My hatch died in traffic on me again today...

[LarsD]

I couldn't find my old thread to update, so I made a new one.

A few weeks ago I was on my way to work and my 91 died while sitting at a light waiting to turn. I assumed at first that my TFI or PIP had died. The car was cranking real slow like the timing was retarded or advanced too far. Then all of a sudden it cranked normally and fired right up. I got to work, and found that I hadn't fully tightened the cables on the starter solenoid (both the main line and the starter cable). I cranked them down and it seemed fixed. Drove it a couple hundred miles over the next week or so and it acted fine. I thought it was fixed until it just did it to me again today.

These are the voltages of the battery/charging system:

12.67 at rest (hood light on only)
10.5ish while cranking (fired up quick so I didn't get a good look)
14.4-14.5 while idling
14.3-14.4 at idle with headlights and the A/C vent running

The only thing that the car does that I think is odd is the voltage will dip down randomly to 13.5V when at idle. It doesn't do it consistently, regardless of what accessories are on. It has done this ever since I installed the 3G alt over a year ago (can't remember if it did it before or not), I first noticed it because I could hear the fuel pump's whine change pitch. Since I replaced the pump with a 255 unit it does it a lot less.

I figured if the injectors lose their ground the car will die (I assume), but if the injectors aren't grounded, would that cause a slow crank condition? I found the ground wire to the injector harness is chewed up pretty badly (we have lots of field mice out here). It is still connected by a few strands of wire, but not many. But, got home, I fired the car up and wiggled the shakers, wiggled pretty much every piece of harness I could get my hands on and it keeps on running. I unbolted and isolated the ground strap that feeds the injector harness (the one that is holding on by a strand) and it kept running. I unhooked the negative cable to the battery while it was running and it didn't die.

I don't know if it matters or not, but the vss isn't hooked up due to one of the wires being damaged. That only affects the cruise control afaik. It always dies when I tap the clutch to slip it into neutral when rolling up on a light.

I could really use some more ideas, every time it dies, I can get it restarted very soon after. Someone on EECtuning suggested the EEC relay is at fault, could this be so (is it the relay that is on the passenger side fender, under the CAI)? Most times when I've seen a relay fail, it has stuck closed, or ceases to function. I don't want to drive the car now until I can reproduce the failure so I know it is fixed for good this time. I'm sick on not being able to rely on the car.

 

[ID89GT]

Eec relay is up by the computer in the kick panel

 

[jrichker]

The orange ground wire in the engine fuel injector harness is the O2 sensor ground. The computer does not supply power to the injectors, it supplies a ground pulse to complete the power path back to the battery negative terminal.

Dump the 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.

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.

 

[LarsD]

I am surprised it didn't give me more trouble then it has TBH. Now I'm debating to trying to get the caps and fix it myself, or just get a new ECM.

 

[jrichker]

The caps blew for a reason. Unless you are skilled in PCB repair and electronic troubleshooting, get a replacement computer. This is especially true if you are dependent on the car as a daily driver. Look for a computer with a long warranty time just in case there are more electrical problems hiding in the wiring.

The only reason I would attempt a repair is if you are short of money. It 's close to Christmas, and a lot of folks have spent their spare $$$ on Christmas gifts.

The caps are a little different from the common Radio Shack stuff, they have a higher temperature rating and longer service life rating. See www.digikey.com for the caps you need at a very reasonable price. The stock caps are rated at 105*C, and you can use a higher voltage rating with no problem.

 

[LarsD]

The caps blew for a reason. Unless you are skilled in PCB repair and electronic troubleshooting, get a replacement computer. This is especially true if you are dependent on the car as a daily driver. Look for a computer with a long warranty time just in case there are more electrical problems hiding in the wiring.

The only reason I would attempt a repair is if you are short of money. It 's close to Christmas, and a lot of folks have spent their spare $$$ on Christmas gifts.

The caps are a little different from the common Radio Shack stuff, they have a higher temperature rating and longer service life rating. See www.digikey.com for the caps you need at a very reasonable price. The stock caps are rated at 105*C, and you can use a higher voltage rating with no problem.

I ordered the replacement caps already from Mouser. I work in the electronics industry, so replacing some through hole caps shouldn't be a big issue for me. I spent $2.91 on caps as opposed to $96 + tax for a new ECU. I figure if they blow again I'm not out quite so much.

 

[Blown88GT]

Doesn't look as if the cap blew up. Maybe shorted internally which is common failure mode for electrolytic capacitors. I opened my EEC & found nothing out of the ordinary, was hoping to find what you did.

 

[LarsD]

Doesn't look as if the cap blew up. Maybe shorted internally which is common failure mode for electrolytic capacitors. I opened my EEC & found nothing out of the ordinary, was hoping to find what you did.

Well they are over twenty years old. I'm going to chalk it up to them just wearing out. None of the traces are burned, and all the other components on the PCB appear to be fine. You having the same problem as me?

 

[Blown88GT]

No, my issue is worse: http://www.stangnet.com/mustang-forums/threads/bad-codes.848261/#post8536238
I'm quickly becoming an expert on Ford controls. It helps to have been a Controls Engineer for many years.

 

[LarsD]

No, my issue is worse: http://www.stangnet.com/mustang-forums/threads/bad-codes.848261/#post8536238
I'm quickly becoming an expert on Ford controls. It helps to have been a Controls Engineer for many years.

Wow, you got a tough one there.

 

[Blown88GT]

I rarely get the easy ones. (LOL). Story of my life!

 

[LarsD]

Quick update. I got the new caps installed, finally had a day off to reinstall the computer. Car feels a lot stronger now (before some days it would feel good, others, not so much). I feel fairly confident that at least one of the blown caps tied into the timing control circuit. Which would make sense, since when it would die, I'd try to restart it, and it would crank slow (like a low battery, or timing that was way off). Hopefully this is my last thread on the mysterious dying.