ECM wire harness (replace?).

Did you Clean the Carbon out of the Hole the ERG fits in??

Dave 305 wrote:

Yep :). Wasn't much in there.

You can replace or fix it anyway you like. Just be sure to make good connections and make them water tight. I dont think there is a connector at the firewall, it probably just goes through the firewall and it is a grommet of sorts.

Thanks Scott, There is a two piece connection there, but getting it off is what is worring me. I am going to the junk yard/parts store tomorrow to see if I can see how it is hooked to the fire wall (screw/clip). I did a google search, but got nothing. I don't want to do something I will regret later, like break it.

If I splice it I will solider the wires and heat shrink them to keep water out. This should do it (I hope). I was also thinking of incasing the wires in silicon (to a point) just to be sure I am not doing this again in a year or two.

I have a 90 Sierra 305. My egr failed a few years ago, I replaced it, cleaning the port properly however after about 40 min of driving the light comes on with the same code. Shutting down and restarting (stopping at the store on the way home) resets the light but it comes back a few days later, EGR code always.

I've happily ignored it for 3 years, engine runs flawlessly with 550,000km There's no way I'd dive into the wiring harness to slove this issue in my case. As long as it runs well I don't care about the Check Engine light. I check the codes every few months to be sure nothing else is stored. B

Thanks TaskMule, I would ignore it, but when the light comes on my power goes to heck. It is so bad that when I am trying to pass I have to floor it just to get the speedo to move upwards on a flat road (throdle responce = nill). Up until the light comes on the truck runs great.

I did test the wires going to the EGR solenoid and didn't get the voltage I was expecting from a book I bought (Haynes Computer Codes....). I should have had 12v, but I had .500v give or take a few mv. I have 12v on the purple and black to a good ground, but no ground on the gray from the ECM with the engine off and key on. Verdict, bad ECM or bad wire (both suck).

I was wondering if the ECM really knows what the EGR is doing because it gets no feed back from these old EGR valves. They don't have a varable resistance pot (sensor) like the newer ones that relay it's stats back to the ECM. The only way it would know if the EGR is not working correctly is through the O2 sensor, but it only measures O2 not NOx. IIRC the only reason the EGR is computer controled is to make the truck idle/respond better in town.

My light only comes on driving down the highway, never in town. Is yours the same way?.

You won't see a completed ground circuit thru the ECM until there is an actual command to ground -that- circuit. You can ground the ALDL (jumper it) with the key on, this should activate all relays and solenoids, then see if the EGR solenoid is active, i.e., ground the ALDL, connect a test light in place of the EGR solenoid and see if it lights.

Yes it does.

The ECM looks at O2 sensor voltage and MAP sensor voltage when EGR is commanded. Obviously, a MAP sensor problem or an O2 sensor problem can fool the ECM into believing that there is an EGR problem. Could be something as simple as a choked off MAP vacuum passage.

Had one years ago that took a 90+ mile drive on the interstate to set the light off, turned out to be the EGR passage was full of foundry sand from when the manifold was originally cast, it passed all of the functional tests in the FSM.

no, it won't

all that will accomplish is reading the codes

This is out of Haynes Techbook, Automotive Computer Codes & Electronic Engine Management Systems p.8-36.

"During cold operation and at idle, the solenoid circuit is grounded by the computer to block vacuum to the EGR valve. When the solenoid circuit is not grounded by the computer, vacuum is allowed to the EGR valve."

The test I posted in reply to TaskMule is incorect it should have been engine running cold in park, which I just did and got the same results as before .

Hmmm. Wouldn't they throw up a code also?.

Grrr, more to think about and my head hurts as it is.

It would be nice if I could do something like this though. I am going to do a little more research on the subject and try another test I found in another book I have. I also was thinking of hooking my ohm meter to the EGR ground pin from the ECM to known ground to see when the ECM does ground the EGR (risky I know, but it would answer many questions I have).

It would be nice if I could do something like this though. I am going to do a little more research on the subject and try another test I found in another book I have. I also was thinking of hooking my ohm meter to the EGR ground pin from the ECM to known ground to see when the ECM does ground the EGR (risky I know, but it would answer many questions I have).

Repost, I got a 423 trying to read it.

