: Severe spark knock under partial throttle



TopherS
05-17-13, 08:23 PM
Here's another problem that my car is having and I'm hoping it is an easy fix.

When driving at a steady pace, if I push down partially on the gas to increase speed or to maintain speed when going up a slight incline, I get a very bad spark knock...the car sounds like a diesel. Here's what I've done, so far...

1) Timing: I bought my car in September 2011 and the timing was way off. I had the timing set to factory specs. I got better power, but I also got spark knock. So last summer, I took it back to my mechanic...his response was to alter the timing. It got rid of the spark knock, but I had so little power that I could not pull into traffic safely. I've had the timing set back to factory specs. Power's good...spark knock's back. It's never gone away.

2) Last summer, after having my timing reset to factory specs, I changed to using either mid-grade (89 octane) or premium (91 octane) gasoline. It's helped, but the spark knock is still present. I haven't noticed a difference between using mid-grade and premium, so I've stuck with mid-grade most of the time.

The only other thing that I can think to do is when adjusting speed, to adjust it more abruptly rather than gradually...as heavy acceleration (especially to the point that the car downshifts) does not create the spark knock issue.

I've noticed that the problem is worse when the outside temps are warmer. There are also times that coming off the freeway and being on surface streets, that the problem is so bad that the spark knock is accompanied by reduced power.

Any ideas??? I appreciate your help in this.

cadillac kevin
05-17-13, 08:35 PM
My broughams 307 had a similar problem, but only when making a hard right turn without stopping or going WOT then letting off. I never was able to figure it out (tried plugs and wires but didn't help). I ended up dumping B+G 44K in it, which helped noticably with the frequency of the problem, and running premium, which helped more, but the problem persisted.

SafariOne
05-17-13, 08:39 PM
You have to help us out a little too there dude. I have to assume it is your 87 that your talking about. Do you have the 4.1 or the 5.0??? Have you done any adjustments to your throttle position sensor?? Any codes coming up on the DIC?? We need as much info from you as you get from us...... stat.

csbuckn
05-17-13, 09:24 PM
Are you sure its spark knock? Have you tried treating it as a bearing knock and running heavier oils and such?

amunderdog
05-17-13, 09:45 PM
Carbon?
http://www.zhome.com/ZCMnL/PICS/detonation/detonation.html
http://www.misterfixit.com/deton.htm

csbuckn
05-17-13, 10:48 PM
Maybe get an inspection camera in the spark plug hole to see how much build up is actually in the cylinders. Detonation for over a year would make me think the motor has had a rough life. Eventually it should burn off if its not running rich anymore, right?

TopherS
05-17-13, 11:57 PM
Thanks for the quick replies. Sorry about the lack of info in my original post...I was pressured for time...but here's more info:

* Yes, it's the '87 Brougham I'm talking about (5.0L V8).

* I don't believe that the Throttle Position Sensor has ever been adjusted.

* Check Engine Light never has come on, except on startup.

* I jumped the ALDL and get "12" flashing over and over.

* For the past year, I've been running 30W oil at the recommendation of my mechanic (I've had a couple of minor leaks, which have since nearly gone).

* I don't believe that it's running rich...I don't get heavy gas fumes/smell ever.

* My mechanic believes that there's likely a lot of carbon based on the age of the car and the number of miles on it (26 yr old car with 78K miles). He says it was likely never really driven to a point to burn off carbon buildup...and that there's not much that can be done now. He's never looked within the cylinders to see how much buildup there is, though.


I've found a YouTube video that has a similar sound...Cheers again!!!
http://www.youtube.com/watch?v=XiBzxxvy3FQ

cadillac_al
05-18-13, 08:35 AM
You are screwed. Aren't these distributors computer controlled? Normally a distributor is infinitely adjustable unless it is controlled by the computer. My old 307 Olds was one of the few cars I ever had to custom tailor the advance curve. It was a pinger but an adjustable vacuum advance kit allowed me to take out some of that vacuum advance. Half of the problem was it was always locked up in OD at 40 mph.

