Engine 1990 Hard Start. Engine dies when throttle applied

FBodyLover315

Member
Nov 17, 2005
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2
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Hello All

It has been a while. Haven't played with one of these cars in over a decade.

I have just picked up a 1990 Mustang GT from a friend who had it sitting in his driveway for the past decade. ( I couldn't let her die in the driveway)
The car has approximately 42k on it.
It used to run without any issues before it sat.
After a fresh battery installed she barely started but was not running right. Barely idling and would stall when you passed approximately 1/4 throttle.

I have put in the following parts:
New Cap
New Rotor
New Plugs
New Fuel Filter
Fresh Fuel

After all parts installed same hard start bad idle and stalls when you get her started when you pass 1/4 throttle.
I have tested the TPS, swapped the Mass Air with a known good unit and still have the same results.

Here is the strange part for me

When I unplug the Mass Air she will start run for a few seconds and then sputter and stall.
If I unplug the Mass air and also unplug the Idle Air Control it will start and idle without any issue. No sputtering or smoke.

I have verified the computer ground cable at the battery and the grounding strap behind the engine.

I am running out of idea for testing. I do not want to just start throwing parts at it and see what sticks.
If anyone can offer any guidance on this it would be greatly appreciated.
 
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FBodyLover315

Member
Nov 17, 2005
9
2
13
Hey General karthief!

I went through the list finally and you were right! Not enough fuel pressure to run.
Down at about 7lbs when I jump the pump....
Starts right up when I spray in starting fluid....
So now the tank comes down!

Thanks again. I can't wait to get her running again!
 

FBodyLover315

Member
Nov 17, 2005
9
2
13
One more question for you guys out there.

What size fuel pump should I get? 190 LPH 255 LPH?

I do eventually plan on putting a supercharger on once I get her back to a good starting point.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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Here's what I say, do the 190, or even a 155, when you start to plan your upgrades you may need more that you think so get it running and driving now and enjoy it while making the big plans.
 

Boostedpimp

10 Year Member
May 8, 2003
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It's not that hard of a job to drop the tank and swap pumps so you could just go with a 155 then swap it later but me personally given its a return style setup. I have always just tossed a 255 in from mild daily to power adder.
 

FBodyLover315

Member
Nov 17, 2005
9
2
13
When you put the 255 in do you need to put in a new fuel pressure regulator?

I know the job is not that hard I just hate doing the same job twice
 

FBodyLover315

Member
Nov 17, 2005
9
2
13
It's not that hard of a job to drop the tank and swap pumps so you could just go with a 155 then swap it later but me personally given its a return style setup. I have always just tossed a 255 in from mild daily to power adder.
#8
When you put the 255 in do you need to put in a new fuel pressure regulator?

I know the job is not that hard I just hate doing the same job twice
 

FBodyLover315

Member
Nov 17, 2005
9
2
13

jrichker

StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
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Thank you guys so much!

I will prob pickup a 255 pump and throw her in.
Since you sound like you have done this before any issues with the walbro 255 fuel pump?

https://www.highflowfuel.com/i-10384072-genuine-walbro-gss340-255lph-fuel-pump-ford-mustang-gt-lx-1986-1997.html?gclid=Cj0KCQjwjbveBRDVARIsAKxH7vmYYDNOoTBSoGSin9kLdhGn0CFTx26P9djAwmy8cJQX8GLPdJqC3GMaAnKJEALw_wcB

Bad idea, you stand a good chance of overloading the return line and losing the ability to properly regulate the fuel pressure.

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.
 

FBodyLover315

Member
Nov 17, 2005
9
2
13
Bad idea, you stand a good chance of overloading the return line and losing the ability to properly regulate the fuel pressure.

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.

You guys are awesome.

Thank you so much all of you for your help

So After reading all of this I am going to put in a 155 lph pump and just change the pump again when I get her supercharged as I will have to do the fuel lines anyway!
 
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Reactions: General karthief

Boostedpimp

10 Year Member
May 8, 2003
868
243
74
NJ
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.
So are you saying the feed/return lines need to be sized up first in order to properly use a walbro 255 in tank pump? If not you loose pressure at the rail and over heat the fuel that is cycled back through the return line causing a boil off in the tank resulting in extra odor and possible implosion?
 

jrichker

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SN Certified Technician
Mar 10, 2000
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So are you saying the feed/return lines need to be sized up first in order to properly use a walbro 255 in tank pump? If not you loose pressure at the rail and over heat the fuel that is cycled back through the return line causing a boil off in the tank resulting in extra odor and possible implosion?
If you are using enough fuel to require a 255LPH fuel pump. the return line will not be a problem. The problem is when you only need 155LPH worth of fuel, the return line has to be big enough so that it does not cause a restriction. The feed line should be sized to meet the demand of the engine; pressurized induction may require a larger feed line size.

Implosion can only happen if you somehow manage to create a high vacuum inside the fuel tank. Air pressure outside crushes the tank - no fire, no excitement, just the sound of crunching metal.
 

Mustang5L5

This is a big reason why I pulled it out
Mod Dude
Feb 18, 2001
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When I installed my 190LPH pump, my fuel pressure was approx. 3 psi higher than with the stock 88LPH pump I took out. Fortunately I had a adjustable fuel pressure regulator, but adjusting it down to the lowest setting barely got me to the 39psi.

It makes sense though. Your feed line is larger than your return. So as the pump flows 2x the amount of fuel that the stock pump used to flow at, the smaller return line creates a bottleneck which causes pressure in the feed to rise. Usually you can relieve this pressure by way of a thirsty engine. So a modified, 500HP engine might not see this phenomenon, but a stockish motor (like mine) would.
 

FBodyLover315

Member
Nov 17, 2005
9
2
13
Hello All

I just wanted to let you know that I replaced the pump and tank and now she lives!!

Thank you everyone for the help with this!