theory: if we had vacuum tool, all this goes bye bye. we do vacuum tests. see section 2 for just that idea. HOSE jumpers, ways and means... TB means the Throttle body EGR port nipple. 1 TB >?>>>>> MOD(P) MOD(Q) >>> MAIN? (this makes car like a pre 94,) allows testing car not MOVING and tests the VSV, (missing) expected results. some MAIN movement, not a lot, because there is no engine load. be aggressive, on the throttle, (pump it) 2 TB >>>>> To MAIN no MOD. if you get main movement now, the MOP above, is dead for some reason. (cat or mod) if this cause will move the main or the TB port is clogged. (you can feel the vacuum here gunning the engine, hose disconn.) Hard vacuum: ways: 3 Plenum (old evap nipple) >>>> VSV >>>> MODP,modQ >>>>> MAIN. hard vacuum hits the VSV, on pre 94 the main moves, gunned, on 94+ nothing happens, ECU blocks VSV not moving. how ever pre 94s, this hard vacuum hits the 3 parts and the main moves. weakly but does, based on load, ,that is small. 4 Plenum (old evap)>>>> MODP,MODQ>>> MAIN. (no vsv , a great test for 94/95 cars, >0 MPH cars) this test, the hard vacuum goes to the mod, if there is good engine load, the Main moves, my guess,weak do to light load. any main action at all is good. 4 Plenum (old evap) >>>> MAIN. (pinch hose, start engine, unpinch it and stalls) this stalls the engine. (stalls or shakes at 400 RPM) one more test. that can be done here, to prove the CAT is bad. or that the parts all work and you just need a full engine load. A: Test 1a : we have test 1 setup. (same jumper hose) in this test we bypassed the VSV on the assumption car needs to be moving. yes , 1994 to 1998. I race engine, and main is weak, as expected with light loads, a light load is a weak bark. at MOD (B) nipple, the bark hose is weak. (and is) I remove this hose and run a new hose to my lips. , i blow on it (B) and the MOD latches full ON. and now all throttle gunning nets a full EGR main extension, im simulating a 100% engine load here. with my lips, this works 100% I even have a video of it. if the CAT is bad, missing/rodded out, or blown to bits, (guts gone) the back pressure can be very much NILL. The muffler is not a back pressure device, and is Unregulated by law in fact , car can have a new cat back exhuast or no muffler at all, and be EPA legal. and no back pressure there, at all. (no muf) the CAT is the only device that provide backpressure, on any car. This car needs one, for the MOD to work at all. this 1A test. proves this. cat is still on car. and still has backpressure, to port B. (not at idle, gunning the throttle wildly) you can also do the cat test, to see it if its really there. (using a standard, store bought vacuum tool,the hand vacuum pump with gauge.) --------------------------------------
---------------------------------------------------------------------------------- lets work that idea. using a real tool. that costs $28 at harbor FRIGHT! All tests on a hot engine 180F or more. the hands on to mAIN stall test, passes. A: I take this tool, and connect it to the EGR main, hot idle, i pump to 8 inches HG.(0.3 Bar, 300 kPa) then engine stalls, i stop pumping and the vacuum holds at 8 inches for 30seconds proving the diaphram is not cracked and leaking, see that?, 2 tests fast. B: Ok, A: test passes. i then move my vacuum tool to the EGR TB nipple, orig. hose removed, i start engine and gun it and get some vacuum here. (using built in gauge) if not?, that ported vacuum path is blocked, clean that. C: ok that hose back , i move my tool to the VSV output nipple. I start engine , gun the engine hot and the vacuum seen at B:test , is seen here, this is a pre 1994 car. so you get a vacuum, but on any 94 and newer car, you get no vacuum. (this is normal) so lets say car is 1994 , i pull the VSV (EGR) electrical connector and the vacuum works just like B: test above, good, if not the VSV is BAD. or clogged. D: we now have vacuum to the MOD . if I want, i can do what i want, here. I can cheat and unplug the VSV connector or on post 94 cars, just race engine and the nipple of the on the MOD gets vacuum now, if not?, correct that now. I then do that, i get vacuum to the MOD P terminal, and i next remove the Bark tube. off bottom of the MOD, runing this tube BARKS if not , the path is blocked, fix that now. Ok B hose barks, i then attach a new hose to the MOD Bark nipple , race engine (vacuum at P) and I now blow in the new bark hose. the MOD latches up closed and the EGR main moves, it must move, as i GUN the throttle, this gunning wakes up the TBI EGR port.... and gun it agressively. That is it, mostly OK , all pathes work. now, I gun any pre 1994 engine and it opens the EGR main, a bit. (naturally) I must gun a 1994 and newer engine AND be moving car, to get live testing on these cars, the FSM shows turning the left rear wheel by hand, lifted, hot engine to get egr to activate. this is all true. You can in fact turn the tire by hand CCW even dead slow and the ECU sees the VSS click, and bam, the off idle state, the EGRVSV open. I'd not try running spinning tires off ground, use above in NEUTRAL. In a shop there are no kids and pets. and we do that. but not at home. hope my crude notes helps someone.... and saves you cash and headaches.