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      05-24-2013, 12:16 PM   #1
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Z4M fuel starvation in high G sweepers at high rpm

Has any one else ever had this problem on track. I would have it occasionally 1/50 laps when my car was N/A but now with my newly installed VT-525 and its increased fuel needs it was happening every lap in turn 9 at Roebling road. Its a high speed sweeper where i see sustained 1 G cornering for 8 seconds at high rpm's in 4th at maintenance throttle then progress to full throttle off the apex and onto the front straight. As soon as I go full throttle limp mode kicks in. This occurs in the same spot as before just way more frequently now as my car needs more fuel and is not gas tank level related ( happened on my first hot lap). My plan is to modify the pump basket for better filling and place an Aeromotive stealth 340 pump to maintain the fuel pressure i need. Has anyone else run into this issue????, I'm flattered that I'm driving the car hard enough to do this but it sucks that I'm having to trailblaze a solution. And before any one asks the injectors are good, the fuel lines are good, the filters have been replaced recently as well as the OEM pump.
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      05-24-2013, 03:54 PM   #2
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How much fuel are you running?

Fuel starving is usually related to amount of gas in a tank, for example it is really easy to fuel starve an E36 M with less than a quarter tank on a long right hander
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      05-24-2013, 04:09 PM   #3
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Quote:
Originally Posted by Kgolf31
How much fuel are you running?

Fuel starving is usually related to amount of gas in a tank, for example it is really easy to fuel starve an E36 M with less than a quarter tank on a long right hander
He said it was not level related; happened on the first lap...
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      05-24-2013, 04:18 PM   #4
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Quote:
Originally Posted by Rated M Roadster
Quote:
Originally Posted by Kgolf31
How much fuel are you running?

Fuel starving is usually related to amount of gas in a tank, for example it is really easy to fuel starve an E36 M with less than a quarter tank on a long right hander
He said it was not level related; happened on the first lap...
If you start out with a 1/2 a tank, and fuel starve on the first lap, then it could very well be related.

No note on how much fuel is in the tank
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      05-24-2013, 05:12 PM   #5
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It's happening with a completely full tank in both left and right hand high G turns . I never run with less than a half a tank .This is not a simple bad pick up design problem like in the E36 I'm afraid .
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      05-24-2013, 10:33 PM   #6
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Hmm. I think there is more going on. That doesn't have to do with pick up if it happens when its full. What you are saying is that the stock fuel pump is not keeping up with demand, which is counter to what VF and ESS say about there 500+ hp kits. Send EAS a call to see if they have experienced this with there track car.
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      05-25-2013, 07:11 AM   #7
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Quote:
Originally Posted by seank
Hmm. I think there is more going on. That doesn't have to do with pick up if it happens when its full. What you are saying is that the stock fuel pump is not keeping up with demand, which is counter to what VF and ESS say about there 500+ hp kits. Send EAS a call to see if they have experienced this with there track car.
I agree Sean I think the stock pump is not maintaining the required fuel pressure in those situations. The S54 requires a fuel pressure of 72psi at WOT in its stock NA trim . Now add 8psi from a supercharger and the required pressure is upped to 80psi . Throw in a hot day , high IAT and engine oil temps on track and I find it hard to believe the stock pump can maintain that under those conditions especially at WOT near redline in high G turns. There is a way around the pressure drop tuning wise , extending the injector duty cycle and the motor pulling timing at high rpm but that's not a preferred path . AJ assures me I'm the only ESS VT-525 Z4M in any trim to have this problem including the EAS track car . ??? Even without the limp mode the car runs much stronger on the street than the track . My segment peak speeds were equal to my VT-1 speeds even though my apex speeds were equal , so I know it wasn't making full power on track either. I'm pretty certain it was pulling timing like a mofo even when it didn't limp . I will be getting a PLX multi gauge and a wide band AFR after the fuel system upgrades to do some data logging, but I think upgrading my pump and the fuel basket is what is needed given all the facts.
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      05-25-2013, 01:50 PM   #8
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I assume you are running 100 octane, not that that would help with a shortage of fuel. But it may help with the power that you are referring to.
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      05-28-2013, 02:10 PM   #9
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I have tried using URT advanced 110+ octane mixed in with 93 to help combat heat soak power loss when I was VT-1 but it had no effect on the limp mode. I think I was running pretty lean on track bc the power loss was noticeable, i.e. my end of straight speeds were less than with my VT-1 kit given the same apex speeds. The main reason i upgraded was to have an intercooled setup that was more reliable and consistent on track.
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      05-28-2013, 02:21 PM   #10
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my 500 spec car running 8lbs never get fuel starvation..... AFR logs show consistant ratios right through an all day track session on 26 deg C heat... my car has 10k miles so the fuel pump is pretty fresh..... id look at upgrading this as i will do mine when it starts to show signs of weakness!! Seriously consider running gauges in this car imo... this could have been picked up alot quicker.......

