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1990 Jeep YJ Wrangler 2.5L EGR Troubleshooting


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#1 DogpawSlim

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Posted 27 April 2014 - 05:09 PM

This site has been very helpful with my current EGR issue, but I've reached an impasse. My electronics experience is limited, so I'm hoping for some help diagnosing the problem. The jeep is a 1990 YJ, 2.5l.

My EGR is getting vacuum at idle, so, it idles rough or stalls out when the vacuum line is connected. The diaphragm appears to be working correctly: if I connect the vacuum source, the EGR valve opens and closes when I remove it.

The lower outlet at the EGR solenoid has vacuum at idle, so it does not appear that the vacuum canister is causing the issue.

There is no voltage reading across the pins on the solenoid connector at idle. There is battery voltage from the red wire to the negative battery terminal at idle, and battery voltage from the red wire to the positive terminal when the jeep is off. There is connectivity between the blue wire and the negative terminal when the jeep is off.

The CTS tested fine, per the FSM.

Any help would be greatly appreciated.



#2 Moses Ludel

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Posted 27 April 2014 - 08:31 PM

Welcome to the forums, DogpawSlim! 

 

The best diagnostic tool for the EGR vacuum circuit is a combination vacuum hand pump and vacuum gauge.  You can eliminate a lot of guesswork with this approach.  A quality vacuum hand pump/gauge will last for many years.  I've had the same Snap-On Blue Point pump/gauge in my diagnostics tool box since 1981.

 

Disconnect the source hose from the vacuum canister, and cap off the other canister ports.  Check the canister with a hand vacuum pump/gauge attached to the vacuum source hose.  Create vacuum with the hand pump; the pump's gauge will indicate whether vacuum is holding in the EGR canister.

 

Importantly, the signal for the EGR valve is ported vacuum, not manifold vacuum.  If the vacuum source line to the EGR canister and EGR valve is manifold vacuum, this is incorrect.  An EGR vacuum circuit can be routed through a TVS, CTS or CTO, or other sensors and switches, but the vacuum at the EGR valve, for both carbureted and EFI engines, is ported vacuum. 

 

Note: Some automotive EGR systems use manifold vacuum, switched on and off through either a ported vacuum signal or electrically, to open the EGR valve.  The ported vacuum signal actuates the EGR in the same way as direct ported vacuum.

 

Ported vacuum applies strongly as the throttle begins to open and not at an idle.  Ported vacuum diminishes as the throttle opens widely.  This means that the EGR valve opens fully just off-idle and closes as the throttle opens widely.  This is optimal for EGR purposes and NOx emissions control.  EGR (ported) vacuum functions like the distributor advance vacuum on older, conventional ignition distributors.

 

Below is the Model 81 (your Jeep YJ Wrangler) 2.5L TBI diagnostic procedure for the EGR canister circuit and solenoid.  I included both the overall vacuum circuit diagram and the "Fig. 37" diagram referenced in the test procedure:

 

Attached File  YJ Wrangler 2.5L EGR Vacuum.pdf   224.54KB   17 downloads

 

Note that the vacuum source to the solenoid is the TBI vacuum port.  This is not manifold vacuum.  Check your hose routing, you may have a manifold vacuum source running to the EGR solenoid.

 

The troubleshooting steps should determine whether the EGR canister solenoid is defective.  If the vacuum circuits are correct and the solenoid is not defective, we'll troubleshoot the electrical signal to the EGR canister solenoid. 

 

Moses

 

 

 



#3 DogpawSlim

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Posted 27 April 2014 - 09:54 PM

Thanks for your detailed response, Moses.  I am away from the jeep until next weekend, but I will run the tests with a pump gauge (instead of my finger) and double check the vacuum lines over the weekend and will post my findings.  Thanks again.



#4 Moses Ludel

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Posted 28 April 2014 - 05:35 PM

You're welcome, DogpawSlim...Looking forward to your findings....Moses



#5 DogpawSlim

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Posted 02 May 2014 - 01:49 PM

Back from checking the jeep: the vacuum lines are routed correctly, and the canister is not holding vacuum. 

 

Following diagnostic procedures, there is vacuum to the solenoid source at idle and there is vacuum at the solenoid output at idle.  Based on the diagnositc procedures, I should "check solenoid/ECU operation with the DRB-ii Service Diagnostic Tester and repair as necessary." 

 

I doubt I will be able to find a DRB-ii here in 2014.  Is there a workaround?  Thanks in advance. 



#6 Moses Ludel

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Posted 02 May 2014 - 08:43 PM

When you note that the canister is "not holding vacuum", do you mean that when you isolate the canister and cap off all ports except the test port, the canister leaks down when you pull vacuum at the remaining port?

