EEC does not energize unless key turned to start

[crazypete]

I'm the proud new owner of a 91 mustang gt (bright purple/silver!). She ran like a charm for quite a while. I had to store her for 2 months and when I started driving her again, after about 20-30 minutes, the fuel pump would suddenly die. When I turned the car off and back on again, the pump would not prime. After returning an hour or so later, the car would start right up. Putting the fuel pump on a manual switch for diagnostics reasons surprisingly produced the same stall after 20 mins with the pump still whirring away! I noticed that after such an event, the computer would simply not return any self test codes when queried. The test simply wouldnt engage at all. Then, this weekend, I let it idle for half an hour (I got double 11's on the self test, btw) and it died for good. Check this out, though! The fuel pump will now prime when the car is turned to "start". Then the car will crank, kick in, then spin down peacefully to zero. Holding it at start with the self test wire engaged still produces no response from the computer. All the lights and chimes work normally, but there is no check engine or check oil light (these will also blink on when turned to start). The eec relay will only click when turned to start

I took voltages from the eec relay:
koff
yellow: 12v
red: 0v ground
red/grn: 0v ground
blk/wht: 0v ground

kon
yellow:12v
red: 12v
red/grn: 12v
BLK/WHT: 12v <- huh? that's the ground wire!

so I grounded blk/wht to computer ground and no fuel pump priming, even though the eec relay now clicks

kstart (original blk/wht connection):
yellow:12 v
red: 0v
red/grn:12v
blk/wht: 0v

I can make the fuel pump run by grounding the fp test in the eec connector in the engine bay, so I know shes working.

The ignition column switch seems to be 12v across all the wires in on position except for the starter wire in the back. When turned to start, all the wires on the bottom row are hot.

Please help, this is really wigging me out and I need my mustang fix! There's cruising to be done

Thanks guys, Crazy Pete

[crazypete]

Well, looks like she's getting spark. I pulled a plug and rested it on the header and had my buddy crank it. She was throwing sparks everywhere

I hardwired the fuelpump relay and was able to get a little sputtering as long as the key was on start

[PKRWUD]

Have you tried replacing the EEC relay?

[PKRWUD]

Also, what are the KOEO and Key OFF voltages at the fuel pump relay?

[crazypete]

Thanks for the quick reply guys

here are the voltages for the fuel pump relay

wire koff kon kstart
pink/blk 0v 12v 12v
grn/yel 0v 0v 12v
red 0v 12v 12v
blue/org 0v 12v 0v

Should both signal wires be at 12 volts with koeo?

This is with the eec black/wht wire grounded properly. Yes, I hear a click coming from the eec relay and it does seem to transfer power from it's inputs to outputs. I tried another eec relay that I had sitting around and it produced the same effects.

By the way, most of the eec outputs are at 12 v when I stuck pins into the wires coming out of the harness. It just doesnt seem to respond to the self test or function properly.

mmmmmmm..... pete's thinking about a nice carb conversion.

[PKRWUD]

It should be like this:

At fuel pump relay with the key OFF:
P/B wire = Battery voltage (whatever the voltage is across the battery terminals, ie: 12.4v)
All other wires = Zero volts

At fuel pump relay with the key ON, engine OFF (for two seconds after key is turned on):
P/B wire = Battery voltage
G/Y wire = Battery voltage (zero volts after two seconds)
R wire = Battery voltage
B/O wire = Zero volts

At the EEC Power Relay with the key OFF:
Y wires = Battery voltage
All other wires = Zero volts

At the EEC Power Relay with the key ON, engine OFF:
Y wires = Battery voltage
R wires = Battery voltage
R/G wire = Battery voltage
B/W wire = Zero volts

BTW, these readings are all with the specific relay plugged in.

You need to disconnect the 60 pin connector from the ECM, and test for resistance between the battery neg POST, and pins 40, 49, & 60.

Next, test for voltage at pin 1 (key off), pin 37, pin 57, and pin 26 (KOEO).

Write down the results, and post them.

Take care,
~Chris

[crazypete]

Chris, ya da man!

Ok, voltage with koff at

pin 1 (yellow) is 12.4v

with kon

pin 37 (red) is 12.4v
pin 26 (brn/wht) is 0v
pin 57 (red) is 12.4v

with koff, resitances measured as follows

pins 40&60 (blk/wht) were 3.5 Kohms (not good, I think)
pin 49 (org) about 750 ohms

it was about 750 ohms when I touched the metal of the chassis

Now, when I went key on, I noticed that pins 40, 60 and 49 were all at 12 volts! This is bad, I assume

Thanks for your quick answers
Hope to hear from you soon

[PKRWUD]

Last one. If you have a wire at pin 30 in the 60 pin connector, how much voltage does it read key off and key on (with the 60 pin disconnected from the ECM).

