Got a new to me truck, 200K miles, new coil packs, spark plugs, oil, air filter, fuel filter. Went down to N GA mountians today on an errand, and this thing runs like ****. horrible drive line lash, no power, sputters like hell up hills, ok down hills, had to turn off the overdrive, (not that uncommon with a 5.4L with 35" mudders,) I pulled each coil one by one, none seemed to matter. Checked the codes, and getting all sorts of misfire codes, from pulling the coil packs, and a P0171. lean condition bank 1. But, the engine seemed to find a sweet spot about 2700rpm and run OK.

I checked all of the vacuum lines on the throttle body I could find, and re attached them, and tried it again, and idle is way better and power way better up to about 3000rpm, then falls flat on it's face. I think the intake pipe when it attaches to the throttle body was a little loose, So, I think I am on to something with the vacuum leak, just thought I would do some research, and ask a question, things will be better in the morning.

Any takers? Thanks.

 

200k miles is a lot for a 5.4

 

^^^ Not really they go double that pretty regularly. What brand of coils and plugs were put in. Did it run ok when you first got it and this started during the trip or did it run like crap from the time you bought it. There are also some more vaccum lines than just on the throttle body that need to be checked an fixed if missing damaged or broken that can cause problems.

 

Are you getting misfires in the Mode 6 data after clearing any codes? There can be a lot of misfires without setting a code.
What brand plugs were installed? Motorcraft
What brand COPs were installed? Motorcraft or Denso
What's the fuel pressure reading? Fuel pump or relay may be degraded.
What's the intake vacuum reading at idle? Could still be a vacuum leak somewhere or cracked intake.
A single bank lean code can sometimes be a loose exhaust connection.

 

Spray starter fluid, or use propane, around the vacuum hoses-ports as well as around the intake manifold. If RPM changes that’s the proof you have a vacuum leak. If RPM stays the same you might want to do a compression check.

— Dave

 

Clean the mass airflow sensor. A lot of times it gets dirty and cannot feed the ecm the correct airflow data. That will cause a lot of misfires and lack of power.

 

OK, thanks, I will try the starter fluid trick and report back. Coils are unknown brand, I dont remember about the spark plugs. But the truck did run perfectly for about a year, I will also clean the MAF, and re check the vacuum lines...and the idle vacuum reading. I am not sure about the electronic data, ill see if my scanner wil do it, I have an old ultra gauge.

SO where are the other vacuum lines other than than the ones on the throttle body? I suppose the intake manifold, thanks for all the good advice....

 

The things the vacuum lines control could be leaking, too
The heater control valve, vent controls, power brake booster, fuel pressure regulator etc. all have rubber in them, which should be dead ends for vacuum, but can leak.
Capping off the ports at the engine should produce no change in vacuum at idle or a hand held vacuum pump/gauge can test the devices for leaks.
A bad EGR valve can cause poor running.
With a lot of miles there could be gunk build up just below the throttle body butterfly that can cause poor running.
X2 on cleaning the MAF, also check the air cleaner tubing between the MAF and throttle body for leaks.

 

Problem is if you run it when its missing skipping etc you run the risk of ruining or clogging the the cats.

o2 sensors prob need to be changed unless they have been..Also I would pull the plugs and have a look see...motorcraft plugs and coils....

 

I had a chance to check all the vacuum lines, no hisses or leaks, plus, I checked the vacuum off the PCV tube and 24mmhg. Havent had a chance to check the intake manifold for leaks, but that doesnt seem like its leaking.

 

As was previously mentioned check the fuel pressure, has the filter been replaced atleast?. If I'd went to the trouble of pulling the coils I think I'd have pulled the plugs too and run a compression test.

 

I will check for manifold leaks, fuel pressure and compression, thanks again. I was really hoping it was something simple, looks like I am not so lucky. I think I did change the fuel filter. But I am not 100% positive.

 

I checked fuel pressure at the rail, 30psi, doesnt waiver at all and held to about 25 after an hour.I cleaned the MAF sensor, no change. Also, checked the codes again, and I got a p0443, and I checked the purge valve solenoid. it is getting 12Volts, and Ohms tests to 35. I am reluctant to change it, because I am not sure if it can be tested...I am not sure if these go bad often.

 

OK, I am going to do a shameless bump/recap.

Truck starts and idles OK, then gets worse as it warms up. p0171 lean code.(I think many of the other codes were caused by me pulling coil pack wires and vacuum lines)

Has about 1/2 the power it used to. Fuel pressure is fine, 30psi and holds a while. New fuel filter, coils (off brand) air filter, plugs, and pcv valve.

cleaned the MAF sensor, and no change. manifold vacuum reads fine on my gauge, 25 inch of HG (12psi) sprayed starter fluid everywhere, made no difference.

I checked the purge valve solenoid, and it is holding pressure. 35 ohms, getting 12 V. I guess next step is pull plugs and compression test, cross fingers.

 

Try a can of seafoam in the tank. Make sure less than 10 gallons or so in tank. More concentration. I have had lots of luck with that on several vehicles

you can pull injectors and set up a test for spray pattern but it takes time.

You could also pull coils and look for wetness. Could be rain water or coolant.

Also so I have the maf sensor rubber plug come loose out of intake. Put a zip tie around it. Faulty maf readings cause very poor running.