EGR & Exhaust Back Presure

[WhiteKnight]

1990 SOHC Exhaust/EGR Smog questionsI've been told that if the EGR doesn't work--I will burn valves.

And that I must have exhaust backpressure to get the EGR to work.

How valid is this? And is it possible to have too little backpressure for a KA24E to run properly?

If I restrict the exhaust--will I lose much power?

[compactfean]

First off no an egr will not burn valves. The only thing an egr valve does is recirculate exhaust gasses to reduce nox gasses (oxides of nitrogen not nitrious oxide!) If a egr is stuck open (worst case senario) your car will rather idle high during idle or " Honda" idle. The thing about back pressure only applies to back pressure egrs. Check your catalyst and the emmission components your car is equiped with. They will all be abbreviated. If it say bpegr its a backpressure. If it doesn't say bp in the description its not back pressure. I think only the sr20det has bpegr.DO NOT modify or block egr if you live in a smog state. Just subtract the headache. I have been a smog tech for 5 years so anymore questions let me know.

[WhiteKnight]

I was told that the EGR will cool the exhaust gases and without it--the hot exhaust gases would burn the valves. Is this true? Are there valves I can get that won't burn?

And I was told the EGR on the KA24E requires backpressure to operate.
Modified by WhiteKnight at 7:47 PM 12/11/2009

[Wc240]

the KA and almost all nissans run a BPT valve(back pressure transducer) to control the egr. it will not say in the emissions label. it might on some cars, but isnt required to say so, there for wont always say so. open egr will definately give you a s***ty idle.whoever said it will burn your valves and cools the exhoust is blowin smoke. technically it does cool the exhoust, but it does so by routing exhoust into the intake and cooling combustion chamber temps. its possible to reduce your back pressure too much, but its hard. the KA only really needs about 2 PSI to activate the BPT and send vacuum to the egr

[WhiteKnight]

So if I have a Cat, a resonator, and a Muffler....there must be some backpressure? The smog tech said I had none.

And in California; they added on the Egr temp sensor to make things more complex.

[Wc240]

you can measure it yes, you could have a hole or a leak making it unable to make pressure

[rioredstang]

I don't think you can have too little back pressure. No back pressure would be great if we could do that. That's why we put turbos on is to push air into the cylinders. We run open headers on for optimum power. Even with open exhaust we still has 14psi of atmospheric back pressure to overcome. I think in the past before EFI systems to help with tuning the engine when someone bolted on a less restrictive exhaust they would lean the engine and cause damage. I have seen cars at the dragstrip run with closed mufflers then open the headers and slow down their times.

[WhiteKnight]

The smog tech told me today that when he would plug up the muffler the egr worked. So I told him the B.P.Transducer must be bad.

[rioredstang]

I guess I am confused. Does it set a egr code? Are you having a egr issue? Did it fail the emissions test? BPT valves are a common failure for egr faults. The valve will work even with no muffler. I don't see why the emissions tech would check if you don't have any problems.

[WhiteKnight]

I failed for Hgh NOX 5 times so far. I had one or two egr cel codes when I started the repairs. Now the CEL is clear except once in awhile; it comes on for the California egr temp sensor.I"m thinking if he needs to put a plug in the muffler exhaust hole to get the egr to work; it must be the BPT.

[rioredstang]

BPTV is the most common failure. Replace the valve and remove battery cable to clear codes. Test drive for a little while then check codes. EGR temp sensor is used for egr diagnostics. The computer watches the temp sensor to see if the egr valve opened. I have never replace a egr temp sensor. We don't use NOx here, but I think high timing will drive the NOx up. Make sure your basic tune up specs are correct.

[Wc240]

back pressure and atmospheric pressre are two different things. i made a customer take off his three inch exhoust becouse he didnt have enough pressure to open the valve. generally, if you can plug up the exhoust, then it works, its NOT the bpt valve. there is a step by step test in the fsm to check the whole system. all you need is a vacuum pump/gauge. harbor fright has em for like 20 bucks.

make sure your base timing is in spec.hows your other gases? if it wont drive em up too much, try goin to a higher octaneremove your egr and clean the passages, make sure ALL the vacuum lines are good. you could have a small hole, and plugging up the exhoust makes enough pressure to over power the leak. nox is pretty easy to diag.ive had a few sensors go bad, but not often. i doubt its bad. unless that when you clear the code, it comes back right away.

[WhiteKnight]

My timing is at 14 degrees. I cleaned the EGR and ran 91 octane on the last test.... NOx was about 1000 over. I got my car back from a gold shield station a few days ago. They removed the fuel injectors for some type of spray check.

A new cat would have fixed the Nox problem.....injector check was just a waste.

JPDATEI got the 2 year waiver....BAR said next time it must pass or they won't register the car.
Modified by WhiteKnight at 9:09 PM 12/15/2009