starts breaking up at 4500 rpm. - Page 2

Sean Marconette · 10-21-2015, 05:34 PM

If it's an Aeromotive A1000 it can do either carb or EFI, with just a regulator change.
How is the fuel pump positioned and where is it relative to the cell sump? Aerated fuel is possible if the elevation of the pump has to draw the fuel out of the cell. The pump should always have a column of fuel sitting on it, otherwise the vacuum it will pull can make the pump cavitate.

With the foam removed, the return could also aerate the fuel in the cell, unless as others have stated it has a length of hose to eliminate fuel dumping above the liquid level in the cell. With the foam installed that eliminates this issue.

What pump do you have?

Sean

partsbob67 · 10-21-2015, 09:53 PM

thanks for all the responses. was an aeromotive 750 pump and an Mallory regulator on a 94-95 fuel rail. changed to a aeromotive regulator on the rails. then changed to 87-93 rails and a aeromotive reg on that. fuel pressure starts at 40psi and drops to 36psi. then I put a holley pump on it and it did the same thing. voltage is steady at the pump. pump is mounted right below the cell. maybe to large a return line?

buzzinhalfdozen · 10-26-2015, 09:17 AM

You could try installing some sort of restrictor in the return line, just to see if that's the problem again -8 seems big for return. I have an -8 return on mine but it has a -6 to -8 adapter on the regulator when I'm using the EFI setup so it has a smaller hole in that fitting. Really should not be seeing a pressure drop, either your pump isn't up to the task or for some reason your injectors are flowing way more fuel than they should be. Have you verified your tune up?

Dick Butler · 10-26-2015, 10:12 AM

Where are you picking up the fuel pressure for the gauge? For control of pressure on Q jet car needed larger line for return than supply or the line created Higher pressure than regulator could reduce. Obviously with injection needs that is different but maybe where you are plumbed in with gauge isn't giving pressure at correct area for operation information. (I bet on return line air creation getting in pump.) Would explain drop in pressure by bubbles in line.

MikeMoller · 10-26-2015, 01:50 PM

You might also check your battery/connections/grounding etc. Low voltage will cause the injector pulse to be slow and dump to much fuel per pulse.

Marty Buth · 10-27-2015, 10:29 AM

Are your fuel injectors sized properly for the HP you are making? Have you had all of the injectors flowed to make sure one or more of them aren't flowing too low?

partsbob67 · 10-27-2015, 10:21 PM

injectors were fine before I changed the tank and lines. car was running 12.30's until I had this bright idea.

buzzinhalfdozen · 10-30-2015, 10:58 AM

Bob, never saw a reply about what your 02 sensor does during the issue...goes dead lean, dead rich? That might shed some light on what's happening.

partsbob67 · 10-30-2015, 07:59 PM

Quote:

Originally Posted by buzzinhalfdozen

Bob, never saw a reply about what your 02 sensor does during the issue...goes dead lean, dead rich? That might shed some light on what's happening.

sorry, starts to lean out.

ss3011 · 10-30-2015, 08:10 PM

Do you have a good vent on that fuel cell ?

10-21-2015, 05:34 PM	#11
Sean Marconette Senior Member Join Date: Mar 2006 Posts: 977 Likes: 792 Liked 275 Times in 76 Posts	Re: starts breaking up at 4500 rpm. If it's an Aeromotive A1000 it can do either carb or EFI, with just a regulator change. How is the fuel pump positioned and where is it relative to the cell sump? Aerated fuel is possible if the elevation of the pump has to draw the fuel out of the cell. The pump should always have a column of fuel sitting on it, otherwise the vacuum it will pull can make the pump cavitate. With the foam removed, the return could also aerate the fuel in the cell, unless as others have stated it has a length of hose to eliminate fuel dumping above the liquid level in the cell. With the foam installed that eliminates this issue. What pump do you have? Sean __________________ Sean Marconette 84 Mustang 5060 SS/N

