What role does the EGR "Backpressure Transducer" play? What lines should I be getting vacuum from and ???

BIG-time dumb <img src="/forums/images/graemlins/butwiggle.gif" alt="" /> question here but enlighten me please <img src="/forums/images/graemlins/smile.gif" alt="" />

dawn...

Though I run the risk of being an even bigger dumb <img src="/forums/images/graemlins/butwiggle.gif" alt="" /> than I've already been (dumb blonde/brunette syndrome <img src="/forums/images/graemlins/shocked.gif" alt="" />) ....Yesterday I discovered several cracks in my dist. cap. Yep, right at number 2 on the inside and a few on the outside. Ironically, this is where I'm not getting spark all the time. Intermittantly only. Used a cool thing called a "spark tester" last night and seen for myself that the spark was there then...poof <img src="/forums/images/graemlins/ignore.gif" alt="" /> was gone. I am ashamed to admit that I already changed the Rotor, Plugs, Wires, and EVEN the Coil....BUT never changed the Cap cuz at quick glance it looked o.k., and at night, in a dark garage, didn't see any spark there so I ASSUMED (made an ASS outa U and ME) that it was fine. K', though it may not solve all my problems, it may solve some really cool ones. Yeah, I know, you're supposed to start with the simple crap ALWAYS but I guess I just overthunk it. Don't know if it will produce some really cool results to put a new cap on but rest assured, tomorrow my first stop will be Sanels. I will put a new cap, wires (hate the bullcrap ones I got a few weeks ago) and some new NGK's....then see what happens.

Gonna check into the EGR Transducer thingamajig and see why I don't seem to have vacuum where I thought I should and may explain some "running too rich" probs.

Also, while depressing the EGR valve, I get a really funky sound from it. Yeah, it makes the engine bog as it should but there is a deep (not light and airy really) hissing sound from it while depressed. My EGR is OEM and lots of rust (thanx to the North Country, salt encrusted environment I live in), and may be in need of replacement.

Wish me luck and believe in my "Secret Santa"....I believe <img src="/forums/images/graemlins/nana.gif" alt="" /> <img src="/forums/images/graemlins/kewl.gif" alt="" /> !!!

Hey Dawn,
Did you check the distributor cap? <img src="/forums/images/graemlins/rolleyes.gif" alt="" />
But the goodnews is that with all the work you've done, you've practically got a new machine, and you know it's done right when you doityourself! <img src="/forums/images/graemlins/kewl.gif" alt="" />
Hope it works out well for you, let us know how the test drive went!
It's finally gotten to cold here to work out in an unheated garage so now I pray for a chinook or wait for three months...
I now work on my Isuzu vicareously through you.... <img src="/forums/images/graemlins/cheers.gif" alt="" />

It isn't dumb. Engineers put this stuff onto engines to confuse and baffle the week-end mechanic. Oh, for the return of the six cylinder flat head...

In a nutshell: vacuum for the EGR comes from the throttle chamber but, it has to pass two mechanical "yes or no" tests before it gets there. First test; "Is is the engine warm"? That question is from the thermal valve under the intake manifold. If you follow the line from the transducer (toward front of engine) down through the manifold you'll see it terminate on the valve (small cylinder with two ports sticking straight up) the other line attaches to the throttle chamber. When the engine is cold no vacuum can pass through it. This is good because on a cold start you don't want the EGR choking the engine with exhaust gas before it can handle it. It'll just stall. Once the engine is warm that valve opens and allows vacuum to the second test: the back pressure transducer.

The BPT is like a metering device. It's question is "Is the throttle open?". It get's it's answer by measuring the pressure in the exhaust. It's got a diaphram that opens and closes to either let vacuum pass or cut it off. The diaphram is pushed by the pressure in the exhaust (back pressure). It get's that pressure from the same tube that feeds exhaust gas to the throttle chamber and it's fed to the bottom port of the back pressure transducer. It's operation is real simple. At idle the EGR is closed because fuel is at a minimum and exhaust gas would choke the engine. That's why the finger push method on the EGR does what it does. At part throttle the pressure in the exhaust increases so the diaphram in the transducer pushes up and opens the passage for vacuum between the EGR and the throttle chamber. Now you get an increase in fuel so the engine can handle a little exhaust gas.

