Maryland Cherokee Club
CF Veteran
Joined: Jan 2012
Posts: 8,272
Likes: 1
From: Baltimore, MD
Year: 1999
Model: Cherokee
Engine: 4.0 I6 HO
Moderator of Jeeps
Joined: Jul 2011
Posts: 21,029
Likes: 3
From: Frederick, MD from Cleveland, OH
Year: 1993 YJ Wrangler
Engine: 4.0 I6
Here:
'88 Renix Jeep Comanche, automatic
Backfires at certain RPMs (no tach, but always same RPM range), regardless of what gear it's in. Fairly new O2, dizzy, cap, rotor, plugs
Just patched exhaust and made it longer. Still sputters and backfires, but at a lower RPM range.
Jeep occasionally feels like it's jumping forward and backward (not wobble) if holding throttle at the edge of that RPM range. Recently, RPMs will quickly jump, drop, and steady when shifting to overdrive at moderate acceleration.
New TPS.
Suggestions?
Backfires at certain RPMs (no tach, but always same RPM range), regardless of what gear it's in. Fairly new O2, dizzy, cap, rotor, plugs
Just patched exhaust and made it longer. Still sputters and backfires, but at a lower RPM range.
Jeep occasionally feels like it's jumping forward and backward (not wobble) if holding throttle at the edge of that RPM range. Recently, RPMs will quickly jump, drop, and steady when shifting to overdrive at moderate acceleration.
New TPS.
Suggestions?
Moderator of Jeeps
Joined: Jul 2011
Posts: 21,029
Likes: 3
From: Frederick, MD from Cleveland, OH
Year: 1993 YJ Wrangler
Engine: 4.0 I6
Oh, Jimmy.. Also since I replaced TPS and did exhaust (was same day), I can't hold steady ~40-60% throttle on the highway or it will slowly lose forward momentum and then rapidly decelerate like downshifting. After backfiring or stepping on the gas (no shift felt), it resumes normal operation.
CF Veteran
Joined: Mar 2009
Posts: 7,996
Likes: 0
From: Berea, OH
Year: 1998
Model: Cherokee
Engine: 4.0
Backfiring is caused by afterburn, fuel burning in the exhaust....
Unfortunately there are a few reasons this can happen, most often timing, which can't be adjusted on the 4.0.
Sometimes a sticky injector (stays open too long)
Sometimes a vaccum leak at the MAP sensor
Your Dizzy could have jumped a tooth....
Start with some FREE ****....
Clean out the C101 connector? It's mounted on the firewall up behind the brake booster. Almost every signal, if not all of them, for the fuel injection run through the C101.
Unbolt the two halves and clean out al the black tar crap. After that, use a small pick to thighten up the female connectors on the harness. Keep flushing it out with contact cleaner. Add some dielectric grease and bolt it back together. THIS IS THE MOST IMPORTANT THING I WOULD DO FIRST!
Next...get the MAP sensor tested.
Test your injectors...
If none of this...find another similar year Renix and swap ECU's and see if that helps...they control the timing, and can slowly fade.
With YOUR symptoms, the only sensor I would suspect is MAP...but stop throwing money at it until you know. Get it tested...check your injectors...but FIRST the C101!
Unfortunately there are a few reasons this can happen, most often timing, which can't be adjusted on the 4.0.
Sometimes a sticky injector (stays open too long)
Sometimes a vaccum leak at the MAP sensor
Your Dizzy could have jumped a tooth....
Start with some FREE ****....
Clean out the C101 connector? It's mounted on the firewall up behind the brake booster. Almost every signal, if not all of them, for the fuel injection run through the C101.
Unbolt the two halves and clean out al the black tar crap. After that, use a small pick to thighten up the female connectors on the harness. Keep flushing it out with contact cleaner. Add some dielectric grease and bolt it back together. THIS IS THE MOST IMPORTANT THING I WOULD DO FIRST!
Next...get the MAP sensor tested.
Test your injectors...
If none of this...find another similar year Renix and swap ECU's and see if that helps...they control the timing, and can slowly fade.
With YOUR symptoms, the only sensor I would suspect is MAP...but stop throwing money at it until you know. Get it tested...check your injectors...but FIRST the C101!
Moderator of Jeeps
Joined: Jul 2011
Posts: 21,029
Likes: 3
From: Frederick, MD from Cleveland, OH
Year: 1993 YJ Wrangler
Engine: 4.0 I6
Backfiring is caused by afterburn, fuel burning in the exhaust....
Unfortunately there are a few reasons this can happen, most often timing, which can't be adjusted on the 4.0.
Sometimes a sticky injector (stays open too long)
Sometimes a vaccum leak at the MAP sensor
Your Dizzy could have jumped a tooth....
Start with some FREE ****....
Clean out the C101 connector? It's mounted on the firewall up behind the brake booster. Almost every signal, if not all of them, for the fuel injection run through the C101.
Unbolt the two halves and clean out al the black tar crap. After that, use a small pick to thighten up the female connectors on the harness. Keep flushing it out with contact cleaner. Add some dielectric grease and bolt it back together. THIS IS THE MOST IMPORTANT THING I WOULD DO FIRST!
Next...get the MAP sensor tested.
Test your injectors...
If none of this...find another similar year Renix and swap ECU's and see if that helps...they control the timing, and can slowly fade.
Unfortunately there are a few reasons this can happen, most often timing, which can't be adjusted on the 4.0.
Sometimes a sticky injector (stays open too long)
Sometimes a vaccum leak at the MAP sensor
Your Dizzy could have jumped a tooth....
Start with some FREE ****....
Clean out the C101 connector? It's mounted on the firewall up behind the brake booster. Almost every signal, if not all of them, for the fuel injection run through the C101.
Unbolt the two halves and clean out al the black tar crap. After that, use a small pick to thighten up the female connectors on the harness. Keep flushing it out with contact cleaner. Add some dielectric grease and bolt it back together. THIS IS THE MOST IMPORTANT THING I WOULD DO FIRST!
Next...get the MAP sensor tested.
Test your injectors...
If none of this...find another similar year Renix and swap ECU's and see if that helps...they control the timing, and can slowly fade.
Injectors are on my maintenance list. I'll start pricing MAP sensors.
Moderator of Jeeps
Joined: Jul 2011
Posts: 21,029
Likes: 3
From: Frederick, MD from Cleveland, OH
Year: 1993 YJ Wrangler
Engine: 4.0 I6
Hear that, Scott?
CF Veteran
Joined: Mar 2009
Posts: 7,996
Likes: 0
From: Berea, OH
Year: 1998
Model: Cherokee
Engine: 4.0
Moderator of Jeeps
Joined: Jul 2011
Posts: 21,029
Likes: 3
From: Frederick, MD from Cleveland, OH
Year: 1993 YJ Wrangler
Engine: 4.0 I6
CF Veteran
Joined: Mar 2009
Posts: 7,996
Likes: 0
From: Berea, OH
Year: 1998
Model: Cherokee
Engine: 4.0
Moderator of Jeeps
Joined: Jul 2011
Posts: 21,029
Likes: 3
From: Frederick, MD from Cleveland, OH
Year: 1993 YJ Wrangler
Engine: 4.0 I6
CF Veteran
Joined: Feb 2012
Posts: 5,153
Likes: 0
From: Crofton, MD
Year: 1992
Model: Cherokee
Engine: 4.0 I6, 62mm BBK Throttle Body w/ 1" Spacer, Rusty's Airtube w/ 9" K&N Conical