Hello. My 5.4l has a hesitation when I apply just a light accelerator. I just replaced the EGR valve and have done a lot of testing. The vacuum at the EGR valve hose, while driving, is 3 in at slight acceleration and 5 in at normal acceleration. I assume the 3 in is causing the EGR to open a little and cause the stall. Is the vacuum control valve doing this?

 

Hello,
The EGR operation is more involved than that.
Here is an overview of how it works.
First there are several conditions that must be present before the EGR is 'called' to operate.
1. The vehichle speed.
2. The throttle opening angle of the 'tps'.
3. How long the TPS is at the opening angle.
There may be other parameters in play as well.
..Above about 45 mph, the PCM looks at the length of time the TPS is at a stable low angle. This causes a logic decision to signal the vacuum regulator to open and pass vacuum to the EGR valve.
..The vacuum present is lower than the full manifold level and determined by the size of the hoses and passages and by the throttle opening that tends to lower the manifold vacuum depending on the open angle.
..When the EGR opens and the effects are detected by the OX sensors, the igniton timing is advanced and fuel amount is cut.
..The results of all this is a very lean mixture.
..The coils must output there max voltage to fire the very lean mixture.
..If you have one or more faulty coils you will experience a missfire condition when the peticular driveing conditions are present.
..This usually occurrs above 45 mph light throttle in OD and as high as 60 mph and goes away when additional heavy throttle is used that closes the EGR and causes the PCM to exit the EGR routine.
..This coil fault is very often shorted turns and is not a 'hard' failure and does not set a code.
..Hope this helps you understand the complex actions that go on and the issue it often brings to light.
Have the coils stress tested by a dealer to pick out the one that is low in output.
Good luck.

 

Thanks. That is a lot of good information. I have found that with the EGR control solenoid unplugged, all the stall problems go away. It actually runs very well. Blocking off the vacuum to the EGR has the same results. I will do some more testing.

 

Your PCM controls valve operation,- thru the EVR. This only happens @ cruising speed. So for the problem to just go away after vacuum disconnect doesn't make sense to me. I think you'll find the problem to be elsewhere.

Test /go thru fuel system diagnostics, - filter, supply/pressure, regulator, pcv valve, MAF (clean)

Coil maybe, - ignition would be next.

What is/or was the DTC you had before replacing the valve?

What are currant DTC's if you have any?

 

Code 0401 is showing up now but I have the control valve unplugged. The original problem was rough idle, which led me to find the ECG diaphragm was shot and leaking under vacuum test. After changing the EGR valve, it had a bad stall or hesitation at low acceleration.
I agree with the replies that I may be looking in the wrong direction. All the EGR functions seem to be working. I will test the TPS today. Although I said it was running fine, I did have a little hesitation on lite acceleration after I had been throwing my paper route for about an hour. Thanks.

 

I meant EGR not ECG. I did replace the PCV valve and clean the MAP, which helped cold idle a lot. As I said, the EGR valve had a vacuum leak and was frozen in the closed position. It may have just been a coincidence, and the lite acceleration stall may have been there before. The working EGR may have made it more noticeable.

 

Have you disconnected the battery to clear the KAM and let it relearn?

 

The TPS tested good and I also disconnected the battery for a while. I put everything back together, plugged in the control solenoid, all vacuum hoses connected. The test drive had just a slight stumble at lite acceleration. I don't know why the major stall went away.
I agree with jbrew and all the replies that the problem is elsewhere. When I replaced the EGR valve it fixed the EGR system but made an already there problem more noticeable. The problem does not seem to be anything with the EGR system, all tests check out good. I agree that it seems more likely to be a weak COP. I did have an error code about a month ago about a misfire on cylinder 7. I will check that COP first.
Thanks for all the great replies and ideas. I will drive it for a while and see what comes up.

 

It always should be closed for the most part. Well, for the 401, You need to suck test the egr valve first. I've never seen a 5four with plugged plenum/EGR "port". They may fill the port half way up with carbon, but that's usually not the case. Exhaust leak, bad EGR valve diagram, EGR pipe. DPFE may be reporting bad numbers to the PCM.

If I had to guess, it would be the DPFE - not shooting straight w/PCM.

Connect a Multi Meter, - if you have one, to the DPFE.

test: 5.4L dpfe acurratly reporting -

https://picasaweb.google.com/jbrew39...07882591006386

That's how it should react, -if healthy.

 

Update: The EGR, control valve, and DPFE are all working now and have passed every test I can find. I replaced the EGR because of vacuum leak from diaphragm. The stumble, or hesitation is just slight and only when I drive stop and go for over an hour (my paper route). I checked the TPS and the voltage didn't seem exactly linear. I changed it and the throttle response seems very crisp now.
The latest: Idles, accelerates, and runs great when cold. Fine when engine first gets up to operating temp. About two hours into constant driving, has a slight stumble, sometimes worse, when lite acceleration from stop or from cruising speed. I will change the COP's and plugs next because I think something may be going out when the engine is really hot for a while. Thanks for all the help.

 

Update FIXED: The hesitation is gone now. The last problem was the EGR Control Valve. The first vacuum when applying a light gas pedal was way high. The control valve was opening the EGR valve too much and stalling the truck.
In summary:
The cold rough idle was fixed by cleaning the MAF sensor.
The EGR had a ruptured diaphragm which did not open the EGR and gave a vacuum leak when activated at running temps.
The new EGR was stalling the engine because the vacuum control valve was giving wrong vacuum pressures.

 

Mine is doing the same thing, only intermittently. Where is the egr control valve? Thanks




Exrangerowner

 

If you trace the vacuum line from the EGR valve, it goes to the control valve. I put a vacuum pump inline with the EGR and found that the initial vacuum was too high, with the engine at operating temp. It was stalling the motor. I'm not sure that this is common. I had already replaced the EGR valve and the DPFE sensor. It works great now. Good luck.

 

Your talking about the EVR solenoid. That would have to be stuck open which in-turn caused the EGR poppet to stick in the open position - (NOX system). Yea, that would stall the engine or just about stall the engine @ idle.

No, a faulty EVR isn't common, in fact I've never heard of one going bad until now. Definitely possible, just doesn't usually happen. Good job.

 

The EVR solenoid is a 3 port device.
It allows vacuum to the EGR 'when' controlled by the PCM to do so.
Once EGR is no longer required, the EVR closes but 'must' let outside air into the EGR or it will hang open some amount of time before closing under it's own spring pressure as the vacuum leaks off.
On the top of the EVR is a round cap.
Under that cap is a spunge filter to clean the air allowed in to the EGR for closing.
With time and a lot dirt the filter can clog and not allow air in at a very fast rate. The cap can be taken off to access the filter for cleaning.
Dirt that gets by the filter will cause the valve to get sluggish and lock in position.
Further, when the PCM does a routine test of the system, this valve is not just open or closed.
It is pulsed to control how far the EGR is open to get a controlled exhaust flow for DPFE measurement.
If the EVR is not free, a P04xx test sequence can fail (401, 402 etc).
Otherwise at idle, the PCM is not calling for the EGR to operate.
There should be no vacuum in the line between the EVR and the EGR under non operate commands or driveability can become an issue.
Refer back to my first reply for the expansion of how this works.
Good luck.