90 Dodge Dynasty EGR problem

I have a problem with my 1990 Dodge Dynasty.

It has the 2.5L 4-cyl engine, and for some reason the EGR valve is getting
manifold vacuum at idle. It failed the mechanical inspection of my smog
check today for this reason (though miraculously passed the tailpipe test).

I had to install a new cam about two years ago, and at that time had the
vacuum lines all disconnected. I was pretty sure that I had reconnected
them all correctly, since the stiff hoses are pretty much bent in the
direction that they need to go.

I don't have a vacuum diagram, or I could probably trace out what's going
on, but when I tested other lines that I thought might possibly be the
'real' EGR line (that only gets vacuum while the engine is under load, they
also had manifold vacuum at idle.

Is there some sort of actuator that controls vacuum to the EGR in this
vehicle? I tend to think that's the direction I should look, based upon my
rudimentary inspection so far.

Can anybody help me out, or at least point me in the right direction?

Thanks for your time.

 

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.

 

It actually appears that I have to replace the whole EGR valve assembly, as
the vacuum transducer doesn't seem to be a separate part you can order.
Gotta love Detroit.

 

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.

 

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.

 

See Below

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