Car is drinking gas bad.

JACK MEHOFF · September 4th, 2011, 10:07 PM

Ok so I bought a 1987 Mustang GT 5.0 that was in rough shape. I have fixed it up and posted a pic of how it looks today. Well ive noticed the gas mileage is horrible. It's a few things I already have in mind that could be the problem. for starters it has no mufflers. just straight pipes, i already have some mufflers im getting welded in tuesday. it had the factory air box and filter. I removed all of that and put a cone style air filter on the stock hose. Ive changed the oil and filter, Im going to buy some new spark plugs and wires, and I also bought a bottle of Lucas fuel injection treatment. Also the vacuum tree is broken and one of the hoses barely stays on. I have a new tree on the way. Other then Air Filter, plugs, wires, mufflers, fuel injector cleaner, a small vacuum leak.. Is there any other thing ive left out that could help? Because it drinks gas BAD!! Pic taken today

50Droptop · September 4th, 2011, 10:25 PM

The 87 computer is speed density if it hasnt been converted to mass air already.

SD computers rely on steady vacuum supply and the o2 sensors in order to adjust fuel tables.

If you have a vac leak it will run rich. If your 02 sensors are bad it will run rich. Also you need to check the fuel pressure on the rail and make sure the regulator is doing its job... stock pressure should be 32-35 with vac line on and around 40 with vac line off.
Make sure you have a good vac line going to the map sensor on the firewall and the fuel press reg and that there are no vac leaks... If the 02 sensors are old replace them..... SD is very simple. You can mod it all you want: just dont get crazy with a lopey cam because the lopey idle cause low vacuum and the eec will freak out... The comp cams nx264 hr cam is about the max lsa and duration SD can handle and not run rich down low and lean up top...

BULLET20XD · September 4th, 2011, 10:25 PM

A fresh tune-up should do wonders. Ive never know of them to get great mileage. I will say this, i use to own a 89 F150 5.0 and it had platnium plugs in it(i forget the brand) and changed back to Motorcraft plugs. I lost 4 mpg!!! I have always used Motorcraft plugs. May want to do some research on other plugs. Just my 2 cents worth. Im still learning on theses cars as far as the efi and computers and other stuff that can make one run bad.

50Droptop · September 4th, 2011, 10:31 PM

Oh I forgot to mention to set your base timing to 10-14 degrees

JACK MEHOFF · September 4th, 2011, 10:34 PM

Originally Posted by 50Droptop

The 87 computer is speed density if it hasnt been converted to mass air already.

SD computers rely on steady vacuum supply and the o2 sensors in order to adjust fuel tables.

If you have a vac leak it will run rich. If your 02 sensors are bad it will run rich. Also you need to check the fuel pressure on the rail and make sure the regulator is doing its job... stock should be 32-35 with vac line on and around 40 with vac line off.
Make sure you have a good vac line going to the map sensor on the firewall and the fuel press reg and that there are no vac leaks... If the 02 sensors are old replace them..... SD is very simple. You can mod it all you want: just dont get crazy with a lopey cam because the lopey idle cause low vacuum and the eec will freak out... The comp cams nx264 hr cam is about the max lsa and duration SD can handle and not run rich down low and lean up top...

Thanks man.. im new to the 5.0, where would the 02 sensors be? in the exaust? and my friend suggested gutting the cats.. he said the cats might be clogged up.

50Droptop · September 4th, 2011, 10:36 PM

The 02 sensors are in the H-pipe above the cats..... if the cats were clogged you would be way low on power...Id get a off road H pipe and sell the cats for scrap I got 100 dollars for my old cats.

JACK MEHOFF · September 4th, 2011, 11:17 PM

Originally Posted by 50Droptop

The 02 sensors are in the H-pipe above the cats..... if the cats were clogged you would be way low on power...Id get a off road H pipe and sell the cats for scrap I got 100 dollars for my old cats.

alright.. might as well buy some used shorty headers while im there.. haha

50Droptop · September 4th, 2011, 11:25 PM

sure and build a 347 stroker since you have to take the headers off

slow2V · September 5th, 2011, 12:18 AM

Wet Boobs!

Sorry got distracted.

Chris951 · September 5th, 2011, 01:44 AM

Go with autolite 25 copper core spark plugs. 5.0s run like shit with platinums and autolites are great. They're all I run in my mustangs. As for your gas mileage problem, get some plugs, wires, msd cap and rotor ($30 at autozone or oriellys), O2 sensors, and FUEL FILTER (Wix or motorcraft).

And make sure u fix those vacuum leaks. Like stated above, speed density cars will run VERY rich with vacuum leaks. That's probably 80% of your problem. But just for good measure u should do everything I stated as well.

slow2V · September 5th, 2011, 01:49 AM

Human drinking Jameson's bad!

steven95gt · September 13th, 2011, 03:41 PM

all 5.0s run like shit platinum plugs? mines a 95 gt with a cobra swap and hasnt seemed to run right since i went to platinum plugs

