I have a 1997 F-150 with about 125,000 miles. While moving my daughter back to Washington State Univ from central Calif I lost power and the MIL light came on. I was towing a car trailer with a VW Beetle on it. I inherited this truck from my father who cannot drive anymore so I do not know all of its history. I do know that the plugs were really bad burnt when I checked them on the road after the loss of power. I put in new ones with out any change. I got the truck home and checked the code, it showed a P0171 DTC. I did a compression check and had low compression in several cylinders so I pulled the heads and noticed the possibility of leakage between cylinders. I took the heads to a highly reconmended rebuild shop expecting burnt valves. The heads test good except for they needed to be resurfaced. I reassembled the motor very carefully and started it up and still had the same problem. I have checked with a propane tester around all of the gasket areas of the intake manifold including the major vaccum ports ith no results, it did not change the idle. I have changed all of the rubber vaccum lines and check the PCV for function. I performed a vaccum check at a major vaccum port and got a reading of 5-8 pounds of vaccum at a rpm of 360-460 according to my Fluke tester. With the ruff idle I pulled the injector leads one at a time to see which cylinders might be the problem. I found 4 cylinders that with the injector lead pulled did not change the idle. I checked the primary and secondary resistance of the coil packs. the primary resistance was in specs but the secondary was not(14.6 K-ohms warm, 14.3 K-ohms cold). Where else can I look? I'm a rookie on this engine(4.6LW). I'm used to working on bigger and less complicated engines. This thing is driving me nuts.

 

Sounds like you have more than one problem. The P0171 could be a dirty MAF sensor.
4 dead injectors sounds like a wiring or PCM problem. You need a Noid light to test for injector pulse. I got mine @ Autozone pretty cheap. It plugs into the injector plugs and will flash if you have a signal.

 

This engine is not complicated at all, it is telling you exactly what is wrong. You have a lean condition on the bank 1 (passenger side) of the engine. This doesn't tell you why it is running lean on that side, but it eliminates a lot of possibilities that it is isolated to one side as opposed to both. Is there any exhaust or intake leak on the passenger side? Either can trigger a lean code. Any broken or missing vacuum hoses? You replaced the gaskets right? Did you also do the intake gaskets? The O2 sensor will probably be damaged from the warped heads possibly leaking coolant into the combustion chamber. Sounds to me like this truck was badly neglected and abused. You should be reading more vacuum than that, my van pulls 18 lbs of vacuum at idle.

If pulling the injectors wires did not help, then then you need to go to the basics. An engine needs 3 things to work, air, fuel and ignition. On of these is missing. Check for spark on the dead cylinders. If there is a bright blue spark, then that part is good, and you have already checked compression. Are you sure your timing is correct, because firing at the wrong time will result in a no fire condition. Misfires will also sometimes set lean codes. If compression is good, you have spark, and the timing is correct, the for whatever reason the injectors are either not firing, or aren't getting fuel. Make sure the connectors are all secure and are routed to the correct cylinders. It is possible to test the injectors by removing the fuel rail, tying the injectors to the rail, and disabling the spark. Crank the engine, and the injectors should spray a fine mist. Be careful though, as gasoline is obviously flammable.

Hopefully that is not too much, and hopefully that helps.

 

Stoich is 14.7 so lean is above that. How do you get lean? With these Fords it's a vac leak most of the time, but you can go lean due to a lack of fuel too. Don't count that out. What if an injector(or more than one) malfunctioned closed or didn't pulse long enough? Would you go lean? Sure you would. Your vac is way too low. Did you do the vac test Wet as well as Dry? You should have. I'd do a leakdown and suspect bad rings if you put the motor back together properly.

 

Sorry I didn't get back sooner,I hadn't been able to work on the truck. I pulled the coil packs off to check them real good. What the acceptable ohm reading for the secondary resistance for the coil packs? My book says no high than 11.5 k-ohms, mine read around 14.5 Kohms. Also the base between coil pack and mounting bracket was rusty, I have cleaned off the rust and putting some di-electric grease to the surfaces. Do the coil packs ground through their base? Next since I had the coil packs off I checked the camshaft position sensor, my book says there should be battery voltage at the connector with the key on engine off. I don't get anything. The wire shows continuity to through the large square connector just before the PCM connector. I also checked the crankshaft sensor for battery voltage and only had 1.5 volts there. Everything else I checked had proper signal voltage at the connect of around 5.0 volts. What resistance value should I see for my plug wires? Does this sound like a PCM problem?

