boost, backfire problem. Suggestions?

[diabloam]

Hi all, any suggestions as to problem here.

Have been away with work so my 86' 944turbohad been sitting in garage for three weeks or so. Started fine and i went for a long run to warm up etc. However when I boot it, as soon as boost goes above 5psi it seems to splutter and miss, although boost does still go up to about 12psi intermittantly (from recently fitted aftermarket guage) so know turbo is producing boost. The power comes on and off, feels like fuel or igntion is cutting on and off on full boost. Pretty sure its not fueling as when I keept my foot down through it spluttering car exhaust gave a big bang/pop (like unburnt fuel in exhaust, as a big puff of black smoke from back and then fine, backfire?). It has started to improve the more i drove car and on way back to house the now it produced smooth full boost and power, although whether it stays like that i will find out when i use it later, but I am keen to identify problem.

Any ideas what is causing this, is it vacuum pipes or something else, or is it the over boost protection coming on wrongly, any suggestions welcome and appreciated, cheers

The car did this for a wee while last time I left it sitting but it sooned cleared after car was driven for a while. Is

 

[zcacogp]

Suggestion?

Try an S2 - none of that pesky boost stuff to spoil the driving experience!

See here: http://www.porscheclubgbforum.com/tm.asp?m=358121

(In all seriousness, sorry, can't help .... someone will be along soon who can tho'.)


Oli.

 

[diabloam]

not 12psi but 8psi. now that i have used the car for a day, it is now boosting and pulling normally, but any ideas what was wrong with it, cheers

 

[Diver944]

Sorry, I can't think of anything obvious [&:]

Odd that it did it after a 3 week layup, have mice chewed through something under the bonnet?

 

[Peter Empson]

I would guess it could be something like a clogged fuel filter or contaminated petrol, or perhaps just a sulk given you hadn't used it enough recently []

 

[Guest]

Might it be our old friend of the 944 the DME relay again ...?[] It is possible to have damp in the contacts..or the contacts could be shafted. They would get better as the relay warms up. This is what befell mine a while ago.. I changed it out and no problem since .. It could be damp in the dizzy cap or coil as well ...!

http://www.porscheclubgbforum.com/tm.asp?m=335557&mpage=1&key=&#335557

Let us know how you get on

 

[berg944]

What about a sticking barn door in the AFM?

 

[peanut]

well if it was working fine when last left and nothing has been done to it in the mean time then I would go along with Peter.. contaminated fuel.

There is often water in the fuel we buy but because it is well mixed it usually burns off without any drama. If you leave the fuel for a couple of weeks the water and fuel seperate, especially if there is not much fuel in the tank

. The next time you start the car the pump takes up a quantity of the water which clogs your fuel filter and injectors .

I would be tempted to fill the tank and mix the fuel up again or if there is only a small amount in the tank,maybe drain it out and replace the fuel filter clean the injectors.

 

[diabloam]

I changed the plugs in case they had fouled up, but to be honest the ones that came out were fine. Car is behaving fine now so maybe the fuel might have been an issue. Will have further invesitgations to see what is going and keep everybody posted. would the DME fail like that?

 

[TK2015]

I had something similar about a month ago.

I had the car parked on the drive without being used for three weeks (garage was full of crap). The car started fine but as soon as the boost came on it started to misfire. I drove on and gave it a really good run. The more I drove the better it ran. It was during the really damp weather so I put it down to dampness, particularly as the speedo started to play up at the same time. But I also tanked up with Super half way through the run, so it could have been the fuel.

In any case, the car's back in the garage and being used regularly and neither the misfire not the speedo fault has reappeared.

 

[George Elliott]

Diabloam, I agree with Toms line of thought, its nothing more than Ignition Leads which have got a bit damp, - these cars run hot under the bonnet which is good for keeping 'em dry, but the heat is a bit sore on the rubber / plastic components. If the Leads are a bit aged, and they become damp, they will arc down to ground - as the underbonnet dries out this stops occuring.
The routing of the leads is very tight from the Dizzy to the Head - so there are lots of short arcing possibilities.
My car has done it in the past
George
944t
964

 

[diabloam]

Its been fine last couple of days, whilst it has been in regular use. Lead, rotor arm and cap next, where the best place to buy these online anybody, cheers

 

[appletonn]

Bert @ Berlyn, probably.

 

[Fred Hindle]

Check this site out
http://www.ignitioncarparts.co.uk


this page is for the rotor arm.
%2007/87&BHP=110&HP=150&CC=2479&Cylinders=04&Valves=8&VID=02977&e1=M%2044.07&e2=M4407">http://www.ignitioncarparts.co.uk/Products.aspx?Man=PORSCHE&Mod=924&Ser=924%202.5%20S%20COUPE&Year=09/85%20>%2007/87&BHP=110&HP=150&CC=2479&Cylinders=04&Valves=8&VID=02977&e1=M%2044.07&e2=M4407

They're P&P is a bit high but if you can get everything there then not a problem.

Cheers,

 

[DivineE]

If your still struggling mine was the rotor arm and distributor cap (cheap fix about £20 from Bert) I had those symptoms, fine off boost but the spark wasn't strong enough when it spooled so it blew out the spark and backfired, stuttered etc but yes could also be the damp leads, almost definately electrical I'd say.

Regards,

Ben

 

[diabloam]

Thanks everybody. Will get cap and rotor arm and when I return from work next will stick them straight on and see if it misses again after sitting for couple of weeks. Going to tackle the sills next time also next time I am off. Anybody know how much genuine ones are and where is good to get them (also what areas make up this panel, does it run back to end of rear quarter panel or is it just below the door?). Also seen repair panels available for about £45, anybody used them or best to get original.

 

[Diver944]

The genuine ones are circa £130 a side and Exeter OPC sent me one next day when I needed it. Beforehand I bought one of the clubautosport patch panels but the bodyshop refused to fit it due to the poor fit [&:] I should get it back when I pick up my car so anyone can have it for a tenner at Frontrunners.

The sill starts just behind the front wing and finishes at that crease just behind the door. The rear part of the sill is actually part of the rear quarter panel (£500 [])

 

[diabloam]

It appear to be just the bottom, but there is a couple of bubbles on both front wings and at back on quarter panel. I am not yet a member of the porscheclubuk, is the 130 a side for sill a club price or to anybody (might be good reason to join me thinks). Are they also galvanised, thanks all