G50: some EGR and BPT observations--normal??

[3Q Jay]

background: 113k, original EGR and BPT valves and EGR thermistor as best i can tell. upper plenum cleaned 2x at 105k and 113k, second time including lower runners and until spotless. EGR port in plenum is clear.EGR and BPT valves themselves not attempted to clean (how does one service a BPT?). every vacuum hose replaced with genuine nissan vac hose. no cross wiring of hoses. 4 new injectors at 113k (one was flakey variable 11-18 ohms), 1 new injector at 105k (just cause the plenum was off), first 3 injectors and MAF connector at 101k just before i bought it. NEW MAF at 110k, all contacts treated with Stabilant-22. new (NTK) O2s at 113k.no codes.

symptoms: shudder and flat spot at 2000 rpm. power returns to normal at about 2500 and is strong to redline. was similar though not as noticeable prior to the recent massive 113k parts replacement.

test data: config #1-connected 2nd tee into egr/bpt vac zone with gauge. no vac present at idle. at ~1500 rpm warm, the vac needle deflects just a hair (uncal'd eyeball says <0.5 in vac), but the egr valve starts pulsing (as felt by fingers on the diaphragm). i can pull the valve open by hand and get significant RPM drop. again, this is with the BPT in-the-loop. config #2--now, if i disconnect and plug the BPT vac line (3rd leg of the normal tee), i get more of a 'ported' vacuum, 5-10 inches vac depending on throttle opening and rate of opening. the EGR valve opens much further, and i can 'modulate' the engine speed by plugging/unplugging the cap at the port that would go to the BPT. taped the vac gauge to windshield and took test drive, with config#1 couldn't tell any movement (maybe just a hair) on vac gauge during part throttle at 1500-2500 where i would expect EGR to be operational. temporarily unplugged the gauge (vented to atmosphere) and drove some more (presumably the EGR would be 'OFF' with the vented vacuum), but couldn't tell difference vs. config#1. Did not try driving in config #2.also noticing what sounds like a vacuum venting upon rapid throttle release at around 2000-2500. soft, but there. this is with everything hooked up 'normal'.

[maxnix]

Jay, I must be dense, but BPT?

Also, which car? VH45DE or VH41DE?
Modified by maxnix at 9:46 AM 3/10/2007

[Q45tech]

Almost every old Nissan [every brand] has a BPT..................EF/EC-16.Since EGR is the oldest emission technology from 60's........almost unchanged until OBD2. 100-1000 fail per day on Toyota's rare on Q

Shows who has committed the FSM to memory.

Great for triva games.

Does egr pintle leak seal [old dirt].

[3Q Jay]

Brian- it is the G50. ftr, the u13 has ka24de.

[maxnix]

No excess memory cells left. I like the picture of the guy bowing the BPT valve, but I still have no clue as to the acronym.
Modified by maxnix at 2:14 PM 3/10/2007

[3Q Jay]

i don't know what it stands for either. update: took out BPT and to bench. one of the vac ports on top is plugged, just as every other one i've seen.with no pressure coming from the exhaust pressure tube, the 'open' vac port on the BPT is vented. i can suck or blow freely. as soon as i apply ~5psi to the exhaust pressure port on the BPT i can hear the diaphragm, and it cuts off. now from looking at EF&EC17, it appears that would be normal operation. i don't see a way to clean the pintle as the BPT does not appear to disassemble, but the data from above would suggest it's ok, right?

[Q45tech]

the auxiliary valve is a BPT valve (back pressure transducer valve) 31 (first valve)...............

http://www.patentstorm.us/pate....html

Google is your friend and so much faster than brain surgery

We buy at least one per week per shop for ES300 that eat them like candy because the exhaust carbon destroys them............also the pcv vapors carry oil and dirt.

Best to just replace with new as cleaning may not get perfection.

The egr tube must be clean inside as dirt changes the diameter affecting the pressure [on BPT bottom] and thus flow thru EGR.

We all know to clean the EGR plenum passage however it needs to be cleaned all the way to the exhaust manifold itself.

[3Q Jay]

thanks D, i confess i did not google BPT--makes sense.update #2 (before i read Dennis' last post): took out EGR valve itself to get it really clean. it wasn't too dirty, but there was some carbon clinging to the walls. removed the BPT feed port, noticed it is orificed, and cleaned it, too. it was not obstructed. while the EGR valve was out, i used one of those flexible 'dropped bolt grabber' tools to rooter out the big pipe to exh mani. now, i felt the rooter sort of stop at about 18 inches in and didn't go further (was afraid i might be hitting my new O2 sensor). could there be obstruction there near the exh mani--maybe. rest of pipe had some carbon that came out with snake, but not much. snake went in and out nice and smooth up to that point.

buttoned everything back up, with config #1 and didn't tell any difference from my first post (no real vac movement on gauge, but EGR does pulsate).drove this time with both config #1 and config #2 (bpt vac port disconnected and plugged (which i also gather should be the condition when the ehxaust backpressure 'closes' the BPT). now when driving in config#2, i can see lots of vac gauge movement. idle-nothing. ~1500 rpm light throttle in first starts to come on (~10 inch). mash it and goes to zero. steady criuse at 2250 locked in 3rd is over 10 inch.

tech, should the back pressure port from the EGR (the orificed one) be producing enough pressure at 1500 rpm to close the BPT valve? it appears mine is not, and if you say 'yes' that would lead me to either the BPT diaphragm resistance to closing being too high (replace it like the Lexus), or the EGR tube being partially obstructed and not getting enough pressure to the BPT.

