I bought 98’ 4.2. I’ve replaced 3 calipers, 2 brake hoses, passenger front rotor, bearings, ball joint, both sway bar linkages, both side bearings. All this I believe was caused by a vacuum problem. I realized this when I started loosing power, one day I had to turn back down a hill because it wasn’t going to make it up it.

So so when I got the truck it ran rough and loud, noise on top of the cut off exhaust! I replaced plugs, wires, fuel filter, oil and filter, air filter.

While I’ve been chasing this cause ive replaced exhaust manifold and gasket, EGR. EGR solenoid, purge valve, fuel regulator, pvc valve and gasket, hose and gasket on the throttle body line and air intake for purge valve.

Now with all of this it it seems like the more things I replaced the worse it got. It now causes so much pressure I’ve actually turned my key off going down hill trying to release pressure and the engine continued to crank. Forces my gas gage down to E.

I’ve been told to just get rid of it, but I’m invested now. Unfortunately the handful of things it could be aren’t cheap and I’m not going to just keep randomly buying those parts. Does anyone have any ideas? I think one of my charcoal canisters is bad, I just unhooked it and this allowed little longer run time before pressure got too bad.

Here’s behind engine passenger side. And the tank air vent and pump. Not sure these will help I’m any advice.

 

Codes? Have you checked the fuel pressure? Have you checked engine compression?

 

Haven’t checked engine compression. Have a few codes.

I changed the fuel regulator. How would I check the fuel pressure?

 

With a fuel pressure gauge. There's a Schrader valve on the fuel rail.

 

What should pressure be?

 

Minimum 28, maximum 40. If you pull the vacuum hose off the FPR, it should go up 5 to 10.

 

One with 3 hoses is behind the intake manifold passenger side. The other is on top of the gas tank beside the fuel pump. I looked up a diagram and it says tank vent valve at end of tank and a vapor vent valve! But I asked Ford dealership when I got the tank vent valve and he said his diagram didn’t have another valve. Just a pressure sensor. So I have a feeling it’s one of the two causing the problems!

 

A lot of those are o2 sensor codes. What was cut off your exhaust?

 

Truck no longer surges but still has no power. Actually seems to lose power after warm up. Ordered a new charcoal canister and fresh air valve. And 2 o2 censors for the upstream on exhaust! Don’t want the downstream until I can do the exhaust, but don’t want to do that unless I can get it running close to properly! Any ideas on the power problem? Maybe MAF censor?

 

Your ignoring the codes and just guessing
Look at the codes, pick out codes 171 and 174. These tell you there is/are Vacuum leaks.
Code 1506 appear twice. An intake air control issue.
Code 141 appears twice. Fix the harness wiring to these sensors.
The rest will clear when you fix these issues.

 

STOP throwing parts at it! You're wasting your time and money. Do as Roadie and GLC said and check the fuel pressure, Then start troubleshooting the vacuum leaks. The one part that I would change, if you haven't, is the fuel filter. I'm sure that it's overdue. Have you replaced the missing exhaust system? If not I then I would do that, the open pipes could be upsetting the O2 sensors and if you're committed to fixing the truck, then you'll have to fix that sooner of later so you may as well do it now.

The charcoal canister is only for emmissions control when the truck isn't running. It has no effect on how the truck runs, except perhaps if it has a vacuum leak.

Check all of the hoses on the engine carefully, there's a very good chance that you're going to find one or probably several that are leaking. Also get a diagram of where all the hoses connect, With everything that's been done to that engine, there's a good chance that some are missing or not connected to the right devices.

Clean the MAF sensor if you haven't.

Look on Youtube for one of the videos about how to test for vacuum leaks by spraying all of the engine hoses with carburator cleaner. Do that but only after visually checking as many of them as you can and replacing any bad ones.

I think that among other things, that you're losing fuel pressure under load, probably due to severe vacuum leaks. When the engine is under load, the FPR increases the fuel pressure but I think that due to the vacuum leaks, that's not happening. Also when the engine is cold, the system adds extra fuel to make it runs smoother. But after it warms up, it shuts off the added fuel. I think that that's why your engine is running worse after it warms up.