Running lean with P0303

[lugnuts55]

The vehicle is a '96 Explorer Eddie Bauer with 4.0 OHV engine, auto trans, 4wd
Over 200K on the engine.

Last summer I replaced the catalytic converter and it passed emissions and ran fine with no CE lite. Last December, it started running rough again and it threw codes P0303 & P0171. I checked a lot of things and replaced a couple but it still is running lean and #3 cylinder still has a miss. Mileage is down to 12 mpg in town and about 18 on the highway.
Here is what I've done that I can remember. It is not necessarily the order in which I did them.

Checked #3 plug and swapped it with #1. No change. I have since replaced the plugs again.

Checked wire resistance and swapped #3 wire with #2 wire & because of wire length, I couldn't swap with a wire farther away from #3. All wires were good. They were changed about a year ago and they are routed correctly and not laying where they shouldn't be.

Checked Injector resistance and wires. Resistance was 16.2 ohms. the range is 13-18 ohms.

I put a noid lite on #3 injector and it flashes.

The ignition module has been replaced.

I replaced all intake gaskets, lower and upper. That succeeded in stopping the oil leak I had but the lean code keeps coming back as well as #3 cylinder miss.

Vacuum is 20"HG and steady. I cannot find any vacuum leaks anywhere on the engine. I use carb cleaner to spray on hoses and gaskets and any other areas I can think of but there is no change in rpm.

Compression is #1-130, #2-125, #3-130, #4-135, #5-125, #6-130. This is on a warm engine with all plugs removed.

Fuel pressure is 40psi. I am not able to do a cylinder balance test.

In my research, I found mention of the EVAP system. I don't know how to check this but I did pull a hose off the charcoal canister in the back of the car and found a wetness from fuel in the hose. It did not drip or run out but it was wet. I don't think it's supposed have fuel, only vapors.

The fuel pump and filter were changed about a year and a half ago.

Someone told me that Ford valves are thin and sometimes get worn into the head. I assume he meant farther up on the seat. Someone else thought maybe the lifter is not pumping up enough but there is no lifter noise. When I had the intake off, I found I couldn't remove the lifters because of the shape of the head. I am getting very frustrated.

Money is definitely a concern here but I might have to take it in for a cylinder balance test. I was a GM mechanic but not much on Fords. What am I missing here? Anybody have any ideas?

I should mention that I am having some other issues that I feel might be related to this somehow.

During our first big snowfall this winter, I switched to 4WD and it engaged ok. Then a few blocks later, the 4WD lights started flashing and it felt like the 4WD disengaged. Also the 4WD light did not come back on. I can hear the motor on the ttransfer case working when I move the switch on the dash without the engine running so I know it's getting power.
I know the front hubs use vacuum to engage. I'm wondering if this might also be the source of my lean codes.

I also have a little issue with mt EATC. There are no codes when I go into the diagnostics. What happens is that I cannot regulate the temperature on automatic. When I set the temp to 65 on Auto, it gets very warm inside so I set the temp to 60. Then after a while it gets cold and I have to go back to 65. If I go to defrost or floor, all I get is heat. Could this be a part of the vacuum problem and the lean codes?

I saw in a post here about another poor soul with similar problems and 2000StreetRod suggested disconnecting and reconnecting the crankshaft sensor a few times to possibly remove any dirt or corrosion from the terminals. Will this cause a misfire on a cylinder?

I might have left out a few things that I have done and/or tried but if you jog my memory, I can tell you whether I have been there or not.

I'm wide open to any and all suggestions. Thanks, Mike

 

[96eb96]

The EATC problem is probably a broken blend door. It is well documented and there are are a variety of fixes from hack to professional.

What about a running (dynamic) compression test? Leakdown test? That could eliminate a weak spring or other issue.

How do you know you don't have a clogged injector? Did you swap injectors?

Do you have a scanner that can read fuel trims? I usually start blocking off things like the brake booster and vac tees to see if there are any changes. Are your PCV hoses in top shape? The grommets too?

