"bypassing" EGR?

greiswig · **Posted:** Mon Jan 02, 2006 3:03 pm

Not that anyone should do this long-term, but just in case someone has an EGR that sticks open and it will be several weeks before the dealer can get a new EGR valve...

What would be the effects if one were to temporarily install a seal before the EGR pipe? There may be enough sensors associated with the flow that the computer wouldn't like that any better than the open EGR, but...just a thought?

Ranger1 · **Joined:** Mon Oct 17, 2005 7:40 pm **Posts:** 1137

If you already have the infamous P0401 and P0299 error codes, blocking off the egr may save your glow plugs from being overstressed and burned out. It happened on mine. After the dealer first diagnosed/fought/argued/ with the Chrysler Star network, Star finally agreed to send an egr valve, which took 5 days. In the meantime, I had to drive it, and it smoked like a chimney, was loud, lacked power and was generally not fun to drive. Passing another vehicle on the highway was an excercise in geometry, algebra and raw courage...

But, when the egr valve came in and was replaced, I drove home- a day later another error code suddenly sprang up - the P0671, P0674. Dealership technician again diagnosed, then called Star for new glow plugs... had to replace gp's 1 and 4 because they had burned out from overuse. Once Star agreed to ship them (3 days of tests later) it ran without smoking and has ever since. Star really puts Jeep techs through hell to get replacement parts.

If this is happening to you, save yourself and your glow plugs - plug up the egr pipe until your new egr comes in. Check the resistance on your gp's to make sure they're ok (.5-1.5 ohms to ground). If they'r out of range, get ready for a Stellar Star experience getting replacements. iirc, one of the members plugged off their egr and it threw an egr low flow code, but if you have that already, it won't hurt and it almost certainly will help.

greiswig · **Posted:** Mon Jan 02, 2006 9:37 pm

Thanks for the input, Ranger. I don't have the codes (yet), with only 2500 miles on the vehicle. But I expect the system will have the problem eventually.

I figured that just blocking off the EGR pipe would make a flow sensor read wrong, and generate a code. I suppose the way around that would be to just block off the outlet from the exhaust manifold, but plumb a new line from the air filter box into the inlet to the EGR pipe. 'Course that would void the warranty.

Ranger1 · **Joined:** Mon Oct 17, 2005 7:40 pm **Posts:** 1137

Unless the ecm is expecting a fresh air flow drop rate, as reported by the MAF, when the egr is activated. Don't know if it does or not...

greiswig · **Posted:** Mon Jan 02, 2006 10:59 pm

Well, it would undoubtedly violate any number of federal and state laws, anyway. But it was just a thought.

Ranger1 · **Joined:** Mon Oct 17, 2005 7:40 pm **Posts:** 1137

If your egr is malfunctioning, blocking off the egr would produce far fewer emissions than would otherwise occur. Excessive egr produces a bad burn and much excess unburned diesel. Really bad for the environment. Especially if the dealer has someone drive for a week or so with a bad valve.

jdreckard · **Posted:** Tue Jan 03, 2006 2:22 pm

I tried blocking the EGR pipe after replacing the valve twice. The vehicle defineately ran better but generated a code after a shutdown and restart. Therefore I took out the block plate off. I blocked it off by making an Al plate to go in between the flanges of the fitting at the EGR valve. Somehow the computer senses that there is no flow to the EGR. I wish there was a way to fool the computer along with blocking off the pipe. I had a Jetta TDI and had the computer reset to minimize EGR function and it didn't cause any problems.

oldnavy · **Posted:** Tue Jan 03, 2006 2:33 pm

Yes I sure miss using my VAG-COM and tweeking the diesel for optimal performance.

greiswig · **Posted:** Tue Jan 03, 2006 4:42 pm

jdreckard wrote:

I tried blocking the EGR pipe after replacing the valve twice. The vehicle defineately ran better but generated a code after a shutdown and restart. Therefore I took out the block plate off. I blocked it off by making an Al plate to go in between the flanges of the fitting at the EGR valve. Somehow the computer senses that there is no flow to the EGR. I wish there was a way to fool the computer along with blocking off the pipe. I had a Jetta TDI and had the computer reset to minimize EGR function and it didn't cause any problems.