 

If so, the canister is defective and may be a source of trouble.  The canister is in the system to act as a reservoir for vacuum that otherwise would be insufficient to actuate the EGR.  This could be a secondary issue, however, since your EGR is actually opening—though at the wrong time.

 

The DRB-II and DRB-III scan tools can actuate devices like the solenoid as part of a test sequence.  These two scan tools cost a small fortune new.  (Consider the $6000 deposit on a DRB-III scan tool rental from Mopar's TechAuthority.)  There are a variety of aftermarket scan tools that can run many of these same test sequences, in particular the higher end scan tools from Snap-On, OTC and others.  You do need the software for your vehicle, which would be "Chrysler" and "1990".

 

Considering the cost of these scan tools and the diagnostic labor time if you sublet this task to a shop, you might be ahead to simply find a used solenoid from a recycled Wrangler like yours and swap the solenoids.  This would not cost much if we're talking about used parts, and you might learn quickly whether the solenoid is at fault.

 

Moses



#7 DogpawSlim

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Posted 16 May 2014 - 08:05 PM

Thanks Moses.  I installed a new (used) solenoid, but the problem remains.  Do you have any suggestions on where I should go from here?



#8 Moses Ludel

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Posted 16 May 2014 - 08:41 PM

Did you vacuum test the actual canister for a leak(s) yet?  A simple hand vacuum pump test would be helpful.  Vacuum cap all ports but one, then vacuum pump the canister to 20 in/hg or so.  

 

Use a pump and gauge that will reliably hold vacuum.  Watch for a drop in vacuum.  If the drop is rapid, submerge the canister in water with the single nipple/port exposed above the water line, or run a vacuum hose above the waterline and submerge the entire canister.  Use an air hose and nozzle with compressor pressure set low—low enough not to blow the vacuum caps off!  Watch for bubbles.

 

While we're on the subject of vacuum canisters, there's another canister system that often comes up as a trouble code: The fuel cap at the tank can cause a great deal of mischief and will sometimes throw an emission canister trouble code.  For emission control TDCs, the fuel cap issue is easy to test and remedy.

 

Moses



#9 DogpawSlim

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Posted 17 May 2014 - 08:36 AM

I tested the canister at the purge port a few weeks ago, and it would not hold vacuum.  I will try the water trick later today. 

 

The solenoid output has vacuum at idle.  Assuming this one is good, is there any particular ground wire I should check?  Should I pull the ECU and look for burned out parts? 



#10 Moses Ludel

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Posted 17 May 2014 - 03:01 PM

So, if the canister does not hold vacuum after the submersion test, sounds like you need another vacuum canister...Agree?

 

Moses



#11 DogpawSlim

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Posted 17 May 2014 - 03:20 PM

I agree, I'm just trying to sort out the upstream issues first.

#12 DogpawSlim

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Posted 18 May 2014 - 04:22 PM

Instead of considering the solenoid vacuum at idle as the problem, I started thinking of it as a symptom. The MAP sensor tested fine per the FSM procedure, as did the WOT switch. The (new) CTS has 330 ohms resistance at operating temp. The o2 sensor has 17 ohms resistance, which is out of spec per the FSM (5-7 ohms). Is there any other part of the system that could be malfunctioning and tricking the ECU into not engaging the EGR solenoid? Thanks again for your help.

#13 Moses Ludel

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Posted 19 May 2014 - 03:21 PM

Does this warrant changing the O2 sensor?  The O2 sensor is part of the feedback loop for activating the EGR. 

 

Before condemning parts and raising the cost of this project, try this:

 

1) Trigger the solenoid with an electrical signal directly to the solenoid. 

2) Apply vacuum with a hand vacuum pump, and see if the EGR opens. 

 

It's possible that your EGR does not open because the EGR valve diaphragm is leaking.  You can also perform this test by applying vacuum directly to the EGR valve with the hand pump.  See if you can open the valve and whether it stays open

 

As per my suggestion about the vacuum canister, there's another way to test the EGR valve.  You can remove the EGR valve and submerge it in water with the vacuum pipe above the water line.  Apply very light compressed air to the vacuum pipe.  See if air bubbles appear from the other side of the diaphragm.

 

We'll take it from there...

