914-SHO Ground Circuit Tests - Not good

[3d914]

Decided to double-check my ground circuits for PCM and sensors since I forgot to tie the #40 & 60 PCM grounds directly to the body at the battery - terminal cable. Fixed this, but still no reset of PCM.

So I set about checking the ground circuits for the PCM and sensors. I did two separate tests with the PCM connector (PCM disconnected), Ignition switch OFF, and CPP switch OFF (open).

Test A) DVOM positive connected to batt +, and checked volts at each ground position.

• PCM #60, 49, 40 - all good
• Sensors: all good
  • ICMR #15 (BK/LG)
  • MAF (BK/LG)
  • Ref Cont SW/ICMR #17
  • O2 #1 & #2 (BK/LG)

Test B) DVOM positive connected to batt -, and check for continuity at each ground position.

• PCM #60, 49, 40 & sensors - all good

Then I went around the PCM connector looking for any other circuits that might be tying (shorting) to ground. Here's what I found:

• #9 - MAF (T/LB) Grounded by PCM --> OK B & C inside MAF have continuity & goes to ground.
• #16 - Ignition ground (O/R) --> OK Ground is passed within DIS module connectors.
• #17 - Data Link conn/Malfunction lite (T/R) --> OK Appears to ground through the Crank Pos Sensor.
• #19 - FP Mon (PK/BK) --> OK Circuit closed by FP motor
• #20 - Gnd --> OK
• #30 - Clutch Pedal Position sw (P/Y) --> OK Corrected wrong connections

OK, here's what I don't understand:

• MAF #9 - If I check continuity between signal (D) & return (C) on the MAF I get nothing - which makes sense. When I check between return (C) & ground (B) I get continuity. Isn't the PCM supposed to supply the ground side of the return. If return is connected internally in the MAF what will the PCM detect?
• #16 Ignition ground - This leads to the CID, Crank position sensor, and the ICM (DIS). I don't see any connection to ground, so one of these must be grounding this circuit internally right?
• #17 Data Link - the EVTM indicates this is supposed to be a 12V circuit to the data link connector and Malfunction lite. How could it be on the ground circuit?
• #19 FP Monitor - this circuit ties to PCM #5, the FP & cut-off switch (which I'm not using yet), and then to ground through the FP. With the FP off I should not be getting to ground.
• #30 CPP - this circuit goes to numerous sensors (via GY/R wire) when the switch is closed, but mine was open.

This is driving me nuts! I must really have something f#^&ed up.

 

[Shovert]

Seen your PM. I need to know what year wiring is and I remember correct it is 3.0. Maurice

 

[3d914]

Seen your PM. I need to know what year wiring is and I remember correct it is 3.0. Maurice

Maurice, Engine is 95 3.2L & wiring is 95 3.0L (MTX component harness & PCM)

 

[Shovert]

Will look into it. Found this link with wiring diagram and one I will go by. You may already have it. Page 35 and 36 of the pdf. Maurice
http://taurus-club.ru/manuals/Ford_Taurus_1995_wiring.pdf
Edit later in pdf shows all the ground circuits.
Bummer. Will have to fiqure this out. I typed a long answer and page timed out and had to relog in and lost it all. Maurice

 

[Shovert]

Remove computer to test.
9 Wire goes to maf only #50 also to maf only Red to maf and pin 37+57 and other items. other wire on maf goes to ground.
16 to cid,crank sensor, and ignition module. I found these wires with bare wire in harness with metal foil over them. Bare wire went to ground. I had to extend mine. I put metal foil over the original and wrapped used bare stranded wire over the foil and then took that to ground.
17 goes to code reader connection and also one side of check engine light. Other side of light is a hot in run and start. 17 is ground to turn the check engine light.
19 monitor wire for comuter. If remember mine power for fuel pump from ccrm and this wire tells computer fuel pump has power.
20 ok
30 to clutch switch, unsure if switch is [NC or NO] depending on clutch position. I can't see this cause problem. As you know engine runs etc in any clutch position. Read somewhere going by memory [been warned]used by cruise control.


Maurice

 

[3d914]

Will look into it. Found this link with wiring diagram and one I will go by. You may already have it. Page 35 and 36 of the pdf. Maurice
http://taurus-club.ru/manuals/Ford_Taurus_1995_wiring.pdf
Edit later in pdf shows all the ground circuits.
Bummer. Will have to fiqure this out. I typed a long answer and page timed out and had to relog in and lost it all. Maurice

Right idea, wrong diagram. That one is for regular Taurus. I'm using page 35 & 36 of Pavlin. I have the Pavlin for 95 SHO. Wondering more about the weird ground signals I found.

 

[3d914]

Maurice, thanks for the feedback, but still not clear on a couple of them.

9 Wire goes to maf only #50 also to maf only Red to maf and pin 37+57 and other items. other wire on maf goes to ground.

Got the #9 wire going to MAF, but why is it ground. The "B" & "C" pin of MAF connector have continuity inside the MAF. Wondering if this is right?

If the PCM provides the ground side of #9, then how can it be grounded w/o the PCM?

