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  #1  
Old 05-06-2013, 10:25 PM
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Default LDP question

While testing the new LDP in a 2001 Cherokee today it did react differently than the one that it replaced. First, the sense signal DID switch open with each pump of my mity-vac (LDP sol energized). However, with every pump, I lost the vacuum which would immediately close the switch again. With the condemned LDP, I could easily pump the uppper cavity to 25" and it would hold (the reed switch would not open though). Why can't I pump the new LDP over 5" and have it hold? Is this normal for a good (new OE) LDP?
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Old 05-07-2013, 07:06 PM
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That's how it pumps:

OPERATION
Immediately after a cold start, engine temperature between 40°F and 86°F, the 3 port solenoid is briefly energized. This initializes the pump by drawing air into the pump cavity and also closes the vent seal. During non-test test conditions, the vent seal is held open by the pump diaphragm assembly which pushes it open at the full travel position. The vent seal will remain closed while the pump is cycling. This is due to the operation of the 3 port solenoid which prevents the diaphragm assembly from reaching full travel. After the brief initialization period, the solenoid is de-energized, allowing atmospheric pressure to enter the pump cavity. This permits the spring to drive the diaphragm which forces air out of the pump cavity and into the vent system. When the solenoid is energized and de-energized, the cycle is repeated creating flow in typical diaphragm pump fashion. The pump is controlled in 2 modes:

PUMP MODE: The pump is cycled at a fixed rate to achieve a rapid pressure build in order to shorten the overall test time.

TEST MODE: The solenoid is energized with a fixed duration pulse. Subsequent fixed pulses occur when the diaphragm reaches the switch closure point.

The spring in the pump is set so that the system will achieve an equalized pressure of about 7.5 inches of water.

When the pump starts, the cycle rate is quite high. As the system becomes pressurized pump rate drops. If there is no leak the pump will quit. If there is a leak, the test is terminated at the end of the test mode.

If there is no leak, the purge monitor is run. If the cycle rate increases due to the flow through the purge system, the test is passed and the diagnostic is complete.

The canister vent valve will unseal the system after completion of the test sequence as the pump diaphragm assembly moves to the full travel position.
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Old 05-09-2013, 08:52 PM
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Thank you Skip. I guess what I cant grasp is how, when the solenoid is constantly energized with jumpers, the upper cavity cant hold the vac that i am pumping. Heard from cust today, so far so good. I just want to understand this behaior for the next time (if I can remember that long). Many thanks! Neil
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Old 05-10-2013, 03:21 AM
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What a lot of people overlook is that DAIMLER-Chrysler had a lot of German influences for a lot of years. The Chrysler systems morphed the same way the American-Motors (AMC) morphed the Jeep line after Chrysler bought Jeep.

The Chrysler EVAP systems are basically a Volkswagon design. Lots of similarities can be found and read up on in your SI for either VW or Mercedes-Benz (Daimler-Benz)

Here's a cool link to Southern illinois University. This is an "Open Source" description of the Chrysler Evap systems and you can download it and save it.

http://opensiuc.lib.siu.edu/auto_pres/7/

I wish the "educators" in this Province made learning this much fun-!!! LOL. ALL Evap systems are skinning the same cat one way or another looking for either pressure or vacuum and using variations of "ideal gas law"
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Old 05-14-2013, 08:16 PM
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Thanks boys. Jeep has completed monitors and passed SI and I have a better understanding. Now if i can just remember this for the next time...
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Old 05-17-2013, 12:55 PM
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Southern Illinois is one of the very few, I know of 2, schools in this country where you can get a 4 year degree in automotive technology. Because of that, their students are highly recruited by Detroit and the school is highly supported. Not excusing other schools but most don't have big money backing like they do.
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Old 05-18-2013, 05:10 AM
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Quote:
Originally Posted by Skip View Post
Southern Illinois is one of the very few, I know of 2, schools in this country where you can get a 4 year degree in automotive technology. Because of that, their students are highly recruited by Detroit and the school is highly supported. Not excusing other schools but most don't have big money backing like they do.
Hi Skip
So Southern Illinois is one that you know of.....what's the other one??

Perhaps there's more information on their website. The more knowledge that can be disseminated into this skilled trade the better.

