87 Gt Idles But Woulnt Rev

vaccum leak.

Can you hear the fuel pump with the key on? Sounds like it's not getting enough fuel. Possible bad fuel pump.
I bought an 87 four yrs ago that had been sitting for 6 yrs. Had the same symptoms as yours. I clipped on a portable fuel pressure gauge on the shrader valve on the fuel rail. Sure enough it only had 14 psi of fuel pressure at idle. That's why it popped through the intake and wouldnt rev. The fuel pump was running but was bad.
I changed the pump and she came to life again.

Good luck

If it wasn't getting enough fuel, shouldn't it be popping out of the exhaust? Not the intake. When I did my HCI swap I left the stock pump in it for a while and it ran lean as hell, it popped outta the exhaust.

Vacuum leaks usually cause a high/hanging idle. Or at least in my own personal experience they have.

Crustang, I see that you said it had new wires, cap, and rotor. Check to make sure they have the firing order on the distributor correctly. And for s and giggles, see what the timing is set to.

Check fuel pressure:

The local auto parts store will often rent/loan a fuel pump test gauge, so get one and plan on using it. There is a fuel pressure test port located on the pressure feed line just behind the alternator.
Disconnect the vacuum line from the fuel pressure regulator. Check it for evidence of fuel present in the line by removing it and blowing air through it. If you find fuel, the fuel pressure regulator has failed. Reinstall the line, cap the open end and stow it out of the way.
Connect fuel pressure test gauge to Schrader Connect fuel pressure test gauge to Schrader port located just behind the alternator.
Turn the ignition switch on & start the engine. Observe the pressure : you should see 37-41 PSI at idle.
Turn the ignition off, reconnect the vacuum line and disconnect the fuel pressure test gauge. Watch out for squirting gas when you do this.




After you verify fuel pressure, dump the codes. Your 87 won't have a working Check Engine Light, so you'll need a test light.
See AutoZone Part Number: 25886 , $10


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.





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. 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.

crustang450 said:

thanks guys for the info.....i checked the firing order, it was right. checked the timing also it was about 12-15. i think its a fuel issue. but its wierd sometimes it will smooth out and i can give it about 1/8- 1/4 throttle and it will break up then run smooth to about 3k but if i give it anymore gas the rpms just drop and she dies. it will also idle perfect after for about 2 mins and then it starts bogging and dies. thanks again guys for ur info!

Click to expand...

I'd say fuel issue then

Glad it worked out for you. I knew your problem sounded all too familiar to when my original pump died in my 87.