10-21-2015, 09:53 PM	#12
partsbob67 Member Join Date: Apr 2005 Location: rohnert park,ca Posts: 414 Likes: 11 Liked 79 Times in 11 Posts	Re: starts breaking up at 4500 rpm. thanks for all the responses. was an aeromotive 750 pump and an Mallory regulator on a 94-95 fuel rail. changed to a aeromotive regulator on the rails. then changed to 87-93 rails and a aeromotive reg on that. fuel pressure starts at 40psi and drops to 36psi. then I put a holley pump on it and it did the same thing. voltage is steady at the pump. pump is mounted right below the cell. maybe to large a return line? __________________ bob beals 7244

10-26-2015, 09:17 AM	#13
buzzinhalfdozen Senior Member Join Date: Sep 2006 Location: Bellevue Ohio Posts: 984 Likes: 0 Liked 11 Times in 8 Posts	Re: starts breaking up at 4500 rpm. You could try installing some sort of restrictor in the return line, just to see if that's the problem again -8 seems big for return. I have an -8 return on mine but it has a -6 to -8 adapter on the regulator when I'm using the EFI setup so it has a smaller hole in that fitting. Really should not be seeing a pressure drop, either your pump isn't up to the task or for some reason your injectors are flowing way more fuel than they should be. Have you verified your tune up? __________________ Joe Buchanan SS/BX 3117

10-26-2015, 10:12 AM	#14
Dick Butler VIP Member Join Date: Oct 2002 Location: Richmond Indiana Posts: 1,196 Likes: 5 Liked 32 Times in 19 Posts	Re: starts breaking up at 4500 rpm. Where are you picking up the fuel pressure for the gauge? For control of pressure on Q jet car needed larger line for return than supply or the line created Higher pressure than regulator could reduce. Obviously with injection needs that is different but maybe where you are plumbed in with gauge isn't giving pressure at correct area for operation information. (I bet on return line air creation getting in pump.) Would explain drop in pressure by bubbles in line.

10-26-2015, 01:50 PM	#15
MikeMoller Senior Member Join Date: May 2010 Location: Raleigh NC Posts: 637 Likes: 27 Liked 254 Times in 78 Posts	Re: starts breaking up at 4500 rpm. You might also check your battery/connections/grounding etc. Low voltage will cause the injector pulse to be slow and dump to much fuel per pulse. __________________ Mike Moller NHRA 203 Q-R-T/SA

10-27-2015, 10:29 AM	#16
Marty Buth Member Join Date: Nov 2002 Location: Freeport, IL Posts: 467 Likes: 646 Liked 232 Times in 39 Posts	Re: starts breaking up at 4500 rpm. Are your fuel injectors sized properly for the HP you are making? Have you had all of the injectors flowed to make sure one or more of them aren't flowing too low? __________________ Marty Buth 3657 STK

10-27-2015, 10:21 PM	#17
partsbob67 Member Join Date: Apr 2005 Location: rohnert park,ca Posts: 414 Likes: 11 Liked 79 Times in 11 Posts	Re: starts breaking up at 4500 rpm. injectors were fine before I changed the tank and lines. car was running 12.30's until I had this bright idea. __________________ bob beals 7244

10-30-2015, 10:58 AM	#18
buzzinhalfdozen Senior Member Join Date: Sep 2006 Location: Bellevue Ohio Posts: 984 Likes: 0 Liked 11 Times in 8 Posts	Re: starts breaking up at 4500 rpm. Bob, never saw a reply about what your 02 sensor does during the issue...goes dead lean, dead rich? That might shed some light on what's happening. __________________ Joe Buchanan SS/BX 3117

10-30-2015, 08:10 PM	#20
ss3011 Senior Member Join Date: Feb 2002 Location: Southeast Michigan Posts: 909 Likes: 70 Liked 239 Times in 114 Posts	Re: starts breaking up at 4500 rpm. Do you have a good vent on that fuel cell ?