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can bad EGR valve cause spark knock?
http://4g61t.org/forum/viewtopic.php?f=17&t=8903		 Page 1 of 1
Author:  richard lavelle [ Wed May 12, 2004 9:50 pm ]
Post subject:  can bad EGR valve cause spark knock?
first of all, i have an 89 colt hatch with the 1.5 and fuel inj. it has just over 156,000 miles and on really warm days had developed a part throttle pinging sound. i ordered spark plugs from autozone that they said were for the turbo model. added my own fabbed exhaust. went with the coldest thermostat that advanced had and is still knocking. if i go past 1/2 throttle the sound goes away. o2 sensor is also new. the guy at the dealership had similar opinions like the guy at autozone, they both said that if the egr valve was not functioning, that this would sent superheated air through the intake. is that why at part throttle when the car is cold, there is no spark knock? and it only does it after 10 or so minutes. ive dealt with all this for the past year or so by running 89 octane gas, but now that 87 here on the east coast is 1.99$ FORGET ABOUT IT!!!! :o
Author:  recracer [ Wed May 12, 2004 10:45 pm ]
Post subject: 
EGR will cause this problem. EGRs job is to cool Combustion temp below preignition by recirculating unuseable spent exhaust gas back to the combustion chamber to take up space that would be ocupied by fresh air and burnable fuel . it will run better with a working EGR . Ping is the noise you hear when flame front hits the piston before it hits top dead center trying to push the piston back down the wrong way. cant make good power with the engine trying to run backwards . super heated intake air is a false statment.
Author:  The Ethereal [ Thu May 13, 2004 12:03 pm ]
Post subject: 
Check the base timing. Maybe it's off. If it's within specs, look into temporarily retarding it 2 degrees. Also, try unhooking the green-striped vacuum hose going to the EGR. If that helps, block off the EGR.

OOOHHHhh.... Does anybody remember if vacuum of atmospheric pressure closes the EGR on the 4G15? :oops:
Author:  xlr8 [ Fri May 14, 2004 2:04 am ]
Post subject: 
From my knowledge EGR is only used when the engine is cold so as to reduce hydrocarbon emissions and is completely switched off by the time the engine is at op temp. It is used to preheat the intake mixture for a more complete burn (HC emissions are generally produced by rich mixtures).
Author:  The Ethereal [ Fri May 14, 2004 7:45 am ]
Post subject: 
XLR8, I think it's the other way around?
Author:  socrateez [ Fri May 14, 2004 9:46 am ]
Post subject: 
what octane fuel are you using?
Author:  recracer [ Fri May 14, 2004 9:29 pm ]
Post subject: 
Egr works after the car is warmed up. egr on a cold engine will cause a big stumble. A cold engine gets extra fuel for cold start and warm up. Egr would displace that fuel . See my earlier reply. Im a state emissions repair tech that info is correct
Author:  Flying Eagle [ Fri May 14, 2004 10:12 pm ]
Post subject: 
I'll throw my change in the hat.
I had an oil burning 4G15 12V with 114,000 Km's on it. Anything just under half throttle resulting in marbles in the pan. Anything past half throttle sort of drowned it out. I do not get this problem anymore as the valves, rings and seats are all fresh. My engine does not have the emissions EGR provision as some of the other guys do. I ran the 89 octane stuff, and for a short while while the timing was still advanced, things quieted down; however once the computer figured out things were a little out of spec, back came the pinging.

I'm not sure if your only really putting a bandaid on things by using a thermostat and spark plugs that are out of the usual range (but I see what you are trying to do) If your EGR is not functioning, it is safest to get it fixed. If you fix the EGR and your problem does not disappear, you just might have a problem similar to what I was experiencing.

Here's a good question to open things up,

Would a car with EGR only know that the EGR is mandatory because the ECM is communicating with it, or would an ECM ship with the EGR already preset to run?
I would lean to the ECM only caring if the euipment is plugged in because it seems like all of the later model 4G15 12V ECM's interchange.
Author:  recracer [ Fri May 14, 2004 10:25 pm ]
Post subject: 
You could be right on that ,because my colt does not have an egr on it from the factory. i just swaped tb injectors maf and ecu from 94 e 4g37 stuff . the 1.8 this ecu came from has an egr and egr temp sensor and the ecu does not seem to care. I looked up mil codes for the 94 e Egr codes seem to only set on califonia emissions cars
Author:  richard lavelle [ Fri May 14, 2004 10:50 pm ]
Post subject:  egr valve
Quote:
what octane fuel are you using?
now im running 87, but it does it with 89 also, but doesnt do it when i run octane booster(cheap wal mart brand) but what a hassel!
Author:  pumaproton [ Sat May 15, 2004 9:38 am ]
Post subject: 
I did a digram of all my vacuum lines, as with a carb it can get quite complex.

The EGR on mine is controlled by vacuum, with a T piece in the line to a temp sensor.

The EGR opens up and lets exhausts gases into the inlet manifold only when the engine is at normal running temperature and there is a high inlet manifold vacuum, ie when you let off the accelerator.

I blanked my EGR on the theory it will clog up my valves with carbon deposits and also makes the temperature of the inlet stream a little higher.

My car goes well, apart from my 22mpg, but I believe my carb is dying.
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