94 GT Issues

GreenStang302 · Mar 21, 2012

I am always around 100 miles when my gauge gets down to 1/4 tank of gas left. It does not matter if you are in it all the time or driving it turtle style. There is also no change between highway and city driving. When I first bought the car and got it on the road, it got about 115 to half a tank of gas all highway. But that is the only time. It used to get 13 mpg no matter what the driving style was but began to decline. It now gets 9-10 mpg. I measure by filling the tank, resetting the trip, drive it until there is 1/4 tank left, fill it, and divide the miles driven by how many gallons it took to fill. I even bought an SCT chip to see if getting some kind of tune would help. Mileage stayed the same, no matter the tune or driving style. The only code I get is 564.

I know this is not a good gas mileage car, but I have heard of people with more mods that get much better mileage than me. Also, the car has always smelled extremely rich but I have not been able to find a reason why.

List of new parts (Problem was here before all new parts):
Fuel Pump (190), Fuel Pressure Regulator, Fuel Filter, MSD Distributor, MSD Coil, and MSD Spark plug wires, Spark Plugs, Mass Air (76mm calibrated for injector size), Fuel Injectors (24lb), PCM (Used), ECT, IAT, TPS, IAC, and both O2's

List of car mods:
B-Cam, 1.72 RR, 3.55 gears, SCT Chip, x-pipe, and flowmasters.

Any suggestion or insight would be greatly appreciated.

Dino Dino Bambino · Mar 22, 2012

Your injectors are too big for the mods that you have. Did you get the SCT chip custom tuned or did you just buy it off-the-shelf?
What fuel pressure are you running?

GreenStang302 · Mar 22, 2012

The reason I have them is I thought they were causing another issue I had (turned out to be something else). Since I plan on doing an HCI in the near future, I got the bigger injectors. But the gas issue was here long before the injectors. I just put those in last month with the mass air.

No, I bought the chip from American Muscle with the mail order tunes. Not as good as custom but I thought it would have made some kind difference.

I believe the fuel pressure is set at 32psi and 39psi.

JJ95GTID · Mar 22, 2012

I know my car ran rich with a Summit Racing 75mm MAF for 24lb injectors and of course 24lb injectors.
My idle was a little choppy and the exhaust smelled pretty rich too.
Passing emissions was tough because of the unburnt gas in the exhaust (HCs').
I recently put a Kirban adjustable fuel pressure regulator and lowered my fuel pressure 3psi and it fixed all those issues.
Passed emissions easily. Well under maximum allowed values.
My milage wasn't all that bad before. And, I haven't really noticed if it is better now. So, I can't help you there.
I was running a stock replacement fuel regulator before I stepped up to the Kirban afpr.

Other things that effect milage: front end wheel alignment, tire pressure (30psi is what I run), weight (speaker box enclosure, junk in the trunk, etc.), driving with windows down at higher speeds.

GreenStang302 · Mar 22, 2012

My front end alignment is a little off because I lowered my car and I have not yet gotten caster camber plates. As far as things in the trunk, nothing in there heavy besides spare tire. I do drive with the windows down but that is because I do not have AC.

If I stand behind the car running, my eyes will begin to water. Also, if I am in a semi closed in area like a shop, I can not have the car running for more than a minute or the entire place will stink of gas.

I find it weird that my mileage does not change between city vs highway or in the pedal all the time vs driving it considerably slow.

My O2's went bad not too long ago. The symptoms they caused were stumbling at idle but ran fine at WOT and only 56 miles from 3/4 tank of gas

Three50won · Mar 23, 2012

GreenStang302 said:
My front end alignment is a little off because I lowered my car and I have not yet gotten caster camber plates. As far as things in the trunk, nothing in there heavy besides spare tire. I do drive with the windows down but that is because I do not have AC.

If I stand behind the car running, my eyes will begin to water. Also, if I am in a semi closed in area like a shop, I can not have the car running for more than a minute or the entire place will stink of gas.

I find it weird that my mileage does not change between city vs highway or in the pedal all the time vs driving it considerably slow.

My O2's went bad not too long ago. The symptoms they caused were stumbling at idle but ran fine at WOT and only 56 miles from 3/4 tank of gas

Even if your car wasn't running rich you probably wouldn't be able to leave it running in a partially closed shop due to exhaust fumes.

Still tho, it sounds like your car is running rich. I'd say put the 19's back in. Even if the problem was there with the 19's you're definitely exacerbating the problem with 24's. The fact that the mileage doesn't change regardless of driving style is indicative of a rich condition to me. Because if it's running rich, then it's gonna use x amount of gas until you get to a condition where it actually needs more gas...in which case the gas mileage will decrease even more.

Also make sure you look under the hood to see if there are any fuel leaks at the rails or injectors. Maybe you didn't seat things properly.

And BTW, an adjustable FPR is useless if you don't have a gauge to tell you what the actual pressure is. I don't think you can just install a regulator and call it a day. From what I know you have to check the pressure after you install it. For all you know it could be at 45 PSI. I would think that's your problem right there. So just start over...put the 19's back in, put the MAF for the 19's back in, and re-install the stock FPR and see what happens.