You say when you step heavily on your throttle that makes the ping go away. That loss of vacuum with the heavy throttle is causing the computer to get the signal to back off the timing; it's just not sensitive enough at light throttle. If you don't want to change the dist you may be able to help it with some stiffer advance springs. Maybe someone has some tips on how to raise the lock up speed to about 50. That would take some of the strain off these heavy cars going up hills at slower speeds.

outsider
05-18-13, 08:48 AM
if it's carbon build up then you should be able to clean it out with some seafoam poured directly down the carb throat while running. Use about 1/2 bottle and start slow, gradually increasing your rate of pour until it chokes out the car and it shuts off. Let it sit for a few minutes and then start it back up. YOu'll see a lot of black crap come out of the tail pipe if it's carbon build up.

csbuckn
05-18-13, 10:43 AM
After listening to the video, I'm with Al, sounds related to the vacuum advance. Something inside the dizzy seems wrong. Maybe the weights are sticking or broken. Maybe whatever is supposed to control the timing isnt working or getting the proper signal from wherever.

jayoldschool
05-18-13, 10:59 AM
You've been running straight 30W? Bad advice.

Check inside the dist for freely moving weights, springs working. Test vacuum advance mech. Check and set timing, properly according to the FSM procedure. Don't trust a garage. Do a Seafoam or GM top engine treatment.

TopherS
05-20-13, 01:05 AM
You've been running straight 30W? Bad advice.

Check inside the dist for freely moving weights, springs working. Test vacuum advance mech. Check and set timing, properly according to the FSM procedure. Don't trust a garage. Do a Seafoam or GM top engine treatment.

Why bad advice on the oil? I don't know anything about what oils are best, so I'm asking out of curiosity. My mechanic said that the 30W would help slow/stop the minor leaks that I've got...and the oil drip pan seems to be catching less oil since switching...but if there's a better oil, I'm open to suggestion.

I took of the distributor cap this morning and found 1/2 of the ballast resistor (AKA: distributor brush kit) rolling around the bottom...the other half still attached to the small spring by the coil. I don't know how that happened, or how long it's been that way, but it's been replaced now. I have no idea if this has anything to do with my car's issues, but thought it noteworthy.

After replacing the broken part, I took a look at the distributor...I took off the rotor, but I don't know what I'm looking at/for (in respect to the weights/springs). I don't know how to test the vacuum advance mechanism???

Yesterday, I went to buy Seafoam and was told to use Marvel Mystery Oil...that it was better. I did and I now must apologize for any damage to the ozone layer...I smoked out the neighborhood...white smoke was coming out somewhat as I was pouring it down the carb...but after letting the last bit sit for an hour, I drove off and...holy cow!!! White smoke poured out the back. James Bond's got nothin' on my smoke screen. I want to say that the treatment made a slight difference, but I'd bet that's more my imagination. But how long should I see smoke from the car? It appeared to go away after about 10 minutes of driving...but today, I pulled out into traffic and I could see a faint bit of smoke behind me...nothing like yesterday's smoke screen, but a little bit of smoke, nevertheless. Is this normal? By the way...no black smoke during/after the treatment. Not sure if this means anything...

outsider
05-20-13, 06:27 AM
woah i never would have put marvel mystery oil down my carb! Not sure if it's OK to do that, but the seafoam it is ok to do that. With the seafoam i stopped seeing smoke after driving for a few minutes.

jayoldschool
05-20-13, 09:33 AM
30W too viscous (thick) at cold temperatures. You are wearing out your engine every time you start it. Additionally, many 30W oils don't have the correct additive package for modern engines. Change your oil, go with a good 5W30.

