EGR operation

[Chris Cuzynski]

I have looked around in multiple places and still cannot find an answer. First I'll admit this is not on a Binder and second I came over here from Pirate 4x4 looking for answers since they refer you to this site.

My EGR on 2 of my TBI injected vehicles (92 full size Blazer and a 93 K2500 pickup) operates when in park or neutral and under low speed conditions such as driving slow or coming to a stop where the engine almost stalls. It sounds like it has a huge cam in it from the EGR induced lope.

The service engine soon light indicates a Code 32 (EGR) malfunction when I check it at the aldl.

So far I have adjusted the park/neutral switch under the dash on the steering column, swapped the MAP sensor, EGR solenoid, EGR valve, Engine Temp sensor, checked the grounds and all checks out OK. None of this has changed the EGR problem.

I can unplug the EGR solenoid or plug the EGR vacuum line and the engine runs fine. (Except of course the EGR does not function).

In looking at the wiring download and ECM connection identification for the TBI (which I downloaded from here), I see the EGR solenoid has a wire that is in curcuit with the O2 sensor and goes from terminal 87 on the SPST 5 pin relay to the A6 pin on the ecm conn a-b.

If the O2 sensor was bad would it cause this EGR malfunction? Or would the SPST relay or ecm be the likely culprit?

My only way to diagnose these problems are a manual, a digital volt meter and a jumper wire for the ALDL. I do not have the ability to hook it to a real time computer analysis of what all the systems are doing while driving the vehicle. I don't want to throw a bunch of money at parts replacement (For the above mentioned diagnosis I swapped parts out of my 93 suburban) and would like to learn more about these systems so I can repair them myself.

Thanks in advance for any assistance! Chris

PS, I do have my eyes on a couple of old Travealls that I would love to aquire and build into an off-road excursion vehicle.
My first 4x4 was going to be a Travelall until the owner took it skiing the weekend before I was to buy it and wrecked it on an icy mountain road. I've had an unfulfilled desire to own one ever since then.

[Bill usn-1]

What ecm's are in the vehicles?

[Chris Cuzynski]

The original ones from the factory I presume, however I can find out and get back to you.

[Dana Strong]

The Ford systems of that era which I'm familiar with run the electrical control to a vacuum modulator, the vacuum going to the EGR valve, and a position sensor on it gives feedback to the computer. The wrong sensor (or a bad one) will give bad data about return exhaust flow,so that might be a problem. The EGR doesn't directly affect the exhaust O2 much but does affect the nitrous oxides. I don't know which other sensor readings might cause the computer to 'calculate' the EGR requirements wrong; I'd check for vacuum leaks, especially at the vacuum hoses.
You might go to another site which has a few mechanics more familiar with Fords:

Tempo/Topaz Club

It also has a 'sticky' thread under the "Mechanical and Suspension" section which shows how to get into an online manual, although it doesn't seem to work for everyone and the manual doesn't cover all topics the way the Ford manuals do; it does have wiring diagrams though.
Here is the second link given for the site:

Online Manual

If that doesn't get you in, do a search for 'online manual' or related words; someone else posted a thread with another way in.

[Bill usn-1]

Dana,
I'm not following all the Ford talk and links.
He has a 92 and 93 chevy.

I'm just trying to determine the egr system each has.
Like Ford, Chevy used a couple variations.

[Chris Cuzynski]

Bill,

The service # on both ECM's for the 93 Suburban and the 93 pickup are the same number 16168625. The 4 letter suffix is different Truck BDJZ, Suburban BNAZ. So truck is 16168625-BDJZ, Suburban is 16168625-BNAZ.

Then there are ECM serial numbers?
93 truck 868DJZK330475621
93 Sub 868HAZK331325467

These are the ones I swapped parts back and forth with.

I have not worked on the 92 Blazer yet, it just has the same problem.

My daughter has that at college in Monterey and she will be home this weekend.
I am pretty proud of her, she figured out it was the EGR hanging open by herself and unplugged her wires to the EGR solenoid.

[Chris Cuzynski]

Dana,

Thanks for your reply. The EGR system does control NOX emissions. It does that by introducing exhaust into the combustion chamber to cool the mixture and reduce those emissions. I presume the O2 sensor may register some type of feedback electrically to the EGR sensor to open or close the EGR based on a reading sent by the O2 sensor to the computer. My thought is if the O2 sensor is faulty and sending the computer or EGR sensor a message that the engine is in closed loop when it should be in open loop, the EGR will open while the vehicle is in Park, neutral or running at low speeds.

[Dana Strong]

Dana,
I'm not following all the Ford talk and links.
He has a 92 and 93 chevy.

Sorry; my DSL was acting up and driving me crazy and I was in a rush already.... I thought he'd said Bronco.

[Bill usn-1]

Which diagram are you using for your system?
I checked out autozones and they show the 94 but not 93.
Should be close.
also-the 7427/8625/6395 are all the same wiring PCMs.

The only thing common on the egr and heated O2 is the 12V that is used to operate them. You can check that with a voltmeter.
The O2 and speed sensor signals are used to control the egr operation but are not physically connected. It is all thru the software in the pcm.

az wiring

[Chris Cuzynski]

Bill,

I was using the diagram on the site here for doing the conversion and the voltage test sheet for the initial setup.

If the VSS or the O2 sensor were bad and sent bad info the the PCM would this cause the EGR to open at the wrong times? If I unplugged each one would it isolate the problem? Unplugging the O2 sensor would cause the engine to run in open loop, correct?

I initially thought the problem was the EGR solenoid, but when I swapped in a working one from my 93 Suburban to the 93 truck the EGR still opened in park and at low RPMs. When I reinstalled the EGR solenoid on the Suburban it ran fine. Strike one, same with all the other part swaps. I guess I am narrowing it down. Not much left, as you say, VSS or O2 sensor I guess.

If the mileage dropped off a bit and the tailpipe became darker would this be an indication of a faulty O2 sensor? I keep reading there is no reliable way to volt check or electrically test an O2 sensor.

It seems that the PCM would be the last thing to suspect. Would it be advisable to change the O2 sensor, the VSS and finally the PCM to find the culprit?

I am lucky to have one working vehicle I can exchange parts with, but I would like to learn how to diagnose with a volt meter before switching these parts around as I have done with the previously mentioned pieces.

Last question, would the TPS be suspect at all?

Thanks, Chris.