jrichker, Tmoss, anyone that's good with wiring & EEC

[Mike86Stang]

Well I've ben having problems with my car sucking down massive amounts of fuel. Not to mention it won't pull codes unless the Sig Return (Pin47) is grounded to the chassis.

I ran the car for a couple days without grounding the Sig Return wire (got better gas mileage ALOT better) & then hooked up the ground wire to the Sig Return to pull the codes & this is what I got
Fast Codes:
34 (EGR) & 67(ACC)
Memory Codes:
22 (BAP), 29 (VSS..I don't have one), 31 (EGR), 51 (ECT High), 53 (TPS High), 54 (ACT high), 63 (TPS low)

After that I left the Sig Return Grounded ran it & pulled the codes again only getting 34 & 67 again. No other codes returned.

Knowing that there is something wrong with the wiring or the EEC I tested the bat term to the STO wire on the test connector (without the ground) & it read 12.7v. I then turned on the key for the ignition & checked the voltage on PIN 47 & came up with just shy of 5V. All of which says to me the wiring is in good shape.

I then hooked up my scanner without grounding the Sig Return & tried to pull the codes, it beeped once & fizzled out. No codes.I also tried to check the TPS v-ref wire to check for the 5v with the ground to the Sig return removed & it won't read anything. Everytime I hit the V-ref & ground it to get the voltage the injectors fire & the Fuel pump primes.

From what I can determine the wiring seems to be in good condition, but will not pull codes without the Sig Return grounded. If i'm getting voltage at the PIN 47 it tells me the wiring is good (KOEO) & that most likely the EEC is trash.

Can you guys fill me in on your thoughs, sorry for the book but I wanted to cover my bases. Now I feel totally by this stupid problem

TIA
Mike

 

[jrichker]

I'm not sure we are on the same page. I looked at Tmoss's diagram and pin 47 is the TPS signal (Dark green/Lt green wire). Pin 48 is the Self Test input and is the White/Red wire.

Grounding the STI wire (pin 48) puts the computer into diagnostic mode. If jumpering it over to Pin 2 (Black/White wire) on the big computer connector doesn't make the computer go into diagnostic mode, then the wire must have an open circuit. Measure resistance between the Black wire on the big computer test connector and pin 46 on the computer - you should see less than 2 ohms.

Use Tmoss's diagram and measure the resistance between the Pin 46 and the Black/White wire on the BAP. Repeat the process for the TPS, ACT, ECT & EGR. In every case you see less than 2 ohms resistance. The codes seem to point to a missing ground for the sensors.

 

[Mike86Stang]

Whoops! That pin 47 is supposed to be 46 ...the signal return for the sensors (Black wire w/ a thin white stripe). Pin 46 (signal return B/W wire) is what I'm grounding to force the EEC to pull codes. Without it grounded it won't pull the codes. As a side note I don't have ANY wires in pin 2???

I'm trying to determine the best way to check the resistance as you suggested for all the sensors. The only way I can figure I can do so is to use a piece of wire to "lengthen" my test leads but that would throw off the resistance wouldn't it? I don't think that would be a good solution. Any suggestions on how to measure the resistance other wise? I agree with you that the sensors seem to be missing a ground, and I've ran additional ground wires for PINS 60 & 40 & 20 directly to the chassis, which of course made no change.

During the winter I pulled the whole injector/sensor harness & resoldered all connections, cleaned, tightened ,& repacked all plug ends. I measured the resistance while it was off & it all seemed ok at the time. That harness doesn't have the BAP on it though so I don't know if I should look there first? All these problems started after a head/cam swap if that helps ...which was this past summer.

Do you have a link to Tom's charts? I have it on my home pc but it's in storage b/c of a recent move.

Thanks for the reply!

 

[tmoss]

If you have to ground the balck/white wire to get codes, you might have one of two problems. The trans (T5?) must be in nuetral and the trans nuetral switch must be closed to allow codes to be given. If that is right, then you might have a bad EEC ground? Although I have never verified it, I suspect the black/white wire connects to chassis ground.

 

[Mike86Stang]

Tell me your kidding....Funny thing is I know/have known that switch has been going out or has been semi dis-functional for quite some time now. Not to mention I ALWAYS leave it in gear b/c my parking brake is "incomplete".

That would make sense as to why I don't get codes, but still leaves a couple questions.

If that wire is not jumpered(46) the IAB doesn't work...nor the remaining sensors will function as far as I can tell. So that still leads me to believe that there is a missing ground as jrichker mentioned. I wouldn't think that that switch/sensor would be the reason for the rest of the sensors not functioning. That would mean every time you shift that particular ground would always break, which doesn't make a whole lot of sense to me. Maybe I'm missing something

Thanks for the response Tom

 

[Mike86Stang]

BAck to the top.....