on a side note.... how about a review on the 525 kit??
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      05-28-2013, 02:47 PM   #11
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you say you're starving for fuel while cornering while you have a full tank......

Why do you think it's because of the Gs and why do you even think it's fuel starvation...
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      05-28-2013, 02:51 PM   #12
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I honestly can't review it yet bc I'm def not making 525 hp lol. Seriously, on the street I def notice a substantial increase in midrange torque as well as much better throttle mapping with no noticeable increase in lag. The tuning is much more refined vs the VT-1. I'm planning on installing an wideband bung when my DKF midpipe finally comes(didn't want to do it twice). I agree if i was running AFR's I would have picked up on the problem sooner. When the kit is making full power on the street it feels very strong, but the on track performance was horrible bc without fuel ....... Do you frequently hit over 1.1 G's on 100 mph sweepers in the top of 4th gear? (these are the only spots frank limp mode kicks in)
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      05-28-2013, 02:54 PM   #13
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Quote:
Originally Posted by O-cha View Post
you say you're starving for fuel while cornering while you have a full tank......

Why do you think it's because of the Gs and why do you even think it's fuel starvation...
Bc I have ruled everything else out, have been throwing no codes , and have been told by the people that tuned the kit that as well as others that the DME would go into this particular power cut if it was detecting a sudden lean condition. If you have anything to add I'm all ears and plenty frustrated in working this out. I am already working on setting up AFR's and full data logging going forward. I think its more the sustained high RPM's in these turns followed by full throttle application and the older stock fuel pump not keeping up.
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      06-09-2013, 09:26 PM   #14
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As I'm sure you know, a lot of people have a limp mode issue, before and after FI. Seems likely it's the same root cause as yours, so if you really have found a solution then you have done a great service for the whole community!!!

I have never been able to narrow down the circumstances for my own car beyond this:

- Happens once, and only once each track day like clockwork (although strangely seems to have stopped lately, and I have not seen it happen for the last 3 track days despite no changes to anything relevant and all conditions being equal)
- Often seems to occur shortly after a fair degree of redlining (ie. at least a few shifts that really should have been sooner, though not necessarily bouncing off the red).
- The type of corner the car is in or just completed does not seem to be consistent. So for my own issue, revs seem more relevant than G's.

I have always felt heat was an issue. I'm waiting on the upgrade from VT1 to VT2 (been waiting since December!!!) and was hoping that the intercooler would help keep temps under control (tried an upgraded thermostat but that didn't help much at all). But from what you have said the problem may actually became worse!!, which of course it would if it's a fuelling issue.

Anyway thanks for posting this, and your other post about it. Since I have to drop the diff soon anyway for camber arms I've decided to switch the fuel pump at the same time. I hate the idea of my first VT2 track day being a wash!!!

Really looking forward to your comments in the other thread after your track day. Really hoping it goes well for you!!!
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      06-09-2013, 11:38 PM   #15
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Quote:
- Happens once, and only once each track day like clockwork (although strangely seems to have stopped lately, and I have not seen it happen for the last 3 track days despite no changes to anything relevant and all conditions being equal)
- Often seems to occur shortly after a fair degree of redlining (ie. at least a few shifts that really should have been sooner, though not necessarily bouncing off the red).
- The type of corner the car is in or just completed does not seem to be consistent. So for my own issue, revs seem more relevant than G's.
If I didn't know better, it sounds exactly like how and when there is oil starvation or a drop in oil pressure. eXactly.

