anyone try smoke test to find vacum leak?
 

My car suddenly started running lean after a wide open throttle run on the highway. been trying to locate a vacuum leak. I have pressure tested the car but can't find an leaks. I was thinking of bring the car to a local shop that I know does do smoke testing. Has anyone been successful going this route in finding a leak?

I bought a 'smokenator' from Speed Force Racing (I think is was SFR) quite a few years ago, which uses a cigarette to generate the smoke. I've used it to find intake leaks in the past. I don't think they sell them anymore, and the problem with it is the cigarette (smoke) doesn't last very long.

I've been trying to find a 'small evaporative emissions leak' on another car, so went ahead and bought a smoke tester off EBay for ~$100. The EBay tester uses mineral oil and hooks up to your car battery and air compressor. It works pretty good, but you have to be careful the wick stays saturated with the mineral oil or you burn the wick up. The local shops all want $150~$200 to do a smoke test so it was worth the $100 investment to me to get one of my own. Next time I do a check on the 951 I will be using this.

I thought those detectors go for way more than that. just bought one off ebay. Place I was going to bring it to has a $105/hour shop rate. buy my own $95 free shipping.

Just went through this a few week ago . Shop i go to found the leak after 2 smoke tests(split throttle body coupler from intercooler .crack was so fine you could hardly see it(length wise )and would only blow open under boost....

I usually pressure test

To identify vacuum leaks, I usually just spray some carb cleaner on the suspect areas. A leak will increase idle speed, immediately. Leaks on the boost side, before the throttle plate, are not as responsive to carb cleaner, with MAF. Create a known leak, and test.

did both pressure tests and spraying starting fluid. no luck.

very frustrating.

I do not think you have a vac leak. There are other reasons for lean operation. Have you looked at the plugs? You can have a bad injector. Or bad ground to the injectors. One thing you can try is a cylinder RPM drop test at idle. Pop the injector connector off one cylinder at a time, and look for equal RPM drop.

when did you last replace the fuel filter?

I built a smoke machine for $35 or so. $8 air regulator at Harbor Freight, some fittings, some hose, a paint can. Some plans call for a DC dimmer switch but I skipped that, got the right gauge nichrome wire to set it for like 100w of heat dissipation or so. It's enough to burn off the babyoil but not start a fire.

Use Ohm's law to calculate heat dissipation based on resistance and then connect it to your battery. Easy Peasy.

what will looking at the plugs tell me regarding running lean?

I cleaned all the grounds except for the ones under the dash a month ago.

not sure but I want to say 20k miles ago. fuel pressure is 40 # on the rail at idle and 45 when revved (3 bar fpr).

The plugs will show you if the lean condition is for all cylinders, back to gas supply; filter, pump ect. Gas pressure in the driveway, tells very little about gas pressure and flow under load. Have you inspected the gas lines? Got one that is crushed? How about 25 year old rubber lines?

Variation in the plugs color will show you have an injector issue, for the individual cylinder. The injectors do have a final filter/screen in each injector.

Did you spray the carb cleaner around each intake to cyl gasket? I chased a poor idle for some time, before I checked for a leak at the gasket. The gasket had split.

a previous pressure test last month showed a leaking intake gasket. just replaced with all new gaskets. no more leak there.

I got one of those too and hated it. The cigarette burned out too fast, and left ashes in the intake, and the motor smelled like a smoker for week...:surr:

Cheap ebay disco smoke machine?

Found a cheap smoke machine on Ebay for $50. It's a VW diesel...

Have you tried cleaning the MAF? The oiled filter elements tend to get the MAF dirty...

Also, how old is the O2 sensor? Even though the DME doesn't read it at WOT, it still affects cruise readings.

maf is brand new earlier this year. came with dry filter. New O2 sensor a few months ago . Didn't fix issue.

Worth more than some cars :)

http://redlinedetection.com/

How about the FQS setting? Which MAF do you have? I tried running a M-Tune on the fourth setting and it ran so lean while cruising that it started jerking (16-17:1). It smoothed out on the first setting.

Does it run super rich as soon as you get into boost, or is it still lean?

Once, I had a 944 that really leaned out after 30 minutes of driving. I'd pull into the garage the next morning, check the fuel pressure, and it was perfect. After blowing a headgasket, I left the fuel gauge on the car and walked away with the car running. I couldn't believe that the pressure dropped to 15 psi.... A new fuel pump solved the issue.

well, I am happy but confundled a bit. couldn't find any leaks with the smoke detector. I pulled a separate vacuum line to see if smoke would pour out and it did. was disappointed to not find anything. decided to move the fqs from stock to position #1 which ads 3% fuel. Car idles wonderfully with 14.7 dithering afr and everything is good. don't understand how everything went bad after a first time WOT run since putting the new maf. happy boy though.. I think I will keep her.

let me retract my previous post regard happy boy. with FQS at #1 I am hitting afr of 11's at 5psi and into 10's at 15psi. not good.

I disconnected each injector clip one at a time when the car was running and the idle change when disconnecting each injector. Just used a pyrometer on each of the exhaust manifold flanges and the one closest to front of car was near 100 degrees cooler than the rest while the car was idling while warmed up.

That's a big delta in temps. That's where I would start. You want to determine why #1 is cooler. Try the followings, till you figure out the cause:

- swap injectors between #1 and and any other cyl. See if cooler temps follow injector.
- swap spark plugs.
- try a different plug wire on #1
- this may be tough, see if you can swap injector connector between #1 & #2.
- may be a good idea to look at your distributor...

Have you checked the o ring on the throttle screw on top of the throttle body?

sounds about like the direction I am going in John. Just swapped #1 and #2 injectors. will see what results I have tomorrow.

Did all this except cutting and swapping the injector connector. #1 is still much less hot. looking at the distributor cap the contacts 2,3,and 4 all look the same and #1 does look a bit different, but other than that there are no cracks or broken bits. same goes for the rotor.