[Tony P.]

I have an older car, and the only option for valve replacment is one of those universal egr valves where you have to insert washers with different sized ID to control the inlet and outlet sizes. I dont like them, becasue you have to punch the edge of the port over to hold the washers in place. I can see one falling out into the intake.

anyway, question is, how does inlet port size affect the operation of the valve? reason i ask is the washer im supposed to use, isnt very much smaller than the opening without the washer in place. it seems almost the same size to me without actually measuring it.

 

[Action]

It limits exhaust gas flow into the engine. If the EGR vacuum diaphram is intact you might be able to restore the orignal valve.

I will have some data for you on your 400 engine later today. I went digging in my shed.

Action

 

[Tony P.]

It limits exhaust gas flow into the engine. If the EGR vacuum diaphram is intact you might be able to restore the orignal valve.

I will have some data for you on your 400 engine later today. I went digging in my shed.

Action

Ah cool on the 400 info. So if one did use a valve with too large an inlet opening, what effect on operation will that have? to me, it looks like the washer im supposed to insert in the valve is only reducing the opening by like a finger nails witdth.

 

[Action]

The flow rate is to match the intake volume.
A four or six banger can not handle as much.

The exhaust gas has some unburned fuel. Just not a lot. Recycling some of that lowers NOX I think.
EGR is only supposed to open on a warmed up engine and part throttle operations and not WOT. Usually that translates to 30 MPH or faster.
Too much and the air/fuel mixture will be off. Performance or power will suffer.

Action

 

[redrag]

egr lowers combustion temps. this reduces oxides of nitrogen

 

[DesertXL]

egr lowers combustion temps. this reduces oxides of nitrogen

+1
but it also lowers the thermal efficiency of the engine and lowers MPG's resulting in using more fuel and thus creates more CO2 and CO. Go figure.

Cheers

 

[2thpic]

i unhooked my egr valve and caped off the vac. port that runs to it.

 

[Tony P.]

Does this sound like an EGR problem? 1977 Ford LTD. 400 engine. EGR vacuum controlled from carb EGR port and a two port PVS switch. Car cold starts ok, but idle seems a bit low. Once car warms up,usually after a couple miles or so, it will start to stall at stop lights. After a few cycles of this, it seems like it gets hard to start, but it still starts.

My other train of thought on this is a hot ignition coil or module is failing from the heat.

 

[redrag]

hard start not from egr

 

[Action]

If the engine stalls coming to a stop when warm is usually idle speed too low. Or incorrect air fuel mixture.

And yes if EGR is open at idle many times the engine will stall. It is not usually a swift stall.
In fact, that is a test for EGR. Warm up engine and at idle, force the EGR to open, the engine should stall. If the engine does not stall, the EGR was open or the EGR tubes are clogged closed.

A heat soaked ignition module that fails would be a swift stall no matter what engine RPM. The module would stop sending current to the coil. Generally, a primary ignition failure is not conditional on engine RPM.

Action

 

[Tony P.]

Yeah gonna check the EGR over the weekend. In a grab bag of parts I got off eBay, it happened to have the exact OEM valve that is on the car. Cleaning it up and gonna swap it as I'm sure the one on the car is carboned up.

I suppose if it was ignition module related, it would stall anytime, not just at idle.

 

[Action]

I suppose if it was ignition module related, it would stall anytime, not just at idle.

Yes.

If the current EGR valve is stuck open or partially open you have found a cause of a stall at idle. If it works (opens and closes) only then would the control over the EGR valve be suspect. You can check EGR valve operation without removal in most cases. Forcing the valve open at idle should produce a stall or at least a stumble. And in forcing the valve open manually do not use your fingers. That sucker is hot to the touch.

The control over the EGR valve operation shoudl be delayed during cold engine warm up. (Usually with a PVS valve) And only off idle or part throttle operation would be when the valve is activated so the valve only comes on the vehicle is moving at 30 or 40 MPH or faster. I forget how that is accomplished. Might be a throttle position operation or a vacuum signal from carb higher up in the venturi.

If the EGR opens and closes easily and the control side of the valve is connected and working, then EGR is not the rabbit you are chasing for an engine stall at idle.

Action

 

[Tony P.]

This one is controlled off the carb EGR port to a PVS then to the EGR. The line from the EGR carb port has a tee wich goes to an air cleaner TVS to the air pump control valve.

It runs ok at highway speed. Then stalls at idle off highway. Seems to point to sticking EGR to me.

 

[Action]

Let us know what you find.

Does your carb have a dash pot?

Action

 

[Tony P.]

By dash pot do you mean the solenoid that's supposed to set curb idle? The carb in the car is a high altitude carb, and as I was coming throught the parts lists, it doesn't list a dash pot or idle solenoid for the carb. I've already put a tach on it and it is 650 Rpm in drive as what is on the underhood sticker. She hits like 850 in park. Idle does fluctuate a bit though. I'm a mechanic by trade, but not an auto mechanic. I repair electric subway cars. I've been grabbing any 1970s era auto repair book I can find as well as any 197s era Ford CTP publications I can snap off eBay. And reading them.

 

[Action]

In it's simplest form a dash pot is used on carbs for vehicles with automatic transmissions.
It slows the closing of the throttle plates of the carb so stalling does not occur when the driver takes their foot off of the accelerator. Otherwise the throttle plates would slam shut with the torque converter keeping the engine and transmission connected. The load can induce a stall. A dash pot just slows the last 5 ot 10 percent of travel before the throttle closes.

The picture attached is of a dash pot from the 60s.
Later, in the 70s, other idle control items were added and a dashpot was part of those. Like solenoids and stepper motors that were vacuum or electrically powered.

Action

 

[Tony P.]

There is no mounting bracket on the carb for a dash pot or even an idle solenoid.

Cars has been out other time without issue. This is a recent problem.

 

[redrag]

you can eliminate the egr as an issue by making a block off plate from a tin can. put it on and see if it makes a difference

 

[Tony P.]

My carb only uses the throttle stop adjusting screw to set curb idle. I could look around for a dashpot and bracket and give it that a try. See if it helps, if the stalling is related to abrupt closing throttle plates

 

[Tony P.]

The EGR valve is the least of my worries right now. Now I have a coolant leak to track.