EEC does not energize unless key turned to start
 

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

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

Have you tried replacing the EEC relay?

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

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.

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

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

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?

******. 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.

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?

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?

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?

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

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)

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

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

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.

NO!!!

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

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

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.

Ok, I tested resistances all around

Between pin 50 and ground was about 4 volts, but resistance was infinite between pins 50 & 9 , 50 & 40 and 50 & 60. This was with the key turned on and the maf disconnected.

I wanted you to test them with the key off, but that's okay, THIS TIME. ;)

With the KEY OFF, disconnect the MAF sensor, and test for resistance between the "B" pin at the MAF connector and the battery negative post.

If resistance is less than 5 ohms, disconnect the 60 pin connector, and measure the resistance between the "C" pin at the MAF connector and pin 9 at the 60 pin connector, again, with the KEY OFF.

If resistance is less than 5 ohms, connect the MAF harness and the 60 pin connectors, backprobe pin 50 at the 60 pin, and start the engine. Check the voltage between pin 50 and battery negative post.

If voltage is between .2 and 1.5 volts, the ECM is bad, and needs to be replaced.

Hey, thanks for all your help, man

It looks like the eec went bad on the car. I'm not surprised because of all the electrical happenings in the car. I'm gonna sleep on it, but I think I'm gonna do that carb conversion. Worst case, I just put the FI system back in and replace the eec

Thanks again!

Okay, then let me give you some pointers to make it easier.

EFI to Carburetor Conversion

I. Introduction

This article is for anyone with an '86-'95 Mustang that is contemplating converting from the Electronic Fuel Injection (EFI) to a carburetor.

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II. Why Are You Converting?

The first question you should ask yourself is why. Why do you want to go from fuel injection to carb? If your car is a daily driver that is fairly stock then you are just wasting your time and money. Your gas mileage will decrease, you will lose some low end torque, you will lose some drivability, you will increase your exhaust emissions, and decrease the value of your car. If you have a street/strip car and are looking for a cheaper way to build more power then a carb setup might be for you. If it is a race car and you don't care about drivability then a carb is a smart choice. Don't get me wrong, a good well thought out carbureted combo is a very good system. But if you are switching to a carb just to solve your problems with EFI you might be surprised. A carburetor requires work to get it right. You may be trading in your problems for a whole new set of problems that you know nothing about. Before doing anything carefully weigh out your decision to remove the factory system from your car. In the end I hope that whatever decision you make turns out to be the best for you and your car. GOOD LUCK!!!


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III. Mechanical Changes

Intake and Carburetor: Of course if you are converting from EFI to carb you must have an intake manifold and a carburetor. Just be sure to size the components to match your combination properly.

Fuel System: You will need a new fuel pump and pickup. Do NOT use the existing EFI pump. You can either use an electric low pressure pump designed for a carb (like the Holley red or blue pumps) or go with a mechanical fuel pump. In either case you must replace the fuel pickup on top of the gas tank with a purpose built pickup that does not include an in-tank pump. If you have a drag car it may be time to upgrade to a fuel cell or modify your existing tank for a bottom sump. At this time I also recommend you go with new fuel line from the tank to the carb. Use 3/8" minimum or larger based on your needs. Remember that many sanctioned race tracks will only allow up to 12" of rubber fuel line so go with aluminum wherever possible, and keep the lines in-between the frame rails for safety. To use a mechanical fuel pump you must change the front timing cover on the engine to one that accepts a bolt-on fuel pump. You may also need a fuel pump eccentric to drive the pump.

Ignition: Replace the distributor with one from an '85 manual transmission Mustang. This distributor has a steel gear to be compatible with a roller cam. Also use a Ford Duraspark II ignition box. A complete MSD distributor and box could also be used as a step up from the factory stuff.

Brackets & Linkage: Any fox body accelerator linkage will work as long as the car was equipped with a carbureted V8. Look for a '79-'85 V8 Mustang or an '83-'88 V8 T-bird if you go junkyard searching. You will also need the throttle cable bracket attached to the intake manifold and a throttle return spring.

Transmission: This is probably the most critical step of the whole process. If you have a manual transmission you have nothing to worry about. However, if you have an AOD automatic you need a TV (throttle valve) cable. You can purchase this from Lokar Performance (NOTE: this is the same cable that Windsor-Fox Performance carries except $25 cheaper from Lokar direct). Setup is critical so follow the instructions included closely. Setting up the cable wrong will lead to a burned up transmission in very short order.


