90 Dodge Dynasty EGR problem

The black vacuum transducer is bad. The transducer should have manifold vacuum to it. The transducer is spring loaded to the bleed vacuum position. The 3rd line to the transducer (at the bottom of the transducer) is the exhaust backpressure line. As exhaust pressure increases the transducer allows more of the manifold vacuum through to the EGR valve (less vacuum bled to atmosphere). When the transducer goes bad it either allows no vacuum to the EGR valve or it allows manifold vacuum to the EGR valve all the time (as in your case).

Bill

Howdy Bill, Thank you very much for your reply. I figured it had to be something like that because all the lines had manifold vacuum in that area, and I was looking for one that only had vacuum under engine load. I truly appreciate your response. I assume the vacuum transducer is the black valve that sits almost on top of the EGR? I'll go ahead and replace that and hope for the best. Thanks again, David.

Yeah, buy the transducer and get the EGR valve free, for a small phenomenal fee. That's a deal :)

Hi again Bill,

Well, I replaced the assembly, and still had the same problem. There's vacuum on the EGR side of the transducer at idle. :(

I traced the vacuum line that feeds the EGR transducer, and it terminates on the passenger-side fender wall on a valve that has an electrical plug on it, and 3 vacuum outlets (well, one inlet, one outlet (to the valve), and the other is plugged). Could this be the source of the problem?

I went ahead and put the old EGR valve back on since it doesn't appear to be the problem (hopefully whatever the 'real' problem is doesn't cost me $60 like the EGR valve did).

I guess my main question is, should the EGR have manifold vacuum at all times? I wouldn't think so, but I figured that it received varying degrees of vacuum pressure as the exhaust backpressure built up during acceleration.

Thanks again for all your help... It's much appreciated. David.

acceleration.

Is this a California Vehicle? I could be wrong but I don't think the EGR valve has the solenoid on it, With Key on you should have 12 volts on I think it is a dark blue wire, The engine controller should ground the solenoid with the grey wire. If you remove the gray wire do you loose vacuum to the EGR?. If so then you need to trace that wire back to the engine controller for a short to ground or a bad engine controller. If you disconnect the connector at the solenoid and you still have vacuum and assuming the vacuum harness is connected properly you have a faulty solenoid.

Glenn Beasley Chrysler Tech

Yes, this is a California Vehicle. The EGR valve is controlled by the vacuum transducer, not a solenoid. I was just asking if the vacuum to the transducer was solenoid controlled.

The way I assume it works, is that at idle, the solenoid controlling the vacuum feed (where I traced back to) closes and cuts off vacuum to the vacuum transducer so that the EGR closes. This prevents the 'vacuum leak' effect on the engine that makes it idle roughly. Then when a certain RPM is reached, the solenoid opens, allowing vacuum to travel to the vacuum transducer, opening the EGR. Then it's just the exhaust backpressure (that connects with a line from below the EGR to the bottom of the transducer) that provides varying levels of vacuum to the EGR to open/close it more or less, depending on engine RPM.

This is just from what I've gathered over researching the past couple days on EGR systems... I really should get myself a dummy book on this particular model car. :)

If you could explain to me how the system works on this car I'd greatly appreciate it... (once I get an understanding of how things are supposed to work it makes it much easier to diagnose and fix).

Since I replaced the EGR assembly (vacuum transducer and all), and the problem persisted, I assumed that the problem was further up the chain, so I traced back to the solenoid on the passenger-side fender wall. Even with the power connector to the solenoid disconnected, vacuum could travel freely through it (I partially connected the connector assembly and could feel vacuum on the remaining two ports), so it appears that the solenoid may be faulty. I'll also check to see if the engine controller is bad, or if it's shorted to ground.

Thanks for your input, I greatly appreciate it.

David.

No, it is throttle opening (TPS). When the throttle is closed the PCM de-energizes the solenoid by ungrounding it. After the engine has reached a minimum coolant temperature and the engine has been running a minimum amount of time, when the throttle is opened the PCM grounds the EGR solenoid and allows vacuum to get to the EGR transducer.

the solenoid opens, allowing vacuum to

If you disconnected the solenoid electrical connector and vacuum still flowed through it then it is stuck in the open position. Sorry, It's been a long time since I have seen this model. The later models have the solenoid incorporated into the transducer and the models older than yours used ported vacuum with no solenoid.

David the solenoid is faulty

Sorry, It's been a

Bill I think that model/year had the solenoid on the EGR valve, the only difference was if it was a California Vehicle the solenoid was mounted on the fender and not on the Valve