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Renix Dead Spot And Idiling Low


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good idea.. I took a small break in the updates due to waiting for fuel injectors and such.

 

The main issue is a rough/low idle that likes to "hunt" for the right idle. So the rpms will drop and then the engine will catch itself so it does not stall. In the morning is when it is the worst. When warmed up you can still notice it but not as extreme. You can almost feel and hear a slight miss which is when the rpms drop. All other rpm ranges are okay and the truck runs great besides at idle. I will post videos of what the gauge is doing soon.

 

Things that I have done to try and cure the issue:

  • All of Crusiers RENIX tips and tricks: upgraded engine grounds, sensor grounds, indexed distributor, "advanced" the CPS, valve cover mod, cleaned throttle body and IAC and adjusted TPS correctly, ECU pin refresh.
  • All new vacuum lines
  • MAP sensor hose is good and sealed
  • clean air filter
  • NEW: TPS, EGR valve and transducer, IAC, ICM and Coil, exhaust manifold gasket and bolts, cap and rotor and wires and spark plugs, O2 sensor.
  • Recently installed 746 volvo fuel injectors (ultrasonically cleaned)
  • Tested grounds on all sensors and ECU grounds. Also check continuity from ECU pins to component.
  • Tested for O2 heater circuit. Works correctly.
  • Tested TPS, MAP, Manifold air temp and coolant temp sensors, egr solenoid, relays.

 

Other Notes:

 

So the CPS is a MOPAR replacement. It is about two years old now though.

I have tested the MAP and checked out good. Did not replace yet.

I have an upgraded brake booster from a 96 XJ. Bought brand new.

Cat and muffler are not clogged

My vacuum pressure at idle is 15 HG and my fuel pressure is 31 psi at idle. When the vacuum hose is taken off the fuel pressure regulator the pressure jumps to 39 psi.

 

 

 

I believe I covered everything. :ack: :papers:

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Okay. Thanks for the re-cap. 

 

Even though the O2 sensor heater circuit tested good, that's not a guarantee that the sensor itself is working. 

 

There is a test for that.

 

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. 
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Also... The new o2 sensor I bought was a Bosch but it looked different than the stock sensor. The stock sensor protruded outwards more and the new one has a shorter tip. Does this matter if they are different??

Did it come with the plug already installed? I'm not a big Bosch fan FWIW. I prefer NTK. Do the test? 

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Well.... I replaced my MAP with a Duralast MAP sensor. And the idle is a lot smoother! It does not fluctuate nearly as much as it did. I will have to drive it around more to really notice the difference. The rpms in drive are still around 500-600 when they should be around 700-750. So still a little low. I am going to completly take off the throttle body and do another through clean. I did this before at the beginning of the year but I may as well do i again. 

 

So conclusion for now is that with a combination of everything I did... the MAP seemed to be old and wore out. The problem is that there is still a low idle. The ground upgrades and checks helped a lot.

 

One more thing I did today. I took out that dumb flap in the airbox for the "hot air" during cold start. It isnt required just helps heat the motor faster. I lost the tube that goes to the exhaust manifold anyways so it wasnt doing anything. more airflow now haha  :yes:

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I'm the second owner and the first was an old guy that drove it to golf and back haha he didnt mess with anything. Yeah ill be sure to get the air bleed. What is that for by the way?  :???:

We'll discuss that later. Get that plug out and check the adjustment on the throttle stop first. Post 14. Be sure the butterfly isn't digging into the bore of the body. 

 

So, runs great now but just low idle? 

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Maybe a little dead spot still. Okay so I have the throttle body. I see some type of cap/plug on the outside and a small circle object on the inside diameter of the air passage. The throttle plate almost hits it. But doesnt hit the sides so it is properly set. Which plug is this bleed plug? inside or outside? Then do I just try and get it out by picking it from the sides of the plug?

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Maybe a little dead spot still. Okay so I have the throttle body. I see some type of cap/plug on the outside and a small circle object on the inside diameter of the air passage. The throttle plate almost hits it. But doesnt hit the sides so it is properly set. Which plug is this bleed plug? inside or outside? Then do I just try and get it out by picking it from the sides of the plug?

Outside. Yes, pick it. 

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