KB E85 Cobra fuel issue breaking up. Return system

FastNick01

Member
Established Member
Joined
Oct 31, 2008
Messages
406
Location
Southside chicago
Car is an 03 Cobra KB2.8LC with full bolt ons, stock shortblock, stock cams/heads. Makes 24lbs on E85. Just put a fresh tank of E85 and Plugs are BR7EF gapped to .020. I have the full Lethal 1400rwhp return fuel system with 80lb injectors.

Finally got the chance for my friend to log my car with a snap on veras and under boost it's fuel pressure is 47psi while normal driving but under throttle/building boost it dropped to 0 or low single digits and the car would miss hard, start popping etc.. I have the lethal 1400rwhp return setup with twin 465's, -Aeromotive 4 Port Pro Series EFI Fuel Pressure Regulator. Car still runs smooth driving around town, no idle problems, no problem starting the car cold/hot..Another friend mentioned a fuse on each fuel pump

Question is would a bad regulator cause this? Vacuum line maybe, Are one of my pumps gone?

Any fuel system experts help me out. Thanks in advance and yes I've searched the forum.
 

Bdubbs

u even lift bro?
Established Member
Premium Member
Joined
Jan 8, 2010
Messages
16,039
Location
MN
Might not be your problem but 80lb injectors seems to small on 24lbs and e85. I'd also want head studs if I was pushing that much boost. I'm sure your aware that anything over 23lbs the chance of the heads lifting is increased.

You should be data logging fuel pressure drop across injectors. Also other fuel parameters, volts, and see how much vacuum you have.
 

cj428mach

Well-Known Member
Established Member
Joined
Sep 21, 2012
Messages
7,609
Location
Kansas
I agree 80's are probably too small for that setup, though that wouldn't be the cause of your pressure drop.

I believe lethal fuel systems have standard relays that run each pump, I'd pull the relays and manually jump each pump to see if it runs. If they work then I'd look at the lines and filter for obstruction.
 

Juiced46

I love being Blown
Established Member
Joined
Sep 7, 2003
Messages
4,192
Location
North Haven CT
I have seen this before. The Lethal hat with 465s does not fit very well without modifications. The pumps are probably sitting too far down in the hat. You will need to trim the rubber line on the hat where the pump slides in and trim part of the nipple on the pumps as well to get them in further. You need to measure the depth carefully to make sure you have proper clearance.

What also sometimes happens is, when you remove the tank, people use a jack in the center, it slightly bends the tank up causing that clearance gap to be less.

The pumps are probably sucking right off of the bottom of the tank, it is being sucked dry in the sump because they are too close to the bottom of the tank. Your base pressure should be set to around 38-40psi with the vac line off the regulator. With boost, since its 1 to 1, you should be seeing +24psi when WOT so around 65psi or so.

Also how is your fuel system configured? Is it dead headed or are you feeding the rails first?
 

Bdubbs

u even lift bro?
Established Member
Premium Member
Joined
Jan 8, 2010
Messages
16,039
Location
MN
^^^^
Base pressure should be whatever your tuner tells you to set it at. Mine is 45 psi.
 

Juiced46

I love being Blown
Established Member
Joined
Sep 7, 2003
Messages
4,192
Location
North Haven CT
I was giving an example since every combo is different. Typical starting point is around 40psi, thats why I said around.
 

R3dfireCobra

Member
Established Member
Joined
Jan 24, 2014
Messages
291
Location
St Augustine, FL
While I do agree with you on has nothing to do with fuel pressure dropping to zero. Why run your plugs so tight? Typical for higher boosted applications are .025-.029 for these engines. Strictly an observation but seems unnecessarily tight. I do agree with you on modifying the hose on the hat and fuel pump to bring the pumps up as that is what I had to do on my 465s and lethal hat to make sure it wasn't sucking on the bottom. The gap at the bottom of the pumps to the inner mold line of the fuel tank is indeed very important. And like you said make sure you don't crush your tank with a jack.
 

