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Hello fellow Dirt Mongers,
I am a bit stumped pls.
I’m having a bit of trouble testing my egr valve operation on this motor. I believe I understand how the valve is controled by the PCM, and by all accounts (schematics, tech sheets, forums, videos) I seem to be right. 5 pin connector, Middle 3 connections are 5v ref, pintle position potentiometer, and ground (not part of my dilemma)… outer two pins are 12v feed from PCM and PCM provided PWM ground, which is my dilemma. What I find is almost the opposite. First, I can manaully energize the soleniod with 12v and watch the pintle open and close & with corresponding signal from the pintle position pot for the PCM. Now, @ KOEO by DVOM & @ the EGR harness connector (disconnected), I’m reading a constant ground on the PCM ground control pin where I’m expecting to find open connection (EGR should not be in any commanded open state). And, at the 12v feed (Where I expect to find a constant 12v), I’m finding almost zero volts. ~34 mv. I disconnected the PCM connector (C4 black) tested the EGR wire harness for continuity and ground short between the EGR connector pins and the PCM pins (16 & 20). No opens or continuity to ground found, but when I reconnect the PCM C4 I have constant ground at the connector. So, I’m convinced the PCM has internal damage, idk maybe an internal short on the ground control circuit took out the 12v feed. But ! , I have two other same era vans also with the 350. I test the others the same way and find the same results? So, either they’ve all failed in the same way, or I’m so damn lost :] Oh, and MIL is no help & clean.
Thanx much!
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I have a 2000 GMC van with the same engine. I think you logic may be a little flawed if I understand your essay. Most controlled devices on GM cars are controlled by the ECM providing ground to the device while 12V is fused direct to the device. In order to check the ECM output you will need to measure with your multimeter plus on 12V (+) and the negative lead on the ECM output.
Are you testing the EGR because you have a check engine light on? If not, do you have a driveability issue that leads you to believe it’s a faulty EGR?
@hondaguy453 no mil, just driveability which, as you’ve guess, is my primary goal. I’ve been going through systems and every improvement I make is noticeable, but still not there yet. I’ll go into more detail:
found timing chain pretty darn sloppy. replaced.
found CMP Ret timing a couple pubes off. adjusted.Starts and runs fairly smooth with a slight miss here and there. But my biggest issue is when I punch it, it hesitates & I do hear a short burst of sucking sound. Not sure if it’s vacuum leak or throttle opening. But testing for vacuum leak with my vacuum gauge, I don’t believe. It runs pretty steady @ 18-19 PSI. And, even after reviewing vacuum diagnosis w/ Eric video, I believe she’s running normal. Fuel pressure to 60PSI and drops to 55 ish. Bleed down holds… but I’d say bleeds somewhere around 1/2 to 1 PSI per 60 seconds. So, I started looking through systems and am current @ EGR :]
@Jotmon1 Hi, thanx. If I understand you correctly, I measured KOEO across Battery & EGR harness connector (disconnected):
B+12V – PCM control circuit = 3mv
B+12V – pintle circuit ground = 12V
PCM 12V feed – B- = 40 mv
5V pintle ref – B- = 5VOk, I would swear I saw different before, but I stand corrected regarding the ECM control circuit. But I should still have 12V feed, right?
Ohhh, gotcha gotcha. If you have a vacuum pump you can test ref voltage to make sure voltage changes in reference to the pintle position. You can also suck on the vacuum line going to the egr valve if you don’t have a vacuum pump.
This one’s the electronic one. I wondered maybe it was jammed open a little causing my grief. But removing it, it was fine. cleaned it out some. reconnected to wire harness. I can watch the pintle movement on my scantool while I push the pintle around with my phillips head. That’s what got me pokin around the egr which lead to my voltage issues.
Gotcha gotcha. Have you tried to move the pintle with your vehicle running to see if it would stall? And does it move pretty freely when you do try to move it?
Well, Instead of while it was running. KOEO, de-installed with harness connected… I injected 12V (less than 5 seconds at a time) from battery to the PCM 12V feed (which doesn’t seem to be there from the PCM) and can eyeball the pintle move as well. Yes, pretty freely. So I;m convinced the EGR itself is working properly and reporting back properly. I want to call the PCM, but when I looked at my 2 other 350 vans, they all seem to have a missing 12V feed in the identical manner also which has me questioning myself here.
which, come to think of it… again, there shouldn’t have been any ground for the soleniod to energize?
I think you’re okay here man. You might be looking in it too deep lol. Especially because you get the same reading with the other vehicles. For more peace of mind you could have someone get in the car and blip the throttle to check if the voltage and pintle move.
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