3400 Diagnostic Question

[Bigern]

Hi All,

I'm doing some diagnostic info on my 2004 Monte Carlo LS with a 3.4L. Has 270k miles, so alot of things likely need replacing. I'm going through and trying to make sure that everything is operating as designed from factory, i haven't bought the credits to edit the tune yet, though i will in the future, but i'm trying to diagnose an issue with a lean condition under load. I had an EVAP large leak code, which i replaced the Purge Solenoid, the Vent Solenoid, and gas cap. That was taken care of. I was still getting LTFT over 20% under acceleration. I cleaned the maf sensor, and the throttle body with their respective cleaners. I sprayed down the intake with carb cleaner and found a small vacuum leak near the EGR valve. As this was the original EGR, I ordered a Delphi replacement for the EGR valve, even though i had no codes that required it. I replaced the vacuum lines and PCV valve as well, to make sure i wasn't missing anything else. After replacing the EGR valve, the car started throwing a P0404 code for EGR Valve Circuit Range/Performance Problem. The original issue of lean under acceleration still exists, though Idle LTFT went to the negative side and the Idle rpm came down to 600-700 from 800-900, so i believe the vacuum issue is taken care of.

My question is, should i attempt to clean the EGR, or just attempt an RMA for it.

The other issue i am seeing is the O2 readings on VCM Scanner are not matching. I'm including a log of a short drive if anyone can take a look. It appears as though something is adding around 0.4V to the baseline O2 sensor value, though when i look at the voltage reading from B1S1, it appears much more natural. It just appears glitchy in places and is something that i had not seen when i was working on my '13 Silverado. I Disconnected the battery for 10+ minutes in hopes the ECU would relearn the parameters for the EGR, but the P0404 came right back, and that is the scan that is attached.

Any tips for either the EGR issue, the glitchy issue, or the Lean under acceleration issue would be greatly appreciated.

Thanks,
Bigern

After Battery Disconnect.hpl

[blindsquirrel]

A good rule of thumb for these times we live in: All new parts, no matter the brand or price tag, should be assumed defective until proven otherwise.

[badcoupe]

Prob junk egr, as far as the lean code,how’s your fuel pressure? I typically smoke test for vacuum leaks which are many times the root cause of lean codes. It’s been awhile since I’ve seen a 3.4 but iirc they only have one upstream oxygen sensor that reads both banks, H02S B1S1. See if you also have a B2S1 but I’m betting you don’t. The b1s1 will be your main one to monitor; s2 is downstream used for catalyst monitoring.

[Bigern]

Yeah, I set up an RMA for the part, though i gotta buy new then get a refund once they receive it back. I wasn't aware at first but this ECU does allow you to track the commanded position, actual position, and voltage of the EGR valve. So after logging that, I saw that the spike in ignition timing i was seeing were when the EGR was attempting to open. The EGR does not react well to voltage though, and its very erratic. I've included a couple of screenshots, the first is the EGR trying to operate while driving, before it gives up on it and leaves it closed, which would explain the lean condition under acceleration cause the VE table is expecting some exhaust gasses in the intake. The second screenshot is where i found you can set the EGR position manually. It appears to react well when setting to 50% and 30%, but freaks out when attempting to set it to 20%. So I either have a bad EGR, which is possible, or i have a wiring issue hidden somewhere giving some bad reactions. Any other thoughts are appreciated however. EGR Valve and Timing.pngEGR valve manual.png

[Bigern]

Yeah its a lateral V6 with a crossover pipe and only a single set of O2 sensors. I did check the fuel pressure, 50 PSI with the vacuum line off the regulator, and 40 PSI with it on. Leaked down to 35-33 with the key off. I have a new regulator coming just in case, i was getting conflicting information on if 40+ psi was enough, or if it needed 52-59 psi. Also need to throw in a new fuel filter but the line is rusted solid to the filter, and i need to buy some tools to cut and patch the line next time i get paid.

[Bigern]

Hi all, still having a touch of an issue. I got a replacement EGR, still having the same issue. The reported position of the EGR is all over the place, Oscillating from way open to way closed, even with a replacement EGR. Included is a screenshot of the second new EGR. So the question I have is, should i assume this make/model of EGR is not compatible or is it more likely i have a wiring issue on the signal wire returning to the PCM? EGR Valve replacement.png

[TheMechanic]

Need to post the OS. Can't remember to well but there were some software issues during that time with EGR. I remember possibly this one that there were two different manufacturers of the EGR valve. One was Siemens I believe and other was Delphi. Was a bulletin. Not at home so I can't check.
Use Blindsquirell 's website find.
https://tis2web.service.opel.com/tis2web/

[Bigern]

I pulled the calibration ID, thank you for that btw, no mention in the notes about EGR however. Would I need to take it to a dealership to verify that I had the correct calibration for the PCM? I have HP tuners, but i have not bought the credits for this vehicle just yet. Included a snip from your link. PCM Calibration.png

[TheMechanic]

You would just perform a read and see if the OS is the 8823. Also if you notice the EVAP enhancement for P0449.
Often times what is said as a correction is only part of some solutions that are corrected.
Have you commanded EGR operation with a scan tool? Adjustment is usually in 10% increments. Just see if the commanded and actual line up within a couple %'s

[Bigern]

Thanks, Looks like I am one behind on the calibration, its showing Cal ID: 12587799, which is one behind the current one of Cal ID:12618869. Which means i do not have the P0449 update, though i have not thrown that code. The code i get is P0404 due to the wild swings of the EGR. See screenshot Current Tune and Screenshot.png.

