Unsolvable Explorer Rough Idle. Any OBD II experts?

[2000StreetRod]

Are you able to datalog PIDs or can you only view them in real time? I'm curious about your fuel source, spark source and torque source to see if they are normal.

 

[Cashcrazy]

I believe I can datalog with forscan. I'm letting the engine cool so I can try another damper. I'll give it a try later. I actually feel like the damper is not functioning properly and may be the issue.

 

[2000StreetRod]

I just finished reading your other thread from beginning to end. My first comment is that I commend you for your persistence in trying to resolve the rough idle issue. Today is the anniversary of the documentation of the problem. In my years on this forum I encountered another member (Dick Berg) who also had an unsolvable rough idle on his 2nd generation Explorer. He, like you, tried everything that I and others suggested but was never able to win the battle. I never got over not being able to help him enough and I don't want to experience that again. I wish that I was as knowledgeable on the 3rd generation PCM logic as I have become on the 2nd generation but now that I have a 2003 Centennial Explorer (with 4.6L) I hope to catch up.

The idle speed control implementation is a closed loop system. As I recall there are calibration constants for desired idle speeds in Park/Neutral, for A/C compressor engaged/disengaged, and when transmission is engaged and the vehicle is moving slower than a specified speed. The PCM commands the IAC valve to a duty cycle and determines the engine speed using the crankshaft position (CKP) sensor signal. The PCM compares the actual engine speed to the desired engine speed and adjusts the duty cycle to reduce the error. I seem to remember that the PCM stores the corrections in a table to reduce the repetition of learning them each drive cycle. The accuracy of the CKP sensor and the accuracy and response lag of the IAC valve affects the deviation of the idle speed. If the IAC valve is slow to respond to a commanded duty cycle change then the PCM will command a larger change. If the IAC valve is inaccurate it may overshoot the commanded duty cycle causing the PCM to command a new duty cycle in the opposite direction to compensate. The result is a varying (oscillating) idle speed. A fast response IAC valve will increase the frequency of the oscillation. An accurate IAC valve will reduce the amplitude deviation of the oscillation. According to your other thread's description of the rough idle this oscillation may not match your symptoms. What are your min and max engine speeds at idle in park when the engine is fully warmed up? Are you able to read the commanded idle speed PID?

 

[2000StreetRod]

Please confirm again that the high voltage ignition wiring is correct.

Please note that cylinders 4 thru 6 on the driver side are in numerical order but on the coilpack they are not. Many members incorrectly hook up the ignition wires for cylinders 5 and 6.

 

[Cashcrazy]

Thank you 2000StreetRod. It has been a long year with this rough idle and it's really burning me out. I test drive a 2014 f150 and I really noticed the smoothness at red lights. Anyway, It's still pretty rough after replacing the damper. It wasn't the magical fix. I'll hook the pressure gauge up again in the morning after the engine cools again. I also unhooked the battery and then took it on a drive hoping clearing the computer would be beneficial. I'll map out the idle speed after I get the kids down. I'm pretty close to throwing in the towel and selling. I spent most of the day messing with it and driving getting parts.

 

[Cashcrazy]

I just confirmed the wires are correct.

 

[Cashcrazy]

The graph shows the LT trim 1, LT trim 2, idle RPM(no AC), and desired RPM. The upper for the RPM is 766 and low is 697 RPM. This is for a warm vehicle. The desired RPM is a constant 732rpm.

 

[Cashcrazy]

Same graph with the AC on. Highest RPM is 835 and lowest 756. The idle get worse with the AC and doesn't get better when I turn it off again. Desired RPM 784.

There is really not much more I can do at this point other than replace the intake gaskets, valve cover gaskets, and injectors. I'm starting to believe this is a issue with the programming with the ECM. I don't feel like taking it to a mechanic is feasible because of the amount of time that it would take would catch up with the car value quickly. It very odd that StreetRod said this was the anniversary, because I have just about decided to move on.

