Goofy question about smoke testing for vacuum leaks.

[Juanhmi]

So, I got the Amazon smoke machine to test for vacuum leaks, hunting for the source of my lean running codes. I'm an amateur mechanic and I've done a lot on this old thing, but there's still a lot that's new to me. So I plugged the smoke machine into the brake booster line and the only places I see smoke coming out are the IAC, EGR, and the air scoop near the radiator, and a little out of the air filter box. This was with the engine off. Should I see smoke on the idle air control valve and the exhaust gas recirculation doodad or do those two things need attention?

It's worth noting I just did the upper and lower intake gaskets and thankfully I didn't see any leaks from those.

 

[J_C]

I don't know if smoke can come out the IAC "vent/filter" (see attached diagram) but it should not come out the base "air flow inlet"/"air flow outlet" area where the gasket is.

Smoke should not come out the EGR, if coming out breather holes those are to let the diaphragm inside move and most likely means that diaphragm is cracked.

You are supposed to block off the air intake snorkel before the MAF sensor, (like put a plastic bag over it secured with a strap or rubber band, or at least stuff a dense piece of clothing or towel in, whatever to impede the smoke coming out there) that allows to test intake snorkel leakage of unmetered air after the MAF, and cause far more smoke to go everywhere else.

If smoke is coming out on the filtered side of the air filter box, you should try to seal that so it isn't letting unfiltered air in. If coming out the pre-filtered side, that's nothing to worry about. Either way it is not the source of a vac problem since it is upstream of the MAF sensor.

I assume you have reason to believe you have a vac leak? If you haven't yet, be sure to clean the MAF sensor, as a dirty one can fail to measure how much air as is coming in, could cause same issues as a vac leak.

 

[Juanhmi]

I hadn't thought of blocking off the air intake so smoke can find its way into more places. Good tip.

I've been through it on this rig with lean codes. The upper and lower intake gasket was probably one of the bigger jobs I've attempted and it went well but didn't solve it. I've got new O2 sensors ready to go in, which should be done anyway, but I doubt that's what's going on. If I cold start the vehicle, fuel trims are good (below 5%) but once I warm everything up, and especially on a hot day, they approach the 25% mark which throws lean codes on both banks.

I'm just making sure I really thoroughly diagnose the vacuum tree before moving any further (the MAF is a new Delphi unit and clean), but I think my fuel pump is getting weak, causing the computer to try and throw more fuel at the engine. Today after a drive in hot weather, I checked the fuel pump relay for corrosion and it looked okay, but it was too hot to touch which I think suggests a high power draw/i.e. the pump struggling. Plus lately, on hot days, it's taken a lot of cranks to start the engine. Haven't measured fuel pressure at the rail while the engine is hot yet but will soon. It's low 40s on a cold start.

I've DIY'ed just about everything to this truck, but to be honest working on fuel systems scares me, so if it needs a pump I'm going to have someone do it. Just want to make sure there's not some 49 cent vacuum leak going on first! But at almost 250k miles, and with all the other stuff I've seen that seems original to 1999 Motorcraft, I bet it's the original fuel pump and it's time for it.

The other thing I haven't messed with is the EVAP system. It comes up "not ready" on a scan so I want to figure that out.

It's funny... I've relied on this old thing for a long time, but I had a conversation at a dealership the other day about new vehicles and there's no way I'm going to financially handle a new, or even used truck. The market is absurd. Gotta keep her on the road!

 

[J_C]

The contacts in the relay could be bad, would be ideal to measure the current draw with a clamp ammeter but I don't know what the right current is! Fuel pressure you can measure with a loaner tool from Autozone, or Advance Auto, etc. I don't know about the '99 OHV, did it keep the old OHV, dual/return fuel line setup? If so then fuel pressure should be upper 30's to mid 40's PSI. If there is no return fuel line then closer to 60PSI.

I'd also use a scan tool to check the reported temperatures, a bad temp sensor data can screw up the air:fuel ratio.

Evap system, you can just unplug the vac line to anything and plug where it connected to the intake to see if this fixes the fuel trims. Similarly if the EGR might be leaking, I'd try that first. Then again there might be an EVAP vac sensor and this trips a trouble code same as if your gas cap was off.

 

[Juanhmi]

Good advice on the evap for sure, I'm going to get after that first. I've done the temp sensor, and taken fuel pressure readings at least on cold start - looking at 42 psi or so, and I think with the year there's no return system so I ought to be seeing closer to 60. I think that fuel pump is getting sad when it gets warm.

The thing about a vacuum leak being an issue to me is, all the climate vents work perfectly and are pretty responsive to changes on the dial. I know that's one of the first things to go when vacuum goes haywire on these Fords.

I ordered a new relay for the fuel pump, easy ten bucks, the old one said Ford on it so I assume it's over twenty years old. The contacts did look a little crumbly.

 

[EB4X]

I didn't read through long posts / response but it is normal for smoke to come out of the IAC during test...

 

[Runnin'OnEmpty]

Juan, There's a hose running between the throttle body and an EVAP purge solenoid
located in the area below the battery tray. These hoses deteriorate very quickly (because of heat)
and will cause unmetered air to enter the throttle body, if they are cracked or broken.

The hose is easy to trace once you've located it. It's attached on the underside of the TB and
runs below the A/C compressor to the EVAP valve. It will turn your hand sooty black when
you touch it...

 

[410Fortune]

my guess is weak fuel pump, hot relay, lean both banks, good vacuum and smoke tests

Check fuel pressure

Ford P0171 & P0174 Lean Codes

A weak or failing pump will work good when cold, then fail to deliver fuel quickly as they heat up

 

[Juanhmi]

I think fuel pump is imminent. Actually had a start where I had to crank it 6-7 times yesterday, that’s never happened before.

 

[Juanhmi]

Update on this whole situation... Explorer has been at the shop two days for a fuel pump. Just really didn't feel like doing it myself. Yesterday they dropped the tank and got the pump and sender in just fine, told me it'd be ready in the morning, they received a defective filter and had to order another one.

Today they called and said when they went to install the filter, the line from the filter to the pump was pretty much disintegrated inside. Guess that was probably part of my issue to begin with. They said that line is absurdly hard to find new and they'd get back to me. Said they'd cut the labor in half on dropping the tank again to replace it, which I assume you'd have to do. A bit worried my vehicle is gonna be in parts jail for awhile. Anyone run into similar problems?

Seems like an honest shop so far and it's 5 minutes walking distance from my house. I'm sure they're having a tough time sourcing parts like everyone else...

At least the fun part is I get to commute in the old farm truck for awhile.