Also, what kind of tranny do you have?

[PKRWUD]

******. I'm sorry, that's not going to be the last one. I also need you to measure the resistance at pin 20 (& good ground), just like you did for 40 & 60. Then check pin 46 for voltage key off and on. If it has no voltage at either, test for resistance at ground.

[crazypete]

You still da man!

ok, I grabbed pins 40, 60 49 and 6, cut them and grounded them to the pin60 computer ground. The new resistances are now all flat zero (at least on this cheap voltmeter) to the neg battery post.

pins 30 and pin 46 are zero volts under both conditions

after I grounded the pins 40,60 and 49, the car suddenly came to life! She liiiives!

but now I have a check engine light and codes I've never seen before like 56 and 66 (maf high and low) and code 79 (pin10 shorted to +v) on koeo and codes 98 (koeo did not pass) and code 56 again on koer. I never had a problem with the MAF before... I did remove the neg battery cable overnight, so the computer might be "relearning" the engine. The car is a good ole T-5 equipped unit.

should I attach pin 46 to key on power, now?

[crazypete]

wow, ok

the mass air sensor has 3 wires on the circuit wiring diagram, but 4 wires in real life. There's a red, which is 0v keyoff and 12 v keyon.
black 0 ohms off but 12 volts with key on
ltbl/red 0v both cases, I guess because the engine's not running
tan/ lt blu. This is 0v off and 3-4 volts with key on

I guess I need to ground the mass air sensor, too, right?

[crazypete]

ok, that cure all of the mass aitflow sensor problems. Yipee

now, I still have that code 79 (pin 10 hot). Where does this wire go? I checked the top of the compressor and I just see 2 black wires. Where should I dig to find where the wire goes?

[crazypete]

I take it back, I'm still getting code 66 (maf voltage too low)

[crazypete]

ok, I read the posting " again, How to cure code 66 (maf below minimum voltage)"

and here are the results:

dk blue wire continuity: 1 get 1 ohm between the maf harness and the ecu harness

tan wire continuity: 1 get .5 ohms between the 2 harnesses

black is solid 0 ohms ground

all resistances between all of the 3 wires is infinite

red is 12 volts at key on

backprobing the blue wire while the engine is running , I get about 1.5 volts (analog voltmeter, so I can olny approximate)

[PKRWUD]

Sorry, I was booked all day. i am getting ready to spend some time with a new "friend" right now, and then I'm going to crash. I'll look into your results tomorrow. You're doing well, though!

Take care,
~Chris

[crazypete]

lol, hope you had fun dude (nudge nudge)

After a lot more probing, I would say that the voltage is more like 1.0 volts at idle and it shoots to 2 volts if I tap the throttle linkage. The car is idling like crap, really fluctuating between 500 and 800 rpms, shaking, smells like all hell and is pouring moisture out the tailpipe.

I solved code 79 by cutting the black/yellow wire. Nuff said. The a/c was discharged anyway and I have this strange feeling that I would be hunting grounds with the a/c system the same way I am with the computer.

Thanks for all your help, though, you've been a lifesaver

[PKRWUD]

Hey man, I've been very busy, and have been neglecting several threads. Do me a favor and summarize what's up now, and where you're at.

[PKRWUD]

Originally posted by crazypete
should I attach pin 46 to key on power, now?

NO!!!

You never said what the resistance was between ground and pin 20.

[crazypete]

ok, here is the current situation:

I'm getting code 66 telling me that my maf is below minimum voltage. When it probed it, it was actually at 1.0 volt at idle rather than the .6 it is supposed to be. It is actually above minimum. It's smells real bad and is pouring moisture from the tailpipes and is idling really erratically

The pin 20 was at zero ohms (or an ohm or two).

I've given some serious thought to ordering a holley avenger 570, an edelbrock performer intake, tapping into and pressure regulating my fuel lines and building the simple brute musclecar I always wanted. Now that the a/c system is also electrically haywire, I can rip that out and use an a/c elimanator kit.

Not like I'd lose any reliability right now. I couldnt even get her to start this morning

[PKRWUD]

You need to test resistance between pin 50 and pins 9, 40, & 60. Trick is, though, that the MAF has to be disconnected, and the ECM connected (you will have to back-probe the wires at the 60 pin connector), with the key OFF.