97 f150 mt/ac 2wd 4.2, 102k miles

Started losing hp, no miss, cel on with po 1537/1538.
Repaired vacuum line to IMRC from IMRC solenoid, code cleared without a return. No other codes present.
Slight popping through intake with heavy acceleration, still no hp.
MAF, IAC, DPFE values average and within range with scan tool datastream.

Fuel pressure 35psi static, 40 psi at idle, new fuel filter.
Engine vacuum at idle 18"hg, upon acceleration vacuum drops to zero then reads about 2 psi positive pressure. So I thought the cats were plugged, replaced all with new. Still no jive, truck is still running sluggish and will barely reach 45 mph
Fogged evap system for leaks, none found. Sprayed everywhere with carb cleaner, no leaks found.

Im leaning towards a valve timing issue now but have read through the forums for days now and see that the timing set is not a common issue.

Seems like a lot of knowledgeable guys on here so does anyone have anythoughts, maybe something im overlooking.

 

You mentioned a popping noise paired with slow acceleration and that to me sounds like maybe the coil pack is bad. Has the coil pack been replaced with in that 102K miles? Seems very common that it goes bad in the 4.2 V6 around 80k miles, mine did. If it hasn't I'd try that and replace the plugs and wires while you're in there.

 

Just finished up plugs and wires, motorcraft.
Swapped coil pack with known good off wifes truck.

No luck.

 

Argh that sucks. Thought for sure that would have been your issue since you haven't had any luck finding a vacuum leak. Hopefully someone with more experience will give you some more ideas to check. From my experience, I'd say keep looking for a leak. Around the same time I did my coil pack and all, I also had to do the upper and lower intake gaskets, plus the plenum isolator bolts and the PCV elbow back near the firewall. I got all the parts from Ford and she's been running strong ever since. My truck also acted exactly what you are explaining in your first post. I think my codes at the time were the P0174, etc. Good luck man.

 

When you changed the cats out were they broken up inside? I've had them cork up the muffler when they go. Does the vac gage still show a positive pressure when you are on it?

The only other thing I can think of would be to check the air intake, maybe sucked something up where it comes in through the fender, take the whole thing apart. It's a long shot........but maybe!

But it does sound like a back pressure problem. How is the exhaust flow at the tail pipe?

 

I thought the muffler was probably stopped up too, so I cut it loose n run with the open pipe. Flow from exhaust is good. Already checked the inlet duct for obstruction n found nothing vacuum still going into the + on acceleration. Im stumped n ready to send her to the big Ford junkyard to the west.

 

Bummer!

 

Could it be your fuel filter?

 

any lifter noise? PCV valve good? o2 sensors flipping correctly? I have seen bad o2s cause a similar prob without setting a code.

 

O2 crosscounts well within range, heater test ok, resistance test ok on all o2's.
No lifter noise with just an ear, hav'nt listened around the engine with a stethoscope. New PVC and elbow just to be on the safeside

 

Well I bit the bullet and tore down the timing cover and found the chain had jumped and timing was retarded by one tooth on the cam gear. replaced the timing set and now shes running like a champ again.

 

Don't you just want to kick yourself in the butt sometimes? ha ha

Glad you got it.

 

Congratulations! or should it be I'm sorry?
I'm just glad you fixed the problem.
That just made your Month, didn't it?