Would that cause limp mode if there were a slight drop in oil pressure?
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      06-10-2013, 10:31 AM   #16
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Quote:
Originally Posted by gmd2003 View Post
Bc I have ruled everything else out, have been throwing no codes , and have been told by the people that tuned the kit that as well as others that the DME would go into this particular power cut if it was detecting a sudden lean condition. If you have anything to add I'm all ears and plenty frustrated in working this out. I am already working on setting up AFR's and full data logging going forward. I think its more the sustained high RPM's in these turns followed by full throttle application and the older stock fuel pump not keeping up.
"Ruling out everything else" means nothing. Without positive evidence you are just grasping at straws. There is NO way you are getting fuel starvation with a full tank from cornering Gs.
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      06-10-2013, 12:10 PM   #17
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I already said It was sustained RPM's and transition to full throttle in the high speed turns not the actual G's that I believe was the issue. It only happened in high speed turns with high G's thus that descriptor . My OBD II data logging and scanning of the ECU was not helpful in determine the problem , I was asking if any one else had issues under the same conditions on track .
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      10-06-2013, 06:21 PM   #18
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I've had same thing happen x 2 this year

I've done a lot to z4m but this happened since going to full hoho slicks and pulling over 1g at high rpm. Happened at road atl top of esses and amp hairpin. I've had constant Exhaust fault since cat delete but no clear code with these 2 events. I also have ess tune but still na. Seems to be a limp mode as car just dies then starts right back up. Please post more as u get it sorted. Thanks.


Quote:
Originally Posted by gmd2003 View Post
Has any one else ever had this problem on track. I would have it occasionally 1/50 laps when my car was N/A but now with my newly installed VT-525 and its increased fuel needs it was happening every lap in turn 9 at Roebling road. Its a high speed sweeper where i see sustained 1 G cornering for 8 seconds at high rpm's in 4th at maintenance throttle then progress to full throttle off the apex and onto the front straight. As soon as I go full throttle limp mode kicks in. This occurs in the same spot as before just way more frequently now as my car needs more fuel and is not gas tank level related ( happened on my first hot lap). My plan is to modify the pump basket for better filling and place an Aeromotive stealth 340 pump to maintain the fuel pressure i need. Has anyone else run into this issue????, I'm flattered that I'm driving the car hard enough to do this but it sucks that I'm having to trailblaze a solution. And before any one asks the injectors are good, the fuel lines are good, the filters have been replaced recently as well as the OEM pump.
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      10-06-2013, 06:25 PM   #19
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My thought was a possible oil starvation. I was going to get gauge setup.
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      10-06-2013, 06:32 PM   #20
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This thread is a bit more up-to-date, from around page 5.

http://www.zpost.com/forums/showthre...=871393&page=5
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      01-04-2015, 10:30 AM   #21
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I had this happen to me today during some spirited driving. Entered very long, slightly downhill sweeper in 4th gear around 4-5K RPM. Powered out and shifted into 5th. About 3 seconds after I exited the turn I got a SES light and limp mode. Stopped the car and shut it off for about 10 seconds and then restarted the car. No light or limp mode afterwards. This was with 1/4 tank of fuel remaining.

Certainly scared the crap out of me (thought I did something catastrophic). Anyone else have this problem recently? And has there been a solution?
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      01-04-2015, 10:49 AM   #22
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Quote:
Originally Posted by SlickShift
I had this happen to me today during some spirited driving. Entered very long, slightly downhill sweeper in 4th gear around 4-5K RPM. Powered out and shifted into 5th. About 3 seconds after I exited the turn I got a SES light and limp mode. Stopped the car and shut it off for about 10 seconds and then restarted the car. No light or limp mode afterwards. This was with 1/4 tank of fuel remaining.

Certainly scared the crap out of me (thought I did something catastrophic). Anyone else have this problem recently? And has there been a solution?
In my case it was fuel starvation but it was from undersized injectors . Test you're fuel pressure and make sure that is adequate as a starting point . Are you stock , tuned , FI ?
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