Taurus Car Club of America : Ford Taurus Forum - View Single Post - Engine stops while driving every 3 months!
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post #10 of (permalink) Old 04-20-2017, 05:45 PM Thread Starter
Andrei
Junior Member
 
Join Date: May 2016
Location: Tampa
Chapter: Southeast
Year: 2004
Model: Ford Taurus
Engine: 3.0L 12v Vulcan V6
Posts: 62
Rep Power: 7
 
Quote:
Originally Posted by chartmaker View Post
I would do an electric test before any long trip. As below.

Battery cable/wiring check
This should take about 5-10 minutes.
Tools. Digital VM, range 200MV to 2.0V.
Hood open.
  1. Key on (not start) Blower on high, lights high beam.
  2. Probe leads, Pos battery post to mega fuse (or older cars use post on fuse box) Not the cable ends, but, post to post to bridge the cable.
  3. Volts range ~100 mv or less. ( 0.10V or less)
  4. Neg bat post to engine metal 50 mv or less.
  5. Neg bat post to body metal 100 mv or less.
On the pos side, high reading = bad cable, or ends not good connection.
On the body ground (fender) high reading = bad cable or ends not good connection.
If you have a high number, then measure one step at a time; that is post to clamp, clamp to wire, wire to eyelet, eyelet to fender etc. Find the weak connection, and fix it.
On the negative side, the ground is split with one to the body, one to the engine block and then the ground strap from the block to the body near the passenger side firewall. Thus the body is double grounded. You need both. Engine strap to firewall is important as this is the ground to the PCM.
Ground strap test. Key off . Remove the battery ground to the fender from the fender. Turn HL on high beam. They should light normal. If not the ground strap from the block to the firewall/PCM post is bad. Clean the fender where the neg cable bolts on, put the ground cable back. Fix the ground strap. The ground strap keeps the PCM and engine block/Alt at the same ground level. When the engine is running, the negative current path is mostly engine block-ground strap to the body, bat cable to fender is secondary.
Alternate test of ground strap: HL high, blower max, start engine and idle in N.
Test volts engine block or Alt to the body common post for the ground strap/PCM. Max 75 mv.

-chart-
I did the check - VM set on 2000m, on positive post to mega fuse indicated 230mv (which I understand is very high). Neg to engine-31. Neg to body -81. (which look normal, according to your indications).
I'll go ahead and look ate the connections and maybe get another cable from Advanced. I'll keep you updated.
Thank you for your help!
UPDATE - funny thing - I went out to fiddle with it some more, did the strap test and tightened all the cables, including the battery posts (they were fairly tight but I could tighten them quite some more). Did the test again (3 times to make sure) and the positive reads 46mv now, with the high beams and blower on 4. Could that have been it? And should I go ahead and replace the cable? Thank you!

Last edited by Andrei; 04-20-2017 at 06:10 PM.
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