Did you look at the code freeze frame data? Does it happen when warm or cold? There is a theory that the vac leak seeks the weakest cylinder for the misfire.

I would say clean your MAF sensor, but it usually creates lean codes on both bank 1 and bank 2.

 

[lugnuts55]

I did change the #3 injector when I changed the intake gaskets. I have a code reader that has freeze frame and the lean codes happen warm or cold. The fuel trims are in the 20% neighborhood. Sometimes both banks indicate a lean condition. The miss is very noticeable after the engine is warm, probably because the idle is lower. I replaced the PCV valve and hose and grommet last week. I have followed every vacuum hose that I can find and isolated it and sprayed it with carb cleaner with no noticeable changes. I have cleaned the MAF sensor and disconnected it to see if it changed the way the engine runs. No change except for setting a code.
I want to check the vacuum lines going down to the front axle to see if there is leak there.

I am at the pull-my-hair-out stage with this problem. When I read about the crank sensor, I thought it was worth a try too.

I know a leakdown test is a good idea but I can't do it. I have to wait for my social security check to take it in.

I will look into the blend door issue if I ever straighten out the misfire issue.

Thank you for the reply. I appreciate the help. MIke

 

[96eb96]

harbor freight has a leakdown checker for around $30 and you can find 20% coupons online. I think that should be a last step though.

If the other bank is at 20 it is at the threshold to throw a code. Did you do any checking with the EGR system? Maybe plug the EGR vac line and see what happens. If this helps your DPFE may be bad. ALso a vac gauge may be helpful.

There are also cases where the EGR valve can sit open a bit and let air in. You can check with a hand vac pump but its hard to tell if its sealing properly. Everything is just under the threshold to set an EGR code, but will give some lean symptoms.

Its a PITA to take the EGR valve off though to check it, sometimes the tube can bend if you dont heat the flare nut and try to take it off. Be careful there.

The 4x4 system has two vacuum relays somewhere in the front passenger side of the truck. I'm going to give you the troubleshooting steps from the factory manual:

Pinpoint Tests

PINPOINT TEST A: DISCONNECT AXLE/SHIFT MOTOR DIAGNOSIS (4WD)

A1 INVESTIGATE WHETHER FRONT AXLE CENTER DISCONNECT IS ENGAGING
Start engine and depress brake pedal. Place transfer case in 4H position.
Raise vehicle so all four wheels are free to rotate.
Place transmission lever in drive (automatic) or 1st gear (manual) to confirm transfer case engagement in 4H. Let wheels rotate slowly.
Do both front wheels rotate?
Yes No
CHECK wiring from GEM controller to vacuum disconnect switch on axle. GO to A3 . GO to A2 .

A2 CHECK FOR FRONT DRIVESHAFT ROTATION
Check transfer case. Repair as necessary.
Does front driveshaft rotate?
Yes No
GO to A4 . REPEAT A2 .

A3 CHECK 4WD INDICATOR LIGHT OPERATIONAL
Check 4WD indicator light is operational.
Is 4WD indicator light working?
Yes No
Repair is complete. CLEAR DTC codes. INSPECT 4WD indicator switch wiring and lamp for damage. REPAIR as necessary. PERFORM A3 again. If results are satisfactory, repair is complete.

A4 CHECK VACUUM SHIFT SYSTEM FOR PROPER OPERATION
Place transmission lever in neutral position.
Remove vacuum hoses from axle shift motor ports.
Start engine. Test for vacuum at hose removed from outboard port on shift motor.
Is vacuum between 33.6-67.3 kPa (10-20 in-Hg)?
Yes No
GO to A5 . GO to A9 .

A5 PERFORM VACUUM TEST
Stop engine.
Connect vacuum pump to the outboard shift motor port and apply 50.5 kPa (15 in-Hg) vacuum and rotate right wheel.
Is front axle engaged?
Yes No
GO to A6 . GO to A7 .

