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Discussion Starter · #1 ·
Nippon 139000-0120 BPT
ISUZU part 8942135720

This is the vacuum/exhaust pressure EGR transducer. I see them 'out there' for $73 and up. IS there a cheaper source? Honda?

For my '90 2.6L fuel injected SpaceCab. All the discussion about EGR, as well as idle RPM and mileage got me to checking my EGR (I replaced it a couple of years ago) but the BPT is original and is non-functional. I have to verify 100% with a vacuum gauge, etc when it gets warmer here in a couple of days, so if I need to order one, I'm looking for the best place, and right now, it appears only the Isuzu parts places seem to carry it. I've only checked a couple of the major parts houses....
 

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Discussion Starter · #3 ·
K, thx.
 

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Don't take his last one though, 'cuz I'm going to need one pretty soon, too. ;)
 

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Discussion Starter · #5 ·
Well, as I thought about it, it got me to thinking and remembering; when this truck was new, and I mean new (15 miles on it) up until several years ago, I know it would get between 22 and 25 mpg on the highway running back and forth from Sierra Vista, AZ and Tucson AZ. I went back and checked my records and it seems that them mpgs have tapered off, but slowly. Also, I've noticed for the past several years, (same time frame) that the engine seems to be running 'hotter' than it used to when it was new (I attributed this to the gauge and sensors). But now, I got to thinking about the EGR and it's system, so I decided to check it.

The OEM back pressure transducer (BPT) is still in the engine. I've had it off several times for various maintenance tasks, so I'm sure I have the hoses hooked up correctly. There are only three. Also, I replaced the EGR valve two or three years ago as I vacuum tested the OEM unit and found it faulty then, so I R&R'd it.

I identified the metal pipe that curves up from the end of the the intake manifold where the exhaust gase is ducted to the EGR, etc. When the engine is running, exhaust gas does come up thru that pipe (at idle). There is a short piece of vacuum hose that connects it to the bottom of the BPT valve. On the valve if you look at the top so you can read it, you see to the left port the word "carb" and on the right "EGRV". The 'carb' port connects via a piece of vacuum tubing to a metal pipe under the TB, and from there, it appears to connect back to the VSV. The "EGRV" port connects to the EGR valve itself.

I pulled the BPT and checked the port that connects to exhaust gas, I could create a suction on it (low exhaust pressure) and could create a positive pressure and that side of it seemed to work fine. No bleed off to speak of. However, between the 'carb' and EGRV port, I could not create any difference in pressure. It blows thru both ways.

With the BPT out and disconnected, I hooked up the Might-T-Vac directly to the EGR and created a vacuum and stalled the engine. That proves EGR is working. However, when I try to measure vacuum at the line coming from the VSV, I get no vacuum at idle (which I would suspect, because you do not want the EGR to open and stall the engine). I revved the engine several times and could not get any noticeable vacuum at all on that line to the VSV, which indicates MAYBE a wonky VSV. So I bypassed that, and hooked the BPT back onto the exhaust gas port. I hooked the EGR valve back up, but used a "T" fitting and and put constant vacuum on the "carb" port via the port used for the cruise control. At idle this did not affect anything, the EGR valve stayed shut, which is what I'd expect because exhaust gas pressure is positive at idle. What I did not get to do was to put remove or put the vacuum pump on the bottom port of the transducer to simulate low exhaust pressure. I ran out of time before I had to come into work. And I need some longer pieces of vacuum hose to T-shoot with.

Anyways, I think that while the valve/spring action on the exhaust side of the BPT is working ok, I believe that when exhaust pressure is low, I may have a bad VSV (shouldn't vacuum be there most all the time to activate the EGR valve on demand when exhaust pressure is low?). Also I believe that the BPT, if the VSV is working, and is allowing engine vacuum to suck ambient air due to a leak on the vacuum side, bypassing the EGR valve and not drawing it open. This would constitute a vacuum leak at the manifold and cause a lean(er) mixture as the air, due to its entry point, not being metered by the ECM.

So I MAY actually have two issues here.... so I'm looking for some better insight. I know this EGR system on the '90 is supposed to be totally mechanical, but if I put vacuum on the carb side port and on the EGR side port I can't feel any vacuum; when I had it off I could I could blow straight thru it. If I blocked off either port on the BPT with my finger, and blowing thru either from carb to egrv or egrv to carb, it I can hear a leak...this leads me to conclude that the BPT is wonky, eh?

