Engine Random Hesitation And

[TonguePunchTheDirtStar]

Recently purchased a 1987 mustang gt. I also have never written on a forum before however I have searched many. I'd like to start by saying if I am going about this wrong I'm sorry ahead of time.

I have had the car for about a month and a half. Runs strong and came from a good home. The guy befor me rebuilt the motor about 25k ago. Car has roughly 130k on it. Hard to tell since new sport comps were installed and mileage reads 11k.

Driving on the interstate the other day the car suddenly shut off. I pulled over. Turned off the car the rest of the way than fired it up no problem. Drove 5 - 10 miles and it happened again. Ran just fine from the day I picked it up. This is the first problem I've had. I continued to drive but got off the highway on slower main roads. Instead of shutting off randomly it started to just hesitate randomly. Seems at first like it was losing fuel but with some thought seems more spark related. But either way it bogs down out of no where.

I started to give it gas when I felt it comming on and it seems to fight through it enough that it doesn't stall and it goes back to driving fine. After there is No power loss, shifts and accelerates fine. Again completely random. However I do feel as though going over bumps may instigate it some. But not all bumps cause this nor does the size of the bumps seem to matter.

Something else worth noting is that when this happens the sport comp gauge for rpm will drop to zero even before the motor has shut off it may jump some too and when I feather the gas and it fights through it will reactivate and read normal. I also noticed the gas gauge will sometimes go to empty and come back or go beyond full than come back during this hesitation. Not sure if it depends on how much fuel is in there for what direction it goes but it jumps around too. All other gauges remain steady and normal.

The hesitation is almost expected to occur on all drives. Sometimes sooner than others also sometimes hits harder than others. As of now always comes back to normal seconds later and drives fine.

It does effect the drive ability and reliability of my car and I could really use some input. The car does have the MAF swap, cobra intake mani., cold air intake of course. Headers but stock from there back. Please let me know what you think. Thanks.

 

[jrichker]

Does the problem occur only with a warm engine and not when the engine is cold?

 

[TonguePunchTheDirtStar]

It seems to happen no matter what the temp. But occurs more at temp. I have felt it right after starting but mostly after driving. Definitely happens before at full temp. Worth adding I checked the dizzy and it seems worn inside. Like the rotor and terminals for each plug are touching inside there perhaps not alowing good spark. It's a motor craft part. Maybe the wearing is normal.

 

[jrichker]

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.

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.

Your 86-88 5.0 won't have a working Check Engine Light, so you'll need a test light.
See AutoZone Part Number: 25886 , $10

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) Equus - Digital Ford Code Reader (3145It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $22-$36.

 

[TonguePunchTheDirtStar]

It was a vacuum leak! Hose connecting the oil filler cap assembly to the intake had come off. Plugged it back in with some good pipe clamps and runs perfect. Strange. Good to go id say. Unless it decided to run fine while I was testing it after.