You should have used Seafoam. Stop taking advice from old mechanics and know-it-alls at the parts counters, and start listening to people that use and work on these cars every day (and have done so for a couple of decades).

brougham
05-22-13, 10:09 PM
It could be something wrong with it that the timing is advancing too fast. It can also happen with older engines that the ring on the harmonic balancer has moved a bit so the timing isn't really set where you think it is. Two more things to keep in mind if the seafoam doesn't do anything.
I've never had an engine that would ping because of carbon build up but some types of engines are more picky to things like that then others.

jamespowers
05-22-13, 10:25 PM
if it's carbon build up then you should be able to clean it out with some seafoam poured directly down the carb throat while running. Use about 1/2 bottle and start slow, gradually increasing your rate of pour until it chokes out the car and it shuts off. Let it sit for a few minutes and then start it back up. YOu'll see a lot of black crap come out of the tail pipe if it's carbon build up.

I thought you put the Seafoam down the PCV hole or have the vacuum from the brake booster suck it into the engine. I have only put it in my gas tank so I am not sure here but I understood that running it through the PCV orifice would clean out the build up the best since that is where you see a heck of a lot of build up directly. Then again, I just had my carb rebuilt and don't want to put it down there and screw anything up I just got fixed. :p

brougham
05-22-13, 10:32 PM
With a carberator sucking seafoam into one of those hoses is the same thing as pouring it down the carb. If you hold open the throttle with the engine off and look down inside the carb it goes straight into the intake.

TopherS
05-23-13, 12:15 AM
An update:

* Since using the Marvel Mystery Oil, it seems that the car is a touch more smooth/responsive and acceleration a bit more brisk...but again, I could just be trying to wish this into existence.

* I've been trying to notice if there's been any more smoke...but it's been raining for past 2 days, so it's hard to tell...but haven't seen any.

* As you all pointed out, the treatment might have cleaned the top end, but the spark knock is still there. I even noticed it knocking right at startup the other day (warm engine).

* I don't know if this has anything to do with it...but Monday was about 75*F and yesterday/today have been over 20*F colder...and I've noticed less knocking as it's been colder. And when the problem was really bad last year, it was when the weather was warm...even had issues with power loss with hot weather.

* I'm not due for an oil change for another 2K miles, but it's been 2 months since the last oil change so it's nearly time...I'll switch to 5W30.

* I've never in my life worked on a distributor, except to change the cap/rotor. NAPA has reman distributors for about $135 or so, but I don't know if it's worth changing or trying to work with the one I've got...but since I don't know what I'm doing, I have to rely on mechanics for help. Advice?

jamespowers
05-23-13, 02:46 AM
An update:

* Since using the Marvel Mystery Oil, it seems that the car is a touch more smooth/responsive and acceleration a bit more brisk...but again, I could just be trying to wish this into existence.

* I've been trying to notice if there's been any more smoke...but it's been raining for past 2 days, so it's hard to tell...but haven't seen any.

* As you all pointed out, the treatment might have cleaned the top end, but the spark knock is still there. I even noticed it knocking right at startup the other day (warm engine).

* I don't know if this has anything to do with it...but Monday was about 75*F and yesterday/today have been over 20*F colder...and I've noticed less knocking as it's been colder. And when the problem was really bad last year, it was when the weather was warm...even had issues with power loss with hot weather.

* I'm not due for an oil change for another 2K miles, but it's been 2 months since the last oil change so it's nearly time...I'll switch to 5W30.

* I've never in my life worked on a distributor, except to change the cap/rotor. NAPA has reman distributors for about $135 or so, but I don't know if it's worth changing or trying to work with the one I've got...but since I don't know what I'm doing, I have to rely on mechanics for help. Advice?

If you are going to change the oil soon then you might as well flush the oil system with some Seafoam as well. Put about 1/3rd of the can of Seafoam in the oil and run it for no more than about 100 miles. By then it will be so black that you will want to change it anyway. :p

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With a carberator sucking seafoam into one of those hoses is the same thing as pouring it down the carb. If you hold open the throttle with the engine off and look down inside the carb it goes straight into the intake.

I am sure you are right but my carb is already clean. :p