back fire in the intake

ok i have a 92 lx 5.0 its started missing and back firing in the intake, what i have done- full tune up plus new distu. new injectors fuel filter upper intake(found a crack in mine) new upper and lower intake gaskets check for vac leack with brake cleaner and couldnt find anything swaped pcm with my buddys same prob. checked alt for elct noise found nothing only big lead i have had is my fuel pis is at 21 running and 23 key on engine off but i have a new filter so could the pump relay clause all this?
 
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Where is your timing set at? You might wanna check it. And check if the engine is running lean...perhaps an injector not firing or a valve stuck open. Make sure the injectors are all connected to the proper wires. If the engine won't start then make sure your spark plug wires are all connected properly, functioning properly, without cracks, and are going to the correct plugs. Maybe take the plugs out and make sure they're gapped properly and not damaged (make sure the gap has not been shut closed and the boot is intact). Your fuel pressure should be in the 39 to 44 psi range while the engine is operating.
 
timing is at 14 im running e3 plugs not sure how to gap them or if you even can with norid lights all the injectors fire it will start and try to run for a min or 2 but stalls out. and you say the fuel psi should be 39 and least mine at best is 23 so should i start with the fuel pump?
 
Yea I missed the low fuel pressure in your original post. You're prolly looking at getting a new pump. Technically the pump won't operate if the relay is bad...but electrical problems are sometimes intermittent. So it could be the relay...but more than likely it's the pump. So now is the time to upgrade.
 
ok got the pump in today nice and simple checked fuel pis 36 koeo car runs ok when warm but will not run right and all cold i can feel driving it that the timing is a little low but i check it and its at 10 i bumped it up to 14 but still not sure y when cold it will not stay running. Any ideas??
 
Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on.

Dumping the computer diagnostic codes on 86-95 Mustangs

Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.

Codes may be present even if the check engine light hasn’t come on, so be sure to check for them.

Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.

Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. On a manual transmission car, be sure to press the clutch to the floor.
Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.

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If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

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The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

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The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.


WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and driveablity problems

Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, and clutch (if present) is pressed to the floor, and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see Equus - Digital Ford Code Reader (3145) – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.
 

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