silverstang1996

My stang backfires a lot at startup, I'm real tired of it and it could harm the engine so I want to fix it. My first thing to check out would be the timing, how do you go about that? Would it be cheaper for me to go to autozone, buy/rent a timing gun and measure it like that? Here my other question comes into play, if it is indeed off, how do I correct it? My other option would be to take it to a shop and have them check/fix the timing, but would that be quite expensive?

defconfire

I don't think you can with a mod motor. You'll have to take the timing cover off turn it until the timing marks align. I think it can take something like 52 rotations.

cliffyk

There is no base timing adjustment on our cars, it is all handled by the PCM. The crankshaft and camshaft position sensors provide information to the PCM from which it determines when to fire the spark and injectors.

The crankshaft position sensor provides the timing data, the cam sensor tells the PCM when the #1 cylinder is at TDC on the compression stroke, and the PCM then figures out which COP to fire from there.

Steeda makes a kit that let's you change to position of the crankshaft sensor the trick the PCM (it thinks relative to TDC), however that is not needed on any but highly modified engines and is in fact a very crude way of adjusting timing as compared to using a tuner.

If have custom tune that it may be related to your backfires at start-up, if you do not than it is most likely some other problem. Leaking injectors can cause backfiring problems.

silverstang1996

Well I have a custom dyno tune for the car. What confuses me is that sometimes it won't backfire for a long time. Then days like yesterday, the 5 out of the 6 times I started it up it backfired. The only time it didn't was when I went into a convenient store to get something to drink and started it back up within minutes.

defconfire

Does It burn any oil?

cliffyk

I assume from your account name that we are talking about a 1996 Mustang? How many miles on it?

It sound to me like leaking injectors, have you ever done a fuel pressure leakdown test?

The system should hold fuel pressure within 5 psi for at least a minute after shutdown. If not then something is leaking and if gas is not leaking out anywhere then it's either a fuel system check valve or one or more injectors...

silverstang1996

No the car doesn't burn any oil, yeah I'm talking about the 1996 car. I'll check the injectors again but I don't think they are leaking, atleast just the quick lookover I did I didn't see any or small any gasoline.

cliffyk

I was talking about their leaking into the intake manifold, not to the outside world.

If the get clogged they often don't seal properly and will leak raw gas into the intake manifold after you shut the car off. This can create a puddle(s) of raw gas in the intake that can cause a backfire when you start the engine.

A fuel pressure leakdown test can rule this out, or "rule it in" depending one the outcome.

mustangman281

On a returnless fuel system like in the 98+ mustangs the pressure would stay but on a return style pressure drops rather fast. An easy way to check if your injectors are leaking take off the intake tube and open the TB blade. Smell in there if there is a really strong smell of gas then you have a leak.

To me it sounds like you have a bad tune. Do you know what tables your tuner messed with?

myslow2002gt

It's not even needed on highly modded engines either. It's a waste of money, IMO.