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| flat spot https://forums.tipec.net/viewtopic.php?f=27&t=11662 |
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| Author: | stag estate man [ Thu Sep 15, 2011 8:47 pm ] |
| Post subject: | flat spot |
hi all. Ive recently bought a 1987 manual 928s4 and i am chuffed to bits with it!  I have a very minor niggle with it in that on hard acceleration sometimes there is a slight hesitancy almost like turbo lag this is not at any particuler rev range just a flat spot . does anyone have any suggestions on how to sort this i am hoping it could be the plugs need a clean! cheers Grahame |
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| Author: | Lee 944 [ Thu Sep 15, 2011 8:56 pm ] |
| Post subject: | Re: flat spot |
Can't believe I'm getting in before Brett. Change the, Plugs, Rotor Arm, Distributor Cap. Not check and clean, but change. Is that right Brett?  Joking a side, Brett is right. If you haven't changed them, then you haven't ruled them out as the cause. You could be chasing your tail finding the problem.Then do the plug leads and then take it to JDS Porsche in Oxford for a SharkTune. It could be your MAF or fuel filter too. |
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| Author: | Brett928S2 [ Thu Sep 15, 2011 9:07 pm ] |
| Post subject: | Re: flat spot |
Hi  Lol Lee , well done Precisely what I would have said, CHANGE all those things...NOT check... CHANGE for new... plus air filter and fuel filter (under the back) All the best Brett
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| Author: | stratfordshark [ Thu Sep 15, 2011 9:36 pm ] |
| Post subject: | Re: flat spot |
Lee 944 wrote: Then do the plug leads and then take it to JDS Porsche in Oxford for a SharkTune. It could be your MAF or fuel filter too. All good advice, except JDS is in Cambridge! |
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| Author: | Lee 944 [ Fri Sep 16, 2011 10:31 am ] |
| Post subject: | Re: flat spot |
stratfordshark wrote: Lee 944 wrote: Then do the plug leads and then take it to JDS Porsche in Oxford for a SharkTune. It could be your MAF or fuel filter too. All good advice, except JDS is in Cambridge! Geography was never my strong point. I'm going to try and drive round Europe next May, I might be asking for directions a lot. I want to go to JDS next Easter when Phil takes his new 6 ltr GT there.
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| Author: | stag estate man [ Fri Sep 16, 2011 4:42 pm ] |
| Post subject: | Re: flat spot |
hi all Thanks for the advice i will start with the new plugs and go on from there. the car was serviced last year with the previous owner but the bill does not say the plugs were replaced.the car has only done 1000 miles in a year and 700 of those were by me in just over a month it needed the cobwebs blowing away! its only got 74000 on it from new so is not even run in yet for a 928 cheers Grahame |
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| Author: | Lee 944 [ Fri Sep 16, 2011 7:07 pm ] |
| Post subject: | Re: flat spot |
Mileage isn't the big deal, time is. The cars don't like sitting about and things deteriorate. Cam belt is the biggest one. Work Shop Manual ( here on in known as WSM ) states that it is something like 30,000/40,000? miles between belt changes, but the manufacturer states it only has a shelf life of approx' 4 years or so I think. So things like breather hoses and seals degrade over time, although the WSM says there not due to be changed. I'm just thinking here, I'd had a beer last night as you can tell by my geography mistake so didn't register, but I had a similar issue except it was not so pronounced. I found that all the seals round the injectors had perished. They were a few quid each direct from Porsche, so I replaced them all. The fault was diagnosed when I sprayed break cleaner down under the inlet manifold. |
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| Author: | Lee 944 [ Sun Sep 25, 2011 7:49 am ] |
| Post subject: | Re: flat spot |
I would just like to make a quote from this page. JDS Porsche wrote: Weak running can result in a significant loss of top end power, hesitation and "flat spots" when the throttle is opened quickly for maximum acceleration. For those that haven't looked through Johns site, I suggest you have a wee look and find out if any symptoms match his suggestions. |
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| Author: | stratfordshark [ Sun Sep 25, 2011 9:40 am ] |
| Post subject: | Re: flat spot |
If it is weak mixture then the handy thing is that on the analogue dash S4s there is a pot to control mixture strength at bottom of central electric panel (later ones have cat and cannot be varied). You can check the CO level using fairly cheap meter with sensor bunged up exhaust (I had digital one from Halfords to change level on my last car when it failed MOT on too high CO). The pot has about 20 turns I recall so you have very fine control on mixture. Someone may have fiddled with it in past and not had measuring gear to return to correct level. |
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| Author: | Dave Mac [ Sun Sep 25, 2011 4:37 pm ] |
| Post subject: | Re: flat spot |
If the MAF is weak, that will hold the car back under hard acceleration. When i bought my S4 it would get to 100 then struggle after that. I fitted a new one, John Speake rebuilds them. |
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| Author: | stag estate man [ Tue Sep 27, 2011 12:12 am ] |
| Post subject: | Re: flat spot |
Hi all Thought i,d put some fuel injecter cleaner in with the petrol and it seems to have sorted out the flat spot on the car so i,m really pleased Will still fit some new plugs though .I may also send the MAF off to JDS for a check over as i dont think its ever been changed and from what i,ve read it can transform the cars performance. Is there any difference in the MAF from a non cat s4 to a later cat equiped car? Cheers Grahame |
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| Author: | stratfordshark [ Tue Sep 27, 2011 6:55 am ] |
| Post subject: | Re: flat spot |
No difference Graham. Same MAF on all S4s, GTand GTS |
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| Author: | kenthepipe [ Tue Sep 27, 2011 1:32 pm ] |
| Post subject: | Re: flat spot |
Lee 944 wrote: Mileage isn't the big deal, time is. The cars don't like sitting about and things deteriorate. Cam belt is the biggest one. Work Shop Manual ( here on in known as WSM ) states that it is something like 30,000/40,000? miles between belt changes, but the manufacturer states it only has a shelf life of approx' 4 years or so I think. So things like breather hoses and seals degrade over time, although the WSM says there not due to be changed. I'm just thinking here, I'd had a beer last night as you can tell by my geography mistake so didn't register, but I had a similar issue except it was not so pronounced. I found that all the seals round the injectors had perished. They were a few quid each direct from Porsche, so I replaced them all. The fault was diagnosed when I sprayed break cleaner down under the inlet manifold. Extract quote=== (manufacturer states it only has a shelf life of approx' 4 years or so I think ) So.., I wonder how old the belt,s are when you buy one ?? like if it,s been on the shelf as it were ,for say two years ? does that mean your short changed by two years ? ......., 
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| Author: | stratfordshark [ Tue Sep 27, 2011 6:23 pm ] |
| Post subject: | Re: flat spot |
Yes it does, which is why better to get parts from people with high turnover of 928 items unless OPC. But I expect shelf life is longer than in the high heat - and ozone - of actual use. |
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