[Diy_efi] Fuel injection problem, cont'd.

[charlesmorris at direcway.com]

Thanks for the tips, everyone... unfortunately I have already tried these things as follows:

>Speed density? 
 
I assume by that you are suggesting I check the air flow meter? This early (L-Jetronic) system does not have a throttle position sensor nor a MAF sensor, just a flapper type volume meter.
That would make sense for a fuel-related misfire problem except: the pump should be able to maintain 43 psi at the rail regardless of injector duty cycle from 0 to 100%. It's not misfiring because the injectors aren't properly pulsed, it's because the rail pressure is dropping. Anyway, if for some reason the system "thought" the engine were stopped and was trying to cut off the fuel pump, the voltage to the pump should go to zero and it doesn't. It keeps audibly running and confirmed by 13.05 volts on my DVM while driving.

> My first thought is the tank isn't vented properly and you are pulling a
>vacuum on the tank...  Try it around the block with the gas cap off and see
>what happens...

I forgot to mention I already tried that, no change. There is no emissions equipment on this car (as was factory original in Euro-spec '81 vehicles) and the tank is vented to atmosphere with a 2 psi residual pressure valve that also allows air back in. Tried loosening the cap anyway. 

>It sounds like you've double checked any flow restrictions all the way to
>the fuel rail.  Have you cleaned the injectors?  Maybe they "gummed up" when
>it was sitting in storage?

I had thought of that - and have had them cleaned and flowed by Cruzin Performance early on, once discovering the gummed filters - but that would make the rail pressure normal or high, not low. Even if they stuck open, the pump is more than capable of supplying all six at 100% duty (only about 1.8 liters/min required, the Walbro is rated for over 4 liters/min), and that would not be hard to detect from flooding!

At this point I think it almost has to be something "weird" like a "rock" of crud that rolls forward and jams in a fitting only when under flow, or a line that's getting kinked by the left rear control arm only when the car is on its wheels, etc.

-Charles



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