Yes, i can command the EGR to any %, and on the first replacement, it would work fine on anything over 30% commanded. With my second replacement, it doesn't seem to want to track for any percentage. I just doublechecked the wiring at the connector side today and cannot identify any issues. When I get a chance i need to do some testing on the electrical side, make sure its getting 5V on the high reference side and so forth.

At this point though, after replacing the fuel pressure regulator, i think i may be getting some leak down from the injectors, that's a separate issue from the EGR, but still i'm getting very rich idle, 20-25% negative fuel trims at idle and low load scenarios.

Thanks for your time so far.

[TheMechanic]

Injectors in those years were marginal when they introduced ethanol fuel. At the dealer we had a HUGE issue with Corvette injectors until they produced the green stripe multec to replace the factory injectors. LOT's of warranty. Engineers claim was the ethanol was eating away the insulation on the windings of the injector causing them to short.

[Bigern]

I failed to remember how much the evap would put back into the intake, and i had just filled gas, so likely the extra fuel was from the EVAP canister. Though I did have one other question. I went through and performed a test on the EGR, and it will stabilize on 100-30%, but not below 30%. This is only when the engine is not running. See photo of the test. EGR Step Check.png.

What i'm seeing is when the EGR is operating, i'm getting large spikes in ignition timing, around 15 degrees. It doesn't track very well, its either an extra 15 degrees, or nothing. I can't find anywhere in the tune file about the EGR adding timing. I am wondering if i have a wiring issue that is disrupting other systems. In this example, its the spikes in ignition timing while the EGR is operating, before it shuts it off and throws the code. Also the generic O2 sensor seems to have a floor at 400mV. The B1S1 tracks fine, but the generic sensor seems to have this bottom to it. I'm wondering if i have a bad ground, or a stray voltage somewhere. Next time i get the opportunity to work on the car, i'm going to clean up the grounds for the PCM and the Ignition Control Module and also inspect the Harness at a few splices if i can find them.

[TheMechanic]

Should be in the Spark tab Advance>EGR

[Bigern]

I'm only seeing min temp to enable EGR diagnostics. That's ok. I'm starting to suspect that the Linear Pot in the EGR valve is fouled.

[Bigern]

Wasn't the linear pot. Took the EGR apart today and it actually has a hall effect sensor in the Delphi model i bought, not a linear potentiometer. My next step is to try to source an OE EGR from a junkyard to verify that it not the Delphi Model that's causing the issue, mismatch of design or some such. I had some help today and was able to verify when the valve is oscillating, it is not an error in the sensor, the pintle is actually chattering as well. So it's either an issue with the second replacement EGR, or a wiring/PCM issue. When the engine is cold, and i manually operate the valve with key on engine off, I can get the EGR to track decently for everything over 15% open. As soon as the engine starts however it starts going all over the place. I don't know if i am getting stray voltage on the control wire causing it to go fully open all the time, or if my PCM is not generating an appropriate waveform to operate the valve, or if the valve is not responding to the waveform in the appropriate way. More to come.

[TheMechanic]

Like I said, seems to me there were 2 different EGR valves. One was Delphi and one was Siemens. Maybe someone swapped it and never got it sorted out. Again this was a while ago so I may be totally off.

[Bigern]

Like I said, seems to me there were 2 different EGR valves. One was Delphi and one was Siemens. Maybe someone swapped it and never got it sorted out. Again this was a while ago so I may be totally off.

Thanks for all your help TheMechanic. I grabbed two junkyard EGR's over the weekend for about $8.00 apiece, and put the better of the two on my car, lo and behold the issue went away. Junkyard EGR.png

Looks like the issue was with the Delphi EGR valves. In spite of being a recommended replacement for the GM EGR, neither of the two worked without throwing the P0404 code. At this point I have 2 spare EGRs, even after sending the original back for warranty replacement credit. One of the new Delphi and another GM Junkyard. When I get a chance I will disassemble them, study them, and see if i can find any difference between the two. It is my suspicion that the Delphi part has a recoil spring that is far too weak, thus causing the oscillation of the valve when powered by the PCM in my car. I have a video of how bad the chatter was, and I will update the thread with said videos after I get them onto the laptop. Hope that if someone comes across this in a google search in the future can benefit from my attempts to nail down the issue.

[TheMechanic]

Does the functioning one look slightly different? Or missing the Delphi insignia? Is it a different part number stamped on it?

[blindsquirrel]

https://www.mcmaster.com/products/springs/

[Bigern]

I'll take a second look and try to nail down some part numbers tonight, for now here is the video of how bad the chatter on the valve was. https://streamable.com/x9awml