Hey whatsup guys, my 93 melted the egr vacuum modulator after replacing all vacuum lines, and has code 25(lean air/fuel mixture).

It will not rev past 3000-4000 rpm, idle is fine, exhaust smells like it will likely not pass smog, the last egr vacuum modulator melted at 3000rpm after ~20sec, valves were adjusted 10k ago and sparkplugs replaced

I am planning on replacing the upstream O2 sensor and egr vacuum modulator again, what else should be checked before starting down this melted rabbit hole?

Thanks

Modulator gets fed an exhaust flow signal to activate entire system. ( Thicker bottom hose). But it should be able to handle it as is its designed function. Simplest method for testing EGR is vacuum pump the small line on the top of EGR valve when idling. Like 2-3 in/mg (barely opening EGR) is generally enough to make engine sputter or die when idling when warm.

The additional amount of variables is astounding: timing, exhaust leak, 02 signal, VAF signal etc etc. It sounds like you're on the right track for 02 sensor. Rather common and easy to change. A LEAN signal (whether false or otherwise) would cause ECM to add fuel to compensate, which would actually cause RICH exhaust and exhibit your scent symptom.

Pump vacuum from the EGR and let me know what happens. (Shit, attach a hose and suck with your mouth to operate valve and it should give you some sign of idle fluctuations when warm). We gotta start from square one for a solid diag.

All the best

-4Reak

My mistake, thinkin of a Toyota CAR EGR. Just looked at pics and 3.0 doesn't appear to have "exhaust signal" hose. Please do the vacuum/sucking test and report.
Good luck
-Mr Show

I should do the sucking test on the top smaller hose from the EGR valve? What exactly should I be watching for while performing felacio?

Thx 02 Out

Update

I swapped in a new 02 sensor, egr modulator, egr valve and the truck now smells far better but it still does not want to rev past 3k, what could be causing this?