And should the VSV valve provide constant vacuum or only open at specified times (this would make the EGR system dependent on an electrically-controlled VSV, then?). As I said, I revved and popped the engine several times but could not detect any vacuum on the VSV line that connects to 'carb' port on the BPT. If it is supposed to provide a constant source of vacuum from the intake, and it does not, then I either have a bad VSV or a blocked line. Again, I didn't have time to check it all out and will try to finish up tomorrow morning if I get time....sorry it's kinda long and involved, but I figure if somebody else needs to check the same thing, then it might be worth repeating here, and I do have a method to my troubleshooting.
 

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The BPT is supposed to be a vacuum leak from side to side until there's positive pressure on the bottom port. It's a relatively tiny amount of air even at idle, so it doesn't affect metering.

Federal emissions doesn't have a VSV in the EGR circuit, is yours plumbed similar to California's?
 

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Discussion Starter · #7 ·
I follow....at idle there is positive pressure coming out of the exhaust. With the 'carb' side plumbed to the VSV port, there is no vacuum coming from the VSV at idle (should there be?).

Even if I block off one side or the other on the BPT, I can get air flow thru it, so it's not 'sealed' port to port, so to speak. Prob a bad seal. It can suck ambient air IF there was vacuum from the VSV, which there is not; so this renders any vacuum function of opening the EGR ineffective when exhaust back pressure lessens.

As for the VSV itself: I purchased the vehicle brand new in Honolulu in Oct of 1989 in Hawaii. Hawaii had, and still does have, emissions testing as part of it's inspection process. I believe the truck was first hit the docks at in CA from Japan, before being shipped to Honolulu; so it's possible it is plumbed for CA. Never gave it much thought. I know that when I set the idle I have to disconnect the electrical connection at the VSV to adjust idle speed. Since I've never seen a "California" Isuzu's engine, I have nothing to compare it to. :idea:

Apeiron said:
The BPT is supposed to be a vacuum leak from side to side until there's positive pressure on the bottom port. It's a relatively tiny amount of air even at idle, so it doesn't affect metering.

Federal emissions doesn't have a VSV in the EGR circuit, is yours plumbed similar to California's?
 

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Well unless I'm mistaken, a Federal 4ZE1 doesn't have a VSV, and a California one doesn't have a BPT. :?

If it's Federal, the only VSVs should be for canister purge and fuel pressure control.
 

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Discussion Starter · #9 ·
So you are saying I have the best of both worlds? :(
 

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Discussion Starter · #10 ·
So you are saying I have the best of both worlds? :(
 

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Discussion Starter · #11 ·
...8942135720: 198707-transducer; back pressure: c: 8944146150: 198602-198706: exc. california emission system(nb7) transducer; back pressure: b: 28 bracket; transducer; …
 

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Check the Applied Model column. 8942135720 is for a 2.3
 

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Well, it looks like the California system didn't go completely insane with their regulated vacuum system until 1992, but in 1990 there was an EGR cut VSV with a BPT.
 

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Discussion Starter · #14 ·
Yea, the fact that is says "carb" on one the ports instead of VSV is a tip off, I guess. So I have to deal with both. I'm not familiar with just HOW the VSV works to provide vacuum to the 'carb' side of this transducer; does it supply constant vacuum (in which case it does not, so is either defective or clogged) or does it shoot vacuum to the transducer only under certain conditions. I can bypass the VSV but as the BPT seems to be leaky it would not matter as it won't operate the EGR correctly, so I need to replace it in any case.....just a bit convoluted.
 

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The EGR vacuum source is a port above the throttle blades, so you won't have any vacuum at the input to the VSV until the throttle opens far enough to expose the port.
 

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Apeiron said:
The EGR vacuum source is a port above the throttle blades, so you won't have any vacuum at the input to the VSV until the throttle opens far enough to expose the port.
Got ya!

20130306_144515.jpg


20130307_130117.jpg
 

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Yea this is the conglomeration.

the only part number on the bottom device is: Hitachi AESE1218-22 with 9819 beneath it. The PN on the upper, cylindrical device is almost illegible.

20130307_121701.jpg
 

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Discussion Starter · #18 ·
Yea I would LOVE to extricate my engine from the CA emissions crap as this vehicle will prob never live in CA........Fed OK, CA bad.... :idea:
 

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Discussion Starter · #19 ·
So I happen to be looking on Isuzuparts.com; I see that there is a "CA" EGR valve and a "FED" EGR valve..what in the hell is the difference as the CA EGR valve is more epxensive. When I got the EGR valve I have I wasn't asked it was CA or Fed;....arggghhhhh....this is starting to be a headache.
 

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Differently shaped pintle changes the metering at partial opening.
 
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