Test EGR valve

[wadamt16]

Hi, I have 1993 Seville 4.9. I got a new EGR valve but it didn't help. I tested it with vacuum pump, it won't hold pressure at all, same with old one. Is that new EGR valve bad or just different type of EGR that vacuum pump won't work?

Thanks!

[Logan]

There are 2 types of the older style EGR valves. Negative pressure and positive pressure. One type (I dont remember which) will not respond using a vacuum pump.

[wadamt16]

Ah I see. when I bypassed the EGR vacuum solenoid. the valve actually open. The solenoid is opened when no power. I disconnected the power to the solenoid and it won't open but I can feel a bit of vacuum.

[BodybyFisher]

You can not test these EGRs using vacuum. Someone will chime in, but it has to do with it needing a back pressure before it opens,

I see you are over here also asking the same question, the answer given you is wrong

http://www.cadillacf...valve-same.html

If this is you also, this is a wrong answer

http://answers.yahoo...20102952AAUZXdc

We used to have the designer of the Northstar platform here, you can not test the EGR using a vacuum pump as Logan stated above, as I recall. He also said, do NOT use an aftermarket EGR valve the OEM valve is calibrated properly for the 4.9.

Install it, connect the hose and drive the car, if something is wrong, you will get a code. What are your symptoms on the 4.9 leading to your changing it?

[BodybyFisher]

Here are the different types of EGR valves, someone correct me but I believe the 4.9 has a positive backpressure type and it can NOT be tested using a vacuum source.

Description of types

There are currently six types of EGR systems in use. Going from the

oldest (and perhaps the most familiar) they are:

* Ported (late 1960s to present)

* Positive backpressure (1970s to present)

* Negative backpressure (1970s to present)

* Pulse-width modulated (early 1980s to present)

* Digital (electronic) (late 1980-early 1990s)

* Linear (electronic) (early 1990s to present.)

Two types of backpressure EGR valves are normally used­positive

and negative. On GM cars, they are identified by the last letter of

the part number stamped on the diaphragm housing on top of the valve.

(Prior to 1988, they were not identified and can cause some confusion,

so be careful when ordering a replacement.) The letter 'P' stands for

positive backpressure and the letter 'N' for negative backpressure. If

there is no letter it operates on ported vacuum.

On the positive backpressure EGR valve, a control valve located in the

EGR valve acts as a vacuum regulator valve. The control valve manages

the amount of vacuum to the EGR diaphragm chamber by bleeding vacuum

to the atmosphere during certain operating conditions. When the

control valve receives a backpressure signal from the exhaust through

the hollow shaft of EGR valve pintle, pressure on the bottom of the

control valve closes it. When the control valve closes, the full

vacuum signal is applied directly to the EGR valve diaphragm which

opens the valve and lets the exhaust gas recirculate.

On the negative backpressure EGR valve, a hose connected to the upper

part of the EGR valve supplies a vacuum signal. Manifold vacuum is

also applied to the lower diaphragm through an intake port at the base

of the EGR valve. When manifold vacuum in the lower chamber isn't

strong enough to overcome the spring tension on the lower diaphragm, a

bleed valve closes, allowing vacuum in the upper chamber to open the

EGR valve. Exhaust flow opens a check valve in the pintle so that

vacuum bleeds to atmosphere and the valve rises, but tries to drop

again so it dithers to control EGR flow.

The pulse-width modulated EGR system is controlled entirely by the

powertrain control module (PCM). The computer controls the flow rate

by sending electrical signals to a solenoid vacuum valve between the

PCM and the EGR valve. The solenoid pulses up to 32 times per second.

To determine the pulse width, the PCM relies on a ported vacuum

signal.

On computer-controlled EGR systems, the ECM controls the vacuum signal

to EGR valve via a solenoid valve. The ECM uses coolant temperature,

throttle position and manifold absolute pressure (MAP) signals and

sometimes other inputs, to compute the vacuum solenoid operation.

Whenever the engine is cold or is idling, the solenoid valve blocks

vacuum to EGR valve. When the engine is warm, and the rpm is higher

than idle speed, the solenoid ground is broken and vacuum opens the

EGR valve.

The digital EGR valve allows the precise amount of EGR flow without

using manifold vacuum. The valve controls EGR through three different

size orifices for seven different combinations of EGR flow. When the

PCM energizes a solenoid, the swivel pintle is lifted to open the

orifice.

Some engines have a linear (electronically controlled) EGR valve. It

has a control solenoid and EGR valve position (EVP) sensor. The sensor

works on the same principle as a throttle position sensor. The return

voltage signal ranges from 0.3 volts when it is closed up to 5.0 volts

when it is fully open. The PCM controls EGR flow by pulsing the signal

to the EGR solenoid. This provides better regulation of EGR flow than

with conventional vacuum controlled EGR valves.

