Taurus Knock/EGR Troubles


Old 06-27-05, 08:41 AM
Thread Starter
Join Date: Sep 2004
Posts: 238
Received 0 Votes on 0 Posts
Taurus Knock/EGR Troubles

The car: 94 Ford Taurus, 3.0l , V-6 w/ 165K

Once again, the car is knocking really badly. Last November I pulled off the upper intake and rooted out the EGR passage.

This weekend, since I did not know what else to do, I put on new plugs, cap, rotor and air filter. I also checked the timing per emissions label instructions. The cooling system seems to be fine and the computer had no stored codes. All this kept me busy but did not fix it.

The egr valve and recently rooted-out passage still work. Opening the valve with a vacuum pump makes the car idle poorly especially with the idle air control valve unplugged. The EGR valve will also hold vacuum forever.

When I connect a vacuum gauge with a tee between the EGR valve and its vacuum source I get and unexpected result. The vacuum is zero at idle. When the throttle is opened and held steady, the vacuum immediately shots up and then drifts back to zero in about three seconds. I expected the vacuum to remain constant and hold the valve open. The car seems to be correctly saying give me EGR and then immediately says ok I have it and I have had enough.

When the vacuum gauge is connected directly (no tee) to the vacuum source and the EGR valve gets no vacuum and is closed, the above test yields a steady vacuum. Here the car seems to be saying give me EGR and I will keep asking until I get it.

I have two of the fairly expensive EGR pressure sensors one is Ford and one is Wells both used and neither is know good or known bad. In a time wasting exercise, I swapped them out with the same result.

How does the system work? Maybe the vacuum in the test with the tee is normal and I have another problem. Why do I only get EGR vacuum when I open the throttle but not steady vacuum when I hold the throttle open?

Thanks for any help.
Sponsored Links
Old 06-27-05, 02:02 PM
Visiting Guest
Posts: n/a
Your vacuum situation would be normal,slight opening on accell then closed. The solenoid for the egr is controlled by the ECM and it knows you are sitting still so it closes the valve. Ideally drive the car with the gauge installed and see what it does. When it is pinging you should see vacuum. If not suspect a knock sensor. If you have vacuum it sounds like the ports are plugged again. With that mileage you could also have quite the carbon build up behind the intake valves, try a couple of bottles of Chevron Techron the next two tanks of gas and see if that helps. The EGR pressure sensor has no controll on the valve it is only a monitor.
Old 06-28-05, 02:55 PM
Thread Starter
Join Date: Sep 2004
Posts: 238
Received 0 Votes on 0 Posts
comptech--no knock sensor?

Thanks-will try it.

I imagine the egr system works, since I get no CEL.

I have looked for a knock sensor on the car and in varous wiring diagrams and found nothing. I can id each wire coming out of the ECM and none hook up to a knock sensor. Could it be called something else?

What does the carbon build up behind the valves do? This build up is likely since the egr passage was blocked with the stuff.
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Ask a Question
Question Title: