82 Grocery Getter

Since I still see locks on all the other topics/threads and cannot post on those, I entered what is below here....


I have a situation with knock / detonation, but ONLY when the car has been driven several miles or at highway speeds (bascially only when the engine reaches a full or hot temperature). When the motor is cold or driven for only about 10 minutes, there is no knock. And it ONLY does it when accelerating from a slower speed or when pulling away from a stop. If I hear the knock begin, I drop the pedal a little quicker and further and the knock temoparily stops. I can basically predict when the knock is going to occur.

The car:
'82 Olds Cutlass Supreme.
3.8 Liter / 231 cubic inch Buick V6 (VIN code "A")
Automatic transmission.
61,000 original miles.

I changed the plugs and wires as per factory specifications. Ran a can of BG44K in the fuel one time. The timing was advanced AND retarded and the knock was still evident, so it was returned to the specs on the label under the hood. I run the highest octane gas (91 to 93). All vacuum lines look fine.

After some research, I'm considering a new EGR. Also, I thought since it only knocks after reaching full temperature, perhaps I should put a colder thermostat in it (like a 180). The factory specs are for a 195, I have no idea what is in, but I assume it's a 195.

Any suggestions would be appreciated.

Thanks,
Chad

dwsshay

[quote=dwsshay;78540]my son pickup done the same thing the port holes under intake were cloged oil could not get back down fast enough to go thew oil pump cleaned it up ran great again not sure if thats it im not much of mechanic hope it helps

easytobedead

well i know you might have a bigger knock soon..............hope not.

Lady72nRob71

Pull the EGR valve and see it it is clogged with carbon. If not, check to see if the valve works right (attach a short length of clean vac hose and suck on it.)
A 180* Mr gasket t-stat is recommended.
I assume no trouble codes?
Let us know what you find...

82 Grocery Getter

Why might I have a bigger knock soon?

Chad

82 Grocery Getter

Many thanks for your input, Rob! When I get the opportunity, I shall check into the EGR... probably gonna put the new 180* stat that I have in it also. As for trouble codes, I haven't checked, and I don't even know how. I'll check my Haynes & Chilton manuals about that I guess.

Thanks again!

Chad

jensenracing77

i seem to remember a car doing this and it was the vacuum advance was goofed up somehow. if i remember right it was advancing all the time, i just cant remember. try to unplug the vacuum advance and plug off the line and test drive it. i wouldn't want to leave it that way but it may give you an idea what to look for.

Bluevista

The knock can get worse when you bend rods or blow a hole through the top of the piston, broken ring lands, good stuff like that.
This explains it better than I ever could.

http://www2.zhome.com:81/ZCMnL/PICS/...etonation.html

ricdiculus

Are you sure your not running hot? Those idiot lights in the dash are not the most reliable. Another thing to check, could you be running lean? a overly lean charge will cause detination. are there any other issues when the knocking occures like missing or 'dead spots' in the pedal. Just to point out when you increase the throttle past a certain point it should retard the timing a few degrees because of the lack of engine vacum, which sounds like your situation. Try jensenracing77's idea and drive it without the vacum advance connected to the distributor. You should still check all your emmision stuff and make sure it is all working correctly, as any problem here could also cause a lean condition. Hope this helps...

Lady72nRob71

Good point.
I would advise any car buff to invest in an infrared thermometer (IRT) to instantly check your car's temp. Check it right on the manifold beside the temp switch.
I bought a nice expensive ($45) IRT and it worked well. I later bought a $10 cheapo IRT from Harbor Freight and it read only 1 degree cooler than the expensive one. So get whatever fits your budget. Just note that the cheaper ones lack a very wide measuring range.
These are also great for checking your A/C systems, meat temps, oven calibration, even your own temp!

82 Grocery Getter

Hello, ricdiculus... and thanks for your input!

Try not to laugh too hard (anyone who responds) when it comes to my lack of knowledge automotive wise.

Actually, someone on another Olds forum suggested that it may be running too hot, and that I should invest in a pocket-type infrared thermometer. I think I'm going to do that. As far as it running lean, according to the research I've done in Haynes & Chilton manuals I don't beleive I can adjust the richness/leaness on that 2bbl carb, but I'm going to double check that as well. I know when I changed the plugs and wires last weekend, the plugs looked like it's burning well... there was no buildup, carbon, etc... they just had a light brownish/red color to them. There are no other issues that occur when the knocking starts... no missing or dead spots in the pedal... it picks right up and accelerates fine.

