Diagnosing a vacuum leak - LotusTalk - The Lotus Cars Community
 
LotusTalk.com is the premier Lotus Forum on the internet. Registered Users do not see the above ads.
Reply
 
LinkBack Thread Tools Display Modes
Old 01-21-2009, 12:12 PM   #1 (permalink)
OSX Black hat
 
charliex's Avatar
 
Join Date: Feb 2005
Location: Las Vegas , NV
Posts: 10,000
Diagnosing a vacuum leak

Vacuum leaks are a very common problem on cars, they're sometimes tough to find, so here are some tips.

First off lets go over the simple bits

Rough idle, lots of causes, dirty/bad maf , airflow, dirty/bad throttle body, bad fuel, bad 02 sensors, exhaust leaks, bad spark plugs, wrong gap, bad injectors.

High idle, air's usually getting somewhere it isn't supposed too, bad throttle body, bad iac , intake leakes, injector leaks.

Stalling or misfire on acceleration, bad spark plugs, big leak, coil problems.

there are lots of things that cause it, even more than i've listed but those are the common ones, the most common are maf sensor,iac, throttle body and leaks.

for the idle problem leaks are the easiest to check for,

1. Get an OBD II reader that can show you the short term fuel trims (STFT) in realtime, ie it has to be able to show it updating, not just a code reader.

2. Read the STFT normal range is -4 +4 but can be as much as 8.

3. If the STFT reads over 8, a lot, and swings around this is the first sign.

4. Raise the idle by increasing the throttle to 1500/2000 RPM, check the STFT's again, if they're back in the normal range , its very likely its a small leak. Give the engine time to sort itself out after raising the speed, its not super fast to react.

5. If its still reading in double figures and swinging around, time to take a look at the MAF, IAC and TB.

We're assuming the O2 sensors are working here, and there are no obvious issues, the primary O2 sensor is very important to make sure its all running right.

Small vacuum leaks only tend to affect the idle because of the relatively small volume of air passing, when the engine speed is raised, the air increases enough so a small leak doesn't make much of a difference.


Spraying the engine bay with non residue leaving contact or maf cleaner is good way of finding leaks, but they can be tough and expect to use a case of cans for the tough ones, make sure its well ventilated area, i do not recommend use of carb cleaner, you might damage the engine.

A hosepipe with a very small stream of water is also a good way to pinpoint small leaks, just be careful of the electronics.

Spray one part at a time, give it some time to settle in, if you hear a change, wait for it to clear out and try it a few more times, eventually you ought to be able to cause the engine speed to change or stall on demand.

Any tubes, o rings, gaskets etc are targets, the pipes on the IC, the throttle body are the typical suspects.


The long term fuel trims are also valuable to look at, large positive values in here, double figures, show a problem in manifold leaks, misfires and fuel pressure , injectors ( the car is running lean, so the computer is adding a lot of fuel )

Negative numbers means the car is running richer than its supposed too, large numbers in the LTFT mean that the computer is subtracting large amounts of fuel to maintain where it wants to be, this suggests fuel pressure problems, defective injector, air blockages, you'll be looking for largish STFT and LTFT for big problems.

The computer will throw a code after about 17%, this isn't to be ignored it means somethings up.

So large positive value STFT and/or LTFT means its adding fuel because of a lean condition, not enough fuel or too much air is being delivered.

Large negative values mean too much fuel is being delivered, or not enough air.

I'll add more stuff to this thread including traces of some of the sensors and so on so you have reference to them,but you will need something capable of viewing a trace, so an oscilloscope or good OBDII reader that can graph stuff out, scopes are very useful and not that complicated, don't be put off by their apparent complexity, you can get them cheap off fleabay or new ones at $150+ but the money is in the accessories, i'll go into that later..

cheers.
__________________
Black Exige S / Elan M100. Don't run a smaller pulley without an upgraded fuel pump! http://www.goth.am ecu stuff.. New reflash box coming soon!
charliex is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 01-21-2009, 12:51 PM   #2 (permalink)
*
 
shay2nak's Avatar
 
Join Date: Dec 2003
Location: Calipornia
Posts: 22,064
do you remember what my fuel trims looked like?
__________________
** save ~10 lbs gain 1 hp ** EQ: Y=(190*X) / (1984-X) where Y is (HP) and X is (lbs)