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IV. Electrical Changes

The electrical changes described here are for a 1990 Mustang. All '89-'93 mass air equipped Stangs will be very similar. '86-'88 speed density and '94-'95 mass air Stangs will also be close but some changes will be necessary.

Your car is divided into two harnesses; the EEC harness and the main or "chassis" harness. The EEC harness contains all of the computer related sensors, actuators, and such. It also contains some of the wiring for the air bag system. The chassis harness contains everything else; headlights, fuel pump wiring, instrument cluster, etc., etc. In order for the EEC to receive power from the battery, control fuel pump, and the airbag to work properly, the two harnesses must mesh together at some point. There are 4 of these points:


--Two connectors near the computer (passenger-side kick panel). One is green, one is gray. Both are 8-pin connectors I believe. One is rectangular and the other is round.

--Two connectors near the driver's side hood hinge and right above the master cylinder. One is gray, one is black. They are both round, 8-pin connectors. One of the connectors does not utilize all 8 pins.

The first thing to do is the part that's the most fun! LOL Disconnect the battery (of course!). Remove the computer and the EEC Power relay that sits directly above the computer. On the 60-pin connector that plugs into the computer, remove the black plastic "cap" which holds the wire bundle at a 90 degree angle to the connector. Unplug the two 8-pin connectors mentioned above, unscrew the bare wire ground and you should be able to pull the harness up into the engine compartment. The oval-shaped grommet will come with the harness, so use a screwdriver to pop it out of the hole.

Once you've got that done, everything you need to remove is under the hood. Just start at one end of the harness and work your way around and disconnect everything you come to that attaches to the EEC harness. As a minimum, you're going to have to remove the upper intake to get to all this. This should include the following items:


--TAB/TAD solenoids
--EVR solenoid
--MAF meter
--Air Bag connector below MAF
--Round 8-pin connector below MAF
--EVP solenoid
--TPS
--IAC
--All 8 injectors
--Water temp sender
--Oil pressure sender
--TFI module
--ACT
--ECT
--Carbon canister solenoid
--ground at starter solenoid (single pin connector)
--Two connectors located near brake booster

I'm sure I'm forgetting something, but just disconnect everything you come to and the entire EEC harness will pull out. You will be shocked at how much all that copper weighs..LOL

Once you've got everything out, it's time to start re-wiring. All the re-wiring will take place at the two connectors by the brake booster that you unhooked earlier. This is how you will tap into the chassis harness and get things like the fuel pump working again. Best way to accomplish this is to tap into the wires just below the connectors. You can use those little plastic splice connectors...works great. Be sure to tape up the open ends of the connectors to prevent water from getting in there.


On the Gray Harness:


---Wire #16 (red/light green - 16 Ga) to the ignition trigger/turn-on lead. On my MSD it's the thinner red wire.

---Wire #11 (Dark Green/Yellow - 20 Ga) to the negative side of coil or the "tach out" port on an MSD. This is the line to your stock tach.

On the Black Harness:


----GROUND #97 (tan/light green - 18ga) to a suitable chassis ground. This creates the ground for the primary side of the fuel pump relay.

---Wire #39 (red/white 20ga) to the temp sender.

---Wire #31 (white/red 20ga) to the oil pressure sender.

---Wire #361 (red 16ga) to #16 (the wire you ran to the ignition turn-on above). This creates the positive voltage supply for the primary side of the fuel pump relay.

Only other thing that you need to do is when wiring in the fuel pump itself. Just get the polarity right on the two wires that are coming off the stock EFI pump. Then cut them and extend them out to where your new pump is.

On the underside of the car, you can disconnect the O2 sensors and oil level sensor (side of oil pan) and pull that harness out too. You could rewire the oil level sensor to still be operational if you wanted.

After that, you should be good to go! As far as wiring the ignition, you'll have to run wires to the positive side of the battery and chassis ground as well as wire the pickup to the distributor.

Just in case you didn't know, the smaller the gauge (Ga) of a wire, the bigger around it is. That should help you to distinguish between the right wires. Your fuel level gauge will still work properly (providing you didn't put an old carb tank in the car) and your ammeter should work fine as well.

Take care,
~Chris