Engine Is there something wrong with my engine or is this just normal modded fox behavior?

AnthonyA1234

Active Member
Aug 17, 2020
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My car has come a long way from when I first got it. When I got it it ran pretty crappy but now I’ve gotten it to the point where it runs great. It’s a 92 gt with edelbrock heads, cobra upper and lower intake, and x303 cam. I had a issue with a surging idle so I changed pretty much everything you can. The car has a brand new distributor, coil, act and ect sensors, o2 sensors, injectors, pro-m calibrated maf, iac, egr, fuel pressure regulator, fuel pump, and probably more things I’m forgetting to mention. The thing is though is that I feel like there still may be something wrong with it. The car drives and idles amazing now but I’ve had some people tell me it smells like it’s running way too rich but I always just figured it’s because it’s catless. It was also rarely misfire after a cold start. And it always happens exactly the same I’ll pull out of a parking lot and when I get on the road right after I shift into second and give it gas again it’ll bog down a little and I’ll hear a pop from the engine and then after that it’s fine it’ll run great and no more misfires. And this happens very rarely and it’s very random. A month ago there was like a good week where it would happen everyday and then it stopped and now just yesterday I had it happen again. The only thing I can think it can be is a leaking lower manifold gasket causing a vacuum leak. I suspect this because I did a smoke test and had smoke coming out of my leaky oil pan gasket and another forum member told me that smoke shouldn’t end up in the crank. I also had very slight amount of smoke coming up from around where the Pcv valve is but it was the valve itself it was the metal under it so that looked like the manifold gasket leaking as well.

But the fact that the car runs so good makes me wonder if it’s just the mods this car has and the fact that it isn’t tuned that makes it misfire sometimes? Could this be a possibility or does there have to be something wrong?
 

Dan02gt

mazing how much gas smell came from that tiny hole
10 Year Member
Mar 2, 2003
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Could be a vacuum leak, but what you are seeing is somewhat common for modded foxes. When your car is still cold it's in open loop and not using the O2 sensors to correct fueling for your mods so you can end up with a lean or rich condition.
Before I had mine tuned it would do that same thing on occasion. It hasn't happened after the tune. I also noticed that my car doesn't smell rich at idle after the tune either. My tuner focused very heavily on correcting the fueling. This was mainly done by getting the MAF transfer as accurate as possible.

You should pull your computer and see if there is a chip installed in the J3 port.
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
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When you do a smoke test, the entire internal cavity of the engine fills with smoke. That includes the crankcase but there should be resistance for smoke to freely flow there as the PCV should prevent backflow. However, the smoke can also make it's way into the combustion chamber and past the rings as well. Smoke will also fill the lifter valley and travel down through the oil drainage holes into the crankcase cavity, so yes, the smoke will eventually make it's way down there and even up into the EGR system.

So smoke coming out of the oil pan gasket is not normal and is a vacuum leak. You want to fix that.

Is it the cause of your problems? Hard to say but it's certainly not helping
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
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I would advise sticking to one website, asking about an issue on two or three websites can get confusing, I guarantee you can get information overload right here on stangnet.
 

AnthonyA1234

Active Member
Aug 17, 2020
253
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When you do a smoke test, the entire internal cavity of the engine fills with smoke. That includes the crankcase but there should be resistance for smoke to freely flow there as the PCV should prevent backflow. However, the smoke can also make it's way into the combustion chamber and past the rings as well. Smoke will also fill the lifter valley and travel down through the oil drainage holes into the crankcase cavity, so yes, the smoke will eventually make it's way down there and even up into the EGR system.

So smoke coming out of the oil pan gasket is not normal and is a vacuum leak. You want to fix that.

Is it the cause of your problems? Hard to say but it's certainly not helping
Is there anywhere else it could be leaking or is it most likely the manifold seal?
Could be a vacuum leak, but what you are seeing is somewhat common for modded foxes. When your car is still cold it's in open loop and not using the O2 sensors to correct fueling for your mods so you can end up with a lean or rich condition.
Before I had mine tuned it would do that same thing on occasion. It hasn't happened after the tune. I also noticed that my car doesn't smell rich at idle after the tune either. My tuner focused very heavily on correcting the fueling. This was mainly done by getting the MAF transfer as accurate as possible.

You should pull your computer and see if there is a chip installed in the J3 port.
Ok that’s good info to know. I took a look at my computer a while back and it was completely untouched. It still had the factory tape seal on it. I’ll most likely get the car tuned in the future like you.
I would advise sticking to one website, asking about an issue on two or three websites can get confusing, I guarantee you can get information overload right here on stangnet.
Yea I’m only on this site when I said that I meant another forum member on this site. I actually think it was you that told me that was what it could be haha.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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I said it could be what? Sorry short memory, alot of times new members come on here and it's ' this guy on another site said it was this' or 'told me to do that ', some are looking for that 'magic' part or twist of the screw driver that makes everything work like new.
 

90sickfox

Wasn't a pretty sight...and I've got big hands
SN Certified Technician
Mar 2, 2015
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A mustang engine running stock computer and a MAF should be completely sealed. Any gasket leaks or bad hoses can cause unmetered air to get in the engine. The MAF is the only place that air should enter the engine. The air in the vapors that goes through the PCV system and in the intake has already been measured by the MAF. The oil pan gasket can allow fresh air to be sucked into the engine during decel and at idle, depends on how bad the leak is. Usually it wouldn't affect a car when on the accelerator. A leak in the intake gasket could cause that.

The hose that goes from the oil fill tube to the throttle body pulls vapors and air when accelerating. When in decel or idle the vacuum raises in the intake and it pulls vapors and air through the PCV hose into the intake. The reason I say it shouldn't cause an issue when on the gas is because the crankcase is pressurized at that point because gases get past the piston rings. It would push oil and vapor our of the pan leak. However, vacuum increases when off the gas, so, air can be pulled in.