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940 acceleration

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Old Jun 15th, 2019, 17:55   #1
360beast
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Default 940 acceleration

I have an odd issue with my 97 940 turbo, completely standard apart from an mbc set to 8psi.

Sometimes I put my foot down and it goes like poop of a shovel, other times my mate in his 95hp 360 can easily keep up and even goes faster occasionally. No warning lights on the dash and I have had it on the smoke machine at work to look for vacuum leaks but there aren't any.

Usually if I build up the speed slowly and don't use full throttle it seems to accelerate quicker too!

Any suggestions?
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Old Jun 15th, 2019, 21:22   #2
Laird Scooby
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First thought on that is the fuel filter Luke. Second is a dirty MAF, third is a sticky/lazy FPR, fourth, broken/loose baffle in one of the exhaust boxes causing a temporary blockage (could even be the cat) and fifth is a sticky wastegate so it's not giving you the boost you should be getting.

Could also be the fuel pick up in the tank but the only way is to check through everything methodically. Might be a lazy/worn fuel pimp as well, got a feeling you said you changed the pump though or was that your mate who has bought the red one?
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Old Jun 15th, 2019, 21:28   #3
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Quote:
Originally Posted by Laird Scooby View Post
First thought on that is the fuel filter Luke. Second is a dirty MAF, third is a sticky/lazy FPR, fourth, broken/loose baffle in one of the exhaust boxes causing a temporary blockage (could even be the cat) and fifth is a sticky wastegate so it's not giving you the boost you should be getting.

Could also be the fuel pick up in the tank but the only way is to check through everything methodically. Might be a lazy/worn fuel pimp as well, got a feeling you said you changed the pump though or was that your mate who has bought the red one?
Brilliant advice as usual Dave, that should give me some.stuff to play with!

Yeah it was my mate who fitted one to his red 940.
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Old Jun 19th, 2019, 02:14   #4
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If a lighter throttle is working think about weak spark.
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Old Jun 19th, 2019, 05:03   #5
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sucked inlet hose between turbo and air mass measure (Filter)
feel if this is soft.
good luck, Kay
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Old Jun 19th, 2019, 17:14   #6
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sucked inlet hose between turbo and air mass measure (Filter)
feel if this is soft.
good luck, Kay
The one going from the AMM to the turbo? If so then I can squeeze it quite easily.

I will pull the plugs, clean and gap them too.
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Old Jun 19th, 2019, 18:10   #7
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You could try putting a few hose clamps around that intake hose to make it keep it's shape. Never tried it myself, but it sounds like it would work.
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Old Jun 19th, 2019, 21:09   #8
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yes, the hose between AMM and turbo

the hose clamps will help if you stitch the hose to the clamp and seal it afterwards.

No joke, stitch it with stainless steel wire or buy a new hose.

good night, Kay
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Old Jun 21st, 2019, 16:18   #9
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Pulled the plugs out earlier, all need gapping again to 0.7mm, number 4 and another cylinder were way too big, amazing how much difference there was in the electrode gaps seeing as they are all less than 10k miles old and were all set to 0.7mm.

So far it seems to be running nicer and I haven't lost power when booting it!
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Old Jun 21st, 2019, 17:19   #10
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That's kind of worrying Luke. If everything is ok, those plugs should only be 0.8mm at the most after 10k miles.

What plugs are you running in it? (Make and type)

Which two were the largest? You've said #4 and i'm guessing #1 was the other with #3 a second choice. It sounds as if the two largest gaps were running lean - did those plugs have a whitish, glazed appearance?

Couple of things worth doing, compression test on all 4 pots, injector flow test on all 4, check injector "O" rings particularly where the injectors go into the manifold and check the manifold for corrosion at those points, check the inlet manifold gasket for leaks, also check all your valve clearances if anything is untoward in the previous tests.

Glad you've found the main symptom/cause of the rough running but what has caused it in such a short mileage?
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