I have a little more info if it helps.
With out the Jumper wire on the signal return, I have the 5v V-ref on all signal wires & on all Signal Return wires & of course on the v-ref wire. SO basically I have the 5v v-ref on every single wire going to all sensors (didn't check O2's).

Does that help or clarify anything???

TIA
Mike

 

[tmoss]

BAck to the top.....

I have a little more info if it helps.
With out the Jumper wire on the signal return, I have the 5v V-ref on all signal wires & on all Signal Return wires & of course on the v-ref wire. SO basically I have the 5v v-ref on every single wire going to all sensors (didn't check O2's).

Does that help or clarify anything???

TIA
Mike

CLASSIC example of a bad ground or bad ground wire. Check your EEC ground. Check it for continuity, pull on the connections, etc.

 

[jrichker]

Whoops! That pin 47 is supposed to be 46 ...the signal return for the sensors (Black wire w/ a thin white stripe). Pin 46 (signal return B/W wire) is what I'm grounding to force the EEC to pull codes. Without it grounded it won't pull the codes. As a side note I don't have ANY wires in pin 2???

I'm trying to determine the best way to check the resistance as you suggested for all the sensors. The only way I can figure I can do so is to use a piece of wire to "lengthen" my test leads but that would throw off the resistance wouldn't it? I don't think that would be a good solution. Any suggestions on how to measure the resistance other wise? I agree with you that the sensors seem to be missing a ground, and I've ran additional ground wires for PINS 60 & 40 & 20 directly to the chassis, which of course made no change.

During the winter I pulled the whole injector/sensor harness & resoldered all connections, cleaned, tightened ,& repacked all plug ends. I measured the resistance while it was off & it all seemed ok at the time. That harness doesn't have the BAP on it though so I don't know if I should look there first? All these problems started after a head/cam swap if that helps ...which was this past summer.

Do you have a link to Tom's charts? I have it on my home pc but it's in storage b/c of a recent move.

Thanks for the reply!

Lengthening the test leads won't have much effect on the test. You might add .2-.5 ohm if you have good connections. You can use the chassis ground if you are sure that the engine block ground and computer power grounds are good.

Pin 2 doesn't show up on Tom's drawing, the link is http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

According to the internal schematic I have of the computer, pin 46 does go to chassis ground inside the computer.

The BAP and have identical functions and the wiring is the same for both.

Keep looking, I'm sure you will find that there is a open circuit between the pin 46 and the black\white wire that connects the sensors. No sensor ground, and all the voltages will go up to whatever VREF is.

 

[Mike86Stang]

OK well I double checked all grounds... everything looks solid. I even ran jumper grounds directly to the chassis from pins 40 & 60. Still no change.

I checked the voltage at PIN 46 at the EEC & it's measuring the same 4.98v (vref). Which tells me the wiring for the signal return is good. If I unplug all sesnors (ecept MAF & O2's) then the voltage on the signal return wire drops to "0". V-ref stays where it's supposed to & I get .2-.3 v on the actual computer wires to each sensor.

What I'm thinking is that the internal (to the EEC) ground for the v-ref wire is bad.
The reason is is that the wiring seems to be in good shape & if I jumper signal return to ground everthing works normal for the most part.

Without the jumper & with the car out of gear & with or without all sensors disconnected (no jumper wire) when I try to pull the codes it does nothing at all.
I just get a constant STO signal, again telling me that the signal return wire or the internal ground for the EEC is BAD. I really don't think this is a wiring issue anymore I think the EEC is bad.

I tried measuring the OHMS between the signal return wire & PINS 40 & 60 , of which I got infinate OHMS again making me think the internal ground is shot.

Can you guys confirm or deny this based on the info I gave?

Thanks again for your time & thoughts!
MIKE

 

[jrichker]

I do believe you are on the right track.

The internal diagram that I have for the A9L shows pins 40, 60 & 46 all wired together on the PC board. I would tap into the Black\white wire and ground it to the one of the ground wires on either pin 40 or 60.

 

[tmoss]

Yeah, I think you have a handle on the problem. You could take the EEC cover off and see if you can see a burned ground connection - might be able to fix it with solder and wire if the EEC electronics are not hurt.

 

[Mike86Stang]

Alright fellas! THanks for all the help & insight I'll let you know what happens!~

jrichker....any chance you can e-mail me a copy of that internal diagram?? [email protected]

Thanks again!
Mike