16 to cid,crank sensor, and ignition module. I found these wires with bare wire in harness with metal foil over them. Bare wire went to ground. I had to extend mine. I put metal foil over the original and wrapped used bare stranded wire over the foil and then took that to ground.

OK, so this is a valid ground. Cool.

17 goes to code reader connection and also one side of check engine light. Other side of light is a hot in run and start. 17 is ground to turn the check engine light.

I thought the same thing, but EVTM (page 24-4) says its 12v start/run into the PCM - see also page 61-2. So if its power, how is it on my ground circuit w/o the PCM plugged in?

19 monitor wire for comuter. If remember mine power for fuel pump from ccrm and this wire tells computer fuel pump has power.

I agree, but it should not be grounded this side of the FP, it should be 12v (from 12v at #5 CCRM).

20 ok

Agree.

30 to clutch switch, unsure if switch is [NC or NO] depending on clutch position. I can't see this cause problem. As you know engine runs etc in any clutch position. Read somewhere going by memory [been warned]used by cruise control.

Switch is NO for run, NC to start. I had it open, so it shouldn't be grounded.

 

[Shovert]

Page 35 and 36 wrong page??
Pin 9 may read to ground with hooked to computer or MAF plugged in thru them. If unplugged from them should not read ground.
Pin16 is not a ground unless read thru items. But is wrapped in metal foil and foil is grounded.
Pin 17 I can see read 12vdc if read thru the light bulb. Bulb can act like a wire.
Pin 19 like said run from fuel pump and reads that signal back to computer. Maybe reading ground thru computer.
30 unsure.
Like said unplugging computer may get rid of grounds. Maybe reading the circuitry in it. Maurice

 

[Shovert]

A thought. Since having wiring trouble and or computer. A suggestion. I took a 1/4" thick piece of plywood and mount the 93 Mustang harness [car it was going it. It is already EEC-IV] Modified to fit the 3.2 wiring diagram.

Notice the green tape, That is body shop tape. Easy to write on, stays on, peels off easy and don't leave a residue. I mark every sensor and other connections so wouldn't have to constantly look at diagram to ID connectors.
Notice in picture in center the foil covered wires I mentioned in last post.
You do the same, remove computer and all sensors etc. Then ohm out every wire per the wiring diagram. I did this on my 89 Mustang conversion to turbo. Also done a 16 year old conversion to turbo on his harness.
http://i177.photobucket.com/albums/w224/mgman75/Turbo17 harness/100_0893.jpg
One warning do not, DO NOT, use too large a probe in computer side. You can actually loosen up the connection and cause problems. Maurice

 

[3d914]

Thanks Maurice, that's a start.

Pin 9 may read to ground with hooked to computer or MAF plugged in thru them. If unplugged from them should not read ground.

Correct, I see the same. If I unplug the connector from the MAF, then I don't get a ground signal on #9 PCM socket. However, I'm still not sure if the MAF leads B & C are supposed to have continuity between them. Can you check a SHO MAF that you have to see if internally B & C have continuity?

Pin16 is not a ground unless read thru items. But is wrapped in metal foil and foil is grounded.

OK, so I'll have to check all the connecting items in this circuit to see if any of them are passing ground from one lead to another.

Pin 17 I can see read 12vdc if read thru the light bulb. Bulb can act like a wire.

OK, I'll dig a little deeper on this and disconnect the cluster portion to see if that has an effect.

Pin 19 like said run from fuel pump and reads that signal back to computer. Maybe reading ground thru computer.

Remember, I'm doing all my checks w/o the PCM - just to the PCM connector.

30 unsure.

You & me both.

 

[Shovert]

Found this on the pin 30. It is the section 19 of the eec-iv test procedure. Maybe some help. Maurice
Also I will remove and test my Maf and let you know.
http://www.rothfam.com/svo/reference/volumeH/1988/Section 19 - EEC-IV Pinpoint Tests FA-KR.pdf
More maf testing.
http://ww2.justanswer.com/uploads/apjp02/2010-08-31_003658_MAF.pdf

 

[3d914]

Also I will remove and test my Maf and let you know.

Maurice, do you have to remove it to check the pins?

 

[Shovert]

I remove the maf and brought it inside of house. I had to warm it up. We got snow outside. car is outside not in garage.
All wires to ground. [open]
a to b 6.04m ohm
a to c 6.04m ohm
a to d 5.04m ohm

b to c 34 ohm not stable maybe temp related.
b to d 3.857 k ohm
c to d 3.85 k ohm
3.2 maf f1zf-12b579-aa
reading may change on you. It seem temp related I say if close ok.
Wire colors
A is red
B is Black may have tracer
c is Orange/red
D is Blue/red
Maurice

 

[3d914]

I remove the maf and brought it inside of house. I had to warm it up. We got snow outside. car is outside not in garage.
All wires to ground. [open]
a to b 6.04m ohm
a to c 6.04m ohm
a to d 5.04m ohm

b to c 34 ohm not stable maybe temp related.
b to d 3.857 k ohm
c to d 3.85 k ohm
3.2 maf f1zf-12b579-aa
reading may change on you. It seem temp related I say if close ok.
Wire colors
A is red
B is Black may have tracer
c is Orange/red
D is Blue/red
Maurice

Thanks a lot - that's more than I expected. Looks like there is continuity then between B & C. That at least explains the ground signal then on PCM #9.

