Hello all. So 1990 F250 7.5 E4OD is down on power and this valve in the picture makes a horrible high pitch rattling noise over 1500rpm. It is on the passenger side of the engine.

Pulled codes and all I get is code 34 EGR.

 

Did some Google searching and found it is a diverter valve for the smog pump and catalytic converter. So what would make this thing make a horrible high pitch rattling noise??

I got code 34 EGR, is the EGR valve also connected to the diverter valve? Would a bad EGR valve cause a huge loss of power?

 

Sounds like you have 2 problems, the EGR is not part of that smog system. The high pitched noise could just be a leak, that valve is vacuum actuated.

 

It is a high pitched vibrating/rattling and vibrating very fast you can feel it when you put your hand on the valve, its not just a noise and not a leak.

So for the EGR code should I replace the EGR valve first or the EGR position sensor first?

 

Trucks starts, idles, drives perfect at low rpm but if your press down on the throttle it has no power and that valve starts to rattle.

 

The valve is likely busted internally and needs to be replaced.

Code 34 is the EGR position sensor reading high when valve is closed, the sensor could be bad but the valve may also be not fully closing, you should inspect all elements of the system to find the cause.
There should be no vacuum at the valve at idle.
Applying vacuum directly to the valve should make it open and the engine should stumble.
Remove vacuum and engine idle should stabilize.
See the link for a great step through.. EGR Valve Position (EVP) Sensor Testing & Replacement - FSB Forums

 

Maybe the Catalytic converter is plugged and over pressurizing the smog pump it would also cause a the loss of power.

 

the diverter runs to the air pump , my guess is air forced into it something is broke, i would pull the diverter, see if there are any peices

 

Thanks guys, I will do some investigating later today and tell you what I find.

 

So the only thing I got done today was test the EVP, going to pull off and inspect the diverter valve tomorrow. So the FSB thread said the EVP should have the below specs and what I got is in Bold

• Reference Voltage (5v at pins VREF and SIG RTN) 4.82v
• EVP Sensor Resistance (< 5000 ohms at pins VREF and EVP) 4280 ohms
• EVP Sensor Resistance (> 100 ohms at pins SIG RTN and EVP) 4340 ohms

So the bottom reading says it should be greater than 100 ohms, how much greater? my reading is higher the the one that is supposed to be less than 5000 ohms.

 

So I got some time to do more testing today and want to make sure I was doing proper testing. I did vacuum tests for the EGR system with my vacuum pump/tester.

I had the truck running and pulled both vacuum lines off of the EGR solenoid, I had 20 on my pump/tester on the supply line from the manifold, then I hooked the pump/tester to the line going to the EGR valve and pumped it up and the truck died. So that tells me that the EGR valve is working properly, correct??

Then I put both vacuum lines back on the solenoid and pulled the line off the EGR valve and hooked the pump/tester to that line. I started the truck back up and when I revved up the engine and I got between 15-20 on the tester so that tells me my solenoid is good, correct?

So in the previous post I think the EVP readings are off so I'm going to pick one up tomorrow. Is there anything else I am missing? Does it seem to you guys the EVP is why I get code 34?

 

The EVR should never allow vacuum to the EGR valve unless the truck is at part-throttle/low load. Perhaps revving the motor made a difference but at idle there should be Zero vacuum at the EGR. Measure the EVP output with the Key On Engine Off. Then start the truck and measure the EVP again. The signal outputs should be almost identical. The EVP should read between 0.24 and 0.67volts at idle with a closed EGR valve.

 

The EVR never gave any vacuum until I revved up the engine, it had Zero vacuum at idle. I only did resistance checks on the EVP with the engine off. I will have to do Voltage checks tomorrow on the EVP with the engine running, what Voltage am I looking for on the EVP with the engine revved up?

Thank you rla2005!

 

It does not really matter because your error code is for closed EGR problems.

 

Here is some more info about EGR issues:


https://www.ford-trucks.com/forums/1...-symptoms.html