'07 Lotus Exige S310


WTC 2
shay2nak is offline   Reply With Quote
Old 01-21-2009, 01:00 PM   #3 (permalink)
Registered User
 
Mr. Oz's Avatar
 
Join Date: Oct 2005
Posts: 324
One of these Smoke machine leak detector, leak locator, leak finder evap leak tester makes it very easy to pinpoint a suspected leak. I use one of these even for oil and coolant leaks.
__________________
Dan
08 2-Eleven Launch Edition

You must be fast cause you were haulin azz when I passed you!!
Mr. Oz is offline   Reply With Quote
Old 01-21-2009, 01:08 PM   #4 (permalink)
OSX Black hat
 
charliex's Avatar
 
Join Date: Feb 2005
Location: Las Vegas , NV
Posts: 10,000
Ara, %20ish
Mr oz, yep those are coming up!
__________________
Black Exige S / Elan M100. Don't run a smaller pulley without an upgraded fuel pump! http://www.goth.am ecu stuff.. New reflash box coming soon!
charliex is offline   Reply With Quote
Old 01-21-2009, 01:17 PM   #5 (permalink)
Registered User
 
codymac's Avatar
 
Join Date: Nov 2005
Location: where the east tapers out and the west begins
Posts: 9,293
Images: 19
Am I the only one that's used propane?


Comes from my two stroke background where an air leak = instant engine death.
__________________
torque (trk) n. - an excuse for the lack of momentum.
- let's bring back CanAm & Group B!
- have you hugged your Exige today?
I'm currently working on my performance driving merit badge.
There's always somebody faster, sometimes it's me.
codymac is offline   Reply With Quote
Old 01-21-2009, 01:18 PM   #6 (permalink)
Moderator Extraordinaire!
 
tesprit's Avatar
 
Join Date: Apr 2006
Location: Sharpsburg, GA
Posts: 2,808
Quote:
Originally Posted by codymac View Post
Am I the only one that's used propane?
Nope, that is the method I use too!
tesprit is offline   Reply With Quote
Old 01-21-2009, 01:19 PM   #7 (permalink)
OSX Black hat
 
charliex's Avatar
 
Join Date: Feb 2005
Location: Las Vegas , NV
Posts: 10,000
Ok pictures of some typical places for leaks.

The S, the stock hose clamps are good enough until they're removed a couple of times, then they ought to be replaced, so i remove my ecu a fair bit, i'd forgotten to tighten this one, which helped when i did this tutorial

Small leaks, idle tends to be ok, trims are + 4-8%





Throttle body and intake, make sure nice and tight



Hoses here, especially if you're changed to a cup air box, check that the extra hose is terminated properly. STFT will read +


check the cap is seated on the T junction, middle of the picture, next to the yellow label.


Check here, especially if you've put catch cans on here, we've had some reports of catch cans interferring with the idle. STFT will read +



From factory here should all be tight, any aftermarkets check here with the spray can. and the dipstick!


Swapped injectors? spray here, lots and lots of it. Under the IC into the injectors.
__________________
Black Exige S / Elan M100. Don't run a smaller pulley without an upgraded fuel pump! http://www.goth.am ecu stuff.. New reflash box coming soon!
charliex is offline   Reply With Quote
Old 01-21-2009, 01:22 PM   #8 (permalink)
jtj
Registered User
 
jtj's Avatar
 
Join Date: Feb 2007
Location: Dallas, Tx
Posts: 270
Quote:
Originally Posted by Mr. Oz View Post
One of these Smoke machine leak detector, leak locator, leak finder evap leak tester makes it very easy to pinpoint a suspected leak. I use one of these even for oil and coolant leaks.

our oem jag smoke tester works great on any make and model. There is no second guessing. Smoke comes out where the leak is. Almost any sealed system can be tested with the smoke machine. The fuel trims are the easiest way to confirm you have a vac leak, and if you have the car long enough to drive it some distance, they will confirm you fixed the leak as well. I will admit that I only use the machine about half the time, because half of the vac leak cars I see (Jag and Lotus) are the result of people trying to do repairs or add on parts themselves and doing an extra horrible assembly job, resulting in a leak big enough to pull your shirt off when you open the bonnet. Those are usually pretty obvious as to whats leaking and require no further diag.
jtj is offline   Reply With Quote
Old 01-21-2009, 01:30 PM   #9 (permalink)
jtj
Registered User
 
jtj's Avatar
 
Join Date: Feb 2007
Location: Dallas, Tx
Posts: 270
Quote:
Originally Posted by codymac View Post
Am I the only one that's used propane?