I'll check the ohms next.

 

[3d914]

OK, with Maurice's tests and my tests, here's where I stand:

• MAF #9 - If I check continuity between signal (D) & return (C) on the MAF I get nothing - which makes sense. When I check between return (C) & ground (B) I get continuity. Isn't the PCM supposed to supply the ground side of the return?

  There appears to be continuity between B & C inside the MAF allowing B to be grounded by C. This is how MAF #9 is picked up on the grounded circuits.
  

• #16 Ignition ground - This leads to the CID, Crank position sensor, and the ICM (DIS). I don't see any connection to ground, so one of these must be grounding this circuit internally right?

  I checked the related components and found that by disconnecting the DIS module #16 no longer was on the ground circuit - so the DIS is connecting to ground internally.
  

• #17 Data Link - the EVTM indicates this is supposed to be a 12V circuit to the data link connector and Malfunction lite. How could it be on the ground circuit?

  I traced this circuit through numerous components (ICM/DIS, CAM PS, Ignition coil, Noise Suppressor) and was not able to find the ground source. I wasn't able to get to the Crank PS but it's likely the source.
  
  

  [*]#19 FP Monitor - this circuit ties to PCM #5, the FP & cut-off switch (which I'm not using yet), and then to ground through the FP. With the FP off I should not be getting to ground.
  [*]#30 CPP - this circuit goes to numerous sensors (via GY/R wire) when the switch is closed, but mine was open.

  
  Still working on the remaining two.

 

[Phoenix]

This is getting quite complicated , and I only wanted to throw something in the fire...

Did you have grounds linked from the intake to B- , and Ground from the block to B-

Ground the heck out of it. I once had some really weird issues , and it was bad grounds. It absolutely needs good ground or its gonna bite you.

Specially true for engines that are out of their element.

Im not saying its that , but I wanted you to be aware of that. (because electrical harness issues are really rare.)

 

[Shovert]

Phoenix. Thanks sometimes it takes someone with new idea's. He has remade his harness so much. I think maybe there can be mistakes. On mine I do have the braided ground cable on the intake. I have heard of that problem. My 2.3 turbo Mustang has to have that also. I would wrap foil on outside of the wires that go to the ignition idea. On the wiring diagram it is a "O" with a wire attach to and goes to ground. Just wrap with foil and take bare copper wire around it and take to ground. Unsure if this is for the radio in car or the ignition talks to other things. Unknown to me. Maurice

 

[Phoenix]

Phoenix. Thanks sometimes it takes someone with new idea's. He has remade his harness so much. I think maybe there can be mistakes. On mine I do have the braided ground cable on the intake. I have heard of that problem. My 2.3 turbo Mustang has to have that also. I would wrap foil on outside of the wires that go to the ignition idea. On the wiring diagram it is a "O" with a wire attach to and goes to ground. Just wrap with foil and take bare copper wire around it and take to ground. Unsure if this is for the radio in car or the ignition talks to other things. Unknown to me. Maurice

That ground strap is essential , if you dont hook it up , it wont start. It basically grounds the DIS , because the DIS is on one part of the intake , that part is connected with rubber hose wich cancel your ground (if no strap) and if you have some paint on your intake , the 2 bolts for that part of the intake wont ground it because of the paint.

Also the back of the DIS (and intake) needs to be paintless , It serves as a heat sink AND as its ground.

Like I said try to ground the F out of it.

 

[intimdatr]

I moved the ground strap up to the Crossover tube bolts so i know its hooked up and has a clean connection. Looks tacky but is very effective. And it you have to the Bottom Left bolt is the grounding bolt (i think). Ive been told to run a small wire around the bolt and tighten the bolt back down and run the wire straight to the Neg terminal if you are having issues.

Edit: You can see the strap in the upper left hand corner.

 

[3d914]

Phoenix, this is a good point and one reason why I'm going around again on the ground circuits - which of course raised other questions. I did change my ground for the PCM so that it's not just tied to the cradle but is infact attached at the point where the batt - connects to the engine cradle. This hasn't changed anything, but it at least eliminates the question. I also have several other grounding points and one large one from the block to the cradle (frame).

Regarding the DIS - it is mounted to the cradle (following suggested procedures o this site) and the ground connection appears to be a good as it tests with little or no resistance.

Most of the questions being addressed may not be real issues - except for my understanding. Especially in cases where schematics indicate a voltage circuit, but I pick it up doing my ground circuit checks. We're down to the last two. I seriously suspect that #30 is going to be the same as #16 & 17.

It's #19 that has me bugged, as it shouldn't see ground on the plus side of the FP circuit unless the FP were on. Gonna tackle that one tomorrow - I hope.

Thanks again guys - and keep the ideas coming.