[BodybyFisher]

See this link, regarding TESTING postive backpressure EGR valves

http://www.tomco-inc..._Tips/ttt26.pdf

See this statement

Remember that the positive backpressure

EGR valve will not open when vacuum is applied

to the vacuum port. Therefore when checking

this valve just applying vacuum will not be an

effective test. You must create enough

backpressure to move the lower diaphragm

enough to seal the upper diaphragm. Just revving

the engine may not produce enough backpressure

to accomplish this.

Its amazing how much MIS-information is out there, there is something to be said for the experience on this board. In addition when you returned the one to Autozone they should have been knowledgeable enough to KNOW that you can not test it with a vacuum source. My god, talk about the dumbing down of America.

[wadamt16]

WOW! That was very useful information. I am very happy about that! Yes, that is me on yahoo answers. Here is what's wrong with my car. It stalls pretty bad only when I drive at low RPMs (around 1000 to 2000 RPMs), usually in mornings but does not stall that much after work (around 5pm). I checked vacuum hoses for cracks and replaced almost all of them. I cleaned the throttle body and bought new EGR valve, new air filter, and new fuel filter. Nothing has helped.

I have 3 error codes from my car, P071 history, I052, and I039. P071 is for MAP, I believe that was from me when I tested the MAP with DMM and pump to make sure it works. I started with around 5 volts at no vacuum pressure. When I pumped, the voltage dropped. With lower pressure, there was lower voltage. Please tell me if I tested it correctly.

LOL @ AutoZone comment

[BodybyFisher]

Glad I could help

Have you checked fuel pressure? I would put a gage on, and see what happens when it stalls, the ideal thing to do is to get one with a long hose connect it and tape it to the windshield.

If you had a bad EGR you would get a pindle code, I dont think this is related to the EGR

Have you disconnected the battery? What caused this code >> I052 ....................................................... Keep Alive Memory Error

Don't discount a PCM problem we have seen intermittant problems caused by the PCM

P071 (E071) ................................................ Intermittent MAP Signal

[BodybyFisher]

By the way, after you install the EGR, start and idle the engine, before it gets too hot, reach up under the EGR and press up to open the EGR the engine should stall or begin to stall, release it and it should recover

[wadamt16]

I haven't check the fuel pressure. It runs very smooth when I give it more gas. Whenever I feel stall bad, I just press more gas, it stops stall but will stall again when slow down. Yeah I had disconnected the battery in a few weeks ago. I keep thinking could be need to clean injectors, change spark plugs, and distributor cap.

Should I clear all the code and see if I052 and P071 come up again?

If you still think I should check the fuel pressure, I would happy to do that.

[wadamt16]

By the way, after you install the EGR, start and idle the engine, before it gets too hot, reach up under the EGR and press up to open the EGR the engine should stall or begin to stall, release it and it should recover

I did that before and it does like what you said.

[BodybyFisher]

Are these the only codes you have gotten during this problem? I always want to know that my fuel pressure is good to eliminate the pump and fuel filter issues. I dont think the OBD1 system will tell you that your fuel trim is heavily lean as the OBD2 system does, but someone will correct me if I am wrong.

It is possible that you are having a problem with your ISC (idle speed motor) or that it is out of adjustment.

Adjusting the ISC, TPS and minimum air can do wonders for your engine. Do you have the directions on how to adjust them? With my 91 Seville, I used to do the detailed adjustment process and my 4.9 always ran beautiful.

That said, the ISC has a closed throttle contact that when the throttle is closed it extends its shaft to stop stalling, you may need to clean it, replace the ISC or adjust it. Does this stall happing in park or during a ride or both? Personally I never had problems with my ISC but many have.

[wadamt16]

I will try to get the fuel pressure tester tool. I have a new fuel filter too. Yes I need the directions for that stuff. The stall usually happens during the ride. Sometimes when I turn the engine off, the ISC knocks for around 10 seconds. Sometimes in the morning when I start the engine and watch the ISC keeps extending the shaft every time it tries to stall until it warms up.

[BodybyFisher]

This sounds like a balky ISC motor. Many of our members are familiar with ISC motors as they have had issues with them and hopefully they will chime in.

I do believe a clicking ISC means its bad, needs a cleaning or it is out of adjustment.

I also believe this is your stalling problem. Stick with us and we will help you through this. Ill pull out my 91 4.9 manual and see what I can find on adjusting the ISC, TPS and minimum air.