John B

iTrader: (10)

I have been analyzing the ATAP data and FP for my motor and notice that:
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• <font size="2" face="Verdana, Helvetica, sans-serif">avg timing between 4000-6000RPM ~26° WOT</font></li>
• <font size="2" face="Verdana, Helvetica, sans-serif">avg injector PW ~19 at WOT</font></li>
• <font size="2" face="Verdana, Helvetica, sans-serif">avg 02's 0.892 at WOT</font></li>
• <font size="2" face="Verdana, Helvetica, sans-serif">avg LTFT's 4.98 at WOT</font></li>
• <font size="2" face="Verdana, Helvetica, sans-serif">fuel pressure starts at 56PSI then drops to 53PSI at WOT high RPM
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<font size="2" face="Verdana, Helvetica, sans-serif">Here are my questions:
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• <font size="2" face="Verdana, Helvetica, sans-serif">Is my timing low due to the high injector PW at WOT making the motor think I have a larger load than I do?</font></li>
• <font size="2" face="Verdana, Helvetica, sans-serif">I have my MAFT set at +4% rich at WOT to achieve the 0.892 02 readings...is this to compensate for the low fuel pressure?</font></li>
• <font size="2" face="Verdana, Helvetica, sans-serif">Is the low fuel pressure causing my injectors to stay open longer creating the illusion of a larger load therefore causing the PCM to pull timing?</font></li>
• <font size="2" face="Verdana, Helvetica, sans-serif">Why would my fuel pressure drop as the RPM's climb? I have a Walbro 255 pump.
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<font size="2" face="Verdana, Helvetica, sans-serif">Thanks!

WILWAXU

iTrader: (6)

<img border="0" title="" alt="[Razz]" src="gr_tounge.gif" />

John B

iTrader: (10)

Anyone?

ChrisB

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by John B:
<strong>Is my timing low due to the high injector PW at WOT making the motor think I have a larger load than I do?</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif"></strong>

Timing is a function of MAF flow rate, rpm, and any knock retard you have. These are the only real factors that are going to effect your timing.

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">I have my MAFT set at +4% rich at WOT to achieve the 0.892 02 readings...is this to compensate for the low fuel pressure?</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">

Loaded questions - stock O2 readings are pretty imprecise, so no valid assumption can be made on what you had to do to achieve a give mV reading.

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">
Is the low fuel pressure causing my injectors to stay open longer creating the illusion of a larger load therefore causing the PCM to pull timing?</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">

Not pull timing, no. With respect to closed loop operation and it's effect on WOT fueling (if the l-trims are carried across) your injectors may stay open longer.

[/quote][qb[
Why would my fuel pressure drop as the RPM's climb? I have a Walbro 255 pump.
[/QB][/QUOTE]

No idea, it really shouldn't be. You might check your fuel filter.

Chris

John B

iTrader: (10)

Chris, thanks for the responses.

y2khawk

iTrader: (5)

My turn <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

Is my timing low due to the high injector PW at WOT making the motor think I have a larger load than I do? I have my MAFT set at +4% rich at WOT to achieve the 0.892 02 readings...is this to compensate for the low fuel pressure?

Lower timing _MIGHT_ be due to your MAFT settings at 4%+. Reporting more air will give less timing. More calculated load that way. Dropping FP will require the bump from the MAFT to get the O2's up.

Is the low fuel pressure causing my injectors to stay open longer creating the illusion of a larger load therefore causing the PCM to pull timing?

No, PCM has no idea of the FP. PW has no influence on timing.

Why would my fuel pressure drop as the RPM's climb? I have a Walbro 255 pump.


Supply restriction. Like chris said, check the filter. The lines are not the restriction, as i ran stock sized lines just fine. Still have the line damper unmodified?? It's a nasty restriction, and with 19ms PW at WOT you close to 100% duty cycle. That's alot of fuel to get throw that damper.

<img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

John B

iTrader: (10)

Harlan, I have my base set at +10% rich and WOT set and additional +4%. I needed to bump my base to get the 02's headed in the right direction (it was initially running too rich at WOT with even lower timing) so is this now causing the low timing?

I have LS1_Edit and just thought that I would start with the MAF table and begin tweaking by bumping it up around 10% to compensate for the MAFT and then bump the PE values a bit too but I guess I am wondering if I should be doing something different. Ideas? Harlan/Chris?

Pro Stock John

iTrader: (34)

You could put a fuel gauge on the scrader valve and see what's it's doing.

O2's are useful for a basic tune. Beyond that it's got to be done on a wideband or you need to make runs at the track and need to try adding or subrtracting fuel to see what it will do.

My car has .890 02's but with a 12:1 AF... Not good. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

Harlanski, tell me more about this damper mod, would I benefit? Should I just go to the 97 style rails and change my setup?

chasgiv3

iTrader: (1)

John, I believe the line damper is the silver mechanical gizmo that sits in between the two fuel rails. This can cause a restriction and can be modified to eliminate that said restriction thus eliminating the pressure drop.

One other thing to check. Is the Walbro making a good electrical connection. There may be a voltage drop to the pump causing it to lower its volume potential which eventually causes it to drop fuel pressure at high rpms.

The other thing to consider is the pump itself or any kinks in the line or a leaking fuel line that bleeds off pressure.

John B

iTrader: (10)

Ahhhhhhh, good point chasgiv3. I'll have to get a voltmeter and some extra long wire and do some more Freeway thrashing at WOT and watch the volts <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

PSJ, </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">You could put a fuel gauge on the scrader valve and see what's it's doing</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">That's where I did measure the FP. I used an extra long hose and just taped the gauge face to my windshield when I took it out for some WOT runs (boy did I get some funny looks!).