Smoke Test on a 1998 Ford Explorer OHV

[CynthiaK]

Hi,
I just did a smoke test on my Explorer searching for a possible vacuum leak.
The only place that smoke escaped was near the knob on the idle air control valve.
Is this the vacuum leak or is it normal for smoke to escape from the valve when the vehicle is not running?
Thank-you in advance.

 

[wollimann]

My mind, no smoke should come out of the breather cap.
Very small ammount of air gets in and out of the cap only to compensate
the movement of the diaphragm, so the valve solenoid has no big resistance.

Never did a smoke test, so i can't say if it's normal.
Maybe someone else has more experience in IAC airflow?

 

[C420sailor]

I believe this is the only place smoke should escape.

You can pop that black “knob” off and plug that nipple if you want (for smoke test purposes).

 

[410Fortune]

Successful smoke test
Some will escape through the iac breather yes

 

[CynthiaK]

Thank-you for the replies!
Smoke was pouring out so I wasn't sure if this was normal or not.
My explorer was revving at 2 at startup and stayed like that for a couple of minutes before droping back down. It is now revving above that.
It was suggested that there could be a vacuum leak so I did the smoke test and only found smoke at the IAC valve.

 

[Blandy]

Hi,ll
I just did a smoke test on my Explorer searching for a possible vacuum leak.
The only place that smoke escaped was near the knob on the idle air control valve.
Is this the vacuum leak or is it normal for smoke to escape from the valve when the vehicle is not running?
Thank-you in advance.

I'm fairly certain that "knob" on the idle air control vents to the atmosphere, BUT a leaking. IAC diaphragm could be the cause. I do know that the intake manifold gaskets have a tendency to leak coolant into the intake passages.

 

[CynthiaK]

I'm fairly certain that "knob" on the idle air control vents to the atmosphere, BUT a leaking. IAC diaphragm could be the cause. I do know that the intake manifold gaskets have a tendency to leak coolant into the intake passages.

Thank-you for the reply!

The intake manifold gasket has been replaced and during the smoke test, there were no other leaks other than behind the knob of the IAC and it was a huge amount of smoke. If it does vent to the atmosphere then I would imagine a huge amount of smoke is OK?

I took off the IAC, cleaned it and put it back in. The truck started fine, revved to about 2250 and then went right back down to about 1500. I shut it off and restarted it and it ROARED to about 2700, stayed there for a while and then finally went back down to normal.

The roaring on start happens quite a lot and it remains roaring for sometimes up to a couple of minutes. When I am driving up hills or doing a cloverleaf, the truck jerks.

I have put injector cleaner in and replaced the fuel cap. The fuel filter and fuel pump were replaced awhile ago too.

There are no codes. My husband discovered spark plug wire #5 had come loose so we tested it and it was OK and then plugged it back in, thinking that was the issue but it is still jerking.

I may just replace the IAC in case the diaphragm is the issue.

Other than the jerking on hills and cloverleaves, the truck runs fine.

 

[J_C]

I'd hook up a scan tool capable of Ford specific codes and live data, and look at long term fuel trims. That'll tell you if it's running lean, then if it is, without any smoke test leaks observed, check fuel pressure on the fuel rail valve (should be high 30's to low 40's PSI) and if okay, clean the MAF sensor and check the live data for temperature sensor readings.