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914World.com _ 914World Garage _ My djet fuel pressure testing results.

Posted by: Bleyseng Apr 24 2007, 07:14 PM

on my car at 29-30lbs of fuel @ 3000 rpms cruising the AFR is 13.7 to 1.
bump up the fuel pressure to 35-36 lbs @ the same speed the AFR is .....13.1 to 1.

So in this case it don't adjust it that much but for fine tuning its fine. It seemed to change it across the board including WOT that much.

These are just cleaned and tested 2.0L injectors too.

Posted by: jk76.914 Apr 24 2007, 07:56 PM

Hey Geoff, That's great data. I've always wondered about that. Have you ever tried a pressure regulator that modulates fuel pressure with engine vacuum? Seems to me that it may help some of the part throttle cruise lean misfires that some of us see, if it's set up thoughtfully.

Jim

Posted by: Bleyseng Apr 24 2007, 09:55 PM

I guess I could try one off a ljet setup to see but you shouldn't be having a lean miss.

you could have a MPS thats slightly lean in spec.. the factory ones I have tested are all over the place.
this is why I have said for 10 years now the "Best" way is to pull the WOT stop and tune the sucker on a dyno to get the right AFR under load conditions. You then adjust it to be close thru out the rpm range as the AFR will be like a wave and not flat. You adjust for the best average!

Using a LM1 under driving conditions works great too but its a headache. I need to setup a harness extension so I can have the MPS in the cabin.