1989 Mustang LX 5.0 engine problem

mus89tang

Member
Jun 12, 2019
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Minnesota
Hi all, this is my first post here,

I have a 1989 LX 5.0 that unfortunately sat for several years without proper gas stabilization. Ultimately the gas went bad and the car was run. I emptied the gas tank and flushed it with fresh gas several times and now have clean non-oxygenated gas in the tank combined with a small amount of Seafoam. Here are my symptoms:
1. I go to start the car the first time and it rolls over for about 6 seconds or so then fires up but pretty much dies right away
2. I go to start again and it fires right away but I have to feather the throttle in order to get the RPM's up higher, if I were to go too much throttle it dies
3. I can eventually get the RPM's up high enough through feathering the throttle but trying to move the car in gear it has no power and wants to die.

It seems like it's being starved for gas...or maybe it's getting too much gas?!?! The only thing I have done besides putting in fresh gas is replace the fuel filter. I haven't looked to see what my exhaust looks like yet but I'll check that tonight. Outside of all this, any ideas what my problem could be?

Thanks in advance!
 
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Mustang5L5

This is a big reason why I pulled it out
Mod Dude
Feb 18, 2001
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I'd start with the basics. Check the air filter tract and ensure a mouse hasn't built a nest up there. Check fuel pressure, and pull a couple spark plugs and inspect.

If the fuel had ethanol in it and sat several years, its possible the injectors are in fact clogged and need cleaning or replacement
 

CtotheJ

Member
Apr 22, 2019
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Houston, TX
Sounds similar to the problem I recently went through that ended up being clogged injectors.
The car sat for several years with untreated gas in the tank and wrecked my fuel system.

You should check fuel pressure at the rail first before going after the injectors though...should be around 40 psi.
 

mus89tang

Member
Jun 12, 2019
12
3
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43
Minnesota
Thanks CtotheJ, I'm waiting for my pressure tester to arrive (tomorrow) to check the pressure but that's what I suspect to - clogged injectors.

Does anyone have recommendations on what to use for cleaning them individually? Some videos I've watched showed people using carb cleaner or brake fluid. Any other suggestions?
 

CtotheJ

Member
Apr 22, 2019
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41
Houston, TX
Thanks CtotheJ, I'm waiting for my pressure tester to arrive (tomorrow) to check the pressure but that's what I suspect to - clogged injectors.

Does anyone have recommendations on what to use for cleaning them individually? Some videos I've watched showed people using carb cleaner or brake fluid. Any other suggestions?
I followed this vid like you're talking about to clean mine. Took out my battery, then took out each injector one at a time and hooked it up to the battery while forcing brake cleaner through. It worked really well and was easier than I thought it would be.
Another tip I read was to make sure you use brake cleaner and not carb cleaner so you don't cause damage to any rubber/plastic parts.
 

Boostedpimp

10 Year Member
May 8, 2003
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From my experience i've never seen all eight injectors completely clogged to the point where the car wouldn't run. I've had a stuck injector which resulted in terrible idle/hesitation but the car would start and run. So if it were me, I would start with the easy stuff first like what was mentioned above. Take the intake tubing out and verify there isn't any restrictions like a mouse or snake nest. Verify the fuel filter isn't installed backwards and verify fuel pressure at the fuel rail.
 

mus89tang

Member
Jun 12, 2019
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43
Minnesota
Just to clarify, the car does run but pretty bad to the point it doesn't have enough power to really move much when put in gear. I took the air cleaner assembly apart and there is no obstruction. I made certain the filter was installed the proper way and I'm still waiting on my pressure tester.

Thanks again everyone!
 

mus89tang

Member
Jun 12, 2019
12
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43
Minnesota
I checked the pressure on the rail and only achieved about 10-12 psi and would drop back to 0 when turned off. I then checked at the filter and saw the same but could hear some "leakage" inside my tank so I dropped my tank, pulled my pump and found the rubber hose coming off the pump supply was cracked. I decided to order a new pump and components while I had the tank off and I'm pretty sure this is the problem.
Mustang cracked line.jpg
 

mus89tang

Member
Jun 12, 2019
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Minnesota
Forgot to mention I decided to go with a higher output pump (255LPH) for potential future mods. I spent a few hours yesterday cleaning the tank and flushing out the inside in preparation for my new pump assembly which should arrive today!
 

jrichker

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Forgot to mention I decided to go with a higher output pump (255LPH) for potential future mods. I spent a few hours yesterday cleaning the tank and flushing out the inside in preparation for my new pump assembly which should arrive today!
That was a big mistake...

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.
 

mus89tang

Member
Jun 12, 2019
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Minnesota
Thanks jrichker, this is what I was afraid of considering my engine is still pretty much stock outside of a completely different exhaust setup. I was speaking with my daughters boyfriend who is a mechanic and does quite a bit of modding to numerous makes and models of vehicles and he recommended it. I guess if the main concern for now is the gas heating up then I'll stick with it, I just need to be able to drive the car to a different temporary storage location while I build a new shop so it will only be running for a few minutes, 10 minutes tops. As mentioned above, it could be potentially dangerous to the engine, is that speaking that the gas heats up or could it legitimately cause physical damage to the engine? If the latter is the case then I will order a stock pump.

Thanks again!
 

jrichker

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@mus89tang

It may cause the fuel in the tank to vaporize and evaporate in the tank - poor gas mileage and you and the car stink like gasoline.
OR
If the return line from the fuel pressure regulator has any restriction in it, it may cause high fuel pressure that you can't adjust down to the 37-41 PSI desired range.
 

mus89tang

Member
Jun 12, 2019
12
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Minnesota
Alright, I need to get it moved so I'm going to throw it in, test the pressure and just go with it. I'm running out of time to get it moved and the "Auto Zone's" of my area want a small fortune for an OEM pump. Amazon can get it here in two days but I can't wait for that! : )
 

mus89tang

Member
Jun 12, 2019
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43
Minnesota
Thanks, my plan once my shop is completed is to tear into the fuel system at the motor just to clean things up and get more familiar with everything, call it a "fun" project for a rainy day!
:)