GreenStang302 · Mar 23, 2012

When I put in the adjustable FPR, I did adjust the fuel pressure with a fuel gauge. I did it back in November right after I got the car, so I do not remember the exact psi I set it too but I am pretty sure it was 32 and 39 psi. I kept it close to stock psi. I no longer have the stock FPR.

I do appreciate your idea but I can tell you that it is not the issue. I just changed the injectors and mass air last month. There was absolutely no change in my gas mileage. Also, I did not find any fuel leaks under the hood or car.

This car really has me stumped. I have replaced just about everything.

The CCRM would not be a culprit in this would it? My fuel pump primes so I do not think it could be a faulty relay in the CCRM but that is about the only thing I have not replaced besides wires and hoses.

Three50won · Mar 23, 2012

GreenStang302 said:
When I put in the adjustable FPR, I did adjust the fuel pressure with a fuel gauge. I did it back in November right after I got the car, so I do not remember the exact psi I set it too but I am pretty sure it was 32 and 39 psi. I kept it close to stock psi. I no longer have the stock FPR.

I do appreciate your idea but I can tell you that it is not the issue. I just changed the injectors and mass air last month. There was absolutely no change in my gas mileage. Also, I did not find any fuel leaks under the hood or car..

32 AND 39? Could you explain that a bit further? And what MAF are you using? Is it just a calibration tube with the stock sensor? Because those are worthless IMO...

And as far as when you changed the injectors and MAF...if the car was running rich with 19's why would you put 24's on? 19's are good for 300 hp and 24's are good for about 380 hp. Even at 85% duty cycle the 19's were more than capable of providing adequate fuel with the stock FPR. So you really didn't need to install an adjustable FPR especially if you were gonna run the stock psi anyway.

Here is what I'm saying...when you had the 19's on, you put the adjustable FPR on and set it. It was running rich with that set up. Meaning it is not burning all the fuel it is getting. Until you get to the point where the engine actually needs either the amount of fuel it is getting or more, then you will not see any change in gas mileage. Any change you will see is only going to be a decrease in gas mileage. So with the 24's and the calibrated MAF, your mileage may not change...and if it does it will only be worse. Which is why I said the 24's will only exacerbate the problem.

You have some mods but your car is running rich at idle and while driving. So it may just need to be tuned. Other things to check are the O2 sensors...and the MAF sensor may be dirty.

And don't take offense at anything I am saying...but regardless of what the problem is you still have too much injector for your car. A good shop can tune around it but you're better off with the 19's at stock psi and a custom tune.

GreenStang302 · Mar 23, 2012

I understand what you are saying and no, I do not find you offensive.

32 psi with vacuum line on and 39 psi with it off. I am using a BBK 76mm mass air meter calibrated for the injectors. My O2's are new.

The reason I installed an adjustable fuel pressure regulator was the same reason I got the bigger injectors. I was told my FPR was bad and I planned on doing the trick flow top end kit in the future so I got the things that I could "grow" into so later on down the road, I would not have to buy injectors or FPR again.

I bought an SCT chip from American Muscle (mail order tune vs custom is no comparison, I know) thinking that some kind of tune would be helpful. But, besides smoothing out my idle, it did not make a difference. Car uses same amount of gas in any tune.

Three50won · Mar 24, 2012

GreenStang302 said:
I understand what you are saying and no, I do not find you offensive.

32 psi with vacuum line on and 39 psi with it off. I am using a BBK 76mm mass air meter calibrated for the injectors. My O2's are new.

The reason I installed an adjustable fuel pressure regulator was the same reason I got the bigger injectors. I was told my FPR was bad and I planned on doing the trick flow top end kit in the future so I got the things that I could "grow" into so later on down the road, I would not have to buy injectors or FPR again.

I bought an SCT chip from American Muscle (mail order tune vs custom is no comparison, I know) thinking that some kind of tune would be helpful. But, besides smoothing out my idle, it did not make a difference. Car uses same amount of gas in any tune.

Yea that's weird bro. The only other thing I can think of is perhaps the level sender or the gauge itself is bad. Maybe it's reading lower than the actual gas in the tank. If you care to check for that then I'd say put 2 gallons of gas in the tank and drive it until it runs dry and stalls out while recording the miles with the trip odometer. Then put 2 gallons in and drive it again until it stalls out...once again taking note of the trip odometer. Compare those notes and see what you get. And maybe keep a gallon of gas in the trunk so you don't actually get stranded. Sorry but that's the best I can come up with. Hopefully someone else can chime in with better info to help you. Meanwhile I'll try to look up some info that may help you a bit more.

notch351 · Mar 24, 2012

have you tried replacing or testing the gas cap? if the seal is bad there I know u said the car smells rich when running but for 10 bucks it may be worth a try. what is the gap set at on your spark plugs sometimes that can change over time or if you replaced them with out checking gap. i know they always say pre gaped but i hae found out first hand that that is always not true

GreenStang302 · Mar 24, 2012

No, I have not tried replacing the gas cap. I actually never thought of that. I gapped the plugs to .054

Three50won: Thanks for trying to help. I appreciate it. I have done tons of research and what people say to replace I have already replaced plus some. So, I have no freaking clue.

notch351 · Mar 24, 2012

have you tested the air intake temp sensor. if that is bad it can affect gas mileage i think. as it sends a single that affects fuel delivery depending on the air intake temp/ just a thought

GreenStang302 · Mar 25, 2012

notch351 said:
have you tested the air intake temp sensor. if that is bad it can affect gas mileage i think. as it sends a single that affects fuel delivery depending on the air intake temp/ just a thought

I read about that on the internet. That was one of the first sensors I replaced. But thank you for the suggestion.