FastNick01

Member
Established Member
Joined
Oct 31, 2008
Messages
406
Location
Southside chicago
Wasn't expecting so many responses. Thank you everyone

80lbs injectors were in the high 80's% when I got a tune. Tuned by Tim Barth about 2 years ago, ran excellent before.
Plugs were gapped to .026 initially, then .024 because I thought I was experiencing spark blowout. I will probably bring them back to .024 when I get the fuel issue situated. I will check the issue with the pumps sitting too low and also check relays/fuses. Gonna try and pull the tank soon to see what is going on. Hopefully I can get this figured out. Thanks again to everyone.
 

Juiced46

I love being Blown
Established Member
Joined
Sep 7, 2003
Messages
4,192
Location
North Haven CT
While I do agree with you on has nothing to do with fuel pressure dropping to zero. Why run your plugs so tight? Typical for higher boosted applications are .025-.029 for these engines.

Typically on higher boost applications I start at .024 and go down from there. The NGK BR7EF that OP is using comes gapped out of the box @ .024 also. If there are any issues, then I will gap it down to .018-.020.
 

R3dfireCobra

Member
Established Member
Joined
Jan 24, 2014
Messages
291
Location
St Augustine, FL
Anything come from your findings? I too am now experiencing issues similar to what you are. My car has sat for the better part of a year due to work assignments away from home. Car ran flawlessly before and now I am having fuel pressure loss when going into boost. Both pumps work and car idles at 40psi. I can start the car with just one pump and have 40psi at the reg on either pump. Car drives fine at lower rpms. I wonder if I have a block or crud built up somewhere in the system. Only thing I can think of...

Sent from my SAMSUNG-SM-G935A using the svtperformance.com mobile app
 

Bdubbs

u even lift bro?
Established Member
Premium Member
Joined
Jan 8, 2010
Messages
16,039
Location
MN
You guys run some tight gaps on your plugs. Makes me wonder if .028 is enough on mine running 21lbs.
 

mat50ho

Active Member
Established Member
Joined
Mar 9, 2009
Messages
141
Location
ND
Op did you find your problem. I have the same fuel system and I have the same issues.
 

98 Saleen Cobra

Well-Known Member
Established Member
Joined
Feb 28, 2007
Messages
19,522
Sell 04 Cobra tank and pump setup.

Buy BBRC sumped tank with Weldon external pump with regulator..

Problem solved :)
 

jony51999

Active Member
Established Member
Joined
Sep 12, 2013
Messages
251
Location
MI
Anything come from your findings? I too am now experiencing issues similar to what you are. My car has sat for the better part of a year due to work assignments away from home. Car ran flawlessly before and now I am having fuel pressure loss when going into boost. Both pumps work and car idles at 40psi. I can start the car with just one pump and have 40psi at the reg on either pump. Car drives fine at lower rpms. I wonder if I have a block or crud built up somewhere in the system. Only thing I can think of...

Sent from my SAMSUNG-SM-G935A using the svtperformance.com mobile app

I just dealt with the same thing. Turns out fuel pumps don’t like sitting in E85 for an extended period of time. I had to get new pumps, problem solved.


Sent from my iPhone using Tapatalk
 

mat50ho

Active Member
Established Member
Joined
Mar 9, 2009
Messages
141
Location
ND
Mine has done it since the new/install randomly. Fuel pressure drops to zero during throttle tip in feel like someone turned the key off. Then a split second latter fuel pressure is fine and car drives normal.
 

jony51999

Active Member
Established Member
Joined
Sep 12, 2013
Messages
251
Location
MI
Mine has done it since the new/install randomly. Fuel pressure drops to zero during throttle tip in feel like someone turned the key off. Then a split second latter fuel pressure is fine and car drives normal.

That’s sounds like a tune issue, I believe it’s called the ‘tip in table’ or something like to that effect. It’s basically the same thing that the accelerator pump is for on a carbureted setup. Of course it could be something else but that sounds exactly like this table. It’s one of the harder things to tune from research I’ve done.


Sent from my iPhone using Tapatalk
 

mat50ho

Active Member
Established Member
Joined
Mar 9, 2009
Messages
141
Location
ND
That is true on a non return system. I have the lethal 1400 kit with return. Only the pumps, regulator, voltage should effect pressure and flow. I will start a new thread when I get a chance to work on the car.
 

Users who are viewing this thread



Top