Hunting idle, bad gas milage, hesitation

[TurboedMJ]

Pardon my ignorance, I didn't know the RENIX 4.0l had a cam sensor. Where/how would I test that if it turns out to be relevant? 

[cruiser54]

They don't have a cam sensor

 

That deal inside the dizzy is a sync generator used by the ECU to fire the injectors sequentially.

 

You can unplug it and drive your Renix Jeep and not feel the difference at all. 

[TurboedMJ]

Oh ok. Thanks. I will try the injector thing tomorrow. 

[ghetdjc320]

Notice the oscilloscope readings below. Blue line is “cam”, orange pulses are crank. This is on an HO though. I’ve always referred to “sync generators” as cam sensors since the cam directly drives this sensor. This allows for sequential vs un-timed batch firing. 
 

 

[TurboedMJ]

Got 4.7 ohms with my "new" NGK sensor with a stainless steel body and 3 wires, and 6.3 ohms with the sensor that was in it before (ceramic body, 3 wires). So I put the old one back in and haven't tested the other parts yet. The idle is still hunting. 

[TurboedMJ]

O2 sensor tested good. 

Voltage was 0.25v for about 20-30 secs, then started alternating between about 0.5v and 4.8v. the voltage would change about every 2 seconds. 

[TurboedMJ]

Did the injector thing, any one injector that I unplugged would make the idle steady out at about 500. It ran much better with any one injector unplugged. What does that mean? What should I do next?

[cruiser54]

Have you checked for vacuum leaks between the intake manifold and head? 

[TurboedMJ]

No I haven't. I'll do that next.

[TurboedMJ]

I tested this with starting fluid, there was no change in idle. 

[cruiser54]

Best to use carb cleaner. The starting fluid evaporates too quickly. 

 

I wonder if your EGR might be hanging open. 

[ghetdjc320]

5 hours ago, TurboedMJ said:

Did the injector thing, any one injector that I unplugged would make the idle steady out at about 500. It ran much better with any one injector unplugged. What does that mean? What should I do next?

Interesting. I’d also check vacuum leak. Is it possible these injectors are providing too much fuel? Or… I’m wondering if the fuel pump is on the fritz and can’t keep up with the demand for all 6 injectors?? 

[cruiser54]

vacuum leak means low vacuum to MAP sensor resulting in too much fuel. 

[TurboedMJ]

12 hours ago, ghetdjc320 said:

Interesting. I’d also check vacuum leak. Is it possible these injectors are providing too much fuel? Or… I’m wondering if the fuel pump is on the fritz and can’t keep up with the demand for all 6 injectors?? 

Fuel pressure is good, is it possible that the fuel pressure is good but there is simply not enough volume? 

[cruiser54]

Which is it? Too much fuel or not enough? 

[TurboedMJ]

14 hours ago, cruiser54 said:

Best to use carb cleaner. The starting fluid evaporates too quickly. 

 

I wonder if your EGR might be hanging open. 

The EGR system was deleted on this truck

 

[cruiser54]

Okay.

[TurboedMJ]

Just tested the CPS as it has started to  hesitate to start cranking when I turn the key. Ac voltage was 0.48. is this of concern or is that voltage adequate. 

[TurboedMJ]

Anyone know what this plug is for? It was empty, it is right by the #6 spark plug. 

[Ωhm]

Cruise Control ground, if equipped.

[ghetdjc320]

On 5/6/2024 at 1:13 AM, TurboedMJ said:

Fuel pressure is good, is it possible that the fuel pressure is good but there is simply not enough volume? 

90% of the time it’s your standard main wear components: fuel pump, coil, spark plugs, fuel filter and an occasional cps. All of these are relatively simple to replace and cause all sorts of issues that may seem like they could somehow be something else. I think you’re onto something in the fuel system with the test you performed earlier. I’d suggest: put away the volt/ohm meter and hunt the fuel issue . 
 

edit: Just re read all of the posts and would like to see what your fuel rail looks like. Can you take a picture? Also you didn’t change the pump when you had it out? 

[TurboedMJ]

9 hours ago, ghetdjc320 said:

90% of the time it’s your standard main wear components: fuel pump, coil, spark plugs, fuel filter and an occasional cps. All of these are relatively simple to replace and cause all sorts of issues that may seem like they could somehow be something else. I think you’re onto something in the fuel system with the test you performed earlier. I’d suggest: put away the volt/ohm meter and hunt the fuel issue . 
 

edit: Just re read all of the posts and would like to see what your fuel rail looks like. Can you take a picture? Also you didn’t change the pump when you had it out? 

No it was replaced a little more then a year ago. Here is a picture. 

[Ωhm]

On 5/5/2024 at 11:13 AM, TurboedMJ said:

Fuel pressure is good, is it possible that the fuel pressure is good but there is simply not enough volume?

 

Fuel Flow test - page 6

 

Fuel Flow pg6.pdf

[ghetdjc320]

If it was running good with the old injectors and that’s all that was changed. You could switch them back. Takes just a few minutes. Also entirely possible your fuel pump is done for