GreenStang302 · Apr 6, 2012

I replaced the B303 cam with a stock 95 Mustang GT cam. On my last tank, I got about 13.5 mpg all city. Better than with previous cam but highway/city didn't change much. I did 75/25% hw/city on the tank right after cam swap and I got 15 mpg.

Any ideas as to what would cause my mpg to be the same whether I do highway or city driving?

notch351 · Apr 6, 2012

You never stated weather or not you replaced the gas cap. Like i said if its not sealing you will reduce your gas mileage

GreenStang302 · Apr 6, 2012

notch351 said:
You never stated weather or not you replaced the gas cap. Like i said if its not sealing you will reduce your gas mileage

Oops, I did forget to mention that I changed the gas cap. I did that before I changed the cam.

1slow95 · Apr 6, 2012

First some simple questions. Is your speedometer/odometer accurate? My car always took around 10 gallons when filling up at 1/4 tank, is that about where your's is?

When you changed the cam, did you go back to the stock injectors and MAF? I didn't see it listed so I'm assuming you have a stock upper/lower intake? I also see x-pipe listed but no headers, so you're using the stock manifolds? O/R x, or catted? Auto or 5-speed?

Could be a vacuum leak, but that would probably cause it to run rough too. I would go back to the stock MAF and injectors, remove the SCT chip and run the stock tune, and see how it does now that you have the stock cam. My car with stock parts easily got 20+ mpg on the highway.

You can also try to unplug the O2 sensors and run in open loop all the time. That will force the ECU to run off the base map. The O2 sensors will probably be ruined if you drive too much with them unplugged so you should install plugs or old O2's while you're testing it.
Other than the O2's, the only sensors I can think of that would add fuel are the ECT and MAF.

What about a ground problem? You could try adding a ground wire from the battery to engine block.
Just throwing out some ideas....

How do your plugs look? Do they all match? If one cylinder is lean for some reason it could be causing the rest of that bank to run rich when the O2's correct the a/f. Don't know what would cause one cylinder to be lean though other than an injector problem and you've replaced those.

GreenStang302 · Apr 11, 2012

1slow95 said:
First some simple questions. Is your speedometer/odometer accurate? My car always took around 10 gallons when filling up at 1/4 tank, is that about where your's is?

When filling from 1/4 of a tank, it takes between 10.5 - 11.5 mpg to fill it. (This is all the way full. Couldn't hold more gas if I wanted it too.) My speedo/odometer is a tad off. Every 1 mile I travel, my odometer reads 1.1 miles. I just installed the Ford Speed Calibrator, but I am having issues with it. (Makes the needle jump all over the place quite a bit and sometimes wraps itself all the way around.) Miles still read the same though. I checked with GPS. American Muscle even shipped a new one to me thinking it was maybe a faulty unit but this one is worse than the previous one. I bought a new VSS since it wasn't expensive.

When you changed the cam, did you go back to the stock injectors and MAF? I didn't see it listed so I'm assuming you have a stock upper/lower intake? I also see x-pipe listed but no headers, so you're using the stock manifolds? O/R x, or catted? Auto or 5-speed?

No, I have not had a chance to change the injectors because I am missing one of my stock ones somehow. So, I still have the 24lb with the "calibrated" MAF. Yes, stock intake and headers. O/R x. AODE.

Could be a vacuum leak, but that would probably cause it to run rough too. I would go back to the stock MAF and injectors, remove the SCT chip and run the stock tune, and see how it does now that you have the stock cam. My car with stock parts easily got 20+ mpg on the highway.

I have searched several times for a vacuum leak. Never found one. The chip has been removed for about 2-3 weeks. (Reflashed for stock cam.) I have been running on stock tune since a little before swapping cam back to stock. Highway/city mileage is still very different.

What about a ground problem? You could try adding a ground wire from the battery to engine block.
Just throwing out some ideas....

I have checked/cleaned my grounds but thanks for the advice.

How do your plugs look? Do they all match? If one cylinder is lean for some reason it could be causing the rest of that bank to run rich when the O2's correct the a/f. Don't know what would cause one cylinder to be lean though other than an injector problem and you've replaced those.

Plugs all look the same. Still look brand new.

Someone mentioned that it could actually be running lean causing the ECU to go into "limp" mode making it run rich. I do not know how much truth there is to that or what would even cause it to run lean. Just about everything on this car has been replaced.

Venom351R · Apr 14, 2012

which mass air meter do you have? Just curious. Also is there a way to recheck your fuel pressure?

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