Either way, along with all the suggestions that I've received, I just bought several feet of 5/32" vacuum line the other day, because some of what is on the car looks questionable. I also have a new EGR valve and a few EGR valve gaskets on the way. I intend on pulling the EGR that is on, I may just clean it, but I'll likely just replace it.

Thanks again!
Chad

82 Grocery Getter

An IRT will be my next purchase!

Thanks!
Chad

Oldsmaniac

The symtoms you have mimic a lock up torque converter solenoid problem. I am not sure if your year and a V6 engine have this setup or not. When cold unplug the wire off the drivers side of the trans if so equipped and see how it runs.

82 Grocery Getter

Purchased a $50 IRT today, and will check the temp at the intake where the temp sensor is located soon.

ricdiculus

Well yes and no. there is no mixture screw other then the idle, but If memory serves that car has an electronic feedback carb. There are provisions in the cars computer to adjust the air/fuel ratio, so if it is getting (the computer) bad information, It will cause problems. Best bet is to pull the codes from the computer (check the shop manual, it will explain all) and see if there is a problem with a sensor or frequency valve (that actually adjusts the mixture).

Lady72nRob71

Here is the procedure for dumping any error codes the computer may have stored:
http://tlentz.oldsgmail.com/howto.html#Computer
This assumes the CCC is still attached, operating, and the light works.
If it all works and you get no codes (other than the normal '12' as described in the procedure), then the mixture should be fine.

The mixture can be adjusted on CCC carbs, it is just more difficult and obscure.
A procedure is available here:
http://tlentz.oldsgmail.com/howto.html#Mixture
However, that should be reserved for last resorts. Seek vacuum leaks, etc first.

BTW, any chance this was once a Canada car?

Warhead

One thing at a time guys.
I would go for the EGR first.
Exhaust is recycled in the combustion chamber to knock down CHAMBER temps, which reduces emissions. Engine temp can be fine, and you can still have a detonation problem, because of the EGR valve.
Good luck.
JMO
Jim

Oldsmaniac

I wouldn't replace anything until I knew the part was bad. An EGR is very easy to check. The older ones can be lifted by hand to see if it is not stuck and the idle speed should drop while lifting. It can also be checked with a vacuum source for operation and checked to see if it holds vacuum. You can also check for proper vacuum source from engine to the valve. If your car has a computer and lock-up torque converter I am pretty convinced that that is your problem.

82 Grocery Getter

Well, the knock/detonation issue has been solved. WOOHOO! And it was.............. the EGR valve.

I'd like to thank EVERYone who offered any of their input as I tried to solve the issue.

Many thanks!

Chad

Lady72nRob71

Great! Glad you got it fixed; help is what we are here for...

Was the valve leaky, stuck, just clogged with carbon. or dont know?
Just curious to its failure mode...

Oldsguy

Great news, glad our people could help. I was monitoring this thread because I knew it was beyond my limited "old school" knowledge. Great work team!!!

citcapp

Great news, another successful Classic Oldsmobile forum fix Congrats to all involved

82 Grocery Getter

Actually, when I went back there with a 13mm box end wrench (and it was a VERY tight area back by the EGR valve on this car), the first of the two EGR valve bolts came loose quite easily (with barely any effort to my suprise). When I went to the other bolt, it was ALREADY loose! I probably could have just torqued both bolts back down real good, but I figured that since I was already THIS far, and had already purchased an old (but unused) original OEM Delco/GM/Rochester EGR valve on eBay that couldn't be returned, I may as well put the new one on. Anyway, it was obvious that there was a leak since one of the two bolts was loose and the old gasket was totally blackened with carbon. The old EGR valve's diaphram wasn't sticking or binding, but the ports were loaded with carbon buildup. I probably could have just cleaned it and put it back on with a new gasket... But like I mentioned, since I already had a new one here that I couldn't return, I may as well put the new one (and a new gasket) on. After doing so, I took it for a good run out on a highway, then back through town (where there's more stop signs and traffic lights)... Didn't knock once. Then I took it out in the country-side were there's more steep hills... Didn't knock once. Later in the afternoon/evening, I picked up my Dad and we went away for the evening... Didn't knock once.

Again, MANY thanks to EVERYone who offered their input on the knock/detonation issue! It was MUCH appreciated!

Chad