Cylinder Miss\Rough Run when cold

[ronin2501]

Hello all! Hoping someone who is very automotive savvy can help me out here with an intermittent problem my Explorer is having. Please bear with me this is a little long but I want to make sure I'm providing all the needed info.

95' Explorer 2WD 4.0L V6 Pushrod EECIV (No CEL)
237,000miles

Symptom:
My engine starts right up when cold, but idles rough and continues to do so until it is at operating temp. Once at operating temp and cruising the engine will intermittently lose power. If throttle is increased you can hear a muffled backfire under the hood.

What I've tested/repaired:
-Pulled spark plugs and read/all are normal wear and only 3 months old. (Autolite)
-Found that the number 2 coil was not firing at all. -Replaced the coil, all coils are now firing. It's running better but there is still an intermittent cylinder misfire.
-Replaced ignition wires because the number 2 wire had obvious signs of arcing.
-Replaced the TPS because it was out of range via multimeter test.
-ISC Tested Good
-Replaced DPFE to fix CEL (Confirmed Fixed)
-Fuel Pressure: 37psi @ idle
-Vacuum: 18inhg (tested for leaks anyway and confirmed none)
-EGR valve seems "wobbly" on top part of the assembly. When applying light vacuum to it with a hand held pump the engine bogs down as expected. The valve seems to be operating normally. I am concerned that if the spring is weak in it that exhaust could be bleeding into the intake stream at idle...can someone confirm?
-ECU partial failure common in these?

History:
Replaced all upper and lower intake manifold gaskets 20 months ago due to a coolant leak.
Replaced thermostat
Cleaned MAF and Air Temp Sensor
Seafoam Spray into intake, oil, and fuel (Today-noticeable improvement in idle when warm)


So...if anyone can think of anything I may have overlooked it would be greatly appreciated. I know this is the internet and there isn't much value in "a persons word" on here...but whoever figures this out with me has $20 bucks in it for them. (Hey I drive a vehicle with 237k on it because I'm frugal and thus far its been the most reliable vehicle I've ever owned.) I'll paypal it once I can confirm it's fixed.

 

[Rudy602]

Keep your money - nice gesture, though. Changed your fuel filter lately? I've heard some say corrosion on the crank sensor connection can be a problem so if you remove it and put it back on a couple times it may help. Good luck.

 

[1998Explodasport]

37psi fuel pressure seems a little low. If you haven't changed the fuel filter recently, I would do that.

 

[ronin2501]

Forgot to mention, I changed the fuel filter last may. It's cheap and it wouldn't hurt to do it again. Intermittent problems are annoying...today after the seafoam clean it idled like a brand new engine. Not even the normal amount of vibration I felt before. I had to look at the tach to see if it was even running. Ofcourse once the light turned green it went back to bogging down until I really pressed into the throttle.

I'll check the manual too, but Haynes is known for grossly mis-stating numbers. Do you know what the fuel pressure should be at on this engine? (I honestly went by the standard 37.5 to 40psi for EFI and shrugged it off.)

Also I should mention I stethoscoped the injectors and they ticked steadily

 

[ranger7ltr]

Fuel system pressures per FSM

Return type fuel systems......MY 1998-earlier 30-45 psi dependent on vacuum at the fuel pressure regulator

Returnless fuel systems........MY 1999-later 65-72 psi no variance in pressure

This goes up to MY 2001...After that model year, Ford started to experiment with the PCM modulating the pump voltage to vary the fuel pressure...

Now to the original problem...Have you thought about the fuel injectors needing to be serviced to fix this problem? When I started running my 99 Explorer it had a miss that would stay for 30-90 secs depending on the outside temps... Once I drove the truck and it was warm or hot the miss never happened...If it cooled off it was back... I didn't fix it until I had the injectors rebuilt and flow matched... Getting them rebuilt cleaned out the nozzles at the bottom and flow matching them made certain they all flowed as close to each other as possible...

 

[ronin2501]

Return type fuel systems......MY 1998-earlier 30-45 psi dependent on vacuum at the fuel pressure regulator

Returnless fuel systems........MY 1999-later 65-72 psi no variance in pressure

This goes up to MY 2001...After that model year, Ford started to experiment with the PCM modulating the pump voltage to vary the fuel pressure...

Thanks for the info! This is definitely a return style system with a regulator on the rail. Looks like 35psi would be acceptable.

I had a problem similar to this on my Windstar a few years ago. Couldn't figure it out. Found a hairline crack in two of the NEW plugs. Once those where replaced it ran like new...I was hoping thats all it was with this one...no such luck. I might replace the plugs anyway just in case I'm not seeing a possible crack.

I'm really stumped on this one...

 

[team]

do a compression test and a leak down test

 

[SoNic67]

If runns good till it warms up, the spark plugs and other hardware parts are fine. Looks like the moment the ECU switches from "open loop" to "closed loop" adjustment, then you have the problems.
That's why sounds like a oxygen sensor problem to me...

 

[team]

I am just wondering if you have some kind of crack or something that opens up with heat that's why i recommended the tests. If you get a scanner you can look at your fuel trims for your o2 sensors.

 

[ronin2501]

Well it runs better when it gets to operating temperature. Sometimes it has to be at operating temp for a prolonged period of time. I would think if it was compression\mechanical issue it wouldn't be an intermittent problem. If it where a heat issue and a crack was getting larger I would think it would run worse, not better. If all else fails I'll go for the comp test.

Today I found my trusty CP9145 scanner and my EECIV connector that I couldn't get to work last year. The 12V power adapter fixed that problem....imagine what reading the instructions can do for you! LOL

I read the DLC Info and there are two fields for O2 sensor. One fluctuates normally..and the other sits at 0.00v. (I took these readings when the truck was running normally) How many O2 sensors does the 95 have? Looking underneath I only see one and no place for another. I'll admit I did this in my office clothes in a parking lot so I didn't slide all the way underneath the truck..