A6 PERFORM INSPECTION
Inspect vacuum hoses for leaks, kinks, etc. Repeat as necessary.
Does system perform as required?
Yes No
Repair is complete. REPEAT Steps A5 and A6 .

A7 TEST FORK MOVEMENT
Remove shift motor housing cover. Connect vacuum pump to shift motor port.
Does fork move in and out freely?
Yes No
REPEAT Step A5 . GO to A8 .

A8 REPAIR OR REPLACE COMPONENTS
Remove shift motor housing cover and inspect shift fork, collar and axle shafts. Repair or replace as necessary.
Does system perform as required?
Yes No
Repair is complete. REPEAT procedure from Step A1 .

A9 PERFORM INSPECTION ON VACUUM COMPONENTS
Inspect intake manifold vacuum supply hose connection, transfer case vacuum switch connection, vacuum reservoir and shift system vacuum hoses for proper connection, restriction, leaks and damage. Repair or replace as necessary.
Is there proper vacuum?
Yes No
Repair is complete. CHECK transfer case vacuum switch. REPLACE or REPAIR if switch plunger is difficult to move or binds. REPEAT A9 .

PINPOINT TEST B: DISCONNECT AXLE/SHIFT MOTOR DIAGNOSIS (2WD)

B1 INVESTIGATE WHETHER FRONT AXLE CENTER DISCONNECT IS DISENGAGING
Raise vehicle so all four wheels are free to rotate.
Inspect indicator switch and wiring on shift motor housing for damage and short circuit. Repair as necessary.
Is 4WD indication system functioning properly?
Yes No
Repair is complete. GO to B2 .

B2 CHECK FOR WHEEL ROTATION
Start engine and depress brake pedal. Place transfer case selector in 2H position and transmission in drive (automatic) or first gear (manual). Ease off from brake and let wheels rotate slowly.
Does front right wheel rotate?
Yes No
GO to B3 . Repair is complete.

B3 CHECK VACUUM SHIFT SYSTEM FOR PROPER OPERATION
If 4WD indicator light remains on, place transmission in neutral and disconnect the shift motor vacuum hoses.
Test for vacuum in vacuum hose that connects to inboard shift motor port.
Is vacuum between 33.6-67.3 kPa (10-20 in-Hg)?
Yes No
GO to B4 . GO to B6 .

B4 PERFORM VACUUM TEST
Stop engine.
Connect a vacuum pump to the inboard shift motor port. Apply 50.5 kPa (15 in-Hg) of vacuum and rotate right wheel.
Does front axle disengage?
Yes No
GO to B5 . GO to B7 .

B5 INSPECT VACUUM SHIFT SYSTEM
Inspect vacuum hoses for air leaks, kinks, etc. Repair as necessary.
Does system operate properly?
Yes No
Repair is complete. REPEAT entire procedure.

B6 PERFORM INSPECTION ON VACUUM SYSTEMS
Inspect intake manifold vacuum supply hose connection, transfer case vacuum switch connection, vacuum reservoir and shift system vacuum hoses for proper connection, restriction, air leaks and damaged. Repair or replace as necessary.
Is vacuum within specification?
Yes No
Repair is complete. REPEAT procedures starting from B3 .

B7 PERFORM VACUUM TEST ON ARMATURE
Remove shift motor housing cover. Connect vacuum pump to shift motor port. Replace shift motor if armature does not move in and out freely.
Does front axle disengage?
Yes No
Repair is complete. REMOVE shift motor housing cover. INSPECT shift fork, collar and axle shafts. REPAIR or REPLACE as necessary. REPEAT Step B7 .


Usually a bad crank sensor gives a no start or a "random cyl misfire code." Check the toothed wheel for any issues. It won't hurt to inspect/reseat the connector or reinstall the sensor.