 

Moses



#14 DogpawSlim

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Posted 19 May 2014 - 07:12 PM

The EGR functions fine: opens when vacuum is applied and closes when removed. I jumpered the original solenoid from the blue wire (ECU to the diagnostic port and EGR solenoid) and the solenoid did not activate (still had vacuum at output). If my procedure was correct, I will jumper the new solenoid and see what happens. I forgot to mention that I tested the TPS, but was unable to get the voltage in spec at WOT. I maxed out at 3.8v, and I believe I should be around 4.6v based on the percentage formula. Could this be a potential cause? Also, should the MAP sensor hold vacuum? The voltages tested within spec, but the sensor leaked vacuum when a hand pump was used. Thanks again for your time. Greg

#15 Moses Ludel

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Posted 20 May 2014 - 10:10 AM

Greg, we'll see what your solenoid test produces.  The TPS is one of the signals that could affect the EGR and certainly impacts fuel efficiency and performance, in any case.  Is there a possible short at the diagnostic port you describe?  Is the solenoid always powered up (12V positive) and receiving a ground signal trigger from the ECU (like injectors do), or is the signal to the solenoid a positive 12V current? 

 

I ask this because the solenoid may have an insufficient ground.  Grounds are a chronic and epidemic issue, and this includes engine-to-frame, frame-to-body, body-to-engine.  The usual culprit for major ECU ground issues on the Jeep YJ Wrangler is the junction points near the dipstick and at the firewall.  I would carefully clean these junctions and grounds. 

 

Determine whether the ECU signal to the solenoid is a grounding (negative) or positive source, and make sure the solenoid grounds properly—as should the rest of the system.

 

Regarding the MAP sensor, there is no actual "factory test" noted for this device.  The MAP (manifold absolute pressure) is concerned with atmospheric/altitude or barometric changes that impact engine performance and functions.  It works in concert with the O2 sensor and other signals to help set the A/F ratios.  "Leaking down" with a vacuum gauge test does not necessarily mean a defective MAP sensor, as this is not a suitable test procedure for the MAP sensor.

 

Here's another round of troubleshooting from the factory level.  See if this provides any troubleshooting clues:

 

Attached File  Jeep 2.5L TBI EGR.pdf   2MB   9 downloads

 

Also, I'm curious whether the "emissions timer" is disconnected.  The device is a module to the right of the accelerator pedal.  In the day, the Model 81 and others required a new timer and O2 sensor as part of routine (at 82,500 miles or so) service.  Often, this timer gets disconnected to stop the Engine Check signal from displaying.  In these cases, the O2 sensor can wear out and not get replaced.

 

Moses



#16 DogpawSlim

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Posted 20 May 2014 - 07:12 PM

Thanks Moses, I will replace the TPS and do some further testing and will report back this weekend.

And the emissions timer is indeed disconnected.

#17 DogpawSlim

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Posted 23 May 2014 - 11:26 AM

I replaced the TPS, and it is idling smoother, but the EGR is still getting vacuum.  I cleaned all the ground locations I could find (dipstick support and firewall to head)..

 

I traced the ECU side of the solenoid back to the ECU with a multimeter, and the connection is solid.  I jumpered the solenoid, and the solenoid works as it should (i.e. when the ECU side is grounded, the solenoid closes and vacuum to the EGR is cut off).  I think I've narrowed it down to either 1) there is an incomplete ECU ground somewhere, or 2) the ECU is toast. 

 

I doubt the ECU is toast because this is my only symptom.  Also, the ECU internals look okay (i.e. solid traces and no fried components). 

 

Are there any other ground points I should look for?  Thanks,

 

Greg



#18 Moses Ludel

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Posted 23 May 2014 - 12:43 PM

This is good, DogpawSlim!  Try checking the ECU ground at the ECU itself.  Use ohms resistance and also continuity to ground.  You may have a poor ground at or to the ECU.  If you can locate the main ground lead to the ECU, check that lead for ohms resistance and continuity.  Then do an ohms test all the way from the battery's negative terminal to this ground lead at the ECU.  This will provide a full-circuit ground integrity check.

 

Note: Sometimes the positive battery cable gets replaced with a "universal" cable that has a crimp/butt connector.  A poor positive connection can wreak havoc with the electrical system.

 

Another test that is very useful would be a "lamp test".  Using an old 12V headlamp, place the lamp in the ground circuit at the ECU and verify how "bright" the light shines.  The chassis or ECU ground system becomes the ECU ground source for the lamp. 

 

Lamp positive could be to a battery source or your EGR solenoid "+" side.  Use a lower amperage inline fuse as protection, allow just enough amperage for the lamp to light.  Drop down in test lamp size if the wiring or circuits are very light gauge/amperage.

 

Let's see what turns up...The lamp test run on a quality ground circuit (normal resistance) should be bright, a benchmark for what you want to see "under load" during a ground circuit test.  

