A Question for other Boosted Mustangs

Pentalab

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Depends on the PID he's watching. If he's watching Pressure Drop Across Injectors then seeing 40psi is normal. As long as it stays around 40psi in that instance he's good. If he has an aftermarket pressure gauge then yes, he has issues.

I have 3 x aeroforce gauges plugged into OBD port. One of the pid's is...'fuel pressure'.... and another pid is... 'fuel rail pressure'. They both indicate 40 psi at all times the eng is on. Pressure in manifold will read as low as -20.....and as high as + 5.7 psi...(max boost). FPDC will vary from 40% at idle..to 80% at wot. No bap used, but I did install 10 gauge wire from battery post to fpcm in trunk..which reduced the fpdc a bit. I measured 14.75 vdc across the battery posts..with my Fluke 87 DVM. The aeroforce gauges will also read battery voltage, but indicate 14.4 vdc..... which is .35 on the low side.
 

Laga

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Set the interceptor gauge so it reads... both fuel rail pressure...and also fuel pump duty cycle.
(fpdc). The fpdc will indicate 1/2 of the actual FPDC.

I noticed on my own interceptor gauges, that with...'key on, eng off' the fuel rail pressure is 50 psi....allowing time for the gauges to boot up. Once started , pressure drops to 40 psi..and
stays put... regardless of rpm..... or boost.
I’ll do that later. Yesterday, driving around the fuel pressure would bounce between low 39.X and 40. At WOT it shot up to 69. Never saw a drop more than 1
 

Justin302

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I did some revs last night in my garage and was watching the data. My fuel rail pressure sensor was getting about 13 psi of boost with a fast rev, my fuel pressure would jump up quickly to 52 psi, car would pop and bog as the fuel pressure drops to 32 or lower psi.
 

01yellerCobra

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I have 3 x aeroforce gauges plugged into OBD port. One of the pid's is...'fuel pressure'.... and another pid is... 'fuel rail pressure'. They both indicate 40 psi at all times the eng is on. Pressure in manifold will read as low as -20.....and as high as + 5.7 psi...(max boost). FPDC will vary from 40% at idle..to 80% at wot. No bap used, but I did install 10 gauge wire from battery post to fpcm in trunk..which reduced the fpdc a bit. I measured 14.75 vdc across the battery posts..with my Fluke 87 DVM. The aeroforce gauges will also read battery voltage, but indicate 14.4 vdc..... which is .35 on the low side.

My guess would be both of those are different ways of measuring the drop across the injectors. Sounds like all is good to me. But I'm not a pro.
 

07 Boss

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I have 3 x aeroforce gauges plugged into OBD port. One of the pid's is...'fuel pressure'.... and another pid is... 'fuel rail pressure'. They both indicate 40 psi at all times the eng is on. Pressure in manifold will read as low as -20.....and as high as + 5.7 psi...(max boost). FPDC will vary from 40% at idle..to 80% at wot. No bap used, but I did install 10 gauge wire from battery post to fpcm in trunk..which reduced the fpdc a bit. I measured 14.75 vdc across the battery posts..with my Fluke 87 DVM. The aeroforce gauges will also read battery voltage, but indicate 14.4 vdc..... which is .35 on the low side.


I don't know, that just seems a little weird to me. Think about it. The pressure difference between both sides of the injector (one side in the fuel rail and the other inside the manifold) will determine the amount of fuel given a set injector pulse. If the pressure difference drops to half one would think the amount of fuel would be half also. Now there are multitudes of tables that determine the amount of fuel and maybe injector pulse is changing with pressure difference but something must tell the injector to give more fuel given the changing relative pressure differences.
 

weather man

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This is when I was turbo. Dual DW200's and a BAP.

 

Pentalab

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I don't know, that just seems a little weird to me. Think about it. The pressure difference between both sides of the injector (one side in the fuel rail and the other inside the manifold) will determine the amount of fuel given a set injector pulse. If the pressure difference drops to half one would think the amount of fuel would be half also. Now there are multitudes of tables that determine the amount of fuel and maybe injector pulse is changing with pressure difference but something must tell the injector to give more fuel given the changing relative pressure differences.

