Renix Bouncing rpms, idle?
#1
Member
Thread Starter
Join Date: Nov 2013
Location: North San Diego County
Posts: 120
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1988
Model: Cherokee
Engine: 4.0
Renix Bouncing rpms, idle?
Sorry for the long post but I want as much to give as much info for troubleshooting as possible.
Ok so I've used the search and found close to my symptoms but not exact and no for sure problems solved.
Problem/symptom: start up fine, then the first time I give it gas it starts idling funky and the rpms are bouncing at a consistent rate. It goes normal to almost dying it gets so low. Don't have a tach so I don't know exact rpms but it doesn't bounce back high, it goes to normal idle then down to what I'm guessing is well lower than 100 rpms. It has gotten low enough to die but only a couple times.
This started about a week ago and is completely random in the fact that sometimes it runs perfect for a complete trip then next start up it has the problem and it could be 4 runs in a row good or bad or every other start up. But when it does happen it's very consistent in the bouncing timing. This is my dd so it's pretty frustrating and can't be good for the engine and for sure isn't good for my manual trans as the rpms drop super fast and I'm often putting it into gear with low rpms and its slamming.
I had it running with the idle bouncing and in neutral a while ago and I unplugged the tps and tried to give it a tiny bit of air via throttle body and it tried to stall in the same manner as when I'm driving so I have a feeling it's gas delivery related. The tps is adjusted perfectly with 17 percent of reference voltage and when I read the tps as I give it gas the voltage does increase so it does read a change. Also the car has no problem accelerating or maintaining rpms when the throttle is increased so it makes me question the fuel pump by itself. Throttle body and idle plunger has been cleaned very thoroughly as well as O2 sensor replaced due to bad mpgs and air filter replaced recently. And vacuum leaks checked with vacuum gauge and carb cleaner sprayed all around with both showing negative for leaks.
I'm hoping this explanation of symptoms helps someone pinpoint my problem as I am too poor from being out of work for over a month due to wrist surgery to just start changing parts. Also because it happens in neutral I have the ability to check wires with the engine running so if anyone has ideas on things to check or exact voltages to look for please let me know.
Once again sorry for the long post but hopefully someone can help me out. thanks
Ok so I've used the search and found close to my symptoms but not exact and no for sure problems solved.
Problem/symptom: start up fine, then the first time I give it gas it starts idling funky and the rpms are bouncing at a consistent rate. It goes normal to almost dying it gets so low. Don't have a tach so I don't know exact rpms but it doesn't bounce back high, it goes to normal idle then down to what I'm guessing is well lower than 100 rpms. It has gotten low enough to die but only a couple times.
This started about a week ago and is completely random in the fact that sometimes it runs perfect for a complete trip then next start up it has the problem and it could be 4 runs in a row good or bad or every other start up. But when it does happen it's very consistent in the bouncing timing. This is my dd so it's pretty frustrating and can't be good for the engine and for sure isn't good for my manual trans as the rpms drop super fast and I'm often putting it into gear with low rpms and its slamming.
I had it running with the idle bouncing and in neutral a while ago and I unplugged the tps and tried to give it a tiny bit of air via throttle body and it tried to stall in the same manner as when I'm driving so I have a feeling it's gas delivery related. The tps is adjusted perfectly with 17 percent of reference voltage and when I read the tps as I give it gas the voltage does increase so it does read a change. Also the car has no problem accelerating or maintaining rpms when the throttle is increased so it makes me question the fuel pump by itself. Throttle body and idle plunger has been cleaned very thoroughly as well as O2 sensor replaced due to bad mpgs and air filter replaced recently. And vacuum leaks checked with vacuum gauge and carb cleaner sprayed all around with both showing negative for leaks.
I'm hoping this explanation of symptoms helps someone pinpoint my problem as I am too poor from being out of work for over a month due to wrist surgery to just start changing parts. Also because it happens in neutral I have the ability to check wires with the engine running so if anyone has ideas on things to check or exact voltages to look for please let me know.
Once again sorry for the long post but hopefully someone can help me out. thanks
#2
::CF Moderator::
Join Date: Aug 2011
Location: Prescott, Az
Posts: 43,858
Received 1,522 Likes
on
1,234 Posts
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
Is that new O2 sensor getting battery voltage to it's heating element?
#4
::CF Moderator::
Join Date: Aug 2011
Location: Prescott, Az
Posts: 43,858
Received 1,522 Likes
on
1,234 Posts
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
First, have you done any of my Tips? If so, which ones?