If you floor it the back pressure goes way up, so the transducer pushes the diaphram even harder and closes off the passage of vacuum to the EGR. The whole purpose of the EGR is to reduce co2 and Nox emissions (the solution to pollution is dilution) by mixing in some heat and recycle some spent gases, but it can't be too much or too little cause the computer expects the mechanical things to do their job the same way every time. If you could convice the computer that it doesn't need the EGR maybe you could take it out, but as long as that line of code is in the instructions it better be working.

Believe me this EGR had me confused until I finally decided to stop thinking about it and just fix it. If you watch it in operation the movement of the EGR is so slight you wonder if it's doing anything at all, but the 2.6 is all about little things causing big problems.

O.K., you guys ready for this....I have officially earned the right to be the biggest dumb <img src="/forums/images/graemlins/butwiggle.gif" alt="" /> on the "wire".

I changed the CAP & wires today and voila....picki is happy. No more spitting, sputtering, farting around.

I'm not sure this was the problem all along....who knows, the Fuel Pump Assembly was bad but pressure was always good. Initially I had changed the Rotor, Wires, Plugs, and even the Coil but never changed the Cap cuz in a dark garage I didn't see any spark where there shouldn't be.

The only issue I have now is that the idle is still high especially while in park (2500). I can push on the throttle body and reduce it but not when I try to kick it down with the pedal. I'll bring it in to school tomorrow and see what we can do about that. I also did put in another BPT and I've got an EGR to put in as well. Mine is pretty rusty and I came across a much better one so I'll switch them out.

If I just spent all this time, money, and aggrevation for a $5.00 part, I will forever carry the shame, shame, shame.

I send a huge "THANK YOU" to all who've been patient with me, and concerned enough to chime in with their advice.

All I can say is I hope people will learn from my mistake...ALWAYS start with the simple crap, never assume anything, and don't overthink something...all you'll do is bury yourself in the long run...

Thanks again guys/gals....you're true friends and the WIRE is a great place to hang out.

MERRY CHRISTMAS....You see, there is a Santa, and he just smiled down on me.

dawn...

Oh NO! Here I was waiting for the holy grail solution that would forever change the way we repair the 2.6 Well, I guess it proves it doesn't matter how new the part is, it can still be defective. Just between us your instructor that got zapped checking the plug wires should get a D- for failure to follow through to the right solution. I still can't figure out why it was a problem after the engine warmed up... don't look a gift horse in the mouth. BTW, make sure the numbers on the new transducer match the old. Apparently it matters. I had to bring the old one in for the dealer to match it.

Thanx RT. The only explanation I can figure for the "better cold" thing is that the RPM's were up in such a way that I could feel the skip/miss but once the RPM's kicked down the miss was far worse. I also have to say that while using the "spark tester", there was spark at number 2 when first started up but then it disappeared. Also there was funky sparking coming out of the top of number 3 boot and going wherever it could find a home. Guess there was more to the story than just a busted cap but it is definitely a lesson to be learned.

dawn...

My guess would be thermal expansion... When it heats up, the crack gets bigger.

Dan

No doubt Dan, that makes sense....same as why some thought it was my coil....heat expands stuff. This was an expensive lesson and everywhere I go and people ask "What was it?", I hang my head in shame that it was something so simple. Changing a Cap, whether it looked good or not, would've been a lot cheaper than changing all the other crap I changed.

Learning as I go, but retaining as well...

dawn...

Just to get a good starting point when I buy a new vehicle I do the following:

New plugs, wires, cap and rotor. New air filter, fuel filter, pcv valve. Change the oil and filter and check all fluids. When I get a chance I do the O2 sensor (if it's a single) and flush the rad.

Then go looking for problems.

On mine I ended up finding a large hole in the intake tube, a clogged cat, and a partially stuck open thermostat.

Glad you solved your problem, no matter how simple it was.

Joe