Sudden misfire of cylinders 5678 on 4.6
Need some guidance. A elderly couple needs me to try and fix their 2000 Ford Expedition with the 4.6 V8. The elderly gentleman changed the thermostat hoping to fix a no hot air from heater. This did not fix the no heat problem but the next time they drove the vehicle it had low engine power. They had it checked at autozone with a scanner and it sets misfire codes for cylinders 5,6,7, and 8. Could this be a coincidence that all 4 went bad at the same time or is there a fuse, harness or what that may be causing this problem. I cleared the codes and test drove it and it set the same codes again for 5,6,7 and 8 cylinder misfires. Any suggestions.

 

There isn't enough information to make a guess. What codes were on the vehicle? Have you monitored the coolant temperature and fuel trim? Is the engine in closed loop operation?

Was the correct thermostat installed (same OEM temperature)? After changing the thermostat, was the cooling system bled of air? Bleeding the cooling system is imperative, air in the cooling system can cause a no heat situation and other problems.

 

There is a radio noise capacitor for cylinders 1-4 and another for cylinders 5-8. I believe the 5-8 one is pretty much above and behind the t-stat area. The capacitor ties directly into the power wire for the COPs on that side. See if the wire that comes off the capacitor got pinched or otherwise damaged.

 

The codes are PO305-PO308, PO401 EGR flow weak and PO174 System to lean. RPM's fluctuate from 748-820, Fuel system closed, coolant 185, IGN adv fluctuates between 10-25, Calc load 25-29%. Not sure how to monitor fuel trim or about the closed loop operation.
I checked the radio interference connector and it all feels tight and looks clean.

 

As far as the no heat problem is concerned, if the correct thermostat was installed and the cooling system bled of air, I'm leaning toward a problem with either the heater control valve or perhaps heater core.

The engine is in closed loop as indicated by the "fuel system closed" data pid, which means that the engine has reached operating temperature and PCM is using 02 sensor data for fuel trim.

As far as the misfire situation, you need to investigate why bank 2 is running lean. The lean condition on that bank can cause the misfire codes.

 

So I assume bank 2 is where cyls 5678 are located? There is no doubt it is misfiring. The truck has very little power. Any ideas where to start to try and determine why one of the two banks are running lean? I compared the coil readings between the two banks and they are the same so I don't believe it to be the a ohm problem. A test light lights showing voltage at the coils on the misfiring bank.

 

Given that you also have an EGR code, you might as well start there. A stuck open EGR can cause a lean condition.

 

Thanks again. I'll check that EGR and see how she does.

OK I'm beginning to wonder if this engine condition has to do with either a faulty crank sensor or PCM. Seem like every time I do a test drive the misfires are randomly detected elsewhere. It began with misfires at cylinders 5678 along with lean condition and EGR malfunctions. I repaired a vacuum leak at the PCV line and removed the throttlebody and cleared carbon packed passageways. Test drove the vehicle and malfunctions at cylinders 5 and 6 and EGR malfunctions went away but remained at 7 and 8. I did cylinder compression checks on cylinders 7 and 8 and readings were 120 psi. I swapped plugs and coils from 7 and 8 with 1 and 2. After driving the vehicle nearly lost complete power and showed misfires at cylinders 2 and 5 and lean and EGR malfunction. I pulled over and shut the engine off and let it set a few minutes. Restarted the engine and appeared to have full power. After driving approximately 5 miles with what seemed to be lots of power I stopped and checked and the only code existing at this time is a cylinder 5 misfire. The lean and EGR malfunction did not return. With all the random cylinder misfires might it be The PCM or crankshaft sensor.

 

Sure but why is the whole driver's side misfiring? The EGR problem would affect the whole engine, not just one half.

 

That is starting to sound way too much like a blown intake manifold gasket.

 

I agree, but the starting point isn't as important, what is more important is finding evidence, checking each possible cause and eliminating one-by-one until finding the solution. I didn't suggest the EGR is the problem, I suggested to start at the EGR and check the system, not throw a part at it. If it is working, then great, check it off the list and proceed to the next possible cause.

 

That's correct.

 

Not really. A lean condition is one that has unused oxygen in the exhaust. A stuck open EGR valve is going to insert exhaust (which contains very little if any oxygen) into the intake stream.

 

It might help to read the entire post before attacking. If you recall correctly, I advised that he should find the cause of the lean condition to fix his misfire. Given that the elderly couple hired him for the job, I assumed he could figure that part out. The evidence is as such:

-misfire condition on bank 2
-lean condition on bank 2
-EGR code

If you look back, I advised he should look toward fixing the lean condition. What are the possible causes of a lean condition on bank 2? The list is a mile long, there are way too many possibilities to just guess correctly on the first try. That isn't even the scope, the important thing is to start somewhere, test, then move on to the next possibility. I agree 100% that it could be a vacuum leak somewhere, perhaps intake gasket as someone posted above. Perhaps it could be the 02 sensor on that bank, or a fuel delivery problem, among other things. We really don't know for sure just from reading. It doesn't take too long to test these different components. If you managed to test something and rule it out, hey that's great, you just found evidence and can move to the next thing.

Instead of helping the original poster with knowledge that you may have, you choose to attack someone else trying to help. I'm not really liking this on this forum. If you have knowledge and experience, use it to help others learn that may not have as much as you.

 

Does it have COPs? Or does it have the dual coil setup, one coil on each bank? I know the early 4.6 engines had the dual coil system, but later received the COP system, but don't know when they switched. If it has the dual coil system, perhaps there's a problem with the one on bank 2?