Fuel pressure changed timing?

[Garbage_Mechan]

I finally made time to rework my fuel system on the 91.
It had a Facet Duralift that was making 6psi but dropping to 0 to 1 under heavy load. Added a second Duralift in parallel (why not already had it). Now have 8.5 to 9 psi at idle and light load. 6.5 to 7 under load. Checked timing after and it was at 12. Last time I set it I left it 8.5 to 9. Part throttle is better, but top end goes flat after 1/2 throttle. Fuel mileage is way down.
Did the fuel pressure fool me on the timing?

 

[Thewespaul]

Yep fuel pressure changed your timing, more inlet pressure means theres more pressure working against the transfer pump regulator, which allows it to increase transfer pressure, which increases your hydraulic advance. If you retard your timing now you will get back the midrange and probably have more power than before. Funny that even with two facet's its still dropping fuel pressure with a stock pump.

 

[Garbage_Mechan]

I did reset the timing but I’m wondering if I shouldn’t because there is 9 psi while running the timing test but 6.5 under load so is it retarding under load compared to the timing test?
I think my next move is to try and stabilize the fuel pressure.

 

[Garbage_Mechan]

At what psi does the timing start to move and how many degrees? Would 3 psi roughly equal 3 degrees? I seem to remember Mel posted about it before.

 

[Thewespaul]

You want to minimize pressure drop as best you can, I run the holley bypass regulators. You will have more retarded timing under load then in neutral when youre timing it. In my testing a stock pump loses about 1* per 5 psi, doesnt sound like a lot but these engines are pretty sensitive to timing changes.

 

[Garbage_Mechan]

So after I changed the fuel system and increased pressure it increased my timing from the 9 I set it to 20,000 miles ago to 12. Or something else happened. Cold idle timing advance is working, engine sound changes when applying / removing power. Pressing down the light load timing lever definitely changes engine sound. So I don’t think something is stuck.

 

[Garbage_Mechan]

Wes, also interested in your comment that it was a lot of pressure drop for a stock pump. It was rebuilt by local ADS certified shop I used for years. It is my spare. But fresh rebuild with a lot of shelf time.
My pumps theoretically put out 66 gph. It will fill a gallon jug in 1:20.
Gotta figure this out 10 mpg empty isn’t gonna work!

 

[Thewespaul]

You probably weren’t getting enough transfer pressure with the previous fuel system to overcome the light load advance piston spring, which is why you are seeing so much more advance with more inlet pressure. I would set the timing at 9* now, or play with it and see what makes the best compromise between top end power and economy. Your injection pump is fine, I’m sure you’ve read the other threads were the facet owners are having delivery issues and dropping fuel pressure under load, I was just commenting on how it’s surprising to see it still drop fuel pressure under load with two facet, just further says to me they are really under sized for our application. 66 gph is free flow, I preach the mr gasket 105p pumps a lot, they free flow over 100 gph.

 

[Garbage_Mechan]

There has to be something I’m missing I have timing at 9*. Seems to have better part throttle performance, WAY worse fuel mileage, and past 1/2 throttle there is no change in power or smoke. Just goes flat.

 

[Thewespaul]

Where are you taking your pressure reading?

 

[Garbage_Mechan]

From the port formerly occupied by the vacuum switch on the fuel filter head. Should be just what the pump sees.
I have a Swagelok adjustable spring loaded poppet valve in the return line from the filter head in place of the original orficed return fitting. I’m going to experiment with getting the fuel pressure more constant. But I still don’t get the increase of 3* with more fuel pressure, radical mileage drop and increase in the loss of the top 1/2 of the throttle. (There was already flattening out on top which I previously blamed on low fuel pressure.)

 

[Thewespaul]

Block that off, even temporarily and get some readings. I could see that being your issue.

 

[The_Josh_Bear]

Adding to the mix it looks like your 91 has the Banks turbo-- you may want to try lowering your timing quite a bit and work up from there. Most IDI turbo setups prefer a little less advance than N/A.

When I went from single Facet back to an OE lift pump(6.5-5.5 psi idle to WOT) my timing became much more sensitive. With the Facet it didn't seem to care much where the timing was and so it was a little better advanced, say 9*.
Finally after running a cleaner through I'm all the way down to 6* where she runs the best. I was never a cleaner/lubricity additive guy before but after the lift pump install she ran best at 9.5+*, where most turbo guys run best at 7ish. Thats after a kreen treatment and now some Howes every tank full. I'm still working out the timing bugs but thought I'd share since we are in a similar position.
And anything you can do to make a steady 5 or 6psi will really make you happy behind the wheel.
It's pretty wild how much performance was left on the table with just a Facet for me.

 

[Clb]

So now a rig with....2 facets that are not cutting the mustard!
My truck lost 2.5* and 2# boost running down Oregon coast (long story) changed out filters, nadda.

Got to investigate.

1 more nail in the coffin.
@Thewespaul Wes check my math please...the loss of input psi would back out timing in the ip
right???

 

[Thewespaul]

Yes, less inlet pressure means less hydraulic advance, so more retarded timing.