I think there is an "EGR air flow control valve" that probably senses when there isn't anything coming through. I have no idea what the nature of this sensor is, but it might be fooled into thinking that all is well if it had air from the filter box flowing through it. If it is looking for high temperatures or some exhaust gas component, that wouldn't work. Anyone know?

wenied · **Joined:** Wed Dec 21, 2005 4:01 pm **Posts:** 107

Ranger1 wrote:

If you already have the infamous P0401 and P0299 error codes, blocking off the egr may save your glow plugs from being overstressed and burned out. It happened on mine. After the dealer first diagnosed/fought/argued/ with the Chrysler Star network, Star finally agreed to send an egr valve, which took 5 days. In the meantime, I had to drive it, and it smoked like a chimney, was loud, lacked power and was generally not fun to drive. Passing another vehicle on the highway was an excercise in geometry, algebra and raw courage...
But, when the egr valve came in and was replaced, I drove home- a day later another error code suddenly sprang up - the P0671, P0674. Dealership technician again diagnosed, then called Star for new glow plugs... had to replace gp's 1 and 4 because they had burned out from overuse. Once Star agreed to ship them (3 days of tests later) it ran without smoking and has ever since. Star really puts Jeep techs through hell to get replacement parts.

If this is happening to you, save yourself and your glow plugs - plug up the egr pipe until your new egr comes in. Check the resistance on your gp's to make sure they're ok (.5-1.5 ohms to ground). If they'r out of range, get ready for a Stellar Star experience getting replacements. iirc, one of the members plugged off their egr and it threw an egr low flow code, but if you have that already, it won't hurt and it almost certainly will help.

I just wanted to thank you for that phrase! I was having a bad day at work and it cheered me up!! I even laughed out loud a little.

RTStabler51 · **Posted:** Tue Jan 03, 2006 5:25 pm

Ranger, a bit ot, and forgive me if its a stupid questions as I'm new to diesels, but how does it 'overuse' glowplugs? I thought glowplugs were only used during start up on diesels?

Ranger1 · **Joined:** Mon Oct 17, 2005 7:40 pm **Posts:** 1137

It was explained to me that one of the ecm updates corrected the glow plug duty cycle. If the egr valve fails open, it has 2 effects - one is that turbo boost bleeds out from the intake into the exhaust, and the other is too much exhaust gas is forced into the cylinders. This causes the cylinder head temperature too low, as not enough oxygen is available, and the ecm cycles the glow plugs on to attempt to compensate. It appears a combination of the wrong parameters on the duty cycle ecm software and the stuck egr valve hastened their demise by overuse.

FarmDiesel · **Joined:** Thu Sep 15, 2005 8:49 am **Posts:** 132

Yeah, if you block it off, there is an "insufficient EGR flow" code generated.

I suspect (hope) that some tuners will include an 'off-road only' setting that disables EGR entirely, as it is computer controlled.

oldnavy · **Posted:** Wed Jan 04, 2006 11:08 am

Once we go to ULSD fuel the EGR will not have the same effect as it does now with sooting the engine up. That is what happens even now for those running B99/B100 they report they have little or no smoke/soot under hard excelleration.

n3qik · **Posted:** Thu Jan 05, 2006 8:46 pm

There is two ways to put the CRD in "off road" mode.

One is to block off the pipe from the exhaust going into the EGR vavle. This will only cause one code, P0401.

Two is to remove the wire connectors to the EGR valve and the mixing valve. This will cause codes P0403, P0299, P0401
and P1140.

The second way is good for when on the road but NOT long term. I have done both and liked the first way the best.

greiswig · **Posted:** Thu Jan 05, 2006 9:30 pm

n3qik wrote:

There is two ways to put the CRD in "off road" mode.

One is to block off the pipe from the exhaust going into the EGR vavle. This will only cause one code, P0401.

(SNIP)

I just wonder what the long-term effect of doing this might be. On my old ODBII vehicle, throwing certain codes caused things to go into "limp home" mode, which made things run far from optimally. Richer mixture, ignoring input from other sensors, etc. It would be nice to have some confidence that throwing this particular code caused no other issues other than...throwing the code itself.

Ranger1 · **Joined:** Mon Oct 17, 2005 7:40 pm **Posts:** 1137

"I think there is an "EGR air flow control valve" that probably senses when there isn't anything coming through. I have no idea what the nature of this sensor is, but it might be fooled into thinking that all is well if it had air from the filter box flowing through it. If it is looking for high temperatures or some exhaust gas component, that wouldn't work. Anyone know?"

