96 Saturn P0401

I have a p0401 EGR insufficient flow code. Replaced the EGR valve 2 times, 2 different brands, same problem. With the egr unbolted from the intake (vac port plugged) I can scope the blue wire and it shows the command to open in steps. I scope the brown wire (return) and it shows the valve opening. And the valve opens in steps. Working properly. When the valve is attached to the vehicle, Blue wire shows commend in steps to open but valve will not actually open until it reaches 50% commaned opening. @ 50%, valve opens to 60% (vehicle runs rough), @ 70% valve is open to 90%(vehicle will die). Why will it not open until it is commanded 50%? What am I missing?
I appreciate any help with this problem
Thanks

You're missing the port that's full of carbon and restricting the egr fllow

Jeff thanks for the reply, but, If it was just the port plugging up, I should still show on the labscope that the valve is opening. Un hooked from the intake, I have exhaust coming out of the exhaust port and plenty of vacuum. The scope and even the data thru the pcm does not show it is opening until it gets to 50% requested during manual test.

So are you using a lab scope or a scan tool with bi directional controls than can actuate the egr? ALot of the Gms require a parameter reset with a new egr! Did you perform that? What scan tool are you using that shows 50%? there's video on youtube or Wells manufacturing that shows how to test the GM egr with a 9 volt battery and how to clear the ports

I am using the SnapOn Vantage scope dual pattern. I am using the Mater Tech scanner to actuate the EGR valve. With the vantage hooked up (1st pattern watching command, 2nd pattern watching the acutual (return)). When i go to the EGR test thru the Master Tech it will also show me EGR data while I am commanding EGR to open or close. And as 1st posted, watching the scope and data, unbolted from the car works and data is good, when bolted to intake, commend is there, but no response from EGR until 50% or more.

What it almost appears to be is as if the egr valve is stuck then pops open at 50%. And it even happens with a new EGR of a different brand. I purchased an ACDelco EGR valve to try on the vehicle when I get it back at the shop. Trying to figure out what else I can try or some idea before the car returns.

I looked around for a reset procedure and did not find one.
I had the PCM flashed/updated from the dealer. That was after the first new EGR valve was installed. Same problem.

I take it with those tools you're not a diy'er? The vantage is an awesome tool! Havent' used the Mastertech in quite a few years. So not installed the egr scopes fine, same pattern result as what the vantage shows for applied but when installed it only gets to 50% lift? That's weird! I wonder if you have a lkow voltage on the actuator driver although if it's using the same circuit just not bolted down then it shouldn't matter! What does the MAP sensor do when the egr is commanded? it is responding properly? It to me still sounds like the port is not flowing enough and the valve is opening but the map sensor isn't seeing the pressure change it wants to see! If you haven't seen that video check it out it's the best i've seen that explains egr and port restriction works. I mean it shows before where the valve is actuated and the engine stutters but it doesn't stall! it should stall it

When the EGR is installed, It will open at or after cammanded 50% and have to raise rpms of engine or it will stall. What i can see map is dropping vacuum. very limited time to scroll thru data before pcm locks out egr test. Also EGR is not showing movement until it hits 50% (when installed).
Also do you have a link to that video?
Yes I am a automotive technician over 20years. This problem is a first with this no movement issue. Normal issues are plugged passages, bad harnesses, EGRs, DPFEs, or pcms. And I have always been able to actuate EGR valves and see what they do in respect to function and yet always show movement even if the passages are restricted.

www.wellsmfgcorp.com/video_egr_lq.html

It's a 3.1 in a 97 buick century but I'd imagine the valve is very similar if not the same and of course the port location may be different but still most work the same way.

As well on Youtube there's quite afew video's done by a guy named richpin that all seem to deal with a Saturn.

I do not know if you have a SOHC or DOHC but Alldata list a TSB for this and has to do with having the correct EGR installed because of flow difference between valves.

I would also check the exhaust back pressure maybe too much for the pintle to open untill it reaches 50%. I know you said the intake port is clean but like Jeff said if it is not 100% open 50% of flow maybe needed to get results.

Would this TSB have part numbers to reference? This is the first post on here in along time that's really perked my interest. It's always a nice change to help out a fellow tech in the trenches with a tough vehicle vs the all the diyers with parts from the zone in hand. Hopefully we can get to the bottom of it and he'll stick around to help others. Maybe he could try IATN?

BULLETIN NO.: 01-T-29

ISSUE DATE: May, 2001

CATEGORY TYPE: Engine - 13

CATEGORY: Emission Controls

CORPORATION NO.: 01-06-04-031

TECHNICAL INFORMATION BULLETIN

SUBJECT:
(MIL) SERVICE ENGINE SOON Telltale is Illuminated With DTC P0401 (Install Correct EGR Valve)

MODELS AFFECTED:
1996 - 1999 Saturn S-Series vehicles

CONDITION:
Some customers may comment that the (MIL) SERVICE ENGINE SOON telltale is illuminated with DTC P0401 present or stored in PCM malfunction history.

CAUSE:
This condition may be caused by an incorrect EGR valve being installed on vehicle. The EGR valves used on 1996 - 1999 model year vehicles have a different flow rating than EGR valves used on 2000 - 2001 model year vehicles

Inspect part number stamped into the top of EGR valve. The correct EGR valve part number for a 1996-1999 model year Saturn vehicle is 21006601.