Hi all,
I have a '94 Sedan DeVille, 4.9L. 96,000 miles. When it gets hot (after 30-40 mins of driving) it spark knocks (only when you "get in it"). I put new plugs and wires on it last month as part of a tune up. It sounds to me as it it is only coming from the cyl(s) on the driver's side of the engine.
It has also been settin the P048 code (EGR sys Malfunction), causing the "service soon" light to come on.. I checked the egr valve, and it seems to be fine. i ran some sea foam through the vacume sys as well. The light went off soon after that. It still sets the code occasionally, but I can clear it and it may come on in 3 minets or 3 days. What should i do next?

Thanks!

Are you burning premium? The 4.9 does not have a knock sensor. A faulty EGR will cause detonation I believe. How do you know it is working. Something is amiss if you got that code.

yep....i'm burnin the good stuff. we examined the valve, and it had no tears or rips, or anything else to indicate that it is faulty. i'm beginning to wonder if it is the solenoid sticking?

Look down the throttle body and see if the EGR tubes are plugged up. If so, clean the carbon out with a rod or long screwdriver. It might also be overheating a little from a clogging radiator or weak radiator cap.

yep....i'm burnin the good stuff. we examined the valve, and it had no tears or rips, or anything else to indicate that it is faulty. i'm beginning to wonder if it is the solenoid sticking?
Don't get confused by all the oil company marketing. Premium is not "better" than regular. It just has higher octane, which is nothing more than the fuels ability to resist detonation. Nothing more.

i'll definatly try cleaning the egr tubes tomorrow afternoon. As part of the tune up the coolant sys was flushed and a new thermostat, radiator cap, and heater core were installed.

I forgot about the EGR tubes. That'll do it.

ok guys,
I cleaned the EGR tubes throughly. I also replaced the rubber vaccume hoses coming off the TB, as well as the TB gasket. So i get back out on the road, and it STILL spark knocks. Any ideas? I've heard that putting a cooler thermostat, and puttin spark plugs with a lower heat range might would help. Any advice is welcome! I can't stand my car spark knocking...it drives me crazzzyyyyy. :-)

Do you know how hot your thermostat is? I run a 185 up in Maine and I should probably run a 195. You definitely shouldn't need a 195 down in SC. I don't like to go colder than a 185 in any vehicle. I don't think colder plugs will make much difference.

i'll definatly try cleaning the egr tubes tomorrow afternoon. As part of the tune up the coolant sys was flushed and a new thermostat, radiator cap, and heater core were installed.

Did the pinging begin after work on the cooling system was done? Were the required GM sealant tabs installed? Go into Paramiters and see what the engine temp is when it is pinging. Detonation is a major cause of engine failures. I'd also check base-timing.

Change the gas station. I used to fill at the same station for years only to figure out they put 87 gas in 89 tank. Everytime I drove long distance and had to fill it up somewhere else I would notice a differencein the way my engine sounded, but it took a while to realize those bastards at a local gas station have been cheating customers!

i had same problem. new egr cured it.

I put the thermostat the factory called for, it's a 185 i beleive. and the pinging started after i installed a new set of ac delco plugs in a recent tune up. and yup, i did put the sealant tabs in. and to check the timing, i see somthing about grounding out a prong in a connector to get an accurate timing check? what's the story on that?

Thanks all!

The A & B pins on the ALDL connector must be jumpered together. That puts the ECM into 'set timing mode'. The 'service now' telltale should blink when those pins are jumpered. The base-timing can be checked and adjusted if necessary.

Changing the EGR valve fixed mine too. I dont think I was getting any code tho so it might be something else.