Using a smoke machine to detect vacuum/intake leak?

[Jm2576]

I have a p0171 and p0174 code and want to use a smoke machine to check for vacuum leaks. Where is the best hose to connect to for best results? I don't have a vacuum hose diagram handy. Can a smoke machine detect a leak on the intake manifold? I haven't used one before. Thanks.

My truck is a:
2000 Mazda B4000 4.0

 

[RonD]

Warm up engine first
Let it idle
Unplug 2 wire connector on IAC Valve
If idle drops or engine stalls you do NOT have a vacuum leak
If idle doesn't drop then you may have

Engine off
Unhook power brake booster's vacuum hose, at the booster end, use that to inject smoke into the intake

If idle dropped, so no vacuum issues
Change O2 sensors FIRST, they are the only sensors to wear out after 12 years or 100k miles
Clean MAF sensor
Test fuel pressure if possible, if not change fuel filter

 

[Jm2576]

How many O2 sensors are there for a 2000 Mazda B4000? I tried looking them up but I'm getting mixed results.

 

[RonD]

3 O2's

Should be similar to this picture:

http://imgur.com/wCatTvN

Grey wires come from O2s

2 upstream O2s one on each exhaust pipe near exhaust manifold
1 downstream O2 after Cat converters

They are all the same type/model of O2s, just different length wires attached, but you can use 3 with same length wires as long as that length is long enough to use at all 3 locations

 

[Jm2576]

That is a very helpful photo. Thanks!

Would a bad o2 sensor throw a different code other than a P0171/P0174? Also, is there a way to test them with a volt meter or something? My truck has over 200,000 miles so I'm sure they are way past due, but I don't want to replace them unless I need to.

I still need to check a few other items first but these are on my list.

 

[RonD]

You need to, they start costing you MORE money after 100k miles or 12 years

O2 sensors generate their own voltage
0.1volt, high oxygen, "lean"
0.9volt low oxygen, "rich"

O2s use a baked on chemical to detect oxygen in the exhaust and that reaction generates the voltage, 0.1v to 0.9v
As time or exhaust flows by, the chemical gets used up
When that starts to happen voltage will, of course, start to go down

Lean and rich are not from the O2 sensors and don't mean engine is actually running lean or running rich

Computer ONLY has the upstream O2 sensors to "see" if the air/fuel mix is OK

Computer calculates OPEN TIME for each fuel injector based on engine size, RPMs, throttle position and air weight(MAF sensor)
It then looks at O2 voltage to see if that OPEN TIME has 0.45volt, good burn
If its lower voltage, "lean", then computer opens injectors a bit longer
This is where it costs you money, its a FALSE lean
As the chemical runs out the voltage goes down bit by bit, so computer adds MORE FUEL than needed so.................MPG goes down bit by bit

The computer will set a code if its calculation is off by more that 20%
Or if O2s are not changing voltage very much
But lean codes are first

And it could be something else causing lean codes but you can chase your tail around looking for a FALSE lean because O2s are old
If O2s are newer then you check other causes
Changing the older O2s will for sure get you better MPG if they are over 100k or 12 years old, so not a waste of money

 

[Jm2576]

At 23 years old and 200,000 miles I am way past their life expectancy so I am definitely going to replace them. Do you have a part number or know of a good brand or link to a website to order them? Thanks.

 

[RonD]

Google: 2000 ford ranger 4.0l O2 sensor 3 pack

Those will be the best deals

Bosch brand is what Ford used in Ranger, they cost a bit more
See what local auto parts places have in stock, they are very common models and connectors

 

[Jm2576]

I wanted to post an update to this in case anyone else is having this issue.

I replaced all of the O2 sensors. I sprayed penetrating oil on them a few days before I replaced them. After a few days I crawled below to crack them loose. They came out pretty easy after several days of soaking. For the two in the front, I removed the sensor from below, but pulled them out of the top since that's where the wire clips are located. Driver side clip was kind of hidden behind the engine block but it was secured, so I just had to squeeze and pull to unplug it. The passenger side was easy to find. The clip on the third one below was just a foot or so upstream but had a longer wire.

I also replaced the IAC valve as I was also having an idle issue. The truck runs much better now. I manually cleared the two codes and I am waiting to see if it comes back, but it might take a while since I only drive it once every couple of weeks or a month.

SMOKE MACHINE RESULTS:
I decided to hook up the smoke machine anyway just to practice using it. A lot of smoke came out of the IAC knob, but I think that is some kind of vent or air breather (not sure let me know if I'm wrong). After several more minutes smoke came out of the air filter box too. I thought this might be normal since that's where air would come in from. Is the throttle is supposed to be air tight or shut?

I was about to disconnect everything when I did see a tiny bit of smoke coming from the manifold area. Sort up high where the fuel pressure connection is. Right below the big black plastic housing thing (intake?). It was really slight, so I imagine I have a small intake leak. This might be what was throwing the codes as I've repaired almost everything else on the list. I will post an update to see if the codes come back but I assume I will need to replace the intake gaskets. Maybe the intake itself since its plastic? I haven't done much research on this yet.

Thanks to everyone else for the help and info.

 

[sgtsandman]

I believe you are correct on the IAC. The throttle body plate does not seal. Some are is always allowed to come through. It just regulates how much comes through as the engine demands change.

It sounds like you found the leak but you can plug the intake with a rag and baggie the IAC if you want to make absolutely sure on the manifold leak and see if there is any others.