I ran across a site that had some engineering information on EGR valves, but I failed to save the link. I don't remember if it was Bosch or Pierpoint, but one of the interesting designs they were discussing was the use of Hall Effect sensors in EGR pintles. so that the ECM could perform rationality checks, as well as check to see if the actual valve itself was not in the correct position that the ECM had signalled for. The gist of the discussion was that this enabled a better solution than using flow sensor or pressure drop sensors inside the egr body itself, as the inductive pickup could be located outside of the egr body, avoiding the harsh environment.

Make me wonder if the electric EGR solenoid is a stepper actuator with a feedback wire to tell the ECM when it has reached a certain position. That certainly would allow it to sense if someone cut the pintle and jammed it into the closed position, and set a CEL. It would tell the ECM if/when the pintle becomes stuck and unresponsive to signal command, due to carbon build-up. It could also enable the ECM to cycle the pintle valve on initiation and perform diagnostics on the egr functionality itself.

greiswig · **Posted:** Thu Jan 05, 2006 10:34 pm

Ranger1 wrote:

(SNIP)The gist of the discussion was that this enabled a better solution than using flow sensor or pressure drop sensors inside the egr body itself, as the inductive pickup could be located outside of the egr body, avoiding the harsh environment.

Make me wonder if the electric EGR solenoid is a stepper actuator with a feedback wire to tell the ECM when it has reached a certain position. That certainly would allow it to sense if someone cut the pintle and jammed it into the closed position, and set a CEL. It would tell the ECM if/when the pintle becomes stuck and unresponsive to signal command, due to carbon build-up. It could also enable the ECM to cycle the pintle valve on initiation and perform diagnostics on the egr functionality itself.

It's a good thought, but at first blush doesn't seem to be in keeping with others' experience when blocking off the port. If the sensor merely required a position indicator for the actuator, blocking off the port wouldn't trigger a code. What I'm inferring from what other people have said is that it is actually sensing the flow of gasses through it somehow.

Ranger1 · **Joined:** Mon Oct 17, 2005 7:40 pm **Posts:** 1137

I believe they are using something similar to what the TDI Epsilon project discovered. In addition to pintle valve sensing, they have 2 other tricks at their disposal. In normal operation, when the ecm commands the egr valve to activate, it also activates the mixing/anti-shudder valve on the intake. This increased the draw of exhaust gas into the intake, reducing some of the air flow from the air filter box. The air filter box has the MAF sensor, which is monitored by the ecm. So when the ecm commands egr on, it partially closes the mixing valve, then checks the voltage from the MAF sensor to be sure the air flow has reduced. I read somewhere an estimate that the air flow drops nearly 25% when the egr cycles on. I have no idea if that estimate is accurate.

So if one blocked the egr intake from the exhaust, once the ecm sent command signal to the egr/mixer valve, it would also be monitoring the MAF signals. If they don't drop an expected amount, it would then calculate that egr flow was low. I suspect that if it has pintle position sensing capabilities, its used more for diags and a feedback signal to ensure accurate amounts of exhaust gas are injected. If the egr gets stuck in the open position, it would know the pintle valve isn't rational in regard to command signal/position relationship mapping.

If my guess is correct, one might be able to trick the ecm with spoofed signals from the MAF when egr signal is activated. Or, possibly use an alternate source of fresh air into the egr intake, but that would still leave the lack of reduced air flow signal from the MAF to the ecm once the mixing valve was partially closed to deal with.

greiswig · **Posted:** Fri Jan 06, 2006 2:00 am

Ranger1 wrote:

(SNIP)

If my guess is correct, one might be able to trick the ecm with spoofed signals from the MAF when egr signal is activated. Or, possibly use an alternate source of fresh air into the egr intake, but that would still leave the lack of reduced air flow signal from the MAF to the ecm once the mixing valve was partially closed to deal with.

Ranger1,

Thanks for the lengthy tome! It makes a lot of sense, and I appreciate the technical explanation. I had suggested earlier that I thought the way to fool it might be to make sure that it can pull in some air, even if it is fresh. If you're right about the MAF sensor, that tells one where to pull it from.

Not that anyone should to that, of course...

Thanks again!

"bypassing" EGR?

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