Comes from my two stroke background where an air leak = instant engine death.

propane works well too, and its a lost art with trade school kids. It kinda went by the wayside with 5 gas anylizers (try finding one of those in a dealership today, much less anyone that can use/read it!) you can use an unlit propane torch and a scanner to watch the short term trims change immediatly to pinpoint a leak in the absence of a smoke tester. I havent used it in a long time, but I like to know multiple ways to do things in case I ever need to do it without the latest trend in tools available. Tell a uti graduate that you can set an alignment with string and camber angle guage instead of a $90,000 laser alignment machine and look at the blank face he has from disbelief...

I asked for some shop supply propane once, but "we have a non flammable smoke tester" was the answer. Later that day I helped put out a grease rag fire started by grinding wheel sparks... go figure....
jtj is offline   Reply With Quote
Old 01-21-2009, 01:30 PM   #10 (permalink)
OSX Black hat
 
charliex's Avatar
 
Join Date: Feb 2005
Location: Las Vegas , NV
Posts: 10,000
Movie time

These won't view inline til i change em, sorry about, they're MPEG's

Running at idle with the hose clamp off on the S intercooler pipe, the idle sounds ok , but the trims are too high.
http://goth.am/tutorials/leak/MOV01695.MPG

Raising the idle with a leak, shows that the trims get better at 3000RPM, indicates a small leak.
http://goth.am/tutorials/leak/MOV01713.MPG


Leak fixed
http://goth.am/tutorials/leak/MOV01697.MPG

Still it was easy to find, that the screwdriver found, now where's my spanner gone.
http://goth.am/tutorials/leak/MOV01699.MPG
__________________
Black Exige S / Elan M100. Don't run a smaller pulley without an upgraded fuel pump! http://www.goth.am ecu stuff.. New reflash box coming soon!
charliex is offline   Reply With Quote
Old 01-21-2009, 01:31 PM   #11 (permalink)
OSX Black hat
 
charliex's Avatar
 
Join Date: Feb 2005
Location: Las Vegas , NV
Posts: 10,000
My local dyno has a 5 gas analyser its a great way to find leaks too, I bought my smoke machine from a halloween shop


the UV ones work well since you can see both the leak with the smoke and pinpoint it, but it can get messy.


Here's one from AES, $1,295
AESwave.com Store, lab scopes, scan tools, accessories and training for automotive diagnostic equipment!

uv , costly !
http://www.thesmokemachine.com/Full-...el%206525.html
__________________
Black Exige S / Elan M100. Don't run a smaller pulley without an upgraded fuel pump! http://www.goth.am ecu stuff.. New reflash box coming soon!

Last edited by charliex; 01-21-2009 at 01:49 PM.
charliex is offline   Reply With Quote
Old 01-21-2009, 01:45 PM   #12 (permalink)
OSX Black hat
 
charliex's Avatar
 
Join Date: Feb 2005
Location: Las Vegas , NV
Posts: 10,000
Scopes!

I have a the Tektronix 2024B 200Mhz 4 Channel thing that frank bought me, Amazon.com: Tektronix Digital Oscilloscope 200 MHz, 4 Channel, TDS2024B: Home Improvement its a great scope but its overkill for a car. I'd have to agree with amazon that it counts as Home Improvement!

Then i have my cheap $150 (price went up! ) PORTABLE OSCILLOSCOPE | AllElectronics.com velleman thing, its ok for a car, bit hard to read maybe.


Picoscope Pico Automotive Diagnostics Kit - the ideal automotive diagnostic tool for your workshop fairly common unit, especially if you don't have the modis and all that fancy stuff, comes with all the bits you'll need to interface to the car, 2 or 4 channel, includes sample waveforms and so on to help you see what its supposed to look for. Lots of tutorials around for this one.

