help me trouble shoot this electrical grimlin

[87Saleen#166]

Well I'm pretty much at the end of my wits. I'm wondering if there is a systematic approach to speed the process up and avoid looking in places where I could maybe do some kind of test and help lead me to the area that may be culprit.

Basically what happens is I'm experiencing a voltage drop troughout my grounds (high resistance) and can't get the damn car to idle/run right. My grounds are good and have even added a couple, plus I've read about 500 pages on the interenet of thigs to try, just haven't hit this forum yet, wondering if anyone else has any input on this. Possibly an explanation as to why all of my grounds would go bad with the key on. WIth the key off everything checks out (duh no current draw).

so let me hear what you guys know. thanks! and that surging idle thread at the top is awesome! I'm expereiencing a little of that, but I've narrowed it down to being a grounding (or lack of thereof) issue.

The car is a 87 5.0 with the works: H/C/I/SC/MAF

 

[HISSIN50]

JRichker (the guy who created the idle surge sticky) has a post he puts up, with all the grounds, their locations, functions, etc. It would be worth reading to ensure you have gone over everything............

Off the top of my small bean, I cant think of a reason to not be able to achieve solid grounds. Others on here will know.

Good luck.

 

[Roland69]

Maby you could upgrade all your main power and ground cables with some 4 gauge or bigger and see if that helps. Probly somthing real stupid and been overlooked and you will feel stupid when u find it. Iv'e done that many times.

 

[jrichker]

As suggested...

Grounds are important to any electrical system, and especially to computers.

1.) The main power ground is from engine block to battery: it is the power ground for the starter & alternator.

2.) The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. Any car that has a 3G alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects.

3.) The computer has its own dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to it's proximity to the battery, it may become corroded by acid fumes from the battery. It is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire. The wire goes into the harness at the starter solenoid.

4.) All the sensors have a common separate ground. This includes the TPS, ACT, EGE, BAP, & VSS

5.) The O2 sensor heaters have their own ground (HEGO ground) coming from the computer. This is different and separate from the O2 sensor ground. It is in the fuel injector wiring harness and comes out under the throttle body. It gets connected to a manifold or head bolt.

6.) The TFI module has 2 grounds: one for the foil shield around the wires and another for the module itself. The TFI module ground is a signal ground that terminates inside the computer.

7.) The computer takes the shield ground for the TFI module and runs it from pin 20 to the chassis near the computer.

8.) The computer's main power ground (the one that comes from the battery ground wire) uses pins 40 & 60 for all the things it controls internally.

See http://www.fluke.com/application_notes/automotive/circuit.asp?AGID=1&SID=103#volt for help
troubleshooting voltage drops across grounds. The process works best with normal load applied to the circuit under test.

 

[mustang-a-holic]

Basically what happens is I'm experiencing a voltage drop troughout my grounds (high resistance) .

The car is a 87 5.0 with the works: H/C/I/SC/MAF

Tell me the procedure you are using to come to this conclusion.

I want to know HOW your doing it and WHAT instrumentation your using. What standards are you comparing against?

I could tell you to attach a ground strap 12 inches in diameter to your block and battery and you could still have the same problem. See my point. Need more info.

 

[87Saleen#166]

I set the FLUKE volt meter to mVDC hit the min/max button and then start my descent down the wire(s), the further I get the greater the increase.

I also check ohmage between all of my connections. I read that anything greater than .5 ohms is an issue and I'm getting 2+

so yea am I chasing my own tail or what? I don't really know much about electricity so I'd be mad if i was but also somewhat relieved to be a little closer to figuring out my problem.

 

[jrichker]

I set the FLUKE volt meter to mVDC hit the min/max button and then start my descent down the wire(s), the further I get the greater the increase.

I also check ohmage between all of my connections. I read that anything greater than .5 ohms is an issue and I'm getting 2+

so yea am I chasing my own tail or what? I don't really know much about electricity so I'd be mad if i was but also somewhat relieved to be a little closer to figuring out my problem.

See my post and check out the reference to the Fluke site. There are some excellent tech notes there.

Step 1.) Find the instruction book that came with your Multimeter. Read it and familiarize yourself with how it works and how use it. If you lost the book or didn’t get one with it, do a Google search on the web to find the manufacturer’s web site & download a copy of the manual.

Step 2. ) Make sure that you know what test lead plugs into which jacks on the Multimeter. There are usually several different jacks on most Multimeters, and they have different functions. Make sure that your battery(s) in the Multimeter are good: if you have any doubts, replace the battery(s).

Step 3.) Once you are sure that the Multimeter is functional and you have the leads plugged into the jacks for Ohms ( the upside down “U” symbol), do some simple measurements to make sure that you know how to use it correctly. Set the switch to the lowest range and touch the leads together: you should not see “nothing” but you should see 1.0-0.3 ohms. Measure a 60 watt light bulb: cold it will measure about 17.5 Ohms. It you measure it while it is hot, the reading will be greater.

Step 4.) Make several test measurements using the ohms function and the DC volts function. Remember all resistance measurements must be done with the power off the circuit. This avoids false readings and possible damage to the ohmmeter.. Repeat steps 3 & 4 until you are sure that you can do it without making any mistakes.

Step 5.) Then see http://www.autozone.com/servlet/UiB..._us/0900823d/80/1d/db/3c/0900823d801ddb3c.jsp and carefully study ALL the information under the Heading Chassis Electrical, Basic Electricity – Understanding & Troubleshooting

Step 6.) Go back and carefully re-read both of my previous posts and download and print the diagrams from the link posted.
http://www.autozone.com/servlet/UiB..._us/0900823d/80/16/71/3c/0900823d8016713c.jsp for 79-88 model Mustangs

http://www.autozone.com/servlet/UiB..._us/0900823d/80/19/59/5a/0900823d8019595a.jsp for 89-93 model Mustangs

http://www.autozone.com/servlet/UiB..._us/0900823d/80/1d/db/3c/0900823d801ddb3c.jsp for 94-98 model Mustangs

Step 7.) Apply what you have learned and make the test measurements using the information in the wiring diagrams & my previous posts.