I have tried to get the engine to be more responsive to gas pedal movement after the warm up period for the last 14 months. Began by adding a 0.5 mm self made shims under the CSV housing. Since then I have fiddled around with different sizes until now. I ended up adding two 0.5 mm shims. Finally there is no change in responsiveness when cold compared to when warm and the engine is really running great!
When I took it for a tough test drive I smiled all the way up to 4500 rpm when the engine started to misfire – and it happened again also at different rpm's, but always after a period with the gas pedal floored. I suspected fuel starvation and went to work.
- cleaned the fuel lines
- cleaned the fuel tank filter (not much dirt)
- changed the fuel filter
- did a fuel pump flow check (got 0.75 litre in 15 sec)
And finally today I cleaned the fuel pump filter. Not much info in the manuals so I took some pictures.
One bolt and two nuts holding the pump shield (10 mm spanner).
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I used a clamp on the inlet hose instead of emptying the tank.
This is the new / small type pump. The fuel outlet connection uses spanners 19 and 22 mm.
Remember were the electrical cables belong.
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The pump is suspended in three bolts. Unscrew the nuts at the top with a 10 mm spanner.
It may be possible to unscrew the fuel filter without removing the pump, but not mine.
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The fuel filter sits on the inside of the inlet/nut unit. 24 mm spanner.
This is how much dirt that came out after I tapped it a few times. I also cleaned it with compressed air.
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After installation I blead the pump by the little screw in the by-pass connection. According to the Haynes Manual there should have been installed a hose from this connection via a T to the fuel return hose. I have read somewhere that if not installed you need to bleed the pump with the inserted screw (accessible through a small hole in the shield).
Download Attachment: pump bleed.jpg79.49 KB
Finnaly I did a new fuel pump flow test and the amount went up from 0.75 to 0.8 litre in 15 sec. I used a hose with a clamp to blend off the fuel tank return inlet. I managed to swap between the hoses while holding my finger over the opening – without much spill.
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I then went for a new test drive. And even if I may still have a slight blockage somewhere or a not so good fuel pump (should be 1 litre in 15 seconds) the engine misfire under heavy load disappeared – and this time I kept on smiling.
Per G. Birkeland
69 280 sl aut 834
Norway