A year ago I had some knocking while using 91 octane while accelerating at ~50km/h in HOT temp. The timing has been reset to 15° since then and the problem disappeared.
During the last few days I have been feeling knocking while accelerating at ~70km/h in WET condition. As soon as the rain stopped and the sun came out the knocking stopped.

I have an oscylloscope and checked my knock sensor. It clearly gives me spikes of voltage consistent with the RPMs. How can I diagnose better what is the root cause? The timing is still at 15° sharp and I have new NGK platinum plugs (awesome results!), relatively young wires, cap and rotor. The car runs very nice and with good MPG but just this knocking is bothering me.

Someone suggested that I have carbon deposits that increase compression or glow but how the heck do I diagnose that?

 

Check that your EGR is opening when you rev the engine to at least 2k rpm.
Check your engine temp sensor terminals for corrosion.
If you fuel filter is old (more than 10K miles) you could be fuel starved, replace it.
You checked the knock sensor with an o-scope, but if the resistance is still too high the engine ecu may not read it. check the resistance of the knock sensor at the sub-harness (if its way over 500k Ohms then either the subharness or the sensor is bad, for instance mine was 5Meg ohms).

 

sounds like you got too much carbon deposits in your engine which causes knocking. the other ways beside doing engine overhaul is by using fuel injectors cleaner. you might have to use lot of it, use it properly, and be very persistent about it. try using Amsoil PI. dump in 6 oz for the first full tank and 1 oz there after for around 15,000 miles. by then hopefully, it'll melt most of your carbon deposits.

 

2 words:
Seafoam
ok 1 word

 

Huh... Will try to reply in the order:
1. The resistance of the knock sensor is way higher than 500 kOhm. Dont remember exacly, but it is in Megaohm area. I will doublecheck tonight.
2. How do I check the EGR? Where is it anyway?
3. The Fuel filter is 2 months old.
4. I am using the STP injector cleaner eventually. Should I switch to Amsoil stuff or STP is good?
5. What is Sea Foam anyway?

Thanks!

 

to check the egr, let the engine warm up, place your hand underneath the 'dome' of the egr, there should be a rubber bladder which allows it to move up and down within the dome, next with one hand under the egr and the other at the throttle, rev the engine to see if the engine automatically opens/closes the egr.

Seafoam is great stuff available at napa and few other places. you allow the engines vacuum to suck the cleaner in slowly and it helps dissolve and burn off carbon deposits. don't be surprised if you max turns into 'spy hunter' and emits a strong dense stream of semi-black smoke! Note that there is a high probability that your 02 sensor will get plugged up by the tremendous amount of carbon, and if you over do it (as in add the seafoam too quickly) you can overheat the cat convertor and possibly damage it. My cat is now rattling, and its probably from the use of seafoam.

 

Has anyone tried to spray water into the intake? I heard (!) that it also cleans the engine from carbon deposits.

 

LIGHTLY spray water into the intake, like out of a spray bottle.
anything more may hydrolock the engine

EDIT: Forgot to say while running only

 

whoever said water works good on the intake are ....humm, fruitty!!!!! here, take a look at my gig and I'll let you be the judge:

http://web.syr.edu/~bvtran/DSCF0977.JPG

FYI: That's only the intake part. And that's approx 2-4mm thick of craps you're looking at!!!! When I cleaned it, it took me 2 cans of brake cleaners and 2 cans of throttle body cleaners to melt them. Off course, I can't clean while they're on the vehicle cuz the system is pretty sensitive toward brake cleaner. So, if you really think that water works. You might wanna think again. I've been there and done it. Don't kid yourself, just don't even think about it or you're just wasting your time.

And no you should never spray water into the intake while it's still attached to the vehicle. Why, not? It'll eventually gonna fall into the runner and into the combustion chamber where fuel is getting mixed with air. Thus, it'll kill your ignition. Or worst causing your car NOT to run at all or even stops while you're in the middle of the road.

Now we're just talking about the intake part and that has nothing to do with your combustion system that might be the cause of detonation. As mentioned earlier, there is a possibility that you got too much carbon deposit there that's causing it. I would highly recommend that you try to use Amsoil fuel injector cleaners in the meanwhile. They're very very strong stuffs. When you're using it, be sure you followed the instruction carefully (I've also mentioned before too).

 

what happens when you spray brake cleaner on a rock?
What happens to a rock on the edge of a river bank.

 

Just checked my knock sensor. Its resistance is 501 K Ohm. I was really mistaken when thought it was higher. Guess, I am up for the engine overhaul

 

tell you what...why don't you use up all of your current fuel. Then fill the car up with 93 or + octane and see if that makes any differences. I think you might be interested in trying easier method first before drawing such conclusion cuz engine overhaul ain't easy and fun.

 

Hi,

what should i do if iam up to my last octane rating,

what solution should i use?

what step should i take?

 

I just started to get the knocking today as well after I filled up with gas using 87 octane. But the thing is that I used to put the 92+ octane and had no problems. Then when gas prices went up I resorted back to 87. It ran fine until today when I had to fill up again. So I guess I will have to let this tank go to empty then start putting back the higher octane. I might had some fuel cleaner in to see if that helps.

I know this might be a stupid question?? Plus I just replaced the o2 sensor just recently so I hope that is not the problem.

What exactly does engine overhaul do because I have seen it but never knew really what it was for and why would you use it??

 

I would say if it only once happened that you have used 87 octane of a series of fill ups and got knocking, then the gas was prolly 'a bit' lower than 87. Try to fill up at a different gas station.
But I have been having knocking while using highest octane possible and then with lower octane no knocking at all. It is not always knocking, that is my problem.
For example today she ran just fine...

I am also ckecking the EGR valve like described in Haynes and first I noticed no vacuum in the hose that goes to the EGR valve while warming up. What the hell?

 

That is one of my early thoughts but now the cars runs really rough and when im idling or even on the go it runs really rough like it is going to die. It has stalled twice while stopped at a light but still cranks up. It sounds like one of the cyclinders is not hitting. Which leads me to the wires because I have not replaced them in 3 years or so. I have ordered some new spark plug wires and distrubtor cap. The plugs are fairly new to my knowlegde. I just put a new o2 sensor on like a month ago. This really sucks. It was running fine until last Saturday. I am going to check the EGR valve now myself.

 

Well your knock sensor sound fine. Have you checked your injectors to see if they are out of spec. (11-14 ohms). On the GXE the injectors are known to go bad. If you find one thats out of spec and you plan on keeping the car, I'd suggest replacing all of them.

 

to Tarzan:

I know this might not sounds like a good suggestion b/c most people perferred to have more powers. But you might wanna lower down your time down to 10-12 degree BTC and see if that still giving you detonations.

 

Speaking of I found out what was wrong with my car it had skipped the timing which I know is not very good. So Im glad I took it to my mechanic. He said he had to running good today. I had the timing belt put on in March so he his checking it today. I am going to get the car back tomorrow hopefully. It sounds like it might need a new belt tenisor or whatever it is called.