Using a Smoke Machine - the easy way

[82DMC12]

I've been recommending the use of a smoke machine to find vacuum leaks for a while now, because vacuum leaks cause all sorts of drivability issues in a DeLorean, maybe more so than other cars because of the idle speed management.

There's another thread on here about using a homemade smoke machine and painters tape which is a little bit down the rabbit hole. Here's how to do it EASILY.

1. Buy this smoke machine for $69 (we will see how long that price lasts!) https://www.amazon.com/AutoLine-Pro-Automotive-Detector-Diagnostic/dp/B07JVT1NG2?th=1
2. Buy a 4" rubber cap for PVC such as this one for $6.34 https://www.lowes.com/pd/Fernco-4-in-x-4-in-x-4-in-dia-x-5-in-L-Cap-PVC-Fitting/1000075371
3. Optional - buy some silicone caps so you can cap off the dipstick tube, these are useful for so many other things too - https://www.amazon.com/dp/B08GPJJRY5



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Once you have all the supplies, remove the air box cover so you can see the air meter plate and install the 4" rubber cap over the air meter housing, being careful to square up the cap and make sure it's not tightening over the "fins" on the casting. You should be tightening the clamp over the o-ring on the meter housing.











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Next, remove the oil dipstick and install a well-fitting silicone cap over the tube end. If you don't, you will have some smoke coming out here because the dipstick seal isn't very good.







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Using the breather hose that connects the airbox to the top of the oil filler cap, insert the smoke injection nozzle into the airbox-side of the tube and use a clamp if necessary to keep it in place. If this is your first time using the smoke machine, you might wait until the machine is producing smoke before you insert the nozzle, so you are sure the machine is working first.











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Connect the positive and negative clamps from the smoke machine to the jump start post (positive) and a suitable ground (engine hoist loop) and turn on the smoke machine. After a minute or two, connect the compressed air connection from your air compressor (you do have an air compressor, don't you??) to pressurize the smoke machine tank. After a few seconds you will see smoke coming out wherever there is a vacuum leak. Eventually the smoke has to go SOMEWHERE so you will see small whisps around the cold start plug or throttle shaft seal. These are tiny leaks that have essentially zero effect, but anything else you need to find the source for and repair it.

In this photo you see a small amount of smoke coming out around the CSV but it took well over a minute for it to start to leak. Gross leaks will leak almost immediately. As you run the smoke machine it keeps pressurizing the crank case and eventually it's going to find a way out.

Seal up as much as you can, then you might consider putting the engine back together and getting it hot, then quickly reinstall the smoke machine so you can test it while hot also (since the state of some vacuum switches change when hot).









The air meter is the hardest part to seal off so I've seen people try to use latex gloves and balloons etc but the 4" rubber cap works perfectly and is reusable.

The smoke machine can also be used to check for vacuum leaks going to the mode switch, brake booster, carbon canister, and fuel tank vent leaks!

[Rich]

That's a very good how-to.

As you say, the main issue with smoke testing a PRV is easily and successfully sealing the air intake horn. That and having a decent smoke machine.

Here's a variation on the cap-over-intake-horn approach that's been working well here. (the same cap is also available at Ace Hardware (https://www.acehardware.com/departments/plumbing/pipe-fittings/plastic-fittings/4873303))

Drilling a hole through the rubber pipe cap that seals over the intake horn allows injecting the smoke directly past the air meter plate into the manifold using a conical adapter from the smoker hose. This injects the smoke close to the common intake leak points.

Drill the cap's hole in a non-centered location so the conical adapter won't bottom out on the metering plate brace in the middle of the horn.

Prop the meter plate partially open before clamping the cap into place - a short section of 1/4in (6mm) CLEAN wood dowel placed alongside in front of the metering plate does nicely to allow free flow of smoke past the plate. Use a dowel long enough to reach nearly to the top of the horn. Don't let it fall into the manifold.

Remember to remove the dowel from the intake when done....and don't bend or force the metering plate during this work.

Here's the modified rubber pipe cap and the installed cap with hose+adapter in place:

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PS, no need for comments about what look like original fuel lines in the background. They're not what they look like. Different story.

[82DMC12]

That's a very good how-to.

As you say, the main issue with smoke testing a PRV is easily and successfully sealing the air intake horn. That and having a decent smoke machine.

Here's a variation on the cap-over-intake-horn approach that's been working well here. (the same cap is also available at Ace Hardware (https://www.acehardware.com/departments/plumbing/pipe-fittings/plastic-fittings/4873303))

Drilling a hole through the rubber pipe cap that seals over the intake horn allows injecting the smoke directly past the air meter plate into the manifold using a conical adapter from the smoker hose. This injects the smoke close to the common intake leak points.

Drill the cap's hole in a non-centered location so the conical adapter won't bottom out on the metering plate brace in the middle of the horn.

Prop the meter plate partially open before clamping the cap into place - a short section of 1/4in (6mm) CLEAN wood dowel placed alongside in front of the metering plate does nicely to allow free flow of smoke past the plate. Use a dowel long enough to reach nearly to the top of the horn. Don't let it fall into the manifold.

Remember to remove the dowel from the intake when done....and don't bend or force the metering plate during this work.

Here's the modified rubber pipe cap and the installed cap with hose+adapter in place:

72167 72168

PS, no need for comments about what look like original fuel lines in the background. They're not what they look like. Different story.

Ah, quite clever! It's really amazing how the smoke finds its way everywhere.... and somehow finds a way out. One of these days I'll tinker around with my smoke machine and figure out how to definitely test the evap system. The carbon canister is valved so it might not be quite as simple as pumping it up with smoke. Same with the HVAC system.