Fuel Need Some Help And Advice

88gt40

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Jun 9, 2013
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Ok, so for the last two years me and a buddy of mine have completely tore down a 1988 mustang gt and rebuilt for autocross. We did the engine, suspension, and complete inside. After it was all done I started driving it and found that i would keep losing tfi modules. Well I got sick of that and went with a pro m efi system which bypasses the tfi. So I get it installed and still have the same problem as before, so I call Chris with pro m and he has signs in and remotes my efi to look at it. He says i'm aerating fuel in the tank, so I drop the tank and low and behold even with ten gallons of fuel in the tank the walbro 190lph pump still starts blowing bulbs and thats when the air fuel gauges start showing lean driver side first then passenger side. Has anyone else had this problem, from what I understood a 190 lph pump should run fine on factory lines and rails, but it appears not. Chris told me to put a full tank in it and it should stop it, but all it does is make it take longer to do it. If its only 5 gallons its quick and if its 13 gallons it takes 45 minutes to do it. I hate to spend 750 dollars for -6 line and all fittings plus new bracket from pro m for pump and injector rails and regulator if not needed. I need a little more advice if anyone has had this specific problem. I know for a fact its bubbling the fuel i have seen it through the fill neck with the tank on the ground, is it possible that the return is that restricted? Also I have already watched the video on pro m website, i'm just looking for anymore advice before I drop more money on it. I'm not sure but im thinking the tfi was fine the whole time, because it acts like a tfi is getting hot when it acts up. By the time you change the tfi the air bulbs gone and engine is running fine. Thanks and sorry for the long post
 
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I can't offer advice but I have a similar problem.

Distributors and tfi modules have been extremely picky for me. The only ones I have found for me that works is the mallory tfi distributor and module.

If I put in a stock dis and module, module stops working shortly after the car starts, same thing with the 3 or 4 tfi modules I have. I've tried the 3 or 4 modules on the mallory distributor and none of them work for more than a few minutes and had it fry a ignition coil.

I'm stuck using the mallory dis with the tfi that came with the dis.


Can't explain it. Same thing happens if I swap them around on a completly different car.
 
Since I used the pro efi setup the tfi has been eliminated, so thats been a big help. I'm just having a hard time unloading my wallet on the fuel lines, Its just been strange the way the car was before and now. I can see the fuel bubbling in the tank and i can put the feed line and pump in one bucket and the return in the other and the car runs fantastic. I can't race with buckets, the weird part is when I had the a9l running the car and what i thought was tfi problems with the fuel pressure cranked to 60psi the car ran great, but i could only see bank 2 air fuel mix. Now I see both and the pro m efi system can only correct so far before it dies. I guess I was hoping someone had the same problem and can tell me when they changed everything in there fuel system it fixed it. Thats a long shot
 
I have the same pump as you. I don't have that issue that I'm aware of. When I replaced the pump I replaced the whole bracket the pump is on. I know there are some check valves and things on the bracket, but again, I'm not sure if thats the issue. However I do run a 190 lph pump on stock lines.
 
My buddy has the same setup as me without the efi system and he hasnt had any problems. I wonder if there is something different between the 88 and 93 cars. One thing we did notice on his when we changed his heads was he had a lot of carbon on top of his pistons. Couple of forums I have read states that could be caused by air in fuel also. So we are going to pull his tank down and look next weekend.
 
How much power are you running that requires a 190 LPH pump?
Read below and pay particular attention to my comments at the bottom of the tech note.


Copied from the FORD RACING PERFORMANCE PARTS catalog:

PROPERLY SIZING FUEL SYSTEM COMPONENTS


Fuel Pumps
The following information is presented assuming the above information has been taken into consideration regarding BSFC, fuel pressure and specific gravity of the fuel being used. Most fuel pumps for electronic fuel injection are rated for flow at 12 volts @ 40 PSI. Most vehicle charging systems operate anywhere from 13.2v to 14.4v. The more voltage you feed a pump, the faster it spins which, obviously, will put out more fuel. Rating a fuel pump at 12 volts then, should offer a fairly conservative fuel flow rating allowing you to safely determine the pump’s ability to supply an adequate amount of fuel for a particular application.

As previously mentioned, engines actually require a certain WEIGHT of fuel, NOT a certain VOLUME of fuel per horsepower. This can offer a bit of confusion since most fuel pumps are rated by volume, and not by weight. To determine the proper fuel pump required, a few mathematical conversions will need to be performed using the following information. There are 3.785 liters in 1 US Gallon. 1 gallon of gasoline (.72 specific gravity @ 65° F) weighs 6.009 LBS.

To be certain that the fuel pump is not run to its very limit, which could potentially be dangerous to the engine, multiply the final output of the fuel pump by 0.9 to determine the capacity of the fuel pump at 90% output. This should offer plenty of ‘cushion’ as to the overall “horsepower capacity” of the fuel pump.