September 4th, 2011, 10:07 PM	#1
JACK MEHOFF Enthusiast 2000 Mustang GT 12.38 Join Date: Apr 2011 Location: Virginia Posts: 921 iTrader: 0 reviews	Car is drinking gas bad. Ok so I bought a 1987 Mustang GT 5.0 that was in rough shape. I have fixed it up and posted a pic of how it looks today. Well ive noticed the gas mileage is horrible. It's a few things I already have in mind that could be the problem. for starters it has no mufflers. just straight pipes, i already have some mufflers im getting welded in tuesday. it had the factory air box and filter. I removed all of that and put a cone style air filter on the stock hose. Ive changed the oil and filter, Im going to buy some new spark plugs and wires, and I also bought a bottle of Lucas fuel injection treatment. Also the vacuum tree is broken and one of the hoses barely stays on. I have a new tree on the way. Other then Air Filter, plugs, wires, mufflers, fuel injector cleaner, a small vacuum leak.. Is there any other thing ive left out that could help? Because it drinks gas BAD!! Pic taken today __________________ Paxton Novi 2000, Intercooled, Accufab 75mm, Pro Comp Intake manifold, BBK Ceramic longtubes, BBK o/r h pipe, with Borla catback, 5.0 short shifter, 3.73's, Eibach Pro Kit

September 4th, 2011, 10:25 PM	#2
50Droptop Regular 87 Mustang Lx 13.76@100 Join Date: Aug 2011 Location: Indiana Posts: 124 iTrader: 0 reviews	The 87 computer is speed density if it hasnt been converted to mass air already. SD computers rely on steady vacuum supply and the o2 sensors in order to adjust fuel tables. If you have a vac leak it will run rich. If your 02 sensors are bad it will run rich. Also you need to check the fuel pressure on the rail and make sure the regulator is doing its job... stock pressure should be 32-35 with vac line on and around 40 with vac line off. Make sure you have a good vac line going to the map sensor on the firewall and the fuel press reg and that there are no vac leaks... If the 02 sensors are old replace them..... SD is very simple. You can mod it all you want: just dont get crazy with a lopey cam because the lopey idle cause low vacuum and the eec will freak out... The comp cams nx264 hr cam is about the max lsa and duration SD can handle and not run rich down low and lean up top... __________________ Shawn 87 Coupe The Notch Last edited by 50Droptop; September 4th, 2011 at 10:33 PM.

September 4th, 2011, 10:25 PM	#3
BULLET20XD Regular Join Date: Jan 2011 Location: Chatsworth,Ga Posts: 158 iTrader: 0 reviews	A fresh tune-up should do wonders. Ive never know of them to get great mileage. I will say this, i use to own a 89 F150 5.0 and it had platnium plugs in it(i forget the brand) and changed back to Motorcraft plugs. I lost 4 mpg!!! I have always used Motorcraft plugs. May want to do some research on other plugs. Just my 2 cents worth. Im still learning on theses cars as far as the efi and computers and other stuff that can make one run bad. __________________ 1990 LX 5.0 2000 Expedition 2002 Honda Accord One tea cup Chihuahua guard dog!!!!!!! Last edited by BULLET20XD; September 4th, 2011 at 10:31 PM.

September 4th, 2011, 10:31 PM	#4
50Droptop Regular 87 Mustang Lx 13.76@100 Join Date: Aug 2011 Location: Indiana Posts: 124 iTrader: 0 reviews	Oh I forgot to mention to set your base timing to 10-14 degrees __________________ Shawn 87 Coupe The Notch

September 4th, 2011, 10:36 PM	#6
50Droptop Regular 87 Mustang Lx 13.76@100 Join Date: Aug 2011 Location: Indiana Posts: 124 iTrader: 0 reviews	The 02 sensors are in the H-pipe above the cats..... if the cats were clogged you would be way low on power...Id get a off road H pipe and sell the cats for scrap I got 100 dollars for my old cats. __________________ Shawn 87 Coupe The Notch

September 4th, 2011, 11:25 PM	#8
50Droptop Regular 87 Mustang Lx 13.76@100 Join Date: Aug 2011 Location: Indiana Posts: 124 iTrader: 0 reviews	sure and build a 347 stroker since you have to take the headers off __________________ Shawn 87 Coupe The Notch

September 5th, 2011, 12:18 AM	#9
slow2V Regular 2002 Mustang GT 1320ft. Join Date: Jun 2011 Location: N. Nevada Posts: 241 iTrader: 0 reviews	Wet Boobs! Sorry got distracted.

September 5th, 2011, 01:44 AM	#10
Chris951 Hardcore Enthusiast 1991 mustang 5.0 Join Date: Aug 2007 Location: Mesa, AZ Posts: 1,938 iTrader: 0 reviews	Go with autolite 25 copper core spark plugs. 5.0s run like shit with platinums and autolites are great. They're all I run in my mustangs. As for your gas mileage problem, get some plugs, wires, msd cap and rotor ($30 at autozone or oriellys), O2 sensors, and FUEL FILTER (Wix or motorcraft). And make sure u fix those vacuum leaks. Like stated above, speed density cars will run VERY rich with vacuum leaks. That's probably 80% of your problem. But just for good measure u should do everything I stated as well.

September 5th, 2011, 01:49 AM	#11
slow2V Regular 2002 Mustang GT 1320ft. Join Date: Jun 2011 Location: N. Nevada Posts: 241 iTrader: 0 reviews	Human drinking Jameson's bad!

September 13th, 2011, 03:41 PM	#12
steven95gt Regular Join Date: Apr 2011 Posts: 54 iTrader: 0 reviews	all 5.0s run like shit platinum plugs? mines a 95 gt with a cobra swap and hasnt seemed to run right since i went to platinum plugs

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