SPONSORED LINKS

4.7 backfire through intake and exhaust

Tiny
JERAMIE GROW
  • MEMBER
  • 2002 DODGE RAM
  • V8
  • 4WD
  • AUTOMATIC
  • 150,000 MILES
Just put this motor in. Changed coil pack, spark plugs, cam sensor, check all compression on cylinders, fuel pressure, check cams. Replace timing gears and timing chains. Re-time the motor, check valves and still nothing. It backfires through intake and exhaust and I can smell raw fuel. Cylinder 1 120, cylinder 2 120, cylinder 3 130, cylinder for 140, cylinder 5 60, cylinder 6 150, cylinder 7 150, cylinder 8 145. So if anybody has something that will point me in the right direction I'd appreciate it.
SPONSORED LINKS
Monday, February 10th, 2020 AT 5:29 PM

9 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 33,871 POSTS
Was the engine from the same year as the truck, and which flex plate did you use?

There are differences in the number and spacing of the notches in the flex plate, depending on the model year. Normally when the wrong flex plate is used, the Engine Computer can't figure out which cylinder to fire, so you have a crank/no-start, but I'm not sure how that works out for various years.
SPONSORED LINKS
Was this
answer
helpful?
Yes
No
Monday, February 10th, 2020 AT 6:05 PM
Tiny
JERAMIE GROW
  • MEMBER
  • 5 POSTS
The 8th digit is a N so Mopar said that they would interchange and yes it will run it just backfires and every time I give it acceleration. It will shoot a 4-foot flame out of the exhaust pipe.
Was this
answer
helpful?
Yes
No
+1
Monday, February 10th, 2020 AT 6:08 PM
Tiny
CARADIODOC
  • MECHANIC
  • 33,871 POSTS
What would interchange? What size engine do you have?
Was this
answer
helpful?
Yes
No
-1
Monday, February 10th, 2020 AT 6:21 PM
Tiny
JERAMIE GROW
  • MEMBER
  • 5 POSTS
4.7
Was this
answer
helpful?
Yes
No
Monday, February 10th, 2020 AT 6:23 PM
Tiny
CARADIODOC
  • MECHANIC
  • 33,871 POSTS
Please don't be stingy with the information. I'm trying to figure out if the flex plate could be the issue or if we have to look somewhere else. For 2002, the 4.7L and 5.7L use different flex plates, but they are the same for 2003.

Was this a used engine, rebuilt one, or a crate engine from Chrysler? Did you install the same size as what came out?
SPONSORED LINKS
Was this
answer
helpful?
Yes
No
+1
Monday, February 10th, 2020 AT 6:30 PM
Tiny
JERAMIE GROW
  • MEMBER
  • 5 POSTS
It is the same size and it is a used motor.
Was this
answer
helpful?
Yes
No
+1
Monday, February 10th, 2020 AT 6:32 PM
Tiny
CARADIODOC
  • MECHANIC
  • 33,871 POSTS
Different flex plates were used in different years. If the engine is from a different year, to be safe you have to transplant the original flex plate onto the replacement engine.

The next best suspect is the crankshaft position sensor. Some earlier versions needed a thick paper spacer stuck on the end to set the critical air gap. Yours uses a different type of mounting bracket that sets the air gap automatically, but the sensor can be damaged or bent if it isn't removed during the removal and installation of the engine. The back-firing you described can be caused by an incorrect air gap, and it can be caused by a cracked magnet inside the sensor. I don't know what causes them to crack, but I've read about that solution more than once.
Was this
answer
helpful?
Yes
No
+1
Monday, February 10th, 2020 AT 6:53 PM
Tiny
JERAMIE GROW
  • MEMBER
  • 5 POSTS
Thanks.
Was this
answer
helpful?
Yes
No
Monday, February 10th, 2020 AT 6:55 PM
Tiny
CARADIODOC
  • MECHANIC
  • 33,871 POSTS
Please keep me updated on your progress.
Was this
answer
helpful?
Yes
No
Monday, February 10th, 2020 AT 7:13 PM

Please login or register to post a reply.

Related Engine Backfire Content

How To Fix an Engine Backfire
VIDEO
How To Fix an Engine Backfire
Instructional repair video
Backfire Repair
GUIDE
Backfire Repair
When your engine backfires it can do so in one of two ways. First and the most common way is when the engine is running a small explosion of unburnt fuel is ignited inside...
VIEW MORE

Sponsored links