Happy New Year gentlemen,

I've had much success here keeping my ride alive but I need some help with this one.

96 F150 5.8 EFI Starts and dies, pulled 0171 and 0174 lean codes... checked the fuel pressure, all good. Plugs look like they are rich. Most posts suggest vacuum leak.

If I play with the throttle, i can make her run enough to read a vacuum gauge teed into the line running from the intake manifold to the vacuum reservoir. Reads 12-13 inches at closest to idle, seems low. When I gas it the engine dogs and the vac level drops right off and then comes back a little higher when the engine catches. Can't tell if the vac is the cause or effect.

If I have a vacuum leak, I can't find it, replaced all the lines, PCV valve, checked the EGR... OK, Checked the VPR by pulling the line off and watching the fuel pressure rise a bit... OK.

There's an EVR valve that has me confused. the Haynes manual says to test the vacuum portion of the unit by putting a vacuum gauge on the outlet side and pulling a vacuum on the inlet side... the vacuum should hold with no read on the gauge. When I do that there is no hold, just pulls right thru the vent, not the outlet. Went to autozone and bought a new one, acts the same way... Am I doing it right or reading it wrong???

 

Does your vacuum resovoir hold vacuum when the engine is shut off? It should and if yours doesn't you have a leak.

The EVR is a vacuum solenoid and it should not pass vacuum without being electrically activated, are you sure you have the right device?

 

I was fooled by the EVR vacuum test before....both ports will slowly vent to atmosphere when the EVR is off. At no time should you be able to draw a vacuum between the ports with the EVR off, that is what you are actually testing for.

For reference: Fuel Injection Technical Library » EGR Vacuum Regulator (EVR)

 

Thanks for jumping in.

The vacuum is gone as soon as the engine stops... can't tell if the vac is killing the engine or vice versa. Should I be checking the reservoir independently??? I did not try that, I will.

On the EVR, that's what I thought... and it definitely does not hold. I did the test with the electrical disconnected.

I just looked at rla2005's post regarding an EVR and went to the link he provided... It says that when off, both ports release slowly to the atmosphere. Which is different than what you said and the way I read it.

I'm going to check the reservoir vacuum now and I'll get back to you.

Thanks for your help

 

OK, what timing... I was replying to Conanski referencing RLA2005 and RLA had already posted the link to this thread.

You guys are great.

So are you saying the solenoid will not hold vacuum on the inlet side? The way I read it, when the valve is not powered, no vac will get by to the EGR, when powered, the solenoid will open in increments? to pull in the EGR. I did not get vacuum across the ports when off, but I did not hold vacuum on the inlet side when off.

So the solenoid may be OK and I have another leak.

Thanks for your input

 

Yes you should test the vacuum reservoir independently.

Go back and read the EVR operation and my statement. Both ports vent to the atmosphere with the valve off. That does not imply you should be able to draw a vacuum between the ports with the valve off.

 

RLA2005, can you clarify?

When the EVR is off, no vacuum will go across the ports to the EGR, that I get. But the inlet side, coming from the intake manifold, does not hold vacuum, but rather draws in through the vent. Is that how it works and if this is correct, is it not a significant leak?

 

Yes, the reservoir holds its vacuum. It's the plastic one so I thought it would be OK.

What should the vacuum be at idle and how does it change when the engine revs?

 

That is exactly how the EVR works, it's a small,controlled vacuum leak. It contradicts logic, but that is how I have it as to how it operates.

 

Typically manifold vacuum is in the 17-20 range at idle. Opening the throttle lowers the vacuum. Wide open throttle results in Zero vacuum.