I will PAY YOU if you can tell me whats wrong with my car before I drive it off a cliff

[PNWSVT]

I each fuel rail receives its own feed line from the Y block. Youre saying I still need to provide a crossover?

working down the list of items, I also got a revised tune so ill keep yall posted.

 

[wkornf]

review the data log. what does timing do when it happens? what's battery voltage? etc.. should be easy enough to spot something

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[03' White Snake]

I each fuel rail receives its own feed line from the Y block. Youre saying I still need to provide a crossover?

working down the list of items, I also got a revised tune so ill keep yall posted.

No, sounds dead head. That is how mine is plumbed and I do not have a crossover line.

 

[PNWSVT]

Yeah sounded dead head to me as well.

New tune update:

Car runs way better and is getting closer. Still needs one o2 sensor shut off. My AFRs are getting better at WOT. I did a 3rd gear WOT starting at 30mph and at WOT it’s at 10.5 afr

I wanted to try the new tune first before doing compression and leak down testing etc.

What is weird though is my fuel pump duty cycle is around 5% and at WOT it never went over 30% and I’m running 2 gt supercharged pumps. Not sure if that’s normal.

My voltage and everything else remained constant as well.

 

[wkornf]

you have a return fuel system, duty cycle doesn't mean anything, you need to monitor fuel pressure. but based on your air fuel it's probably Ok


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[bigmoose]

What is weird though is my fuel pump duty cycle is around 5% and at WOT it never went over 30% and I’m running 2 gt supercharged pumps. Not sure if that’s normal.

This seems odd. You have a return system but are seeing FPDC changing. I cannot confirm but I don't think it should do this.

If your tune is not setup for a return system and it is varying the pump voltage it could cause weird issues like you are seeing.

 

[PNWSVT]

Fuel pressure average was 39 +/- 2

 

[Bdubbs]

Have you logged fuel pressure drop across injectors? Obviously your getting enough fuel if AFR is 10.5 across the board.

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[03' White Snake]

Fuel pressure average was 39 +/- 2

This does not seem correct to me. My magnafuel regulator boosts fuel pressure 1 psi for every psi of boost. 20 psi of boost increases the fuel pressure to around 60 psi under WOT.

Do you have a vacuum/boost line hooked up to your regulator?

 

[Liquidsnake]

This does not seem correct to me. My magnafuel regulator boosts fuel pressure 1 psi for every psi of boost. 20 psi of boost increases the fuel pressure to around 60 psi under WOT.

Do you have a vacuum/boost line hooked up to your regulator?

This, though this would be a huge issue if it was returnless, it would be a less obvious problem in a return system because it’s cycles, but still cause fuel issues. The regulator should boost fuel pressure 1:1 like White Snake said.

 

[MG0h3]

When switches to return the fpdm should be 100%


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[c6zhombre]

Sorry if this has been discussed already.....but you are running supercar GT pumps with a return setup? I think you're ok to do that.....as long as they're not staged. Those pumps do not have an internal checkvalve....so a pump not running will have have fuel back feed thru it.

 

[Chancey]

This may not help and you may have ruled it out already, but I had a similar experience in a supercharged and heavily modified 2017 mustang GT I built. Lund and 2 other very reputable tuners could not find the issue. Everything was new and I did the build as soon as I bought the car new. Ran awesome one day, the next it ran like crap! Then the next day great again. Back and forth with no rhyme or reason. Replaced EVERYTHING almost just to make sure I didnt have any bad/faulty new parts. Kept showing the fuel values changing for no apparent reason. Everyone kept leaning towards the o2’s, ECU, vaccuum leak, plugs, etc. Everyone (myself included) questioned gas quality at some point. I was buying fuel from a local chevron station where I bought it for all of my vehicles and had for years prior to this. None of my other vehicles had any running issues at all. Stumped us all when I switched to texaco fuel and it smoothed right out. I know, to this day everyone says it was just a coincidence. But what can I say? It immediately ran better and never waivered again. It cursed me from the day I built it until the fuel change. Continued to run perfect until I traded it for my GT500. I suspect it was some bad gas at that particular station and not related to chevron. Only the modded car had issues with the fuel maybe? Up until then, I was beyond insane mad and hated the car because of the untraceable headaches! I was a breath away from holding it wide open in 1st gear until it exploded! Every tuner (all very good and reputable) said yeah I can get that tuned out... then everyone said they couldn’t figure it out and got tired of trying eventually. Hopefully you will find the issue. Nothing is worse than a mystery problem that cant be found. God speed...

 

[gimmie11s]

OP how is it running?


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[SVT_Troy]

I each fuel rail receives its own feed line from the Y block. Youre saying I still need to provide a crossover?

working down the list of items, I also got a revised tune so ill keep yall posted.

Correct, a crossover on the other end of the rails. I use a 6an for my crossover.


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[Nightmare302]

Correct, a crossover on the other end of the rails. I use a 6an for my crossover.


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A crossover is not needed if you are running a line to each rail.

You have some major concerns, if you are not seeing a 1:1 rise with fuel pressure to boost you have an issue either source vacuum related or reg related.

Also, you should not be seeing changes in your FPDM voltage if you are return style, granted I don't tune much but I never remember showing changes once it was switched to return in PRP.

 

[cj428mach]

Fuel pressure average was 39 +/- 2

Thats correct if you're reading it off the FRPS.

 

[Blown38]

Like CJ said above, if you are running a boost line to the FRPS it should read 39psi thru the OBD port or what ever pressure you set the mechanical regulator to.

For a return system the pumps should be set to run 100% duty in the tune.

Does the tuner know you made it return style?

 

[BlckBox04]

Can I ask another crazy question
Why are you doing 3rd gear pulls on the dyno and not 4th?

 

[can04cobra]

Can I ask another crazy question
Why are you doing 3rd gear pulls on the dyno and not 4th?

I believe he is tuning it on the street not a dyno, guessing due to speeds he would encounter in 4th is why he is doing 3rd gear pulls.

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