How does a 95 3.8L know that the EGR is inop? Help settle a bet.....

I was in a theoretical discussion with my dad about this, thought I'd ask the experts here first...

I know that by disconnecting the EGR cable, the van will run, but will eventually throw a code. But:

Does it throw the code because the computer is verifying a disconnected cable?

Or is some other sensor (O2 etc) sensing that the EGR is not working?

I was on the side that said the computer detects an open connector..

Am I right?

I was going to verify this by leaving the EGR in, disconnecting the cable and hooking it up to another EGR valve that is just sitting on top of the engine, but essentially doing nothing.

Who is right?

the first thing the computer recognizes is an open loop in the egr circuit then it will eventually cause another sensor to malfunction and throw the code for that as well but it will surely notice the open loop on the EGR first. Hope this helps!!

the first thing the computer recognizes is an open loop in the egr circuit then it will eventually cause another sensor to malfunction and throw the code for that as well but it will surely notice the open loop on the EGR first. Hope this helps!!

It recognizes the EGR open loop how? There would be an EGR valve connected to the harness, except that it is not physically connected to the exhaust manifold.

When the EGR valve is installed and operating as it should, it opening up allowing more exhaust gas to recirculate should cause the O2 level in the exhaust (picked up by the O2 Sensor) to drop. If the EGR valve was connected but not attached, the computer signaling the EGR to open (or close) would have no effect on the O2 levels in the exhaust gas. This alone may not be sufficient to trigger a trouble code, but combined with other engine parameters, the computer eventually will notice something is not right and trip a code.

I remember something related to this discussion back with my '90 Talon TSi. The EGR frequently would foul up the intake with carbon deposits. One of the "solutions" was to install a blockoff plate on the EGR inlet pipe. This would have the same effect as not having the EGR valve installed as no gases would be recirculated. At the time, non-California cars would continue to operate as usual but California cars would have issues. Remember this was 15 years ago before ODBII. Now a days, non-California cars have better emissions then what the California cars of 15 years ago had...so not having the EGR valve would definitely be noticed.

For the 3 valve model , indeed it senses that the current is not circulating when required for if there is an open circuit. THi s applies for an open coil. This can be applied to the linear valve of 94 and beyond. But is the valve is stuck but the coil still carries current, there is another way: from time to time the computer trigs a valve on or off and checks for engine rpm change, If the change does not occur for a few times, it throws a code.

In addition, With the linear proportional valve used in 94 and beyond, there is a built in feedback potentiometer whose returned voltage is proportional to the amount of current sent to the coil, thus proportional to the position. If the feedback voltage does not match the variations in feed current, an alarm can be trigged.

For the 3 valve model , indeed it senses that the current is not circulating when required for if there is an open circuit. THi s applies for an open coil. This can be applied to the linear valve of 94 and beyond. But is the valve is stuck but the coil still carries current, there is another way: from time to time the computer trigs a valve on or off and checks for engine rpm change, If the change does not occur for a few times, it throws a code.

In addition, With the linear proportional valve used in 94 and beyond, there is a built in feedback potentiometer whose returned voltage is proportional to the amount of current sent to the coil, thus proportional to the position. If the feedback voltage does not match the variations in feed current, an alarm can be trigged.

LMP, you are a genius!

I did a test run, and for three days it ran perfectly w/o any codes. Then it finally tripped. The code was "EGR low flow". Mind you, I blocked the EGR ports and then just placed the valve connected to the harness on the valve cover area, drove it that way. Silly thing figured out that there wasn't enough EGR... I lose the bet :(