Computer/Sensor Problem? "No Vacuum to EGR valve"

[ZappyShawrk]

Hi everyone!

So first off, this is my first post, I was driven to this forum trying to find answers to my current problem. I did search for a while trying to find exactly what my issue was, but I didn't quite seem to find it. I have never worked on any car or truck, and the used 1989 Ford Bronco I just bought is my first truck, EVER!

And I love it! But it didn't pass smog...

Now, when I bought this beast, it had brand new tires, a brand new engine, motor and transmission, with only about 40,000 miles on the new stuff. The guy who sold it to me had taken it in for a smog pretest, and it passed with flying colors.

I took it in two days ago, and it failed the 25mph test.

Now, I took it to a mechanic, who looked over it for me. He said that everything was checking out fine, that he EGR valve, solenoid, Engine and Motor all looked beautiful, but that something to do with the COMPUTER or SENSOR seemed to not be working (if this makes sense). There is NO VACUUM TO THE EGR VALVE.

I've noticed on some of the other threads that this is a pretty common problem among older Broncos.

My Questions Are:

1) Is there a possibility that when the new engine, motor, transmission were replaced, the wiring for the sensor or computer might not have been hooked up properly? Causing the vacuum to not turn on, and thus, there being no vacuum in the EGR?

2) If it is a simple wiring problem, how would I go about checking, or fixing it? Is it something easy to reach? And is it something someone with little to no experience working on cars might be able to handle as a first project?

3) Is this sort of problem worth taking the truck in to the Ford Mechanic, who is going to charge me an arm and a leg JUST for DIAGNOSTIC, let alone any repair work? Or should any, reasonably priced technician, be able to fix this?

Thanks so much for any help with this, I have little to no knowledge about tech work, but I want to start learning, and since this is the first major issue I've found with my new baby, I'd like to see if I can handle it first. Please let me know how you guys would handle it! And I'm so sorry if this is a re-post! (I definitely did check, first!)

 

[ZappyShawrk]

Also, I went and looked at it this morning. And it appears that one of the main wires (12A581) I believe the one running from the sensor, to the PCM (the computer that controls and initiates the vacuum [?]) has corroded or melted. The ends near one of the connectors (not the one going to the EGR sensor, but the run running out to the PCM (I -think-). Now, common sense would tell me that if that wire is messed up, signal going from PCM to EGR sensor might be screwed.

I'll take pics and post them here. If anyone knows if that (apparently) messed up wire would be causing the 'No Vacuum to EGR' problem, please please please confirm. Also, is this part the wiring (12A581) going from PCM to EGR Sensor an easy fix? Can I find this part easily? For how much?

http://i1064.photobucket.com/albums/u365/ZappyShawrk/196e6769.jpg'>http://i1064.photobucket.com/albums/u365/ZappyShawrk/196e6769.jpg

http://i1064.photobucket.com/albums/u365/ZappyShawrk/a9b38431.jpg

http://i1064.photobucket.com/albums/u365/ZappyShawrk/d3390548.jpg

http://i1064.photobucket.com/albums/u365/ZappyShawrk/33eb245e.jpg

http://i1064.photobucket.com/albums/u365/ZappyShawrk/196e6769.jpg

 

[Rons beast]

Welcome Zappy,

Any wires that are frayed, corroded, or in a poor condition should be repaired.

That said, you do realize that the EGR should only get vacuum in an off idle condition?

I could be wrong about this year Bronc, but the pcm may restrict vacuum if not in gear or above a certain speed.

The EGR is supposed to lower NOX emmisions. What part did you fail?

Finally.....did anyone inspect the vacuum line to be sure it was not broken or pinched?

Good Luck

 

[miesk5]

yo Z,

WELCOME!

Try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19

http://broncozone.com/topic/14269-code-reader/page__pid__74587__mode__threaded

The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test.