I found it was better for me to buy the individual parts i wanted from aes wave and fleabay rather than buy the kit, but i already have scopes.,


Some of the off brand ones such as the Rigol are a good bet , they're cheap n cheerful, a better investment i think than some of the PC scopes.
DS1052E 50 MHz 2-Channel Digital Oscilloscope: Saelig On-line Store

Watch out for some scopes, they claim to be capabable bandwidth wise, but its a trick, they're not that great, if you see one thats 4 channel 200Mhz and $400 run away, most digital ones cheat with all sorts of sampling tricks, but for a car they're usually ok.


probes , i really like these, use them a lot.
AESwave.com Store, lab scopes, scan tools, accessories and training for automotive diagnostic equipment!

this ones a bit scary, "11 inch phil" he wishes, i only use the piercing tools if the acupuncture types don't work, they leave small holes in the insulation and can wear things out about after time, i've worked on a few cars that looked a bit worse for wear and can cause shorts if it strips as the weather/fluids tend to get in.
AESwave.com Store, lab scopes, scan tools, accessories and training for automotive diagnostic equipment!

this ones good too, for thicker wires
AESwave.com Store, lab scopes, scan tools, accessories and training for automotive diagnostic equipment!



you'll need current clamps for measuring some things
nice n cheap
AESwave.com Store, lab scopes, scan tools, accessories and training for automotive diagnostic equipment!

digital scope adapters
AESwave.com Store, lab scopes, scan tools, accessories and training for automotive diagnostic equipment!

Be careful what you buy off fleabay, i bought two that looked perfect, when i got them they were for clamping on to overhead power cables, not what i expected at all, no size reference in the picture.
__________________
Black Exige S / Elan M100. Don't run a smaller pulley without an upgraded fuel pump! http://www.goth.am ecu stuff.. New reflash box coming soon!

Last edited by charliex; 01-21-2009 at 01:56 PM.
charliex is offline   Reply With Quote
Old 01-21-2009, 01:47 PM   #13 (permalink)
OSX Black hat
 
charliex's Avatar
 
Join Date: Feb 2005
Location: Las Vegas , NV
Posts: 10,000
I never have propane lying around, but i have copious quanties of flammable stuff in a can ! remember though no carb cleaner! watch out for switch cleaner vs contact cleaner, one leaves a residue, one doesn't (the contact cleaner usually, check the label), also rubbing alcohol usually has stuff added to it to stop people drinking it that you don't want to put it in the car.
__________________
Black Exige S / Elan M100. Don't run a smaller pulley without an upgraded fuel pump! http://www.goth.am ecu stuff.. New reflash box coming soon!
charliex is offline   Reply With Quote
Old 01-21-2009, 01:47 PM   #14 (permalink)
Registered User
 
Mr. Oz's Avatar
 
Join Date: Oct 2005
Posts: 324
Quote:
Originally Posted by jtj View Post
propane works well too, and its a lost art with trade school kids. It kinda went by the wayside with 5 gas anylizers (try finding one of those in a dealership today, much less anyone that can use/read it!) you can use an unlit propane torch and a scanner to watch the short term trims change immediatly to pinpoint a leak in the absence of a smoke tester. I havent used it in a long time, but I like to know multiple ways to do things in case I ever need to do it without the latest trend in tools available. Tell a uti graduate that you can set an alignment with string and camber angle guage instead of a $90,000 laser alignment machine and look at the blank face he has from disbelief...

I asked for some shop supply propane once, but "we have a non flammable smoke tester" was the answer. Later that day I helped put out a grease rag fire started by grinding wheel sparks... go figure....
Yep I have a gas analyzer, it works well to find fuel leaks also...hydrocarbons. I used propane for a lot of years, one drawback was multiple possible leaks in a compact area making them difficult to pinpoint. Example...is it a intake gasket or cracked manifold? With smoke the leak is visible and easier to pinpoint.
__________________
Dan
08 2-Eleven Launch Edition

You must be fast cause you were haulin azz when I passed you!!
Mr. Oz is offline   Reply With Quote
Old 01-21-2009, 01:52 PM   #15 (permalink)
Registered User
 
TimMullen's Avatar
 
Join Date: Jun 2003
Location: Chantilly, VA
Posts: 12,373
Images: 19
Quote:
Originally Posted by codymac View Post
Am I the only one that's used propane?
Nope. I'm old school - I even have a "special tool". The "tool" screws onto a small propane cylinder (torch type of cylinder) and has a regulator that feeds a long hose. The hose ends in a nozzle that I use to probe around suspected air leaks, spraying a bit of propane in the area. When you get to the leak, the propane gets sucked in, and the engine picks up RPMs and/or runs smoother. It works great.
__________________
Tim Mullen --- There is no such thing as Touring suspension or Touring wheels.

