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Car Forum / Chevrolet / Chevrolet Trucks / December 2004ECM wire harness (replace?).
I have a 90 chevy half ton with a 350 and AC. I have been having the check engine light comming on with a code 32 (EGR), I replace the EGR valve and the EGR solenoid and the problem still persists. I was told that the ECM or the wire/harness was the problem. Well I took a look at the harness comming out of the fire wall from the ECM and it had mud and dirt clumped on it and when I cleaned it I noticed that I had some rotten wires under the mud. Well I what I need to know is how hard is it to replace this harness or even if I should. The way I see it is I have three options: 1. go to the junk yard and get one 2. go to the junk yard and get only the firewall connector and cut the wires and splice them 3. buy a new harness $400. Me I like #2. I also can't figure out how to get the connector on the fire wall off. It looks as if it should just disconnect, but there also looks like it might have screw holding the two parts of it together. I can see a slot? that looks as if it might have a screw, but I can't see inside it because of the AC. I lifted the clips and pulled, but the connector didn't move.  SignatureDave Did you Clean the Carbon out of the Hole the ERG fits in?? > I have a 90 chevy half ton with a 350 and AC. I have been having the check > engine light comming on with a code 32 (EGR), I replace the EGR valve and [quoted text clipped - 17 lines] > looks as if it might have a screw, but I can't see inside it because of the > AC. I lifted the clips and pulled, but the connector didn't move. > Did you Clean the Carbon out of the Hole the ERG fits in?? Yep :). Wasn't much in there. >> I have a 90 chevy half ton with a 350 and AC. I have been having the >> check engine light comming on with a code 32 (EGR), I replace the EGR [quoted text clipped - 3 lines] >> dirt clumped on it and when I cleaned it I noticed that I had some rotten >> wires under the mud. >I have a 90 chevy half ton with a 350 and AC. I have been having the check > engine light comming on with a code 32 (EGR), I replace the EGR valve and [quoted text clipped - 23 lines] > the > AC. I lifted the clips and pulled, but the connector didn't move. 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. >>I have a 90 chevy half ton with a 350 and AC. I have been having the check >> engine light comming on with a code 32 (EGR), I replace the EGR valve and [quoted text clipped - 30 lines] > 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. SignatureDave 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 > >>I have a 90 chevy half ton with a 350 and AC. I have been having the check > >> engine light comming on with a code 32 (EGR), I replace the EGR valve and [quoted text clipped - 42 lines] > 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 [quoted text clipped - 8 lines] > the codes every few months to be sure nothing else is stored. > B >> Thanks Scott, >> There is a two piece connection there, but getting it off is what is [quoted text clipped - 12 lines] >> -- >> Dave 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?. SignatureDave > Thanks TaskMule, > I would ignore it, but when the light comes on my power goes to heck. It is [quoted text clipped - 7 lines] > 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). 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. > I was wondering if the ECM really knows what the EGR is doing because it > gets no feed back from these old EGR valves. Yes it does. > 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. 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. > My light only comes on driving down the highway, never in town. Is yours the > same way?. 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. > > Thanks TaskMule, > > I would ignore it, but when the light comes on my power goes to heck. It is [quoted text clipped - 12 lines] > You can ground the ALDL (jumper it) with the key on, this should > activate all relays and solenoids, no, it won't all that will accomplish is reading the codes > then see if the EGR solenoid > is active, i.e., ground the ALDL, connect a test light in place [quoted text clipped - 25 lines] > foundry sand from when the manifold was originally cast, it > passed all of the functional tests in the FSM. >> > Thanks TaskMule, >> > I would ignore it, but when the light comes on my power goes to heck. [quoted text clipped - 23 lines] > > all that will accomplish is reading the codes 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). SignatureDave >> > Thanks TaskMule, >> > I would ignore it, but when the light comes on my power goes to heck. [quoted text clipped - 23 lines] > > all that will accomplish is reading the codes 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. SignatureDave > > You won't see a completed ground circuit thru the ECM until there > > is an actual command to ground -that- circuit. [quoted text clipped - 4 lines] > > all that will accomplish is reading the codes 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 <snipped actually> 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. > In article <dOpxd.52solenoidi_s54>, > [quoted text clipped - 50 lines] > 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. SignatureDave >> Thanks TaskMule, >> I would ignore it, but when the light comes on my power goes to heck. It [quoted text clipped - 15 lines] > is active, i.e., ground the ALDL, connect a test light in place > of the EGR solenoid and see if it lights. 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 <sigh>. >> They don't have a varable >> resistance pot (sensor) like the newer ones that relay it's stats back to [quoted text clipped - 8 lines] > EGR problem. Could be something as simple as a choked off MAP > vacuum passage. Hmmm. Wouldn't they throw up a code also?. > >> My light only comes on driving down the highway, never in town. Is yours [quoted text clipped - 4 lines] > foundry sand from when the manifold was originally cast, it > passed all of the functional tests in the FSM. Grrr, more to think about and my head hurts as it is. SignatureDave > 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." 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. > 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 [quoted text clipped - 14 lines] > > Hmmm. Wouldn't they throw up a code also?. Since they are rather dumb devices, no, not always. > > > >> My light only comes on driving down the highway, never in town. Is yours [quoted text clipped - 6 lines] > > Grrr, more to think about and my head hurts as it is. 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? >> This is out of Haynes Techbook, Automotive Computer Codes & Electronic >> Engine Management Systems p.8-36. [quoted text clipped - 8 lines] > Whether Haynes is correct or not will have to wait until I get to > work and check the diagnostic procedure in Mitchell. Thanks, that will sure help alot. > 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. Great idea :). > 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. Wouldn't hurt, but it will have to wait till after the new year :(. > >> The test I posted in reply to TaskMule is incorect it should have been [quoted text clipped - 34 lines] > Is your exhaust system stock with the OEM cat-con functioning as > it should? 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 :). SignatureDave 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. > 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. 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. SignatureDave |
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