 

[96eb96]

Also, I heard of cases of severe carbon buildup in these engines, enough to absorb gas and cause misfires. When you did the intake gaskets did you notice any carbon buildup?

 

[lugnuts55]

The DPFE is less than a year old and I just had the EGR valve replaced. A friend has a torch and he replaced the valve for me. In the process, he repositioned the tube it is attached to and it caused a vacuum leak at the upper end where it goes into the plenum. I spent an hour trying to get the right bend back on the tube so it would go into the plenum without being held there. Unfortunately, the lean codes still come back and the miss is still there. I had the same thought about the EGR valve possibly being stuck open a little since it was probably original.

I was very surprised how clean the valley was when I had the intake off. Of course, I couldn't see the valves or pistons.

There was a point where I got a random cylinder misfire but it never came back after I replaced the ignition module and cleared the code. Now I just get cylinder #3 misfire.

I am going out to work on this thing in a few minutes. I will report my findings either later today or tomorrow. I am a retired mechanic with some disabilities so it takes me a little longer to do things that would have been a snap a few years ago. Thanks for the info.

 

[96eb96]

The ignition module is the coil pack on the engine right? I don't think these trucks have a separate 'ignition module' unit.

 

[lugnuts55]

That's what I call it because I was a GM mechanic for many years, but it's the thingy where you put the plug wires.
I checked the vacuum lines going to the diaphragm on the front axle and the plastic storage ball in case it might be leaking. It isn't and the lines are in good shape.
I would like to check the 2 solenoids that control the vacuum to the diaphragm. All I could do was check resistance, one is 70 ohms and the other is 90 ohms. I didn't think to check for voltage going to them but with the wheels off the ground, all 4 turn when in drive.
I also looked at the crank sensor and the terminals were clean inside the weather pack connector. I didn't check resistance or voltage because the car starts and runs.
I'm out of ideas.

 

[textrac03]

Went thru somewhat similar minus 0303 code. Had 0171 and 0174 on a 97xlt. After years of no problem on my 97xlt I decided to play with it. After a tune up, plugs, wires, k&n filter I also changed the thermostat and put in a 180 degree. All ok except a reoccuring bank 1 & 2 too lean. Always at a predictable time after warm up with cruise cont on, recovering from a downhill coast the code would post. No vac leaks detected, I replaced fuel filter no change, egr dpfe no change. I went back to a 192 degree thermosat and problem gone. Not willing to stay with the 192 degree temp thermostat I found that a chip upgrade was tolerant of the 180 degree temp. No more codes. My sons 99 sport experienced the same 171 & 174 codes with the 180 degree. He went back to the 192.

 

[2000StreetRod]

EGR tube seal

I seem to recall a thread about the difficulty of achieving a good seal where the EGR tube enters the intake manifold. One member had to use a second seal around the pipe to get enough contact to avoid a leak. I'm not familiar with the OHV so I might be confused about this. Have you tried spraying your aerosol where the EGR pipe enters the intake manifold?

 

[lugnuts55]

Yes indeed I have. It doesn't change the rpm any that is noticeable but I have thought about putting a second O ring in there, too. It is very hard to get it lined up just right, especially after changing the EGR valve because of the flexibility of the pipe it is attached to.
I was under the car yesterday and one thing I did while there was to inspect the crank sensor as I saw you suggest in another thread. I pulled the connector and it was very clean. I will go for a drive today, maybe to a dealer to get another seal.
Thanks for the reply.
Mike

Almost forgot, I will check to see which t-stat I put in when I changed the intake gaskets. The problem was there before the change and I didn't notice any heating problems but I will look at anything that could be causing this problem.

 

[lugnuts55]

I'm posting this to acknowledge all the people who gave me things to try and this problem is something that seems to be very common with these vehicles.