[Q45tech]

I don't know because we've never measured the exhaust back pressure vs rpm.

I do know the converse that Q with broken open precats don't have enough back pressure to reliably engage EGR at low speed cruising <55 mph..........seen this on emission dyno.

1500 might be a little low to diagnose properly 1832 rpm would be 55 mph.

Try another BPT to see if it behaves the same? Take O2 out and measure back pressure on the road..............sometimes shop and road give different perspectives.

[3Q Jay]

will order new BPT from sponsor on Monday. My pre-cats are definitely not punched. also ordered some test-tube type long flexible brushes will attempt to get the EGR tube spotless on next go-round. i spent a hour on Sunday trying with a crowfoot flare to get the lower tube nut off exh.manif and then decided it might not be necessary.....tech, going back a few posts to the question on EGR pintle, on Saturday, i cleaned the EGR a bit, and put some compressed air on it, and couldn't feel any leaks although my method was in no way calibrated or certain--just feel. any recommended methods for getting the seat of EGR really really clean? new EGR is about $175 from sponsor--don't want to throw money replacing a perfectly good EGR valve if it can be salvaged.was thinking of using 'easy-off' oven cleaner. stuff does have some lye in it-not sure what egr pintle is made of.....

[Q45tech]

Reviewing the FSM shows 1.700-2000 rpm as the test speeds.

The ecu must be primed and ready when it opens egr solenoid to correct for the TINY drop in MAF voltage that egr flow creates.

Too little egr just increases Noxide to much creates divability problems.

What is coolant temperature reported to ecu..............there may be problems if engine is not 170F>.

Not having enough egr won't make the engine stumble.

"Method of controlling a stepper motor driven EGR valve to control the rate of exhaust gas recirculation in an internal combustion engine, comprising determining a desired EGR mass flow rate value that is equivalent to a desired EGR percent mass flow rate value as a function comprising a rotational speed value and an air-charge value of said engine, determining a pressure ratio value across an EGR orifice associated with said valve, determining a required number of steps for said stepper motor as a function of said EGR mass flow rate value and said pressure ratio value to achieve the desired EGR percent mass flow rate value, and limiting said EGR percent mass flow rate value as a function of manifold absolute pressure as it approaches a peak manifold absolute pressure value at a current engine speed, said function being expressed as

pct-- load=MAP/[bp-FNxxg(am)*29.92/bp*sqrt((act+460)/560))]

where pct-- load is percent of peak air flow, MAP is an absolute manifold pressure value, bp is a baormetric pressure value, FNxxg(am) is a pressure drop function across a throttle and air cleaner assembly at wide open throttle at standard barometric pressure, sqrt is a square root, act is an air charge temperature value on a fresh air side of an engine throttle plate. .."http://www.patentstorm.us/pate....html

Remember only 10% of the mass is egr that might only be 2.5 grams per sec at 2,000 rpm low load cruise.

[3Q Jay]

The ecu must be primed and ready when it opens egr solenoid to correct for the TINY drop in MAF voltage that egr flow creates.

Not having enough egr won't make the engine stumble.

thanks for the input. the first quote on ecu primed and ready is actually been in the back of my mind. i'm imagining a scenario where the ecu thinks it's flowing egr (electrical), but isn't (physical). maybe that's irrelevant if the tiny MAF volatge change never happens (flow doesn't change if EGR doesn't open).i was actually (perhaps mistakenly) thinking that a small amount of EGR besides quenching NOx was actually good for driveability and gas mileage (up to a point).

stumble is a bit strong. more like a timing retard (actually might be the case, since Robert's ECU timing map has a plateau if i recall at 2000). NOx passes california test (last measured at 147ppm @15mph on rollers (1424 rpm) 7 months ago).

this is pretty subtle, just trying to get it perfect.

[Q45tech]

EGR is good for cruise mpg because the egr is under a tiny pressure into plenum which means 10% of the gas flowing into cylinder is not under the TB restriction.............less pumping losses............however this is probably 2-3% improvement at BEST.

The main problem is these detuned 32valve performance engines don't perform well below 2000 rpm.

You will notice that the new 4.5 has smaller diameter intake valves and less duration to try to perk up under 2,000 rpm which has always been the 90-95 Q problem.

If you measure the air horn to TB plate length you will see its tuned for 55 mph [1831 rpm].............every 1% helps to try to maintain smoothness.

Unfortunately this tuning varies by air temp and barometer ~~5% 32F>80F