New here..need help after gt40p head swap WHAT SHOULD MY FUEL PRESSURE BE?

Fuel Pressure with the vacuum line to the regulator off should be 39-40 psi. With the vacuum line attached I normally see around 34-35psi on the gauge. And thats typically with a cam that pulls 17-18" of vacuum.

I had a problem kind of like that. The car would drive normal but at WOT at the track, it would fall on its face at the top end. after checking my data logs, I found that the computer was comanding it to run rich but I had 90+% injector duty cycle and the wide band was reading way lean. All my ignition parts were new at that time so I suspected a fuel issue. I did a pressure test and it said near 40 psi. I read somewhere that you should pump so much volume in so much time. Sorry I dont remember the numbers. I did try to let the pump fill a coke bottle with the pressure tester hooked up and it didnt fill it enough. I dropped the tank to find the pump screen had a hole in it & my pump inlet was half plugged with trash. Put the 225 walbro in, turned up my pressure & then I was running in the 60% range at WOT.

After I did my gt40p swap I had some issues also. My plugs were arcing through or around the spark plug boot.. The car would rev fine sitting still, but under load it ran like crap.. I think because the spark plugs were firing when they weren't suppossed to. So I popped the hood in the dark and got down in the engine bay to look for arcing..#4 and I think #7 were the problem.. It seemed like it would only do it once the engine warmed up. I put the accel shorty plugs in, new wires and the high temp boot covers on.. Now it runs great.

Dumping the computer diagnostic codes on 86-95 Mustangs

Revised 19-May-2009 to update drawing for dumping the codes on 86-88 Mustangs with no check engine light.

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.

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

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 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.

Here's the link 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.

See Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical





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.



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.



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.

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.

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.
Or for a nicer scanner see http://www.midwayautosupply.com/p-7208-equus-digital-ford-code-reader-3145.aspx– It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.