I saw a thread about Seafoam and how to run it through the engine while running, other than through the gas tank. The thread was for the 5.0 V8 and I have a 4.0 V6 OHV. I figured out how to do this on my engine and I went out and did it. It did smoke...a lot. But when it cleared out, I drove it. I had cleared the lean codes and the P0303 for the misfire. The lean codes came back but not the misfire. The idle was still a little rough and I wasn't sure I fixed anything.

I knew I was going to make a 400 mile trip so I bought another can of Seafoam and put it in the tank and filled it. The CE light never came on during the trip and the idle seemed to be better. I was watching the mileage also and the average mileage, as seen by the monitor in the car, worked it's way up to 17.3mpg. I am pretty happy with this but I would like to see 20mpg again someday.

I will keep an eye on the situation and I plan to run another can through the PCV hose again and put another one in the tank when I go back home.

The only code that sets now without turning the CE light on is P1500, VSS. The speedo and the cruise control both work but the speedo is 5mph fast. I was under the vehicle checking the wiring and pulled the VSS out. I put my finger into the hole to check the drive gear. It is loose on the output shaft. I tried to find out if there was a clip to hold the gear or if the gear is broken. I found out that the flange is supposed to be tightened enough to hold the speedo drive gear tight on the shaft. I put a socket on the nut but it is very tight and I don't have a compressor to run an impact gun. I will take it somewhere when I get home and see if this is the case.

I thank all of you who took the time to read and post an idea. I am learning a lot about these vehicles and hopefully the problem is fixed.
Mike

 

[96eb96]

If seafoam helps there is probably carbon on the valve or fuel path absorbing fuel or holding it a bit open. That will definately cause misfires.

 

[lugnuts55]

I started this thread two months ago. I have checked and rechecked things during that time. In the process of looking for a cause for the misfire, I managed to fix vacuum leaks so I no longer got codes for lean conditions. I did another compression check, for the fourth time, and got some readings I could use. I found that my compression gauge had seen better days so I borrowed a newer one.
#3 cylinder was the one misfiring according to the code P0303. The left bank was all within 10% of each other but the right bank had 130 on #1, 100 on #2, and 140 on #3. I talked to an automotive machinist that I know and he told me this engine is known for valve seats that wear out and the valve is drawn farther into the head. I decided to buy a head gasket set. At best, I would only have to replace the head gaskets. At worst, well I would find out when I get the heads off. I had done everything I could think of without tearing into the engine so I felt this was the next step.
When I got the right head off, the exhaust valve on #2 was 7/32" into the head. The valve and spring were that much taller than the rest. I felt this was the cause of the problem I was having.
When I got the left head off, I found the same situation but with cracks between the valves.
I decided to replace both heads and do the work myself. It took me about half a day to get them off and about a day to put it back together because of the cleaning. It is running smoother than ever and it even has a little more zip. I will be going on a short trip this holiday weekend of about 250 miles each way so I will get to see how much the mileage improves.
I got both heads for just under $600 and the valves were still good enough to use. There was no carbon in the combustion chambers at all. This engine has over 200k on it. It's nice to drive again and I'm not the last one to leave when the light turns green.
I took pictures of the right head only. I will try to get them here so you can see what I'm talking about.

http://i560.photobucket.com/albums/ss44/lugnuts55/RightCylinderHead.jpg

http://i560.photobucket.com/albums/ss44/lugnuts55/RightCylinderHead1.jpg

http://i560.photobucket.com/albums/ss44/lugnuts55/RightCylinderHead3.jpg

I am not suggesting that all the other posts about misfires will have this problem. This is what my situation was. I also thank all those who took time to read my post and offer a solution. Now I hope the pictures show up.

 

[2000StreetRod]

Congratulations!

Congratulations on finding the source of the problem and fixing it yourself! Also, I want to thank you for posting the description and photos of the valve seat wear. I read an engine performance article describing how to lower the exhaust valve seat in the head to reduce the temperature of the valve on engines that have adjustable valve lash but I never knew that an engine could do it on it's own. It only seems possible if the valve were constantly rotating and grinding it's way into the seat.