I love being married. It's so great to find that one person that you want to annoy for the rest of your life. - Rita Rudner


Chantilly, VA http://members.cox.net/elans4/
05 Lotus Elise - Chrome Orange - No Touring - No LSS - No Hardtop - Lotus Driving Lights - Lotus "Chin Guards" - plain and simple.
94 Miata R Package - Black
72 Lotus Elan Sprint - Colorado Orange/Cirrus White
TimMullen is offline   Reply With Quote
Old 01-21-2009, 01:58 PM   #16 (permalink)
OSX Black hat
 
charliex's Avatar
 
Join Date: Feb 2005
Location: Las Vegas , NV
Posts: 10,000
geez you guys are leapfrogging my tutorials, i'm writing up the hydrocarbons stuff now keep it coming though!
__________________
Black Exige S / Elan M100. Don't run a smaller pulley without an upgraded fuel pump! http://www.goth.am ecu stuff.. New reflash box coming soon!
charliex is offline   Reply With Quote
Old 01-21-2009, 02:11 PM   #17 (permalink)
*
 
shay2nak's Avatar
 
Join Date: Dec 2003
Location: Calipornia
Posts: 22,064
Quote:
Originally Posted by charliex View Post
Ara, %20ish
so I should follow this...

"The long term fuel trims are also valuable to look at, large positive values in here, double figures, show a problem in manifold leaks, misfires and fuel pressure , injectors ( the car is running lean, so the computer is adding a lot of fuel )"

probably not the injectors, but I do use injector cleaner during every oil change. Not misfire, that would throw a code, I think. So exhaust manifold is it.
__________________
** save ~10 lbs gain 1 hp ** EQ: Y=(190*X) / (1984-X) where Y is (HP) and X is (lbs)

'07 Lotus Exige S310


WTC 2
shay2nak is offline   Reply With Quote
Old 01-21-2009, 02:33 PM   #18 (permalink)
OSX Black hat
 
charliex's Avatar
 
Join Date: Feb 2005
Location: Las Vegas , NV
Posts: 10,000
yeah since that was the last thing to be touched, i'd be looking there, especially given the severity.
__________________
Black Exige S / Elan M100. Don't run a smaller pulley without an upgraded fuel pump! http://www.goth.am ecu stuff.. New reflash box coming soon!
charliex is offline   Reply With Quote
Old 01-21-2009, 03:43 PM   #19 (permalink)
OSX Black hat
 
charliex's Avatar
 
Join Date: Feb 2005
Location: Las Vegas , NV
Posts: 10,000
Ok so i'm moving beyond the simple OBD II scan tool and switching over to plastic toaster, to make it easier to view, i just load the CSV files into excel and made a quick graph.

I removed the black cap, pictured above, this creates a leak big enough you can hear it sucking in air, however the idle RPM stays within -/+ 100, this throws a lot of people off into thinking they don't have a leak, my AFR's headed steadily into the 15+ areas here.I can't tell you how many times i've faced a car owner that swears it isn't leaking because the RPM is steady.

Two data logs, one with the cap removed, one without, you can see i opened the throttle up to raise the idle.

My car currently has modified headers and a stock tune, so the trims are a teeny bit off, but you'll get the idea.
Attached Images
  
__________________
Black Exige S / Elan M100. Don't run a smaller pulley without an upgraded fuel pump! http://www.goth.am ecu stuff.. New reflash box coming soon!
charliex is offline   Reply With Quote
Old 01-21-2009, 03:51 PM   #20 (permalink)
OSX Black hat
 
charliex's Avatar
 
Join Date: Feb 2005
Location: Las Vegas , NV
Posts: 10,000
Here are the RPM traces to match the charts, you can easily see which one has a leak and which doesn't by the traces, but if you're listening to the car it's not quite so obvious.
Attached Images
  
__________________
Black Exige S / Elan M100. Don't run a smaller pulley without an upgraded fuel pump! http://www.goth.am ecu stuff.. New reflash box coming soon!
charliex is offline   Reply With Quote
Sponsored Links
Advertisement
 
Reply

  LotusTalk - The Lotus Cars Community > Lotus Discussions > Maintenance and Repairs.



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -8. The time now is 02:43 AM.


Powered by vBulletin® Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO 3.3.2
Garage Plus vBulletin Plugins by Drive Thru Online, Inc.