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Sudden engine lurch and passive anti theft light comes on simultaneously.

  #1  
Old 12-13-2018
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Sudden engine lurch and passive anti theft light comes on simultaneously.

So I was driving home this evening when suddenly the engine 'convulsed' for lack of a better term, and there was a flash of light from the dash. Within a few seconds it happened again and this time I noticed that the light, that came on with the lurch, was the passive anti-theft light and all the gauges momentarily went dead. The second time there was also momentary flashes of the the check gas cap light and the oil light and again the gauges went temporarily dead. This convulsion or lurch happened a third and fourth time within a few seconds the same combination of symptoms. I reduced my speed and continued on my way home. Five minutes later, as I was pulling into my lot the engine lurched/convulsed again with the same list of symptoms.

What we're trying to diagnose is a 2004 Ford Ranger with a recently installed 2002 engine. 4.0L on a five speed standard transmission. This was a direct swap, save for the fact that the 2004 had a EGR the 2002 did not. I've put about 500 km on the truck since the engine replacement, installed a new clutch, new starter and new alternator as part of the process.

Since the engine replacement, I've noticed that the temperature gauge on the dash is no longer functioning. I wasn't worried about it as the fan seems to be actuating and there's been no evidence of overheating. With tonight's episode I'm wondering if it was symptomatic of something else.

I'm not sure where to begin looking for this one. Any advice would be appreciated.

Cheers!
 
  #2  
Old 12-14-2018
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Welcome to the forum

Ignition switch is loosing power, or computer is

This shuts of engine and computer reboots which causes new PATS key test

I would check 12v power connections in engine bay by fuse box

Also Cab Ground is often a ground strap on the back of drivers side head to the firewall, it is often forgotten and NEEDS to be connected, that's the main ground for all cab electrics and computer is often grounded to firewall
 

Last edited by RonD; 12-14-2018 at 01:32 PM.
  #3  
Old 12-14-2018
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Thanks,

I'll check both.

Cheers!
 
  #4  
Old 12-15-2018
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Originally Posted by RonD View Post
Welcome to the forum

Ignition switch is loosing power, or computer is

This shuts of engine and computer reboots which causes new PATS key test

I would check 12v power connections in engine bay by fuse box

Also Cab Ground is often a ground strap on the back of drivers side head to the firewall, it is often forgotten and NEEDS to be connected, that's the main ground for all cab electrics and computer is often grounded to firewall
So the Ground at the PCM is connected.
The ground strap at the wiper motor is not only not connected but is missing outright. This, as I understand it is the ground for the cab electronics. Can I run a ground wire form the wiper motor to another location? Say the aluminum AC/water pump bracket....

Please advise.
 
  #5  
Old 12-15-2018
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Sure, any good engine Ground point to good Firewall ground point is fine.

Engine is grounded by the larger battery Negative cable.


People are often surprised that ground straps are needed, "its ALL metal body parts and frame, so it should just be a good ground anywhere"
Problem is that all these parts are primed and painted FIRST, and THEN assembled, and often using rubber spacers with the bolts.
Engine and trans sit on rubber mounts so can't pass ground to frame or body

The main ground(battery negative) needs to go to the engine because of the starter motor, 70amps, and for the alternator, up to 100amps
Other grounds needed are:
Rad support, headlights and horn
Inner fender, relays and fuse box
Firewall, cab electrics
Frame, tail lights, and fuel pump
 
  #6  
Old 4 Weeks Ago
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Originally Posted by RonD View Post
Sure, any good engine Ground point to good Firewall ground point is fine.

Engine is grounded by the larger battery Negative cable.


People are often surprised that ground straps are needed, "its ALL metal body parts and frame, so it should just be a good ground anywhere"
Problem is that all these parts are primed and painted FIRST, and THEN assembled, and often using rubber spacers with the bolts.
Engine and trans sit on rubber mounts so can't pass ground to frame or body

The main ground(battery negative) needs to go to the engine because of the starter motor, 70amps, and for the alternator, up to 100amps
Other grounds needed are:
Rad support, headlights and horn
Inner fender, relays and fuse box
Firewall, cab electrics
Frame, tail lights, and fuel pump
Well the new ground wire is in and I thought I had the issue licked. Made it a couple dozen kilometers without a buck. Then.... well.... It's definitely an improvement the power drop off lasts just a fraction of a second as opposed to 1 or 2 seconds, but the issue is still there. I'm wondering if the ground location on the firewall has something to do with it. The original windshiled washer ground stud is MIA so I used a self taping screw at the firewall just out of the way of the hood hinge. If everything was grounded to that stud and there's some degree of electrical isolation between that stud and the firewall I've ground the cab but not the electronics.... Just conjecture on my part.

Any advice is appreciated.
 
  #7  
Old 4 Weeks Ago
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I would clean off the paint so ground strap has good metal to metal contact, if you didn't already, lots of AMPs need to pass thru this ground


Does it cut out when truck vibrates, i.e. hit a bump?
Or is it just random
 

Last edited by RonD; 4 Weeks Ago at 03:56 PM.
  #8  
Old 4 Weeks Ago
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I did scrub back the paint to bare metal.

The power interruption seems completely random. I was wondering if now the ground cable might not be sufficient for the amps. The original strap was quite substantial, where now it`s a length of 10 gauge wire held down with a #10 metal screw at each end.
 
  #9  
Old 4 Weeks Ago
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I've been driving problem free since the last report. Not sure if I've licked the issue or not. At least I have a sense of what I'm dealing with. I may add an additional ground wire if the issue returns.

Just wanted to say thanks.

Cheers!
 
  #10  
Old 4 Weeks Ago
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Good work

Hopefully its fixed
 
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