I have been battling all summer to clear up my rough idle and low end loss of power ( truck comes to life at about 2000 rpm in passing gear). Rough idle goes away at about 1000 rpm. 2006 F-150 4.6 two valve 4x4 4r70w auto transmission. I attached some stored codes and data pictures. I don't know what the mass airflow, oxygen sensors, short term and long term fuel trims are supposed to be on my truck. No check engine light lit up. I have replaced all plugs, coil packs, and throttle body. All Motorcraft parts. New EGR assembly from Napa. New Plenum and intake manifold gasket set Fel-Pro. Please let me know if my fuel trim, mass airflow, and all four oxygen sensors data is within speck. What could to problem with my truck be?

 

I've been having similar problems, but my truck has the 5.4l. You can see my post on the same page. Does your truck have the COP coils? Pretty sure that's what my problem is (and hundreds of others). I know you've replaced a lot of stuff, but I'd go over again and make sure everything is tight (plugs and coils and electrical connectors).

Your scanner numbers depend on what you were doing at the time. But your fuel trims look fine at least. How's your mileage? Has it gotten worse with these problems?

 

Heres some new fuel trim and maf data when I am driving the truck. Mileage... I get 35 miles to $10.00 worth of gas. Odometer shows 195193. Truck used to only run rough at idle when the engine got to operating temperature, but now its doing it on cold start and at operating temp. Yes cop coil pack on top of every plug. I have confirmed there is current on all coil and injector plugs.

 

The codes aren’t any help - the PSP and brake switch codes are most likely operator error (the steering wheel needs to turned 1/2 a revolution and released and the brake pedal applied during the KOER test), the P1000 just means the truck has to be driven a certain way to enable all the monitors (more for emissions inspection) and the OCS is related the airbag system and won’t affect driveability.

Here are general specs (not Ford specific) on live data once the engine is in closed loop, at operating temp and at idle:

MAF - At least one gram/second per liter of engine

Upstream O2 - Switches consistently from rich to lean - if your scan tool has a graphing function this will be much easier to monitor

Downstream O2 - Steady, constant voltage with little variation

Short term Fuel trim - Technically anything in the range of -25% to +25% is considered normal, but realistically, less than 5% is what you want to see - don’t worry too much about the long term at this point. The LTFT is used by the PCM to adjust over time - not that it can never be useful, but in terms of diagnosis, STFT is what you want to watch.

MAP - Reflects Engine vacuum (minimum 15 in*Hg but I can’t recall if it will read out as in*Hg or just as negative PSI)

In my experience the most common cause of a rough idle is a vacuum leak. I understand you just did an intake reseal but that doesn’t mean all the vacuum operated controls and accessories are in good order.

I recommend unhooking all vacuum lines and capping them off to see if the idle smoothes out. If so, hook them back up one at a time and observe the effects - if one causes the engine to start stumbling, you found a leak. If not, you need to focus on engine controls.

Check the DPFE sensor voltage as well (I’ll have to double check the correct voltage at idle) - the EGR might be stuck open.

 

Wow, you have explained this to me way better than anyone else. Thank you for taking the time to do that. Every time I hooked up A scanner, I never knew what numbers were good and which ones were bad. Now I have A understanding of fuel trim and other numbers. I really appreciate that.
So I unhooked the egr assembly from the intake, leaving the wires hooked up and the tube that goes to the exhaust. I had A friend hold his thumb over the hole where the egr would normally go, I started the engine with his thumb blocking the hole, and still rough idle. So I guess the egr is in good shape. My goal here was to block off any egr gases incase it was stuck.
I unhooked all vacuum hoses and blocked them then started the engine, still rough idle. Assuming the plastic plugs sealed properly, I may have A vacuum leak somewhere else.
Lastly I ordered A ECU online that was refurbished. I did the key coding, started the engine, and same old rough idle. I sent the ECU back and he told me the 5 volt reference #2 was popped rendering ECU not repairable. What are the chances my truck is burning up the 5 volt reference #2? Or did he just say that to avoid giving me A refund? I probed the maf and all 4 o2 sensors and I am getting current to at least the maf and 02 sensors. I wish I knew how to check 5 volt reference, but there are so many wires coming from the ECU.

 

Start with the basics. Have you cleaned the mass air sensor with cleaner yet? That is the first thing I do when driveability problems such a surging and poor acceleration come up. That has been the problem on several vehicles I fixed for people..

Check the KOEO voltage of the throttle position sensor, then do a sweep test to wide open and make sure the voltage increases at an even amount. You can use a digital ohm meter for this, but I like an analog with a needle for the TPS test.

The DPFE sensors are prone to give problems also, but you tried blocking off the EGR, so it is probably ok.

Get a vacuum gauge and check vacuum at idle, then again at steady 1500 to 1800 rpm and watch for any stead drop off in vacuum to indicate plugged cats.

