Hey guys, this is my first post to the forum. I could use some help diagnosing some problems with my F150.



I have a 2000 F-150 with the 4.2l V6 and manual transmission, and it has 205,000 miles. The problem I am having is P0171 and P0174 codes, a rough or high idle on startup, as well as external coolant leaks on both sides of the engine. The first time I had this problem I took it to a local shop and they replaced the fuel pump and filter, which helped for a while but the problem came back. I took it back and they cleaned the injectors and replaced the 02 sensors and checked for vacuum leaks. Again, the truck ran well for a little while but the codes came back and the truck still idles a little high on startup (1500rpm) then drops slowly down to normal idle at 800rmp. Besides the high idle and very rarely now a rough idle on startup the engine runs fine and has good power. I'm not taking it back to that shop after having dropped $1500 in it without them being able to fix it.

I understand from searching the forum that the lean codes are most commonly caused by vacuum leaks, dirty or faulty MAF, or leaking intake manifold gaskets. I checked all the vacuum hoses and found a bad pcv elbow underneath the top intake manifold. I replaced that but still have high long term fuel trim levels (14% at idle and 10% at speed on both banks). I cleaned the MAF and I also sprayed soapy water around the upper and lower intake manifold, pcv valve, and connections looking for bubbles or hissing noises, but didn't find any. There was some engine oil in the pcv lines and intake manifold and around the pcv valve gasket in the passenger side valve cover. I also took a length of hose and used it like a stethoscope to try an hear any vacuum leaks around the engine. I'm not sure what to try next besides spraying carb cleaner around the intake and listening for a change in idle. Here is the freeze frame data for the P0174.



I also checked the live data and took some notes. The 02 sensors seem to be operating normally as far as I can tell, and the MAF. At idle my Long Term Fuel trim is consistently around 14% on bank 1 and bank 2 indicating its adding a lot of fuel. Which makes sense because my fuel mileage sucks. At speed the LTFT drops down to around 9-10% on both banks. The only thing I thought was odd was the B1S1 and B1S2 were stuck at 99.2. Those are the 02 sensors after the cats on both sides of the truck. Is that normal? The voltage was fluctuating but not the fuel trim.


As for the coolant leak, my reservoir is low by about 2 inches. The coolant does not have an off-color and the system is not under pressure or bubbling. There is no milkshake look to the oil and my oil level is still good after 5000 miles. No white smoke from the tailpipe on start up, or sulfur smells. Still, I can see coolant and oil mixture coming from the head gaskets and down the back side of the engine on both sides of the block, so I'm worried that my head gaskets may be blown. Or possible the head gaskets are just leaking coolant externally and not into the cylinder heads and is mixing with oil seeping from the valve cover gaskets? Here are some pictures I took of the heads, can you guys let me know if you think the head gaskets are blown?

Drivers side of block.

Passenger side of block.

Amount of oil and coolant leaking.

Thanks in advance to the guys who take the time to read this, I know it was a lot. You are helping me out big time. If the head gaskets are blown I think my best choice would be to sell it, because the cost of the repair would almost cost as much as the truck is worth. I thought about just adding some stop leak to the coolant and running it until the engine needs replacing. As for the vacuum leak, I'm thinking about building a smoke machine and testing it that way. If it is the intake manifold gaskets I can change those with some help from a friend. If there are any other things I can try to diagnose it please let me know.

Update 1
Did a Combustion Leak Test for the head gaskets, and they were good. Built a small smoke machine for $25 and used it to test for vacuum leaks. My EGR valve was billowing smoke so replaced it. Now the truck runs like it should on startup and idle. Long-term fuel trims dropped below 10% and it's not throwing a code now. Another leak I found was at the back of the motor where the IMRC rod connects to the valve on the back of the intake manifold. Here's a picture of the seal where it is leaking. This is where the antifreeze leaking down the backside of the motor was coming from and is caused by the lower intake manifold gaskets leaking. I don't have isolator bolts because my intake manifold is all aluminum, but I am ordering the gaskets and will be changing them out ASAP.


Big leak coming from the drivers side intake manifold runner.

 

My guess would be intake gaskets as they can leak coolant and cause vacuum leaks, but it is just a guess not being at the truck of course.

 

Awesome post. You've left little guesswork for us.
Yes, HGs can just have external leaks.
FYI, I think 13% is the threshold before the PCM starts setting lean codes so you're not very far over the line. I notice you haven't mentioned the intake manifold isolator bolts. It's a bolt that holds the lower half of the upper intake down and it has an integral gasket. The original gaskets hardened when cold then sealed better when hot. You can just pop off the intake lid to get to them. Once loose, they must be removed with pliers and a surprising amount of force. When I first started making the repair, I replaced the intake gaskets too. Then I stopped. The intake gaskets on the 4.2 plastic intake will outlast the truck. TSB: http://ww2.justanswer.com/uploads/js...sb05-22-06.pdf

 

Forgot to mention that the downstream O2 sensors aren't useful for diagnosing a driveability problem. They just monitor catalytic converter performance and don't reflect much if anything about how the motor runs.

 

Ok great, I'm going to try the carb cleaner method and do a smoke test and see if I can find any leaks. Will follow up later if I find anything.

 

That’s just wasting time. Just replace the intake manifold gasket and pop in new isolator bolts and be done with it.

It’s a rite of passage for a 4.2 10th Gen F150 owner.

 

Hey guys thanks for the heads up on the isolator bolts. The truck is running better now after I replaced the PCV elbow under the intake. My long-term fuel trims on both banks came down from 14% to 10%. Still seems to be adding some fuel but hasn't thrown the codes again so far. If the isolator bolts are leaking then the intake would be pulling in unmetered air between the two halves of the intake manifold right, but what about the coolant leak problem? I read on the forum that sometimes the lower intake manifold gaskets will fail and coolant will pool around the top of the intake manifold near the heads. This is where I'm seeing antifreeze running down both sides of the engine block, starting from cylinders 2/5 and towards the back of the engine. Since I don't have white smoke or signs of coolant in oil do you guys think it could be the lower intake manifold gaskets? If so, how can I check the intake for signs of antifreeze? Should I add some UV dye to the coolant, pull the spark plugs and check for signs of it?

I'm hesitant to start pulling off everything and changing all the intake gaskets. I have a Haynes repair manual, but a limited number of tools... and experience, haha.

 

I got my abused 2001 4.2l f-150 at 105k miles. It ran rough and leaked some coolant and oil.
After changing coilpack, wires, plugs (motorcraft), fuel filter, upper intake manifold gasket, and isolator bolts it ran much smoother, but still a bit off.
I forget the details, but my fuel trims were off. I finally replaced the injectors and it smoothed out and the idle dropped into the proper range.

I tracked my coolant leak down to the hose on the smaller pipe coming out the top of the water pump. I added a second clamp and that stopped my leak.

I still have a bit of oil weeping in similar locations to yours, but it's not marking the driveway and I do not have to add oil between changes.

Do the upper intake manifold gasket and replace the isolator bolts. While you have the top manifold off you can also clean out the EGR ports.

Get a gas analyzer kit to check the coolant for exhaust gasses to determine if you have a blown gasket. I don't think you do, but the inexpensive kit will tell you.

If you really want to track down the coolant and oil leaks you need to clean the engine.

Good luck.