EGR code fix possibility

[Gumby]

I've been thinking, not often and not very hard, but thinking nonetheless. I know the ECM sends a voltage to the VSV to activate it when the ECM wants EGR. (enough TLAs for ya?) The ECM also reads a voltage from the EGR temp sender confirming that the EGR is, in fact, sending exhaust gasses to the intake.
Knowing that the ECM does not know where the voltage is coming from, just that it wants to see a value, could you run the VSV signal voltage into a resistor to simulate the voltage the ECM wants to see from the temp sender and send it back through the return wire on the temp sender?
The only trick is to figure out what voltage the ECM wants to see when it thinks the sensor is warm, what the voltage is on the VSV activation signal, and what resistor to use. A little research, measurements and Ohm's law and we may have an EGR emulator. For use as test purposes and off-highway use only, of course.

 

[landtank]

Gumby you're over thinking it dude. Just swap in a resistor of the proper value accross the plug for the temp sensor. The value is in the manual.

Of course this isn't fixin s***!

 

[Gumby]

Well, it turns the light off. I'm not sure the problem can be fixed. I think it is too sensative.
If you put the resistor in where you suggest, the ECM will constantly see EGR action and give you a code for that (P0402?) It needs to see EGR only when it asks for it. It asks for it by turning on the VSV. That was my thinking.

 

[landtank]

I didn't give them credit for being that smart. Figured it was more linear. Meet condition 1 and then check condition 2. Figured if you locked in condion 2 then everytime it checked it would be happy.

 

[landtoy80]

What would be the reason for doing this mod?
THere is several things that trigger the EGR. Temp, vacuum and RPM's
Not sure but if you send the wrong signal at the wrong time, wouldn't you trigger a code?

The best mod is to FIX the problem, then the EGR Code wont come up.

 

[landtank]

I just had my truck inspected. Seems that as long as it is OBDII all you need is a clear ECU. That means no sniff test. Let's say someone is having trouble identifying the EGR problem it would be nice to be able to buy some time if the sticker was due.


And the temp sensor is the only thing that will trigger a code. The ECU needs to see a low temp condition at a specified time to realise a fault. By bypassing the temp sensor you're rendering the ECU blind to any problems with the EGR system.

 

[RavenTai]

EGR reduces combustion temps, if EGR was not working could the high combustion temps and pressures damage the piston, head, valves, ect? Or it there enough cooling and pressure overhead in the engine to handle it? It seams that there could be some power gains from a higher combustion temps if the engine can take it, probably would mean lower gas mileage as the inert filler (exhaust gas) would be replaced with fuel air mix

How about the mapping of the ECU? Would it watch the O2’s and set the mix properly or is it counting on that exhaust gas to be there, how would it run with EGR disabled?

EGR is supposed to prevent Nitrous Oxide emissions, hydrocarbons and carbon dioxide would be unaffected AFAIK, I have read that some question the actual harm of minor amounts of NOS (AKA laughing gas) in the atmosphere, any thoughts? In GA ‘96 and later they only check for codes, no codes = pass emissions

But of course I would only consider suck a mod for off road use and then only if the EGR had an expensive fault

 

[turbocruiser]

EGR reduces combustion temps, if EGR was not working could the high combustion temps and pressures damage the piston, head, valves, ect? Or it there enough cooling and pressure overhead in the engine to handle it? It seams that there could be some power gains from a higher combustion temps if the engine can take it, probably would mean lower gas mileage as the inert filler (exhaust gas) would be replaced with fuel air mix

I posted this post recently on another thread. Hope this helps:


OHH OHH OHH, I almost forgot, one ray of sunshine ... I asked a super trusted source ( I forgot to ask permission to share his name so I wont ) about the EGR system lowering combustion temperatures and if that matters much for a turbocharged engine, or a normally aspirated one for that matter. He told me that although it is true that the EGR when open and when introducing, or re-introducing, exhaust gas does cool down combustion temps slightly, this only occurs when the engine is under no load, no boost. Sooo although it lowers the temps slightly it does so at the exact point in time that the temps would average lowest anyways. For this reason, there is really no damage done with a faulty EGR system, it is simply an emmissions equipment thingy. Good to get it right, but not a matter of damage when driving! Whew!

 

[Gumby]

EGR reduces combustion temps, if EGR was not working could the high combustion temps and pressures damage the piston, head, valves, ect? Or it there enough cooling and pressure overhead in the engine to handle it? It seams that there could be some power gains from a higher combustion temps if the engine can take it, probably would mean lower gas mileage as the inert filler (exhaust gas) would be replaced with fuel air mix

How about the mapping of the ECU? Would it watch the O2’s and set the mix properly or is it counting on that exhaust gas to be there, how would it run with EGR disabled?

EGR is supposed to prevent Nitrous Oxide emissions, hydrocarbons and carbon dioxide would be unaffected AFAIK, I have read that some question the actual harm of minor amounts of NOS (AKA laughing gas) in the atmosphere, any thoughts? In GA ‘96 and later they only check for codes, no codes = pass emissions

But of course I would only consider suck a mod for off road use and then only if the EGR had an expensive fault

It is true that high temps could damage parts. Mostly it causes detonation and pre-ignition that cause a lot of damage. I have monitored my ECM and found no knock sensor activity, therefore no spark knock. The rig also runs at 185* in stop and go traffic with the A/C on. I really don't have cooling problems.

My truck seems to run fine with the EGR not working now. I assume the o2 is compensating for the lack of EGR. If anything it would run a little rich in open loop, but then, I doubt the EGR is activated in open loop.

EGR is supposed to prevent Oxides of Nitrogen. NOx. It is quite different than NO2, which is nitrous Oxide. NOS is Nitrous Oxide Systems and is a performance company owned by Holley.

My rig is a 95. If I have a light on, I can sniff test. It passes with flying colors. The light being on all the time masks other problems. I have to scan it once in a while to see if there are more codes than just P0401.

I would suggest such a mod for those of us like Junk who have replaced everything a number of times and still have the code. If it's an easy fix, then by all means clean your modulator or replace the VSV. If you have to take off your EGR pipe because of blockage, then throw in an emulator until you need to pull the motor for something else.

 

[landtoy80]

If you (junk) have replaced all the EGR parts, then maybe you have a vacuum hose off or misplaced.
The qtr mile of hoses under the intake chamber can be a bear to hook up if you have removed it.
I have a couple of hosed that were off after I installed my intake chamber. They were that way for some time. No CE light.
Just a thought.

 

[Scamper]

Kurt makes a good point. The three hoses going between the modulator and the TB are easily mis-installed as they snake around and twist a bit. Doesn't help that Toyota labeled the modulator with PER and the TB with the same letters, but the hoses don't run P to P, E to E, and R to R (what's that all about anyway?!). I always have to refer to the routing diagram on the hood.

When I recently pulled my TB for cleaning, I inadvertently switched two of the hoses. Everything ran fine, but I soon got a P0401. I knew what had happened as soon as I saw the CEL, went home and switched them over after verifying the error, cleared the CEL, and all was good again.

Tom