Both Fuel trims fluctuated between 0, to -5 to +2 every few seconds.
Coolant Temp 187F
IAT 75F
Closed Loop Mode

The only codes I'm getting are for the DPFE Out of range (332) I think. That sensor was bad for years and I swapped it out with another one I had from another Explorer which looks like it was also defective.

Unfortunately because that KOER code is there it won't perform an cylinder balance test.

 

[team]

fuel trims sound fine, if it is an ohv v6 you will have 3 o2 sensors. 2 precat and 1 after cat. the 2 precat will fluctuate fast, after cat should fluctuate slower. The egr related code will definitely give you a rough idle if it is opening at the wrong time.

 

[ronin2501]

New info. Connected the scanner again this morning when everything was nice and cold. This is when the problem usually is the most noticeable.

The Bank 1 O2 sensor is still reading 0.00v (That cannot be right..)
Bank 1 O2 trim is +43 (thinks it's lean so it's adding the max fuel)
Bank 2 O2 trim is -2, then to 0, then to +5 (Normal)

Once everything reached operating temperature again the Bank 1 O2 trim started matching the Bank 2 trim. Mind you there still isn't a check engine light.

So with this new info it looks to be an open and shut case of bad O2 sensor. Right? That's what I thought too. I replaced the sensor and both the 0.00v is still present on bank 1 and the +43 trim still exists. I reset the ECU and tried again. Same results shortly after starting. The trim adjusted from 0, right back to +43.

I disconnected the sensor and checked for voltage. Got 12.2v, tested both the heater gnd, and regular gnd. Both are properly grounded. I don't really know of a way to test the SIG (signal) wire without backprobing the plug (Which I can't reach with the probe wires when plugged in to the
sensor)

I put the Bank 1 sensor on the bank 2 plug and it read normally. So I think the old sensor was good.

Anyone have a pinout of the ECU so I can do a continuity check for the sig wire?
Any other ideas...?

 

[team]

is this bank1 sensor 2 you are talking about? ALso, have you ever changed the intake gaskets? They may be shrinking up when cold and expanding when hot. The ohv motor has a set of rubber o rings on the upper plenum and then typical gaskets at the intake and head junction.

 

[ronin2501]

Yes I replaced the entire gasket set less than 2 years ago. This is the older pushrod engine.
Bank 1 = Sensor 1 (This is the "bank" that is acting up)
Bank 2 = Sensor 2

Thinking it may be an ECU fault. trying to confirm if pin 29 is the bank 1 HEGO Signal wire so I can test for continuity before getting a junkyard ECU. Unfortunately I'm only able to find pinouts for 2.3L, 4.9L and 5.0L

 

[OneLever]

Cleaned MAF

How specifically did you do this. I was under the impression that the sensor elements on these MAF sensors are not to be touched. From my limited knowledge it sounds like the fuel/air ratio is off. The oxygen sensors you have already tested seems to rule them out as the cause.

Well it runs better when it gets to operating temperature. Sometimes it has to be at operating temp for a prolonged period of time.

the spark plugs and other hardware parts are fine. Looks like the moment the ECU switches from "open loop" to "closed loop" adjustment, then you have the problems.

Since it does eventually idle fine, when it has gone to closed loop possibly, that indicates your plugs and wires are fine. However, since it idles poorly at first and then when under load that once again points to fuel/air mix ratio problems. I would hook the scanner up and watch to see when it changes over to closed loop and see if that's when the idle improves.

 

[team]

Yes I replaced the entire gasket set less than 2 years ago. This is the older pushrod engine.
Bank 1 = Sensor 1 (This is the "bank" that is acting up)
Bank 2 = Sensor 2

Thinking it may be an ECU fault. trying to confirm if pin 29 is the bank 1 HEGO Signal wire so I can test for continuity before getting a junkyard ECU. Unfortunately I'm only able to find pinouts for 2.3L, 4.9L and 5.0L

You do realize that each bank will have a sensor one? And each bank can have a sensor 2 (after the cat sensor). On your explorer you will have a bank 1 sensor 1 and a bank 1 sensor 2. Then you have a bank 2 sensor 1.

 

[ronin2501]

You do realize that each bank will have a sensor one? And each bank can have a sensor 2 (after the cat sensor). On your explorer you will have a bank 1 sensor 1 and a bank 1 sensor 2. Then you have a bank 2 sensor 1.

There are no sensors after that cat on this model. Sorry, should have clarified that. I think I see what you are getting at though. The 0.00v could be the sensors after the CAT if it had any?

 

[ronin2501]

How specifically did you do this. I was under the impression that the sensor elements on these MAF sensors are not to be touched. From my limited knowledge it sounds like the fuel/air ratio is off. The oxygen sensors you have already tested seems to rule them out as the cause.



Since it does eventually idle fine, when it has gone to closed loop possibly, that indicates your plugs and wires are fine. However, since it idles poorly at first and then when under load that once again points to fuel/air mix ratio problems. I would hook the scanner up and watch to see when it changes over to closed loop and see if that's when the idle improves.

I used an electronics component cleaning spray to clean the MAF. (The scanner values for the MAF seem within spec.) It does appear the O2 sensor itself is working, but for some reason the ECU is not registering the Bank 1 \ Sensor 1. So the A/F ratio is off for Bank 1, but not on Bank 2. Now that you mention it I've noticed the scanner shows the system is in closed loop mode immediately after I start it up, and click on DCL Data on the scanner. I will check the mode again from a cold start up because the engine was pretty warm the last time I looked at the fuel mode, it could be that it was warm enough to enter that mode. Thanks for the info, I'll let you know what I find.