To determine the overall capacity of a fuel pump rated in liters, use the additional following conversions:
(Liters per Hour) / 3.785 = Gallons
Multiply by 6.009 = LBS/HR
Multiply by 0.9 = Capacity at 90%
Divide by BSFC = Horsepower Capacity
So for a 110 LPH fuel pump:
110 / 3.785 = 29.06 Gallons
29.06 x 6.009 = 174.62 LBS/HR
174.62 x 0.9 = 157 LBS/HR @ 90% Capacity
157 / 0.5 = 314 HP safe naturally aspirated “Horsepower Capacity”

Safe “Horsepower Capacity” @ 40 PSI with 12 Volts
60 Liter Pump = 95 LB/HR X .9 = 86 LB/HR, Safe for 170 naturally aspirated Horsepower
88 Liter Pump = 140 LB/HR X .9 = 126 LB/HR, Safe for 250 naturally aspirated Horsepower
110 Liter Pump = 175 LB/HR X .9 = 157 LB/HR, Safe for 315 naturally aspirated Horsepower
155 Liter Pump = 246 LB/HR X .9 = 221 LB/HR, Safe for 440 naturally aspirated Horsepower
190 Liter Pump = 302 LB/HR X .9 = 271 LB/HR, Safe for 540 naturally aspirated Horsepower
255 Liter Pump = 405 LB/HR X .9 = 364 LB/HR, Safe for 700 naturally aspirated Horsepower

Note: For forced induction engines, the above power levels will be reduced because as the pressure required by the pump increases, the flow decreases. In order to do proper fuel pump sizing, a fuel pump map is required, which shows flow rate versus delivery pressure.

That is, a 255 liter per hour pump at 40 PSI may only supply 200 liters per hour at 58 PSI (40 PSI plus 18 lbs of boost). Additionally, if you use a fuel line that is not large enough, this can result in decreased fuel volume due to the pressure drop across the fuel feed line: 255 LPH at the pump may only result in 225 LPH at the fuel rail.


My Comments:

A lot of people oversize the fuel pump by buying a 255LPH pump thinking that the fuel pump regulator will just pass the excess gas back to the tank. It does, but… Did you ever consider that circulating the fuel around as a 255 LPH pump does will cause the gas to pickup engine heat? What happens to hot gasoline? It boils off or pressurizes the fuel tank! With most of the 5.0 Mustangs having the carbon canister removed or disabled, the car stinks like gas, and the gas mileage drops since the hot fuel evaporates away into the air.
 
I had a persistent problem with overheating and aerating the fuel with a 190lph pump...for YEARS. Not thinking it could be the pump, I insulated every line I could find, I shielded the tank, I wrapped the tailpipes, I went to dumps and back, and it wasn't until the pump started to die that I thought maybe I should go smaller. So I installed a 155lph pump and the problem is almost completely cured.
 
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i should be around 350hp i believe, not sure car wont run long enough to dyno with the fuel problem
tfs1, cam afr 124s, edlebrock performer, 30 lb inj, bbk shorties, 306, scat rotating
 
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Two people have come to the same conclusion; try a smaller fuel pump.

A 155 LPH fuel pump should be more than enough for your engine. I would peg your HP closer to 310-325 at the flywheel
 
What are the symptoms of fuel that is being aerated?

Now you guys worry me because I have a 190, but I have not had any drivability issues. No stumbling, hesitation or anything of the sort.
 
Im going to try that first i will order a 155lph tonight, as for symptoms i have two a/f gauges and after 45 minutes of idle with 3/4 tank i start running lean on river bank the passenger bank. The car starts to detonate and and will not idle, or rev. Its similar to a tfi failure. If you let it sit for about 10 minutes you start the cycle all over again 45 minutes and same thing again.
 
I shouldn't even post this...but I've ran 255 pumps with even less horsepower than 325fwhp and never experienced this problem. Not trying to muddy the water or start an issue, just stating my experience. I don't know why a "heated fuel issue" would lead to blown tfi modules. Sounds like a short somewhere to me. Unless I'm just confused? Which is possible lol. J is a great resource on here and has tons of valuable experience/info posted on this site. I just don't believe this is the problem but a smaller pump isn't a major investment to troubleshoot the issue. Good luck.
 
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It's not causing tfi to go out, I said it was the same symptoms as a tfi. I know a lot of people that haven't had any problems too. That's why I'm trying to figure out why is it just my car. But it's either boiling fuel or aerating it when running.
 
@88gt40,
@A5literMan
The clue is how the car is used; the OP said autocross. Autocross takes a toil on brakes, transmission and engine . The engine runs up and down the RPM range and the body rolls, twists and dives. What does that do to the fuel in the fuel tank? It sloshes around a lot. It is already heated from being recirculated to the hot engine and then back to the fuel tank. The sloshing around causes the fuel to vaporize more than just straight line driving with some gentle curves..
 
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Correct and I have stank that has a different baffle system made by Glenn's performance. The 45 minutes is how long it takes before the fuel really starts bubbling in the tank. With 10 to 13 gallons it takes 45 minutes at idle, with 5 gallons maybe seconds at idle. The car won't even make it to the track right now, it run long enough to get there. The weird part about the whole thing is before I put the new tank in and all the new seals I had a 255lph Waldro pump and I had to run the regulator at 60psi for it to run right a/f mixture. I was instructed to go to a 190lph because the return line is spraying the fuel causing it to aerate at the pump. So I did, and now instead of instantly having a issue Itusually takes depending on level 5-45 minutes to do it.
 
I will try a 155lph pump to see the difference it will make if any, would be nice if y'all could all see what I'm seeing while its idling. I know the return line is to high on the pump bracket, I understand that will make it aerate when tank is low because of the spraying on top of fuel, but for the life of me I can't figure out why it does it when full. It must be boiling, has to be.