 

I did a compression test, both wet and dry. #1 tested 140 lbs and held that for about 3 minutes. #2 tested 90 lbs and held that. #3 tested 75 lbs and held that. #4 tested 0 lbs. #5 tested 130 lbs and held that. #6 tested 0 lbs. #7 tested 0 lbs. And #8 tested 0 lbs. The four plugs on the cylinders with compression showed a white and ashy like a lean burn. The other four plugs were wet and unfired. Is this bad rings, or timing? What should I check next? Is it rebuild time?

 

Do a leakdown to find out where your leakage is. With numbers like that the heads have to come off and if you're high mileage you need to do the bottom end too. If you did wet and dry where are the wet and dry numbers? You don't say if these numbers are wet or dry. Either way you have big problems.

 

how can you get 0 compression on 4 cylinders?????? i have never seen a engine that bad. bad rings would read low, but to get zero is something else!

 

I only did the wet test on the cylinders that had 0 lbs dry and they still showed 0 lbs.

 

Sounds like to big a mess to give any definitive help.
4 cylinders with little or no compression could have a cam out of timing on that bank due to improper indexing after it was put back togather with cylinder heads that were supposed to check out good.
You have to go back and get the mechanicals good before looking at the electronics for issues.
Good luck.

 

First of all let's understand that a vehicle(any vehicle) does NOT get ZERO compression overnite. This happens slowly over time unless there was a catastrophic engine failure. That means this vehicle has been running like crap for a long time. There are many things that could cause ZERO compression. Bent valve, carbonized valve seat, hole in piston crown, blown head gasket. The list goes on. This motor has to come out.

 

Four holes don't just go flat. Not without a whole lot of noise from the bottom end and parts coming out of the pan or case. The valve timing is most likely off from going back together. You said the heads were checked, so that's not it. Your original lean is probbaly from the intake manifold gasket leaking down one bank where it bolts to the head. I am finding this out myself as I currently have that problem and it seems to be common according to a Ford mech at a dealer here in Atlanta. Just hope mine isn't warped. Mine is currently leaking cooalnt somehow. Will be pulling it off this week. Mine has gone 230K though with only being pulled of twice. I forget the one code that comes up that means you basically need to pulled off the intake manifold and clean out all the carbon. The emissions sensors get clogged up. Good luck.

 

I did a leak down test on each cylinder. I charged each cylinder with 20 lbs of air and let it sit for three to five minutes. Only one droped 1 lb psi after around 4 minutes. I left cylinder #8 charged all nite and it leaked downto 5 lbs psi, it was one of the 0 lbs psi during compression check. I did the test at TDC for each cylinder. Do I need to use more air pressure? What do I check next? Could my hydraulic lifters be tighting up with oil pressure and holding the valves open? Visual check of the timing placed Cam lobes where they should be at TDC for each cylinder.

 

No no that's not exactly the way a leakdown test is done.
A special device with gauges are use to access leakdown rate in percentage usually at 100 psi to make leak percentage an easy way to get a reading.
No engine I know of will hold any amount of pressure over a long term like you are trying to do.
The rings have gaps and will not hold pressure very long.
The need for a cylinder to hold pressure is only long enough for combustion and stroke distance without escape into the crank case.
Anything beyond that amount of time is useless.
BTW, checking cranking compression needs to have the throttle held open to pass enough air to fill the cylinder properly. Besure you do this.
Leakage can be by the rings, valves, head gasket, a crack in head, cylinder wall or piston.

 

No engine is going to have such different results between a compression test and a leakdown. You're engine didn't miraculously fix itself did it? You have to use 100 psi in your leakdown tester. You compare the reading of the regulated gauge(100 psi) to the reading of the gauge connected to the cylinder being tested. A max. of 20% difference is allowable. You must be at TDC on the compression stroke to properly perform the leakdown test. Your leakdown results should confirm your compression test results and help you narrow down the faulty area which needs further examination. Did you use a leakdown tester or are you flying by the seat of your pants? If you're in over your head you need an assistant that has more experience.