has said he will do 10% less than euro car parts web prices, other specialists recognise TIPEC and offer discounts try bert at berylyn, think about the porschshop discounts etc etc

Gordon

Regarding the vacuum hoses; if you download the parts catalogue from the Porsche website there's a diagram showing the route of the vacuum hoses on the 944S. I found one disconnected on mine and used that diagram to find where it was meant to be. Turned out to be off of the fuel pressure regulator on mine but then my engine is toast anyway.

Thanks everyone,
I’ll certainly join the club as I feel i have learnt more about the car in this forum than anywhere else. The compression test I’ll look into as well as the hoses. Sort of tempted to give the compression test a go myself. I found this on ebay seems cheap.

http://cgi.ebay.co.uk/HILKA-CAR-PETROL- ... 5d299f44aa


Cheers Tony

Looks OK, check the compressions with coil low tension disconnected & the throttle wide open. Do all 4 & note readings then dribble some oil down each bore & check all 4 again.