How are u measuring fuel pressure ?? Have u plugged a device like the interceptor into the OBD port ?? AFAIK, the injector regulates fuel flow via ECU..which controls the duty cycle.

For the OP, is the 'sock filter' at base of pumps clean ? Mine clogged up one day. Eng ran fine TILL I tried to get into boost (I could only get .3 psi boost)..... at which point, my fuel pressure dropped from 40 psi..down to 5 psi. FPDC was at 98%.

Once plastic sock filter cleaned out with garden hose, and dried, re-installed.... back in business.
40 psi, idle or 6kprm/wot/mashed. 40% fpdc at idle.... 80% at 6krpm/mashed. .... 5.8 psi boost.
 

Pentalab

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I have the Gt500 pumps, my last dyno before I started getting into the new tuning through Lasota was 580whp.

The dual GT-500 pumps should be ample with 93 octane. If not, a dual BAP (single 12 vdc input / dual regulated 16.9 vdc outputs) would do the trick.
 

07 Boss

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I did some revs last night in my garage and was watching the data. My fuel rail pressure sensor was getting about 13 psi of boost with a fast rev, my fuel pressure would jump up quickly to 52 psi, car would pop and bog as the fuel pressure drops to 32 or lower psi.


Sounds like there is some kind of lag from when you get a change in manifold pressure to when the the fuel rail pressure catches up. Does the duty cycle for the pump jump up when the pressure drops? If not it may be a tuning issue. If it is being commanded to pump but the pressure is not there there is a delivery problem. Either a restriction or the pumps aren't working well.
 

07 Boss

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How are u measuring fuel pressure ?? Have u plugged a device like the interceptor into the OBD port ?? AFAIK, the injector regulates fuel flow via ECU..which controls the duty cycle.

Straight from the fuel rail via Autometer Elite. Did you watch the video I posted? You can see rail pressure change with manifold pressure. Relative pressure should remain constant at 39-40 psi above manifold pressure. At least that's the way I understood it. I've never ran fuel rail pressure data from my OBD port so I don't know if it is relative pressure or actual rail pressure that it is reading. If it is reading pressure relative to manifold pressure it is doing what it should. If it remains at an actual 40 psi whether under vacuum or boost I would thing there would be some issues.
 

RLF9409

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I'm following this thread. I don't have as bad of an idle return issue but sometimes I do. Lito tune as well. Doesnt really bother me but I want it to be perfect.
I watched your vids and man your AFR is rock steady at cruise. Does it go lean or rich during WOT?
Do you have a bypass valve? Mine kept getting hung up at times...

Sent from my SM-N920V using Tapatalk
 

Pentalab

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Straight from the fuel rail via Autometer Elite. Did you watch the video I posted? You can see rail pressure change with manifold pressure. Relative pressure should remain constant at 39-40 psi above manifold pressure. At least that's the way I understood it. I've never ran fuel rail pressure data from my OBD port so I don't know if it is relative pressure or actual rail pressure that it is reading. If it is reading pressure relative to manifold pressure it is doing what it should. If it remains at an actual 40 psi whether under vacuum or boost I would thing there would be some issues.

Everybody and their dog, who plugs anything into the OBD port see's the same 40 psi. Only time it reads higher is with key on, eng OFF.... (and allowing 30 secs for aeroforce gauges to boot up)... then it reads 50 psi. So the 40 psi must be above manifold pressure. You proved that with ur autometer connected directly to fuel rail.
 

07 Boss

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Everybody and their dog, who plugs anything into the OBD port see's the same 40 psi. Only time it reads higher is with key on, eng OFF.... (and allowing 30 secs for aeroforce gauges to boot up)... then it reads 50 psi. So the 40 psi must be above manifold pressure. You proved that with ur autometer connected directly to fuel rail.

That's good to know. So in the case with the OP. Is he seeing a dip in pressure from the OBD port or from the actual rail? And I wonder what his duty cycle is when it drops? I wonder if it is trying to catch up but can't or if it's not even trying.
 

06monera96

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40 idle
50 when I hammer it to compensate for downshift quickly and hammering it
40 while going WOT
(38lbs injectors) 8lbs of boost, 438hp/438tq
 

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