 

Moses



#19 DogpawSlim

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Posted 23 May 2014 - 02:35 PM

I can't find a light to hack up for the light test, but I checked the resistance an continuity of all the ECU wires to a solid engine ground.  My results are attached below:

 

Attached File  2.5 ECU Pinout.pdf   356.65KB   0 downloads

 

I'm not sure how to interpret this.  It looks like the main ECU grounds are functional.

 

The "EGR control" wire at pin 5 seems okay all the way to the solenoid (no resistance).  The other side goes to the fuel pump relay, and this wire seems fine as well.

 

I did some further digging into my ECU and found this:

 

Attached File  photo(3).jpg   142.75KB   0 downloads

 

I may have to amend my statement that the ECU isn't toast.  What do you think?  Thanks,

 

Greg



#20 Moses Ludel

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Posted 23 May 2014 - 05:29 PM

Greg, you're being very thorough. 

 

The advantage of a lamp test:  You can have "continuity" and even no measurable "resistance" through a few (remaining) strands of wire.  The lamp test loads the circuit, with the resulting lamp brightness indicating a wire or circuit's ability to carry amperage or current

 

On a DC system, grounds are as important as so-called "hot" or positive leads (on a negative ground system).  The lamp provides a yardstick for comparing a known "good" circuit with the one being tested.  The dimness or brightness is actually a reflection of voltage drop.

 

As for your ECU, oh, boy!  This does look like it at least needs cleaning and testing, as circuits may be either open or shorting due to corrosive and conductive material at the surface.  Try a suitable electronics cleaner, very carefully, and see if you can restore and test circuit integrity.  You may have found a serious trouble spot.  Also consider the signals/sensors that trigger the EGR solenoid.

 

Moses



#21 DogpawSlim

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Posted 07 June 2014 - 11:35 AM

Good news and bad news.

 

I replaced the computer (found a good deal on a reman), and the solenoid now closes at idle (no vacuum at the output).  I am, however, still getting vacuum downstream of the evap canister.  You may remember that my canister was not holding vacuum.

 

Are these canisters repairable, or should I just look for a replacement? 



#22 joshuaragar

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Posted 07 June 2014 - 02:48 PM

Moses,

 

   firstly, I have read many of the articles pertaining to emission problems with the 2.5 Jeep Wranglers on this website. This magazine and forum are one of the most organized and helpful I have experienced on the internet as a whole. Great job, sir.

 

   I am having the current symptons on my 1990 Jeep Wrangler (2.5):

 

     1). It idles well but will heavily bog upon acceleration.

     2). It will ocassionaly stall upon deacceleration (coming to a stop out of second gear, etc).

 

  This problem comes and goes which has me thinking it is most likely due to something being clogged, dirty, disconnected.

 

   If you agree that a good place to start is to clean the grounds, I will do that first. Do you have any way of easily helping me locate the grounds (pictures, etc.)? I am handy but definitely a novice mechanic so basic explanations are most palatable for me.

 

   Thanks in advance!

 

   Joshua



#23 DogpawSlim

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Posted 07 June 2014 - 05:25 PM

I'm sure Moses will chime in, but the ground locations should be 1) the dipstick support tube (the negative battery cable should go here, and three or four black wires from the harness) and 2) a braided strap from the driver's side of the head to the firewall.



#24 Moses Ludel

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Posted 08 June 2014 - 11:14 PM

DogpawSlim...I appreciate your ground source suggestions for Joshua, thanks!  I was busy on the Rubicon Trail this weekend, taking HD video for the Wheelers for the Wounded Rubicon Super Event, and I missed your comments.  If you have more questions, Joshua, we can go from here...

 

As for emission EVAP canisters, they have always been a replacement item and non-rebuildable.  Carbon inside, gasoline vapors and all, this is a volatile product to handle if defective, and nobody wants a defective core!

 

You should be able to buy a new canister, and following the tests that we discussed, the canister does sound defective.  The 4WD aftermarket should offer this part.  If you do need a part number for the original Mopar item, I can help.

 

Glad you replaced the ECU, that was the remaining signal for your solenoid.  It really did come down to no other item left on the troubleshooting list, and you got a positive result.  Good job!

 

Moses



#25 DogpawSlim

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Posted 09 June 2014 - 08:17 PM

Thanks Moses. I ordered a used canister as I couldn't find a new one. I will post the outcome when I get it installed.

#26 Moses Ludel

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Posted 09 June 2014 - 09:04 PM

Good job...Cap off the ports and check the canister for vacuum seal before installing, DogpawSlim...

 

Moses




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