99 1500, 5.2 misfired with no codes

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Perseus

Junior Member
Joined
Jan 23, 2018
Posts
7
Reaction score
1
Location
North Dakota
Ram Year
1999
Engine
5.2 magnum
Need some input here.
Installed a new long block, replaced all sensors and pcm, all new ignition system from the distributor to the plugs and everything in between, had the injectors bench tested and flushed, watched the process, all checked out, reinstalled after thorough cleaning with fresh o rings, installed new o2 sensors fore and aft of a 2 yr old cat.

Probem:
engine was running adequately with not great mileage , averaging slightly less than 9 mpg, finaly replaced the crankshaft position sensor just to be safe, now the engine misfires and even stalled out on the freeway. Engine would turn over but not fire, while calling for a tow truck, I plugged in my analyzer just to try and figure out what was going on tryed it again and it started right up . No codes.
That's when I decided to swap out the pcm.
Had it flashed from the old pcm. No appreciable change.
Pulled off the tps plug and started it up just to see if it would throw a code which it did. Plugged the tps back in, code disappeared.
It would appear that the pcm is communicating, but seems to be using the analyzer as a bypass just to start the engine. Sometimes it continues to run when unplugged and sometimes it doesn't.
Any suggestions ?
 
Last edited:
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Perseus

Perseus

Junior Member
Joined
Jan 23, 2018
Posts
7
Reaction score
1
Location
North Dakota
Ram Year
1999
Engine
5.2 magnum
Update:
The flex plate was out of round and periodically rubbing against the face of the crank sensor.
Replaced that , runs great.

Problem:
What the hell would CAUSE that!?
Wondering if perhaps a tranny, worn out front main seal might allow to much play ,thereby causing periodic oscilltions in the thousandth of inch range. Grasping at straws here.
Input appreciated.
 

dizzyfalldown

Junior Member
Joined
Nov 26, 2019
Posts
1
Reaction score
0
Location
Ellensburg
Ram Year
1991
Engine
5.2l
Need some input here.
Installed a new long block, replaced all sensors and pcm, all new ignition system from the distributor to the plugs and everything in between, had the injectors bench tested and flushed, watched the process, all checked out, reinstalled after thorough cleaning with fresh o rings, installed new o2 sensors fore and aft of a 2 yr old cat.

Probem:
engine was running adequately with not great mileage , averaging slightly less than 9 mpg, finaly replaced the crankshaft position sensor just to be safe, now the engine misfires and even stalled out on the freeway. Engine would turn over but not fire, while calling for a tow truck, I plugged in my analyzer just to try and figure out what was going on tryed it again and it started right up . No codes.
That's when I decided to swap out the pcm.
Had it flashed from the old pcm. No appreciable change.
Pulled off the tps plug and started it up just to see if it would throw a code which it did. Plugged the tps back in, code disappeared.
It would appear that the pcm is communicating, but seems to be using the analyzer as a bypass just to start the engine. Sometimes it continues to run when unplugged and sometimes it doesn't.
Any suggestions ?

Had same truck with similar problem. My problem I finally corrected with the elusive CAMSHAFT positioning sensor. At the time I had a hellava time just finding one ($20 part). Every NAPA, Autozone, Oh oh oh O’reillys tried to push me out the door with a crankshaft positioning sensor some of them even told me there’s no such application. Found one online. Hope that helps


Sent from my iPad using Tapatalk
 

Sherman Bird

Senior Member
Joined
Jun 28, 2019
Posts
1,502
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2,223
Location
Houston, Texas
Ram Year
1998
Engine
5.2
Basic law of diminishing logic: What's the last thing you messed with before the problem.... so it turns out to be workmanship??? Mishandling of the flex plate? Did you coat the torque converter pilot nub with thick, gooey grease? You should have. It's called a flexplate for a reason. The converter to flexplate bolts have a low torque rating for a reason... 22lb/ft, IIRC. That's not much, but must be adhered to if you don't want to destroy the converter.
 

Sherman Bird

Senior Member
Joined
Jun 28, 2019
Posts
1,502
Reaction score
2,223
Location
Houston, Texas
Ram Year
1998
Engine
5.2
Had same truck with similar problem. My problem I finally corrected with the elusive CAMSHAFT positioning sensor. At the time I had a hellava time just finding one ($20 part). Every NAPA, Autozone, Oh oh oh O’reillys tried to push me out the door with a crankshaft positioning sensor some of them even told me there’s no such application. Found one online. Hope that helps


Sent from my iPad using Tapatalk

The vast majority of the parts jockeys are not savvy to true parts knowledge.... just order takers. As my network of knowledgeabled folks either die off or retire, I'm witness that the replacements are just rote order takers that depend on a computer... and they have no roots in repairs, usually. At 44 going on 45 years in the business, I find it quite discouraging.
 
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