Been running lean now for some time, and getting worried because I can hear some detonation...It also idles very high on initial startup, and slowly drops to normal idling rpm 600-700... I have looked all over the place for a vacuum leak, and cant find anything...I have also changed the fuel filter, and had a fuel injection service done(injector cleaning)..Not sure where else to look...Any help is greatly appreciated....97- 5.4 in an E-250 Cargo van...I know its not the F150 or Lightning, but it is my work truck so a breakdown or engine failure would be a big problem....Thanks

 

might be worth it to bring it in and checked over. It is hard to figure out some problems on a board. I would lean towards a O2 sensor... but who knows? you could throw more money at it by changing different parts than it costs to have it in the shop and replace the right part the first time.

 

Follow the PCV hose from the passenger's side valve cover to the rear of the intake manifold. You can remove the dog house inside the cab and really get a good view of it on an E-van.

 

lean codes are indicating 99% of the time a vacuum leak. Do as Quintin states, follow the PCV and CHECK every piece of that line for cracks and/or breaks. Typically it will be on a bend and the bend will feel mushy. That indicates that the line is crap due to oil soaking and age.

 

Ok...I think I can rule out vac leak....i just checked every vac line that I could find, and found nothing wrong..I also got a can of starting fluid and sprayed every line waiting for an idle spike, and nothing....Any other ideas????

 

It is a hose somewhere. I had the same problem, mech fixed it for nothing. Says it's very common. PM me and I'll give you his number.

 

Spraying starting fluid and listening for a spike in the engine is a waste of time. The computer is too fast to compensate. However, use a good scan tool , ovserve the STFTs in real time, and you'll see the spike in the trims when the enrichment hits the intake stream.

Dual lean codes are NEVER O2 sensors. Forget that.

Possible MAF sensor problem, however, given how common vacuum leaks are, you'd really need to disprove that first.

Steve

 

I had a similar problem on my 99 F250 5.4L reading P0171 & P0174. I found my vacuum leak on the elbow at the end of the hose leading from the PCV valve to the back of the engine. You can't even see where it connects to the back of the intake manifold but I could feel it. I pulled it out and the rubber elbow on the end of that hose had completed disintegrated. My neighborhood Ford house was kind enough to sell me a new PCV valve and associated hoses for $51. Unfortunately, you must buy the entire thing. Now I don't have CEL or any codes but still misses intermittently. Does anyone think this might be a CoPs problem? I've cleaned the MAF sensor and replaced my fuel and air filters.

 

I'm having the same problem. My 04 5.4 is throwing the 171 and 174 codes which is both banks lean. I just cleaned the mass air sensor (used the CRC Mass Air Flow Sensor cleaner - just contact cleaner really) and changed the fuel filter. It seems the problem is a little better, but it still gets rough if I let it sit and idle and it eventually will quit running. Very frustrating when sitting in traffic and it decides to quit right when the flippin light turns green. I don't notice any problems with acceleration (maybe a little pinging if I really get my foot into it) and my mileage hasn't changed. Seems like a fuel pressure issue in that if it sits at low idle for a few min. the idle degrades until it finally quits - running out of fuel? Vacuum lines are ok as far as I can tell - I'm sure I can't get my eyes or fingers on every single inch. Could the Mass Air simply be malfunctioning and not pulling enough fuel flow? Is there a way to check it?

 

I will be searching through this SAME problem tomorrow. I will clean my MAF and search through the lines and take pictures of what I find.

 

The PCV hose elbow is available separately. Someone just posted a photo of it and its package late last week.

Steve

 

Yea, I think your talking about this one Steve -

 

have u been listening to dem franchize boys lately. ???

 

Jbrew, that's the elbow I needed. As I said, I purchased the entire assembly but oh well, I'm sure on my 9 year old truck I needed to replace the other hoses and elbows as well.

I cannot figure out this intermittent miss. No codes, but it will idle rough and miss at all speeds then the next time it idles smoothly and runs good for a while... then starts to miss again. Now that I've cleaned the MAF and replaced the fuel filter do I need to reset the PCM??

Also, like TexasPsyclone asked... is there any way to make sure the MAF is working???

 

Sounds like COP's to me . Get on it , Floor it !! WFO .. She'll prolly cough up a code , most likely get a blinking Check Engine Light. Then you can get it read to see which cylinder is giving you trouble.

I wouldn't hesitate and change all the COP's if they were the originals in your 99..

http://cgi.ebay.com/ebaymotors/NEW-I...mZ160111254456

I doubt it's the MAF unless you broke the wire - You would have a check engine light blinding you if you did..

No lean codes and it's been cleaned , most likely fine. Unplug it, start it up to see if it's working , you'll get a light. The best way is by the book I guess volts/power to and resistance. I don't have those numbers in front of me.

You say it misses during Idle ? Try to tie your wiring harness further away from your AC accumulator. If this stops the missing at idle , drive it and test. This has been a problem in the past . I suggest that first , if that doesn't help then replace COP's and use Motorcraft plugs if you change those..