The principles of operation don't change from North American to Asian to European manufacturers as they're all working from the same principles of the numerous laws of physics that are encompassed by the "horseless carriage".

99% of vehicle problems can be thought through if one has a sound understanding of the laws of science, common sense and logic.

This is where we need the CORRECT information and ALL the information from our test equipment.
(This is where I become insistent on accuracy, and value scale the same as the manuals, and NO MISSING PIDS)

The "trouble tree" charts and the "IdentaGUESS" databases can't allow for or consider all the various combinations of vagaries that the automobile is subjected to in real world application.

Finding accurate information such as Southern Illinois has exhibited is a real crapshoot on the "internet".

Last edited by Crusty; 05-18-2013 at 05:12 AM.. Reason: fat finger spelling
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Old 05-19-2013, 08:11 PM
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Default Good stuff

Crusty,
I went back and did some more reading tonight and I must say, that website was quite a find. Thank you for bringing that forth. I kept a link to all the presentations to my desktop. There are some fascinating topics that I intend to re-visit. Its true, the technical jobs that we have and the expectation to "get it right the first time every time" makes the need for this type of detailed explanation a necessity. The technology changes so fast so often that references such as this become a tool. I don't believe someone can possibly be "taught" all this stuff. I'll speak for myself, I just can't accurately remember it all. Not even close. The trick is to have info, such as you linked, the tools to test and repair with, and the wisdom to relate the symptoms to your experiences.
This was my alma mater: http://www.neit.edu/Programs
2 year tech program, 4 year service manager degree (they didn't have when I attended)! Thats curious! Thanks pal.

Neil
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Old 05-20-2013, 06:44 AM
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Quote:
Originally Posted by Trindaddy View Post
Crusty,
I went back and did some more reading tonight and I must say, that website was quite a find. Thank you for bringing that forth. I kept a link to all the presentations to my desktop. There are some fascinating topics that I intend to re-visit. Its true, the technical jobs that we have and the expectation to "get it right the first time every time" makes the need for this type of detailed explanation a necessity. The technology changes so fast so often that references such as this become a tool. I don't believe someone can possibly be "taught" all this stuff. I'll speak for myself, I just can't accurately remember it all. Not even close. The trick is to have info, such as you linked, the tools to test and repair with, and the wisdom to relate the symptoms to your experiences.
This was my alma mater: http://www.neit.edu/Programs
2 year tech program, 4 year service manager degree (they didn't have when I attended)! Thats curious! Thanks pal.

Neil
Hi Neil
I am constantly reading on all sorts of vehicle "systems". While you're correct about the "technology changing so fast", that's exactly what it is.....the "technology".....yet that is merely the "HOW" they are achieving the desired result.

What, When, Where, Why, How......

It is indeed impossible for any single person to be "taught all this stuff".
The imperative of our test equipment is to supply the answers to the above 5 proverbial questions.

I really should be grateful to SnapOn for messing up the EVAP systems on the circa 1997 to 2005 GM vehicles. That made me go looking, and reading, and learning, about the various EVAP "systems".
That's where I learned that all the manufacturers are applying either a vacuum or a pressure on the vehicles' EVAP system and in some way measuring the results. What the specific values or scales are, I don't know, nor do I care.
Each manufacturer has their own values and scales, hi and low trigger points, procedures for creating the vacuum or pressure, and 90% of the time that information can be found in the manuals (unless it's a BMW where they squirrel away that information within their own proprietary scan tool, justifying the hiding of that information by calling it "guided fault finding" which is a joke as no trouble-tree can possibly foresee every variable that may make a system fail)

When we think about all the "disciplines" (electronics, hydraulics, chemistry, metallurgy, mathematics, geometry, etc, etc) in the modern "horseless carriage", it is a challenge to answer the 5 proverbial questions on any given system on any given day.

The answers are ALWAYS in the ROOT CAUSE of one of the BASIC PRINCIPLES of the interconnected disciplines.

It can be both fun and frustrating at the same time.

To quote Hefaus... "Keep Smiling"
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Old 05-20-2013, 02:59 PM
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The other school is Weber State in Utah. Another huge school with big OEM funding. The school I teach at is currently talking to state college to try and set a 4 year degree with an emphisis on engineering. It would be the only one in California.
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