 

[Cashcrazy]

Just for kicks here is the o2 sensor data. RPM in too graph. The upper and lower limits for each graph are as follows: 768-703, .86-.05, .33-.04, .86-.06, .12-.05. The blue o2 sensor graph had a blip to increase the limits but you can see that it evened out.

I'm out for the night.

 

[plasticseng]

Does anyone else think that the switching on the rear O2 sensors is abnormal? The amplitude may not be high, but the switch rate is the same as the fronts. It is my understanding that a good cat will not do that once it is warmed up.

 

[Cashcrazy]

I'm tested the fuel pressure again with the new damper this morning. Just turning the key forward to let the pump prime it has about 59psi of pressure.

After 4-5 minutes of sitting it does drop to about 54psi. FYI this is a $16 gauge.

When running it still has about 65psi of pressure. I tested the damper but removing the vacuum hose and had the same results as the first time. I'd really like to know if this is normal.

 

[Cashcrazy]

Last test. I'm completely out of ideas. I connected my vacuum gauge to the fuel damper and had a very steady reading at idle. When giving throttle it would increase and go back to the 20inhg area. It all looked normal.

 

[2000StreetRod]

The fuel pump only runs for a few seconds when the ignition is switched on unless the PCM knows via the CKP sensor that the engine is rotating. Full fuel pressure is usually achieved by the third activation of the ignition. My fuel pump assembly has a check valve that prevents loss of fuel pressure when the ignition is switched off. That reduces engine crank time after the vehicle has been sitting an hour or more before restart. My fuel filter does not have the return hose to the tank. Your 2003 obviously also has a check valve but it leaks more than mine but in my opinion is not a problem.

Your vacuum at idle is weaker than mine was before I installed the supercharger. Yours is now comparable to mine with the supercharger and is lower than normal in my opinion. Have you ever performed a compression test?

Before I installed the supercharger my warmed up engine with a correct fuel mixture would run continuously at 500 rpm but it was smoother at 550 rpm. The minimum rpm for your last test was 697 rpm. You mentioned in the other thread that sometimes the engine acted like it was going to stall. This should not happen at that engine speed if the mixture is correct. Also, the stock desired idle speed for my engine in neutral (656 rpm) is less than your minimum speed. If your engine is acting like it is going to stall at 700 rpm it is do to something being incorrect and I suspect it is the mixture. The PCM may take a significant amount of time to change the LTFTs when transitioning from mid-range engine speed to idling. When neutral is selected I'd like to see what happens to the fuel trims when the engine has been holding a constant 2,000 rpm and then the accelerator pedal is released.

 

[Cashcrazy]

Embarking on compression test journey

 

[Cashcrazy]

Six posts incomming. Otherwise I would mix up the pictures. Cylinder 1 at idle and reverse to about 2500rpm.

 

[Cashcrazy]

Cyl 2. Idle and reving from throttle body. I may have to circle back to cyl 1 and reving again. The idle is comparable on 1 and 2.

And just turning over with no firing.

 

[Cashcrazy]

Cyl 1-
148-149
42 idle
50 reving

Cyl 2-
148-149
49 idle
60 reving

Cyl 3-
140-145
42-43 idle (approx)
50 reving

Cyl 4-
150
42-43 idle
59 reving

Cyl 5-
155
49 idle
60 reving

Cyl 6-
150
50 idle
60 reving

 

[2000StreetRod]

When I check engine cranking compression I tie the throttle plate linkage so the plate is held wide open. Then I crank the starter until five compressions on the cylinder. After the 5th compression there is usually no increase. With the engine warm your cranking compression should be at least 180 psi and all cylinders should be comparable. Is the 150 psi for cylinder 2 on the first compression? Was the throttle plate wide open?

 

[Cashcrazy]

Throttle plate closed on all tests. I also just swapped out the ignition coil for my junkyard coil and no change. It doesn't look like any valves are sticking from the test. Ignore the pictures. I retested cyl 1 and 2 due to their variances. Engine was at full operating temp as I just drove it running errands.

 

[plasticseng]

Maybe my earlier post got buried at the end of page 2, but does anyone else think that the switching rate on the rear O2 sensors is suspect?