For the Renix years, 87-90, the O2 sensor has 3 wires, 2 black and 1 orange. The orange wire (largest gauge of the 3) is the 12-14 volt power that comes from the O2 sensor heater relay on the passenger side firewall, and that powers the internal heater in the sensor so that the sensor can work at idle, and almost immediately after start up. Loss of that power will hurt gas mileage even with a good O2 sensor.
One of the black wires is a common ground for the heater power and O2 signal to the ECU, so a poor ground will give a voltage feedback from the heater power input, to the ECU causing poor mileage even with a good O2 sensor.
The third wire, also black is a voltage feed wire, 5 volts, from the ECU to the O2 sensor. The O2 sensor is an O2 concentration sensitive variable resistor. At optimal O2 concentration the 5 volt input feed to the O2 sensor drops to 2.45 volts due to losses across the O2 sensor to ground. That same wire if disconnected from the O2 sensor will read 5 volts constant to ground.
At idle that voltage should read 1-4 volts oscillating quickly back and forth roughly once every second. At 2000 rpm it should run between 2 and 3 volts max, and is optimally running between 2.3 and 2.6 volts at 2000 rpm (in park). A digital meter can NOT be used for reading the O2 sensor voltage, but it can be used to test the ground and the 12-14 volts to the heater and the 5 volt feed from the ECU with power on and engine off. You must use an old style analog meter with the needle gauge on the display to see the voltage swing back and forth with the engine runing.
If the O2 sensor readings are not right, say they read 4 volts or 1 volt steady, you have a problem. BUT before you blame the O2 sensor make sure it has good wiring, and make sure the proper voltage is feeding it, by turning power on, engine off to read the engine off voltage feeds (12-14 volts on the orange wire, and 5 volts on one of the two black wires), and ensure the ground wire (power off) reads less than 1 ohm to the battery negative post.
A leaky exhaust system or leaky fuel injector(s), or bad compression, bad rings or leaky valves, bad plugs, wires, cap, rotor, HV coil, and so on, or combination of these, can also cause a lean or rich condition that gives you high or low O2 sensor readings that are not the O2 sensors fault, so try and verify those other items also before buying parts like an O2 sensor to fix your problem.
For the Renix years, 87-90, the O2 sensor has 3 wires, 2 black and 1 orange. The orange wire (largest gauge of the 3) is the 12-14 volt power that comes from the O2 sensor heater relay on the passenger side firewall, and that powers the internal heater in the sensor so that the sensor can work at idle, and almost immediately after start up. Loss of that power will hurt gas mileage even with a good O2 sensor.
One of the black wires is a common ground for the heater power and O2 signal to the ECU, so a poor ground will give a voltage feedback from the heater power input, to the ECU causing poor mileage even with a good O2 sensor.
The third wire, also black is a voltage feed wire, 5 volts, from the ECU to the O2 sensor. The O2 sensor is an O2 concentration sensitive variable resistor. At optimal O2 concentration the 5 volt input feed to the O2 sensor drops to 2.45 volts due to losses across the O2 sensor to ground. That same wire if disconnected from the O2 sensor will read 5 volts constant to ground.
At idle that voltage should read 1-4 volts oscillating quickly back and forth roughly once every second. At 2000 rpm it should run between 2 and 3 volts max, and is optimally running between 2.3 and 2.6 volts at 2000 rpm (in park). A digital meter can NOT be used for reading the O2 sensor voltage, but it can be used to test the ground and the 12-14 volts to the heater and the 5 volt feed from the ECU with power on and engine off. You must use an old style analog meter with the needle gauge on the display to see the voltage swing back and forth with the engine runing.
If the O2 sensor readings are not right, say they read 4 volts or 1 volt steady, you have a problem. BUT before you blame the O2 sensor make sure it has good wiring, and make sure the proper voltage is feeding it, by turning power on, engine off to read the engine off voltage feeds (12-14 volts on the orange wire, and 5 volts on one of the two black wires), and ensure the ground wire (power off) reads less than 1 ohm to the battery negative post.
A leaky exhaust system or leaky fuel injector(s), or bad compression, bad rings or leaky valves, bad plugs, wires, cap, rotor, HV coil, and so on, or combination of these, can also cause a lean or rich condition that gives you high or low O2 sensor readings that are not the O2 sensors fault, so try and verify those other items also before buying parts like an O2 sensor to fix your problem.
