I need help diagnosing a major problem.

I need help diagnosing a major problem, 4.0 SOHC

About two weeks ago I bought a 2003 Explorer with a 4.0L SOHC. I recently planned on doing my usual thing of fresh fluids, filters, plugs, and anything else it needed. So, after finally getting a couple days off, I decide to replace the valve cover gaskets due to a minor leak. So, first I decide to add some Seafoam to the engine, about a half a can to the oil and a half can through the brake booster. I've used that stuff on dozens of vehicles with pretty respectable results.

After running it and it smoking a bit as the Seafoam does, I let it cool down and started disassembling to get to the valve covers. After relaxing with a few beers and taking my time, I put new valve cover gaskets, intake manifold gaskets, throttle body gasket, new spark plugs, wires, air filter and thoroughly cleaned everything. Before changing the oil/filter, I figured I'd start it up just to make sure everything was good. Well, it wasn't.

It'll start and idle, but the second I tap the throttle it dies. A vacuum gauge reads a steady 8, indicating a likely vacuum leak. So, I triple check all connections and everything looks good. I sprayed starting fluid, everywhere, and no increase in RPM. I do hear a high pitch noise from somewhere around the throttle body/back of the engine. But do not see or feel anything wrong.

So. I decided to go get myself a big fat cigar, despite me not being a smoker. I puff as much smoke into the intake (through a hose where the brake booster goes on the intake) and am getting a small amount of smoke rising up somewhere around the throttle body.

I took the intake off again to check to see if an intake gasket was my problem, seemed good to go, checked everything around it, and reinstalled it. Annnnnd still the same problem.

I am not throwing any codes, at least in the few minutes I've let it idle. I took off all the vacuum lines and checked them for cracks and integrity, they are all good to go.


So my ultimate question is this: what the hell could be leaking so bad to make it lose so much vacuum and run so poorly? What am I forgetting? Could the Seafoam have messed something else up? Why am I not throwing a code?

Any ideas guys?

Go back over each component you removed, its likely you have a gasket thats pinched or deformed, allowing unmetered air into the engine. If you removed the throttle body from the upper intake plenum, check the O ring gasket there. You can also use the smoke trick on the outside of the intake rather than the inside....


SVT

RangerSVT said:

Go back over each component you removed, its likely you have a gasket thats pinched or deformed, allowing unmetered air into the engine. If you removed the throttle body from the upper intake plenum, check the O ring gasket there. You can also use the smoke trick on the outside of the intake rather than the inside....


SVT

Click to expand...

I suspect that being my problem. I have removed the intake three times now, meticulously reinstalling it being careful not to shift it. It has new gaskets along with a new tb gasket. I tried blowing cigar smoke on the outside while it's running but the engine fan diffuses the smoke too fast. Blowing it on the inside, it seems like the smoke is coming from the throttle body, wear the return spring is at, and the throttle position sensor, or possible the egr since they're right nest to eachother. It doesn't seem to be coming from the intake gaskets. At least not that I can see. I'll look at it more this evening when I get off work. Thank you for the ideas SVT!

Vacuum gauge showing 8" means a big leak, should be 15-17".

I would remove PCV line from intake and plug hole, start engine then see what vacuum is.
The newer engines run based on a sealed crankcase, even dipstick not being all the way in can cause "vacuum leak" symptoms.

Do the same for brake booster hose, and any other larger vacuum hoses

Checked PCV

Checked EGR

Checked IACV

Checked all vacuum lines.

New battery, mainly since the old one stopped taking a charge.

I am starting to really consider the possibility that there is a blockage in the exhaust, like a meltdown of my cats from the Seafoam. It'd explain the low vacuum, plus, after I first ran it and it threw a code, I attempted driving it to O'Reilly's to have the code pulled. It completely died on me on the way up there. Then, my battery died and the computer reset. So it, for a short period of time, ran good enough to get about a mile...

Thoughts?

Its possible the cats are clogged. You'll need to pull them to find out...

SVT

Just put your hand over the tail pipe and have some one rev the engine, you should feel if exhaust is clogged.

Pull the O2 sensors out, upsteam ones, lol, if it runs better then yes exhaust is clogged.

Blipping the throttle with vacuum gauge hooked up should get a drop to 0 then back up, if it only drops to 2 or 3 then exhaust is clogged

Thank you! It was the exhaust!

Catalytic converter melted down. Diagnosed by taking out up stream oxygen sensors, as soon as I did, my vacuum jumped up to 17, which isn't perfect, but I wouldn't expect it to be just from breathing through a small in the exhaust. The engine will run and rev now with the o2 removed. I ordered new cats today, I actually ordered magnaflow just because I trusted there quality over Walkers and the Magnaflow's were only $25 more. Anyone have any experience with the magnaflow cats?