 

I got some maf cleaner, took maf out and cleaned it. Still the same issue. I may order A motocraft maf and see if that will do anything. I borrowed my buddies vacuum/ cat flow gauge. I am getting good vacuum at idle in the green, but when I rev the engine the vacuum drops in the red. Also when I start the truck the vacuum is low in the red until the engine idles down then it moves to the green good vacuum. Then I took the pre cat o2 sensor out and screwed in the gauge adapter and I have less than 1 psi flow at idle, same for the other cat on the other side. I couldn't do A 1500 rpm cat test because the rubber hose going the gauge kept melting. I even took both bank 1 and 2 upstream o2 sensors out and started the truck incase cats were getting clogged, still rough idle and poor acceleration. His Dad thinks I got the timing off A tooth when I put the timing set in. I told him I was having this rough idle before I put in the new timing set, I did have A bad timing chain tensioner the seal behind it blew out. I would think if I did get it off A tooth, I would hear that out of time sound when I start the motor, but I don't it sounds smooth even cranking.

 

Did you also unhook the PCV tubing when you checked for a leak? It won’t hurt anything to let the PCV vent to atmosphere for a few seconds while checking for a leak.

Vacuum is simply a measurement of the overall mechanical condition of the engine. Vacuum readings are useful for determining whether or not the problem is isolated to the base engine components (mechanical) or control side (electronic) because it measures how well the engine is sealed and how well it can move air in and out.

Some people will swear by watching the vacuum readings and being able to isolate it as valve timing or spark timing or several other issues - I’m not gonna debate all those points - I’m just gonna say that all I use vacuum readings for is to determine if it’s a mechanical problem or an electronic one.

Normal vacuum readings at operating temp are:

1) 15-19 in*Hg at idle. The lower the number, the more worn an engine tends to be. The needle should hold steady but a little fluctuation is typical.

2) As engine RPM changes (increases or decreases), vacuum will momentarily decrease, however once engine speed stabilizes, vacuum should return.

3) Severe needle fluctuation or low vacuum indicates base mechanical problems. An engine is essentially an air pump - anything preventing the movement of air will affect vacuum.

4) 1-2 psi of back pressure in the exhaust is normal. Anything more indicates restrictions in the exhaust.

 

No I didn't unhook the PCV or anything. He just told me to plug in the vac gauge at the brake booster. I took the booster hose off the booster put the adapter and gauge hose to the gauge. Did I do the test wrong?

 

No - you can check vacuum with everything hooked up - I was just asking because oftentimes the PCV tubing can degrade and be a source of leaks.

 

Ok, I was making sure I did it right. Thank you again for your useful information.

 

Am I supposed to have vacuum on bank 2 where the hose goes from the valve cover to the air filter housing? Because I noticed today I do have vacuum there, I thought as the throttle body took in air from the air filter that is what vent the valve cover on bank 2. I understand there is vacuum on bank 1 because of the PCV valve.

 

Yes, that’s normal, it’s just what’s referred to as ported vacuum because it’s upstream of the throttle plate.

That hose is referred to as the crankcase ventilation hose - it provides the same function as the PCV hose except it doesn’t have a valve. The reason it’s run to the air intake tube is because the ported vacuum prevents too much blow-by and oil mist from affecting the air/fuel mix at idle.

Which reminds me - have you tried cleaning the throttle body? Give it a try if not but look carefully for a sticker on the TB stating it has a gel coating - if it does then don’t scrub it - just spray off as much crud as you can and call it good.

You can test the overall integrity of the PCV system by checking vacuum at the engine oil dipstick tube at idle at operating temp. You should see 1”-2” if it’s working properly - I’ll have to find info about the indications if that’s not what you see - I can’t recall it at the moment.

 

I may have not mentioned that in the original post, I put on A Motorcraft remanufactured throttle body I'd say 3 months ago. My Motorcraft remanufactured mass air flow sensor came in today, well truck still idles rough, it may not shake as bas as the old one but still rough idle.
I have another question. How high do these Triton engines rev? Mine only revs to 3900 rpm at operating temperature trans in park. Sorry I'm used to working on the 1994 back to 1985 f-150's I used to own. And they've all reved up to at least 6,000 rpm in neutral or park. So I either have A restricted exhaust, or mot getting enough fuel, weak spark, or these Triton engines just don't rev as high as the older 5.0 Ford engines. I don't go aroung bouncing my trucks off the rev limiter all the time, someone told me his clogged Cadillac converter wouldn't let his engine rev over 3,000 rpm and that's why I did this rev test. I don't have access to A vacuum gauge at the time, I'll have to borrow or buy one and see what that reads out to.

 

I can’t say for sure what the rev limit on your truck is, but with electronic engine control, don’t be shocked by anything - our 2016 grand caravan is limited to something like 2000 or 2500 RPM in park.

I read back through the thread and while I did see where you confirmed the injectors and coils were getting 12v feeds, I didn’t see anything about fuel pressure testing. Have you checked it and what were the results?

I think the possibility of a leak being the cause has been eliminated based on everything up to this point. The only other suggestion I have on that is to remove the intake duct from the TB and air cleaner, apply a thin film of oil (any type will do) or spray lubricant to the inside of the ends where they seal, then reinstall and make sure not to over tighten the hose clamps. Sometimes corrosion can build up and stick to them and allow leaks post MAF.