Run it around to heat the engine up and shift thru all gears incl Reverse. Then turn off all accessories/lights, etc.

Make sure A/C is off and transmission is in Park (automatic) or in Neutral for a Manual & release clutch.

Do Key On Engine Off (KOEO) portion first.

Look Codes up in my broncolinks.com site using the new Search function.

And Post em here according to:

KOEO

&

KOER

------------

12A581 Wiring Assembly (harness) is huge; includes such as;

Body Grounds

Starter Motor Relay Battery

To PCM

Ignition Module

Relay Block

etc., etc.

Prob better to get what you need to repair bad sections w/ Yard Queen harness from pick n pull

Cut connectors w/as much of pigtail as possible

One good source for new Pigtails & Connectors

is Ryan M (FIREGUY50) @ http://www.rjminjectiontech.com/collections/pigtails-connectors

for example;

EGR Valve Position Sensor $16.00

EGR Vacuum Regulator $10.00

60pin EEC-IV connector $25.00 but Terminals not included

Harnesses are available bec of the cash for clunkers AND GOOD VEHICLES mess; For a YARD SEARCH on-line, I use;

http://www.mypartshop.com/

Select All Parts

year, etc, then FORD TRUCK

SELECT Engine Wire Harness

Many hits! BUT $184.00 to $200.00

or

http://www.copartfinder.com

Has Vehicle Pics!

http://www.picknpull.com

MANY CALIF Locations!

This is just a compnay name; so ask local yards

http://www.car-parts.com/

Also for obsolete parts;

Our Sponsor here has been adding some to inventory; Jeff's Bronco Graveyard

Jeff at the Bronco Graveyard has offered a 2% discount to members of The BroncoZone for on line orders. To get your discount, enter the discount code BZMEMBER. Also you must include your BroncoZone User Name with the order.

http://broncograveyard.com

and: by Ford pn:

http://www.partsvoice.com/

http://www.rearcounter.com

http://www.greensalescompany.com

============

Testing; "...Follow this procedure to rule out the EGR/EVP/EVR and then look elsewhere. As a side note, on one truck I had an EVP that tested good, but after replacement it cured my problem.

The EVP is a potentiometer that can mechanically wear and the EVR solenoid can become stuck. On another truck, I eliminated the EGR Code 334 with a TPS replacement and adjustment.

The EGR should only operate during cruising, never during Idle and WOT.

Start by deleting the code and see if it returns.

Then, perform a DTC Test and observe the EGR. When the PCM is in test mode, at some point during the test the diaphram should move and the engine rpms drop.

We now know if the EEC is in control of the EGR. If the DTC returns, continue on.

If no or inadequate change is seen, test the Manifold Red Vacuum line between the Manifold Vacuum Tree and VRESER (MAN port), then the VRESER Check Valve (AMP port) and then Black Vacuum Lines between the VRESER and lower ports on the TAB/TAD/EVR Solenoids.

We have now ruled out an Emissions Manifold Vacuum Leak.

With the engine off, locate the green vacuum line at the EVR (EGR Vacuum Regulator) located in front of the TAD and TAB Solenoids next to the coil. Attach a vacuum tester to the upper vacuum line and see if applied vacuum can operate and hold the EGR Diaphram. Disconnect the other end of the green vacuum line at the EGR. I you want, plug the end of the line with your finger and test again just to be sure.

We have now ruled out the EGR vacuum line and EGR diaphram.

If the line is good and the EGR is not holding vacuum, reattach the EGR vacuum line and remove the EVP (EGR Valve Postion Sensor) located on top of the EGR. The three attachment screws should not be loose causing an air leak. When removed, check the bottom of the EVP for an O-ring and if the position sensor pole can be moved up and down. Next, manually block the now open hole on top of the EGR with your hand and vacuum test again.

We have now ruled out the mechanical portion of the EVP.

