Mythbuster: continuing project thread of my 1303 '75

[effvee]

Walter, you are running a boost senitive fuel regulator arn't you? Is you fuel system looped? I have seen boost senitive regulators in a looped fuel system where the fulel pump pumps the same pressure all of the time, as boost demand are needed. It is the responsibility of the regulator to up fuel pressure. Amp and wire size can come into play if the pump is worn and tired, thus the need for more amps. Can you ECM log fuel pressuee and you not at what boost pressure?

[Humble]

Your car is an animal, 418hp and still going! Hopefully you can sort out the fuel problem soon, sounds like you're on the right track with the boost tee.

As for the fuel pump, I believe you might be nearing it's limits. When I calculated my fuel needs at 100% duty cycle i got 3.8bar (55psi) flows about 230 LPH from the 044 pump and with 4x750cc injectors is 3 liters a minute or 180 LPH, which leaves me a good buffer. IIRC, you had 4x1000 injectors, 4 LPM or 240 LPH but the pump running at 3.5 bar can only supply around 237 LPH. Again, that's assuming 100% duty cycle but it looks like you may need more fuel in the future if you keep going.

Edit: That thought was half baked it seems, I just got back from Vegas so give me a break

I forgot to factor in the rising rate FPR, so here's a couple of quick numbers.
yours: initial fuel pressure 3.5 bar + 1.3 of added boost = 4.8 bar from the pump which is about 210 LPH and you need 237 LPH (again assuming 100% duty cycle)
mine: initial fuel pressure 3.8 bar + 1.7 of added boost = 5.5 bar from the pump which is about 175 LPH and I need 180 LPH (again assuming 100% duty cycle)

damn, I guess we will both need more fuel

[Wally]

Good post Humble!
I actually had similar thoughts, but some things I see IRL at the car just don't add up for me atm: I still do not see _any_ rise in fuel pressure when its comming on boost.
Did another test run last night and there's no increase in FP over the base 3.5 bar when on boost. On the contrary, FP still drops a bit to 3.25 or 3.0 bar with ~ 1 bar boost.
That was with the rerouted boost reference line.
Remember that I tested the FPR at idle with applying boost and it worked then, also matched by the log reading. So the FPR and the fuel pressure sensor read accurately (enough anyways).

With the better wiring (I assume I now have a few Volts more), the test drive last night actually showed the problem to be even worse, even at lower rpm and boost I experienced misfires from lean spikes (log showed very uneven lambda and high spikes).

My thoughts now are that the whole catch tank may be more of a restriction then a help, so I will by-pass that tomorrow and see if a direct feed from a full tank will help.
I am really puzzled so far...

[Bruce.]

A few thoughs to be helpful.

If you can set up a voltmeter to measure the volts across the pump it will confirm if you have a problem with wiring (or a connector). If the volts drop across the pump when it is flowing lots of amps, there is another source of electrical resistance between the pump and the Bat/alternator.

I'm also guessing you have a genuine 044 from a known seller? Apparently there are copies on Ebay which look good but don't perform.

Is the supply to the pump (pipe sizes and tank port) big enough? A fuel pressure sensor at the 044 input would show if there is always positive pressure at the input. If the 044 has to suck the fuel at high flow rates, the output pressure would drop.

good luck!

[Wally]

Thanks Bruce!

I just removed the catch tank and Carter feed pump and now I can maintain my target lambda all the way to redline under 20 psi of boost. Now that was fun

You were probably close with the feed to the 044 not being optimal. The intake line is 1/2" internal from the tank to the feed pump, so plenty big, but entrence into catch tank is only 7mm internal, so almost half that size. For the low pressure Carter pump probably a little too much of a restruction to get to full flow.
Feed to the 044 itself from the catch tank is 1/2" or about -12 iirc, but if there's only one restriction...

Now the 044 sucking straight from the 1/2" from under the tank works well, but at higher boost, the rising rate pressure suffers a little and doesn;t follow the boost pressure quite. That leads me to believe the 044 is somehow running a little on the edge in my set-up.
For now it will do, but maybe a second pump may be wise in the long run.

Thanks for thinking along all!

[Wally]

Originally Posted by Bruce.

I'm also guessing you have a genuine 044 from a known seller? Apparently there are copies on Ebay which look good but don't perform.

Whats a 'known seller' worth these days huh?
The info in this link I recently found comparing a fake chinese copy 044 and a real one was really helpfull.
Just for the record: I have a real Bosch 044

http://trolltuner.com/?p=692