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View Full Version : Wanting to know - Side Effects of a bad EGR



85_600
07-09-2006, 05:43 PM
I'm curious to know if a bad EGR could cause the combustion temps to be higher than normal - IE: Causing detonation?

I'm trying to figure out if a bad EGR *could* have caused my detonation, especailly running 87 octane gas. NOTE: This was on a stock 85 600, no mods.

Thanks,
Paul

Frank
07-09-2006, 05:46 PM
Yes, if it is sticking open.

85_600
07-09-2006, 07:34 PM
Thanks for confirming this.:thumb:

Stevien1
07-09-2006, 07:44 PM
Actually, believe it or not- EGR lowers combustion temperature. It relys on that fact to reduce NOx emissions.

Why? Because the spent exhaust gases take up space in the intake charge (not allowing as much fresh air in the mix) and causes the mixture to be rich. On properly functioning EGR systems, the computer KNOWS when the EGR is flowing, so it pulls a set amount of fuel out of the mix to maintain a good a/f ratio. Since the intake charge is diluted with exhaust gas, less fuel is required to "fire it off", and the combustion temp goes down.

If the EGR is stuck open all the time, (and these old computers don't know when it is), then the vehicle will run rich most of the time. Rich mixture means lower temps. Usually you'll have a lopey idle, lack of power at WOT, and lower gas mileage if the valve is stuck open.

85_600
07-09-2006, 08:17 PM
I was reading up here:

http://www.aicautosite.com/garage/garmenu.asp

Under the EGR topic here:

http://www.aicautosite.com/garage/encyclop/ency08g.asp

And saw that it does reduce the temps. But, along with that I was thinking that extra exhaust gases in the combustion chamber - wouldn't that create higher than normal temps?

I'm trying to figure out why, on 87 octane gas, I detonated and hurt one piston, if not more? The 600 is all stock.

I do have the bad EGR symptoms of surging and lopey idle, so I'm guessing there is something wrong with it, since there are no other codes than a 52.

guyd_15
07-09-2006, 09:01 PM
I forget where I read it, EGR can actually raise the compression ratio. The short explanation, the inert gas introduced actually takes up some space in the cylinder that would normally be fresh intake charge, rather than spent exhaust gases. It would stand to reason that with forced induction this would only make the problem worse. I wish I could remember the source.
Guy

Stevien1
07-09-2006, 11:28 PM
I'm trying to figure out why, on 87 octane gas, I detonated and hurt one piston, if not more? The 600 is all stock.

Could be a bunch of things!

A bad knock sensor/wiring (never seen that before on a 2.2 :thumb: ), oil diluting the intake charge (again, never seen that before.....), carbon deposit buildup raising compression ratio, too much boost, partially clogged injectors, weak fuel pump, etc etc etc. ;)

turbovanmanČ
07-09-2006, 11:32 PM
As Chuck stated, a properly functioning EGR will not cause Detonation but the opposite. If it doesn't work and the computer or engine is set up for it, then it can detonate alot easier.

Holley
07-10-2006, 08:11 AM
If it doesn't work and the computer or engine is set up for it, then it can detonate alot easier.
Not working as in stuck open? (just want to clarify ;))

turbovanmanČ
07-10-2006, 12:39 PM
Not working as in stuck open? (just want to clarify ;))


Not working as in doesn't open due to valve seized, diagrhram ripped, transducer bunk etc.

Holley
07-10-2006, 12:55 PM
ok, so if you bin the EGR and use a blanking plate do you need a computer rigged for EGR-less operation?

I'm just asking as I don't need it for emissions on the Daytona, but as I'm working on swapping the head in the Autumn (going to a Garrett from an AiResearch while I'm at it, new exhaust, etc) nows the time to bin it or not ...

turbovanmanČ
07-10-2006, 01:05 PM
Russ Knizes, is that it, has said it doesn't matter if it works or not, tons of people have ditched it with no ill effects so I am to assume that Mopar didn't change the programming to take advantage of it, so yes, bin away.

Holley
07-10-2006, 03:54 PM
That was what I gathered from other threads, but what would be the difference between that and if the EGR were still there and blocked shut?

turbovanmanČ
07-10-2006, 08:34 PM
That was what I gathered from other threads, but what would be the difference between that and if the EGR were still there and blocked shut?


There would be no difference, either remove it or leave it there disconnected. If you want to be sure it won't leak, just make a plate and bolt it under the valve, that way, it looks functional but really, its not, :thumb:

Holley
07-11-2006, 05:05 AM
I think something got lost in translation here, lol ... this was what I was thinking of when posting those replies:


As Chuck stated, a properly functioning EGR will not cause Detonation but the opposite. If it doesn't work and the computer or engine is set up for it, then it can detonate alot easier.

(thanks for being patient :))