'91 2wd pickup. 3.0 6cyl
Truck is new to me. I'm getting code 71. Reset, drive again, get code again. I've tested the EGR valve by sucking on the vacuum hose while at idle. Resistance is felt; valve actuates and engine dies. According to standard advice, that's a pretty good hint that the valve is OK.

Next, I replaced all vacuum tubes related to EGR. Lots of 3mm and one larger one. Still getting the code.

Before I spend a bunch of money on parts, what could be next steps? Any way to test the temp gauge that is in the intake side of the EGR valve? Any way to test the VSV switch that the EMC controls?

 

Followup - right after I posted this, I found the method for testing the VSV. Apply 12v and the solenoid should click. Mine does, so I'm ruling that out for now.

What next?

 

Here's most of what you want to know: http://web.archive.org/web/201204061...77exhaustg.pdf

Not mentioned in the FSM is ... crud. The output (exhaust gases) from the EGR valve goes to a long tube extending into the plenum. Over time, the plenum can fill up with "crud," mostly from the PCV system. If there is enough crud the tube can be blocked. It is smaller in diameter than the hole in the plenum, so if you have trouble pulling it out its coated.

 

Right...I have that diagram.

If the plenum insert was clogged, then the test of the EGR valve would fail, I think. Adding vacuum to the valve causes exhaust gas to flow into the plenum, which stalls the engine at idle.

Still...I'm going to pull it and take a look.

I'll be testing the temp sensor next.

 

Tested the temp sensor. I'm getting no continuity at all.

 

I don't have a 91 FSM in front of me, so not sure on actual testing specifics/parameters, but I believe you won't get any continuity unless sensor element is heated to XXX degrees. EGR is disabled on a cold start engine.

 

Should have 11 - 16 k ohms at 212 degrees. Less at higher temps. I tested it at 212 and room temp.

 

Try plugging in a 15k ohm resistor to see if that clears the code. That's not a long-term fix (well, for some folks it apparently is) but it will help you rule out other problems. The sensor is ~$200.

 

Is that the resistor that comes in the block-off kits?

 

Final word on this: I put in a 10k resistor and the check engine light stops. I tested my temp sensor and a known-good one to be sure my procedure is correct. Mine is dead, for sure. The good one shows all the right resistance numbers.

I'm going to get a new temp sensor.

 

Good work!