Go Back   DODGE RAM FORUM - Dodge Truck Forums > Dodge Ram Generations Forum > 2nd Gen : 1994 - 2002 > 2nd Gen DIY


2nd Gen DIY

Is my ECU bad?


This is a discussion on Is my ECU bad? within the 2nd Gen DIY forums, part of the 2nd Gen : 1994 - 2002 category!
'98 2500, 5.8L gas. My truck went suddenly from running to cranking without firing. The ECU isn't sending signals either ...


Reply
 
LinkBack Thread Tools Display Modes
Old 05-30-2017, 05:26 PM   #1 (permalink)
Junior Member
 
Join Date: Oct 2016
Age: 45
Posts: 9

Ram Year: 1998
Engine: 5.9L V8
Default Is my ECU bad?
'98 2500, 5.8L gas.

My truck went suddenly from running to cranking without firing.

The ECU isn't sending signals either to activate the fuel pump relay, or activating the spark plugs. The ignition coil and the relay have both tested as good.

From what I've seen, the ECU waits until it gets signals from the crank position sensor and the cam shaft sensor before turning on the fuel pump and the ignition coil. I replaced the crank position sensor since I heard this is a common cause. No improvement.

I think the issue has to be either the ECU or the camshaft sensor, neither seem like high probabilities to me. Am I missing any other likely culprits?

I've got plenty of electrical test equipment, so I can take oscilloscope reading on things if it will help.

How can I confirm the ECU as either good or bad?

If it is the ECU, is it easily replaceable?



Sent from my SM-G950U using Tapatalk


Sponsored Ad
Register to remove this ad.
svdsinner is offline   Reply With Quote
Old 05-31-2017, 07:27 AM   #2 (permalink)
Senior Member
 
Join Date: Feb 2016
Location: Lansing, Michigan
Age: 22
Posts: 1,254

Ram Year: 2001 1500 Sport with enough electrical modifications to make your head spin
Engine: Magnum 360
Default
The fuel pump should prime as soon and the truck is turned to run. Check the ASD relay in the underhood fuse block. Sometimes those go bad and cause this issue.


__________________
I fixed it until it broke.
dudeman2009 is offline   Reply With Quote
Old 06-01-2017, 12:15 PM   #3 (permalink)
Junior Member
 
Join Date: Oct 2016
Age: 45
Posts: 9

Ram Year: 1998
Engine: 5.9L V8
Default
Originally Posted by dudeman2009 View Post
The fuel pump should prime as soon and the truck is turned to run. Check the ASD relay in the underhood fuse block. Sometimes those go bad and cause this issue.
What's the logic relationship between the relays? Firstly, is the ASD relay supposed to energize when the key moves to On? (Or does it energize/de-energize on some other event?) If it does, the fuel pump relay turns on, and if not it won't? (Or do the two relays output work in series? IOW, if the ASD is bad, will the Fuel Pump relay always be de-energized?)

Sent from my SM-G950U using Tapatalk
svdsinner is offline   Reply With Quote
Old 06-01-2017, 07:53 PM   #4 (permalink)
Senior Member
 
Join Date: Feb 2016
Location: Lansing, Michigan
Age: 22
Posts: 1,254

Ram Year: 2001 1500 Sport with enough electrical modifications to make your head spin
Engine: Magnum 360
Default
Originally Posted by svdsinner View Post
What's the logic relationship between the relays? Firstly, is the ASD relay supposed to energize when the key moves to On? (Or does it energize/de-energize on some other event?) If it does, the fuel pump relay turns on, and if not it won't? (Or do the two relays output work in series? IOW, if the ASD is bad, will the Fuel Pump relay always be de-energized?)

Sent from my SM-G950U using Tapatalk
The ASD relay and fuel pump relay should be energized at key on by the PCM separately. They do not come into contact in anyway outside of both being wired into separate circuit of the PCM. The ASD relay is energized by the PCM when it senses a signal from the crank sensor while cranking, in the run mode the relay shuts off after 1.8 seconds if no input is detected from the crank sensor. The fuel pump relay is energized at key on at all times during cranking, however it shuts off after 3 seconds if the engine is not running.


__________________
I fixed it until it broke.
dudeman2009 is offline   Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


<




GM Truck Forum
Ford Raptor Forum
Chevy Tahoe Forum
Chevy Cobalt Forum
Chevy Camaro Forum
Toyota FJ Cruiser Forum
Ford Truck Forum
88-98 GM Truck Forum
73-87 Gm Truck Forum
Ford Expedition Forum
Chevy Equinox Forum
Chevy Cruze Forum
Jeep Liberty Forum
Jeep Forum
Dodge Ram SRT10 Forum
Chrysler 200 Forum
Scion xD Forum
Scion xB Forum
Dodge Challenger Forum
SRT Forum
Nissan Titan Forum
Buick Enclave Forum
Cadillac Forum
Cadillac XTS Forum