Next, reinstall the EVP. With KOEO, check the unplugged harness connector with a DVOM for 5v reference voltage at pins VREF and SIG RTN. Then test the unplugged EVP Sensor for approximately 5000 ohms resistance at sensor pins VREF and EVP. Now apply 10 in. Hg. vacuum to the EGR. You should see a gradual decrease in resistance to approximately 100 ohms. If the vacuum, EGR and EVP test good, reconnect everything, except for the vacuum tester at the EGR and continue on.

We have now ruled out the electrical portion of the EVP.

Disconnect the harness connector to the IAC (Idle Air Controller) located on the side of the Throttle Body and start the engine. Start the engine and note that the idle should be lower than normal as the IAC is no longer in control. Apply vacuum to the EGR and watch for the engine idle to drop. Release the vacuum and the engine idle should return. If all is good, turn off the engine and reconnect the IAC and the green vacuum line to the EVR.

Relocate the vacuum tester to the EGR end of the green line and connect using a "tee" between the vacuum line and the EGR. Start the engine and idle to warm. Idle vacuum from the EVR should be below 1 in. Hg. Now have someone raise the engine speed to 3500 rpm and observe the vacuum gauge for increase and the EGR Diaphram for movement.

We have now ruled out the mechanical portion of the EVR.

If the vacuum lines are good, next start KOER DTC Test with the Vacuum Hand Pump once again located at a "tee" at the EGR. While watching the vacuum gauge, observe for a change in vacuum and EGR Diaphram movement when the PCM activates the EGR during the test. If the test once again fails, either the EVR Solenoid is stuck or the there is a short to the EVR.

Electrically test the EVR. The EVR has two connector pins. One to 12v battery power and the other to PCM Pin #33. Test the 12v to ground and the Signal wire to the PCM for continuity.

Then you can mechanically test the EVR. The bottom port should hold vacuum and the upper port will not unless 12v are applied to the connector pins. Apply 12v, plug the lower port with your finger or cap and see if you can apply vacuum to the upper port.

We have now ruled out the electrical portion of the EVR..." Source: by Seattle FSB (SeattleFSB)



EVP Wiring Diagram in an 89



Source: by SeattleFSB (Seattle FSB) at SuperMotors.net

 

[ZappyShawrk]

Thanks for the replies guys!

And Ron, the smog technician said he had tested it in the 'overdrive' gear. And that it had a really high NOX.

The part where it failed was NO (PPM) at 25mph the max reading sitting at around 592 and what was measured was 914.

When we took it to the mechanic, he seemed to narrow it down to either being a computer or sensor problem, explaining that everything looked pretty good and sound, including the sensor, solenoid and valve itself. He was unable to check lines and hoses though, and seemed to think it was electrical, which is why he would go no further.

 

[chuckles1856]

Welcome Zappy,

Sorry to hear you are having issues with the Bronco. Hopefully someone here can point you in the right direction. It's interesting the smog tech said the really high NOX was due to the truck being tested in overdrive. I had a similar problem with my '91 passing emissions and every time I go now I have them test it with the overdrive turned off. I'm still at a loss why testing a vehicle in overdrive would make any difference?

In any case did you ever pull the codes?

 

[Rons beast]

Thanks for the replies guys!

And Ron, the smog technician said he had tested it in the 'overdrive' gear. And that it had a really high NOX.

The part where it failed was NO (PPM) at 25mph the max reading sitting at around 592 and what was measured was 914.

When we took it to the mechanic, he seemed to narrow it down to either being a computer or sensor problem, explaining that everything looked pretty good and sound, including the sensor, solenoid and valve itself. He was unable to check lines and hoses though, and seemed to think it was electrical, which is why he would go no further.

I'm confused...the overdrive cannot be activated at 25mph.

A computer OR sensor problem, is not what I consider "narrowed down"

Unable or unwilling to check lines?

I think you need to look for a more dillegent mechanic.

Pull codes, and go from there. The codes should point you to a cause.