Drag Week 2012 - Project GIRTST 71 Mustang (get it right the second time)

[dieselgeek]

Although, Bill IS sharing a pressure transducer with his Autometer fuel pressure gauge. One thing he might try is disconnecting the signal wire back to the gauge. It could be an electrical interference issue...?

[milner351]

I'm not sure I'm reading the graphs right - but while under power going through the gears - the vertical snapshot line shows AFRs in the 16 range - while the fuel pressure is oscillating... I'm not sure if the frequency of oscillation of pressure and the RPM of the A1000 are related - but it seems like the pump could be cavitating and "sucking air" in bursts as the impeller passes the input port of the pump.

I have a feeling the AFR isn't really 16?

What was the fuel level in the tank during these passes? Can you fill the tank and do a couple quick WOT blasts on the street to see if the pressure oscillations repeat with more fuel in the tank? That would at least prove or disprove the sump cure idea.

[dieselgeek]

I'm not sure I'm reading the graphs right - but while under power going through the gears - the vertical snapshot line shows AFRs in the 16 range - while the fuel pressure is oscillating... I'm not sure if the frequency of oscillation of pressure and the RPM of the A1000 are related - but it seems like the pump could be cavitating and "sucking air" in bursts as the impeller passes the input port of the pump.

I have a feeling the AFR isn't really 16?

What was the fuel level in the tank during these passes? Can you fill the tank and do a couple quick WOT blasts on the street to see if the pressure oscillations repeat with more fuel in the tank? That would at least prove or disprove the sump cure idea.

During the run the highest AFR I see is when he shifts from 1st to 2nd, and that's probably going 13:1. The high point comes when he stabs the throttle, and here's the problem with that: anytime the engine stumbles, you get a Lean spike even if the stumble was caused by being too rich. You have to look at the SeqPW1 (sequential pulsewidth cylinder 1) to see how much Accel Pump fuel is being added to be sure if this is a too much or too little pump shot issue.

Bill if you can, send me the actual datalogs and I'll go over them tonight after work.

[milner351]

I see - I was looking at the max / min numbers - duh.

[CDMBill]

Yep, but that would only bother me if I knew for sure that they were sampling from the exact same port, hose, etc. I can't remember how he had his regulator plumbed.

Regulator is not vacuum referenced so MAP would have no direct effect, and we are not yet adjusting for MAP changes beyond the 16x16 fuel table.

Fuel set-up is chapter and verse from Aeromotive's fuel system planner for 1300 N/A HP with the exception that I'm running the larger capacity 13110 pro series regulator.(see installation instructions link)

http://aeromotiveinc.com/wp-content/uploads/2009/12/13110.pdf

http://aeromotiveinc.com/wp-content/uploads/2010/02/09Aeromotive_EFI_PowerPlanner.pdf

[dieselgeek]

I didn't realize we weren't referencing manifold pressure.

That makes this situation even more confusing.

Bill, one thing to check before freaking out and swapping more parts - disconnect the signal that goes to your Fuel Pressure gauge and make a pass. The fact that things go sketchy when your electrical system is under it's greatest stress (WOT) has me thinking it's possibly just a noise issue. Maybe we're pulling too much current from that pressure transducer with two devices reading it's output.

[CDMBill]

I'm not sure I'm reading the graphs right - but while under power going through the gears - the vertical snapshot line shows AFRs in the 16 range - while the fuel pressure is oscillating... I'm not sure if the frequency of oscillation of pressure and the RPM of the A1000 are related - but it seems like the pump could be cavitating and "sucking air" in bursts as the impeller passes the input port of the pump.

I have a feeling the AFR isn't really 16?

What was the fuel level in the tank during these passes? Can you fill the tank and do a couple quick WOT blasts on the street to see if the pressure oscillations repeat with more fuel in the tank? That would at least prove or disprove the sump cure idea.

This run was with 17-18 gallons in the 20 gallon tank. I keep it that way for the moment as the small I installed in the tank years ago for a carbed situation tends to starve the pick-up (this is noticable) below 1/2 to 1/3rd full. There is a bout 2 sq. in. of inle to the sump so it isn't a flow restriction, rather a slosh issue IMHO.

AFR down track on this pass was in the low 12's. I added fuel after the True Street laps, but the NMCA changed all the classes to 8th mile after True street Sat. afternoon, in order to get the 460 cars through all of the various ladders with the 7:30am-7 PM Saturday, 9:30 AM-6 PM curfews. My red light 1/8 mile pass later in the day showed 12.3-12.5 afr's for the shorter duration of the 8th mile run.

[Bob Holmes]

Fuel pump wiring is what gauge?

[CDMBill]

Fuel pump wiring is what gauge?

Number 10 for the direct power from the battery through a 25 Amp fuse holder to the relay, and onto the pump. Pump ground also #10 direct to clean chassis ground. We also by-passed the Aeromotive Pump controller in case it was the issue afet swapping the pump out. Interestingly the pump is louder and "angrier" sounding with just the relay in place and the pressure at idle jumped from 43.5 to 45 PSI on both the electrical gauge, the datalog from that gauge and the little analog mechanical gauge that I have tee'd into the fuel pressure port on the regulator.