#5
Member
Thread Starter
Join Date: Nov 2013
Location: North San Diego County
Posts: 120
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1988
Model: Cherokee
Engine: 4.0
Ok looks like I have to find an analog voltmeter and do some testing. Thanks for the description. I'll let you know the results when I test it but probably won't have time this weekend.
#6
::CF Moderator::
Join Date: Aug 2011
Location: Prescott, Az
Posts: 43,858
Received 1,522 Likes
on
1,234 Posts
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
#7
Member
Thread Starter
Join Date: Nov 2013
Location: North San Diego County
Posts: 120
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1988
Model: Cherokee
Engine: 4.0
ok so not only did my car magically start working perfect for 2 weeks but i have been crazy busy. well it started doing the same thing and i have a couple days off so i checked the voltages and i got 5 volts for both the black and orange wire an good ground. So I am not getting enough voltage to the orange wire.
Now do I check if I have 12v to the relay or is something else going to be causing my bad voltage to the orange wire? And which relay is the o2 sensor?
Thanks
Now do I check if I have 12v to the relay or is something else going to be causing my bad voltage to the orange wire? And which relay is the o2 sensor?
Thanks
Trending Topics
#8
Member
Join Date: Nov 2014
Location: Woodstock, GA, originally from S. CA.
Posts: 150
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1987 149k, original owner
Model: Cherokee
Engine: 4.0
Please read Cruiser54's tips, and start with the ground improvement/refreshing. If everything was per his specs, then, if you still have s problem, you can start testing.
The Renix Jeeps run like tops if you follow his tips. He is the fount of knowledge:
The Renix Jeeps run like tops if you follow his tips. He is the fount of knowledge:
#10
Member
Join Date: Nov 2014
Location: Woodstock, GA, originally from S. CA.
Posts: 150
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1987 149k, original owner
Model: Cherokee
Engine: 4.0
Excellent. Any chance to up grade battery cables and replace the braided one from firewall to engine?
My 87 always had an intermittent fast idle that went away when I did the cables and grounds. When it came back later, I knew the TPS was going. Things get easier once the ground work is in place.
Keep us posted!
My 87 always had an intermittent fast idle that went away when I did the cables and grounds. When it came back later, I knew the TPS was going. Things get easier once the ground work is in place.
Keep us posted!
#11
Member
Thread Starter
Join Date: Nov 2013
Location: North San Diego County
Posts: 120
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1988
Model: Cherokee
Engine: 4.0
new developments...
I tested my oxygen sensor relay and it wasn't working properly so i changed it last night. Did a little test drive and it worked good.
Woke up this morning and drove 3 separate trips about 10 miles each and it worked perfect. Then trip 4, worse then before stalling 3-4 times when i start it. Horrible bouncing to the point that it stalled several times without trying to catch itself even after driving a few miles and a warm engine. Before today, I was able to give it gas and keep a high idle with the clutch pushed in at stops to keep it from bouncing or stalling but this trip it would still bounce once or twice before it would match the amount of my foot on the pedal. TPS? Idle valve thing? Fuel pump? any ideas? Thanks.
I tested my oxygen sensor relay and it wasn't working properly so i changed it last night. Did a little test drive and it worked good.
Woke up this morning and drove 3 separate trips about 10 miles each and it worked perfect. Then trip 4, worse then before stalling 3-4 times when i start it. Horrible bouncing to the point that it stalled several times without trying to catch itself even after driving a few miles and a warm engine. Before today, I was able to give it gas and keep a high idle with the clutch pushed in at stops to keep it from bouncing or stalling but this trip it would still bounce once or twice before it would match the amount of my foot on the pedal. TPS? Idle valve thing? Fuel pump? any ideas? Thanks.
#12
Member
Thread Starter
Join Date: Nov 2013
Location: North San Diego County
Posts: 120
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1988
Model: Cherokee
Engine: 4.0
P.S. I have very very very little money so I can't just change things to try it out so if anyone has ways to test things please let me know.
#13
::CF Moderator::
Join Date: Aug 2011
Location: Prescott, Az
Posts: 43,858
Received 1,522 Likes
on
1,234 Posts
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
#14
Member
Thread Starter
Join Date: Nov 2013
Location: North San Diego County
Posts: 120
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1988
Model: Cherokee
Engine: 4.0
The oxygen sensor is brand new. Maybe three weeks old. It is the ngk brand. I don't know how to test it exactly. I tested the connector which had a good ground and correct voltages.
#15
::CF Moderator::
Join Date: Aug 2011
Location: Prescott, Az
Posts: 43,858
Received 1,522 Likes
on
1,234 Posts
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0