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EGR Opens too soon

S

Srgould41

CEG'er
Joined
Oct 20, 2008
Messages
44
I am opening a new thread for this issue now that I have narrowed the problem down to the EGR. Originally I was trying to find out why my engine was stumbling at low throttle.

So here is the issue. When pressing the throttle a tiny bit the engine stumbles and nearly stalls.

The cause is the EGR opening too soon. I have placed a vacuum gauge on it and witnessed the issue. As soon as I press the throttle a tiny bit the EVR Solenoid lets vacuum through to open the EGR. The causes the engine to stumble badly.

This problem has gone on for more than a year now. There are no fault codes being thrown.

I have replaced the O2 sensors, the Mass Airflow Sensor, the Engine Temp Sensor, plugs, wires, etc.

A couple weeks ago I plugged in a brand new EVR Solenoid as I suspected this was bad. It made no difference. The EVR is good.

I see two possibilities. ONE is that something upstream of the EVR Solenoid is triggering it at too low a throttle position or, TWO, this is normal and that the engine management should compensate somehow and isn't.

I have verified the input and output of the TPS and watched it on my computer (I bought an OBD II appliance and computer program to monitor the engine ECU). The TPS seems normal in operation, however the computer does read 17% or degrees at idle. Can't remember which value it said. That seemed high to me, but it operated normally even so.

So can anyone help? Suggestions on what to check?

Steve
 
The EGR works perfectly. No need to pull it. I have put my vacuum pump on it and opened it at idle. Same RPM drop and stumble as I would expect.
 
so you mean to tell me, your EGR isnt working properly, so you replaced everything but the EGR?
 
What year, engine & trans? I'll look over the OBD II system operation summary & see what I can find. What is your DPFE voltage? That's the first thing I would check.
 
In his case, if the valve WERE clogged, it would HELP his problem by limiting the flow that is causing the stumble. However, the valve is completey mechanical and working properly so in the course of troubleshooting a root cause, doing anything with the valve is just a waste of time.

The issue is that it seems the PCM is commanding EGR flow when it shouldn't be... the valve is just doing what the PCM is commanding. Therefor, the problem lies in determining WHY the PCM is commanding the flow.
 
AliasJerk said:
What about the DPFE?
Click to expand...
Yeah, he's my first suspect. It could be giving an incorrect reading to the PCM, and the PCM is commanding EGR flow to get the DPFE numbers where it wants them.

Srgould41 said:
The TPS seems normal in operation, however the computer does read 17% or degrees at idle.
Click to expand...
The only spec I have for the TPS is in voltage. At hot idle, it should be between .53-1.27v.
 
Thank you EVERYONE for all the quick and valuable responses. My bad for not providing more info on the car, engine, etc. Let me give that now.

96 Contour GL. 4 cyl, regular gas model with auto trans.

I have NOT checked output voltage on the TPS. I am not really sure HOW without fabbing up some special jumpers so I can get my multi-meter between the plug and TPS. I did check static voltages at the harnes plug with key on, engine off. They were in spec. TPS resistance is smooth all the way through the throttle range (engine off).

I have not looked at the DPFE before. I do recall a section on how to check it in the manual. I will try to check it tonight after I get home from work.

And thanks SicSE for understanding the issue about the clogged EGR. The EGR does work properly, it is being COMMANDED improperly. I am not always the most clear person in stating things. Just ask my wife!

Steve
 
Alias... When I activate the EGR to open it the engine RPM drops as it should with a normal EGR function. If I open it all the way with the engine at idle then the engine will nearly stall. If I held the EGR fuill open at idle it might just stall, but I have backed off as soon as it was evident the EGR worked normally.

So the problem is not that the EGR doesn't let exhaust flow (clogged tube), it does, the problem is that it opens at too low an RPM.

To further expand on what is happening to the vacuum port...

When I plug my guage into the vacuum port downstream of the EVR and then start the engine I see a tiny flow of vacuum, 1 hg or so... When I barely press the accelerator pedal (I am talking 50 to 100 RPM above idle) it jumps to around 8 hg. When I bring the RPM up over 1500 the EVR goes full open I believe (same vacuum on both side of the EVR). That second phase appears to be the normal operating function.
 
... a lot of people who don't understand HOW the EGR system works....

Your OBDII TPS percentage is normal, don't waste any time on it. Normal voltage reading is around .75-.99 vdc with is just under 20% of the 5 vdc reference supply. 17% of 5 = right in the typical range.

When I barely press the accelerator pedal (I am talking 50 to 100 RPM above idle) it jumps to around 8 hg. When I bring the RPM up over 1500 the EVR goes full open I believe (same vacuum on both side of the EVR).
Click to expand...

Disconnect the DPFE sensor's connector and repeat this exact test. If there is no change in the EVR solenoid's function this time, replace the DPFE sensor.

You can also monitor the voltage applied to the EVR solenoid's input wire. At zero commanded flow, the signal line should equal battery voltage. As the PCM calls for EGR flow, the voltage will drop by an amount that is proportional to the "level" of the commanded flow. At the same time, if you were monitoring the output of the DPFE sensor, you would see a proportional change in the output that tracked (ideally) exactly with the input command to the EVR solenoid from the PCM.

Your problem is either the DPFE sensor or the PCM. FWIW, the PCM should NOT be commanding EGR flow while you're sitting in the driveway...

Steve
 
Last night I checked the DPFE. First off as soon as I pinched the downstream vac hose it crumbled to pieces in my hand. New hose time. The DPFE hose nipples were quite corroded and a little clogged. The wire harnes voltages with ignition on, engine off were correct. I don't have jumpers to allow me to check voltage with engine running. I then removed the DPFE and checked resistance on the bench applying vacuum to the reference port since I could not check voltage output. There was NO changes in resistance with changes in vacuum. NONE. There should have been resistance changes if there is supposed to be some sort of voltage change. Right?

I am going to replace the DPFE and hoses tonight (if the dealer has one). I'll post the results tomorrow.
 
Another concern with the 4 cylinder is a plugged exhaust, leading to burning up the DPFE and hoses.

How does the car run otherwise. Does it seem to be down on power especially with higher loads and speeds? If you have an assistant rev the engine while you stand near the exhaust, does it sound wheezy? If so those are signs of a plugged exhaust. Even if the DPFE is functioning properly (and it sounds like it may not be), the readings will be messed up if the exhaust is restricted.
 
FIXED

It was, indeed, the DPFE. Last night I replaced it along with the hoses. Placing my vacuum guage on the EVR port going to the EGR saw no vacuum at idle or just above. The one thing I regret not doing was to open the throttle more until I could see the EGR get vacuum. I may do that over the weekend to be certain the system is fully functional.

Thank you all for your aid!!!

Steve
 
no problem. DPFE's occasionally do fail on the contour, at least its a cheap part.
 
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