Then according to your manual, you would have EGR function on a cold engine or at idle. This is not the criteria for setting an EGR code. Whether Haynes is correct or not will have to wait until I get to work and check the diagnostic procedure in Mitchell. Meanwhile, you can "Tee" a vacuum gauge into the EGR vacuum hose, tape the vacuum gauge to the windshield and test drive the truck on the highway to see if there is a vacuum signal to the EGR valve. GM TBI units such as yours are notorious for sludged up vacuum ports in the TBI unit, you may want to remove yours and give it a real good cleaning.

Since they are rather dumb devices, no, not always.

Here's more... Most GM EGR valves are back pressure modulated, any change in exhaust back-pressure will effect the way they operate. Is your exhaust system stock with the OEM cat-con functioning as it should?

Dave, just fix the wires first. Then clear the ECM by pulling the neg battey cable. Take her for a test drive and see what happens. Since you replaced the EGR and soleniod I would bet it will be fixed.(assuming the vacuum lines are good and the ECM wasn't damaged by having bare wires) :) Either way the wires need to be fixed first.

Here's the code 32 flow chart from GM for a 1990 C/K 10 w/ 5.7 L engine; (4.3 and 5.0 also)

------------begin GM text Disconnect EGR solenoid vacuum line from throttle body. Ignition "on" engine stopped. Ground diagnostic terminal. Install a hand held vacuum pump with gauge to throttle body side of EGR solenoid. Apply vacuum and observe EGR valve diaphragm. valve should move, does it? Yes No Un-ground diagnostic Is SES light flashing? terminal. If not, see quad driver Vacuum should bleed check. off and valve should If yes, connect vacuum pump close, does it? to EGR valve side of harness Apply vacuum and                       observe valve, valve should move, does it?

--------------------end GM text

The first paragraph in the flow chart pretty much explains that

1) the EGR solenoid passes vacuum to the EGR valve when it is energized. 2) Grounding the ALDL energizes the EGR solenoid.

The yes leg in the flow chart pretty much explains that

1) the EGR solenoid vents vacuum when it is de-energized. 2) un-grounding the ALDL de-energizes the EGR solenoid.

Cadillacs more often than not work the exact opposite though...

Grounding the ALDL to energize solenoids and relays has been part of the GM diagnostic routine since 1981 and remained procedure until the appearance of OBD1.5 and OBD 2 in 1994-95

The only solenoid it doesn't energize is the TCC solenoid, but that is usually due to the open XX gear switches.

This isn't to start or win an argument Gary, it's to help the OP figure out what's wrong with his truck considering that his Haynes manual is giving bogus info.

Thanks aarcuda69062, The valve is good (brand new and so is the solenoid). I will try grounding the ALDL as above and see if I get an EGR solenoid to ECM ground this way.

Thanks, that will sure help alot.

Great idea :).

Wouldn't hurt, but it will have to wait till after the new year :(.

Hmmm, I have been suspecting a bad cat-conv all along, but haven't found the $$ to get a new one yet. My valve is a neg back pressure type by the way.

A little story, The cat-conv was my first suspect because of the lose of power, but when I went to the muffler shop the guy told me to fix the EGR before he would put a cat on because it would screw it up again, (This sent me on my code 32 quest) he did put a new muffler and tail pipe on though. After the muffler replacement I noticed some flakes (looked like galvanzation (sp?)) comming out of the tail pipe, I went back and told him of it and he said it looks like it came from the cat. I doubt this because it was gray and clean not black and dirty, it went away in a day or two. I also had a rich condition and have had black soot/smoke comming out of the pipe (also spurting on the ground), I put a complete tuneup on it and the black smoke quit, but the soot is still there (just not as bad now and seems to be getting better, less spurting). I am also getting white carbon on my plugs and figured it was because of the EGR, but could also be because of a clogged cat?.

I did a vacuum test to see if the cat was clogged and the vacuum gauge was a little slow returning from a snaped throtle, but not bad IMO. This is the first time I did a vacuum test of this kind so I really didn't know what I was looking at.

Like I said in another post if I can find out if the EGR valve/solenoid/ECM are working correctly I can rule them out and feel better about a $200+ cat-conv replacement job :).

Thanks Scott, I haven't had a chance to look into a fix/replacement today X-mass and all, but plan on it soon. I hope the ECM is good, but I won't rule anything out after this.

The vacuum lines are good and I get 20in of steady vacuum at idle at the intake side of the solenoid.