Detonation/Pinging Under Load

[mckrishes]

Hello. I have a 1998 Honda Civic LX with the d16y7 engine. I am having problems with detonation/pinging under load. No problems during idle, coasting or very light acceleration. I use 87 octane gas. Using 93 octane will just about eliminate the problem, but I’d like to find the cause. I used a scan tool, and it appears that I am running rich. Here are the values:

At idle:

1. MAP 5.1 – 5.8
2. Short term fuel = -14.8
3. Long term fuel = -11.7
4. O2 pre cat 0.095-0.780
5. O2 post cat 0.8-0.7

At 2300 rpm:

1. MAP 4.5-5.2
2. Short term fuel = -7.0 to -13.3
3. Long term fuel = -11.7
4. O2 pre cat 0.095-0.720
5. O2 post cat 0.095-0.115

From the O2 sensor readings, it appears I have a bad catalytic converter based on Eric’s video. So far I have done the following:

1. Verified the cat is not clogged
2. Verified good intake pressure on the engine
3. Checked for vacuum leaks using Eric’s method
4. Air filter is clean
5. Set the ignition timing to stock (which helped a lot)
6. Ran some injector cleaner in the tank
7. Verified coolant is full with no air in system

I am trying to figure out what direction I need to go in. I haven’t checked fuel pressure, cleaned the MAF sensor or checked for compression. Not sure if something is wrong with the MAF. I appreciate your help.

Topic

[mckrishes]

I just started my car this morning after sitting all night and according to the scan tool, the car was in closed loop immediately and it stayed that way even after warming it up. However when I throttle up to 5000 rpm, the car goes into open loop. Fuel trims are still in the negative when at idle.

[mckrishes]

New info. Short term fuel trims get worse with increasing rpm. Goes from -10 to -29. Also the upstream O2 sensor stays in the range of 0.6-0.7 with almost no fluctuation.

[Andrew Harris]

I would start with some basics.
Check your fuel pressure. High fuel pressure will make a vehicle run rich.
Check the fuel pressure regulator and make sure the vacuum line going to it isnt sucking fuel in from a ruptured regulator diaphram.
Check engine vacuum beleive this system uses MAP for fuel control and low manifold vacuum will result in a rich condition.( Valve adjustment, timing belt jumped, low compression)
Check MAP sensor itself. Should read 3.0 volts at sea level with key on engine off.
I would also verify compression

[mckrishes]

Fuel pressure and regulator are good. But I forgot to check for stable fuel pressure with the engine off so I’ll do that tomorrow. I tested the MAP and it checks out good. I checked for vacuum leaks again and found none. Will check for compression tomorrow. I changed the upstream oxygen sensor and put a Denso one in. There is some improvement with the trims at idle, but essentially the same results with increased rpms of 4000-5000 Still runs rich at -11 stft or so at idle. Worsens with wide open throttle, -22 to -25 at stft. Ltft hovering around 8-11. Ignition timing is about perfect. Spark plug advance is at 11.5-12 after warm up and at idle.

[Mike]

If you’re experiencing detonation, you should also look at your cooling system efficiency and the internal condition of the engine with respect to combustion chamber deposits.

The short answer to why an engine detonates is that there’s too much heat in the cylinder, causing the fuel to auto-ignite/explode, rather than burning in a smooth controlled manner.

It’s kind of odd that you’re experiencing detonation with an engine that’s running rich. A rich fuel mixture cools the cylinder better, thus avoiding detonation. If anything, a lean mixture will make detonation more likely. If you’re running rich and have detonation issues under load, I would check for combustion chamber deposits. They might be causing an artificially high compression ratio, pushing the fuel’s octane rating beyond it’s limits. If deposits aren’t your problem, the cooling system could be at fault.

[mckrishes]

Did a compression test and here are the results :

Cylinder 1 – Dry = 115 Wet = 150
Cylinder 2 – Dry = 114 Wet = 160
Cylinder 3 – Dry = 112 Wet = 190
Cylinder 4 – Dry = 120 Wet = 150

Fuel pressure is 31 psi after turning off. 30 minutes later it was 28 psi. 1 hour later it is 27.5 psi.

Cooling system appears to be working property. Will check combustion chamber for deposits as soon as I can. There is no air in the system. Readings are good according to the scan tool. Are you suggesting to physically checking the thermostat and the ECT temp sensor? Will this cause my car to run rich? It’s odd that my negative fuel trims get worse with acceleration.

[Mike]

The results of the compression test tell me that you are dealing with worn piston rings and cylinder bores. You are probably experiencing blow by, which could be causing deposits to accumulate in the combustion chambers.

These deposits aren’t the kind that would artificially raise the compression ratio, though. What I’m thinking is the presence of hot incandescent deposits, causing pre-ignition (when the fuel/air charge is ignited before the proper time), which in turn could lead to detonation.

If the mechanical condition and internal oil control of your engine needs attention, I doubt that we can put much faith in your electronic data. You could be oiling your catalytic converter, which will throw the readings for a loop. A picture of your spark plugs would be useful.

[mckrishes]

Here is a picture of my spark plugs.

Attachments:

• IMG_0489.JPG

[Mike]

Going by the results of your compression test, I was expecting oily plugs. They actually look pretty good, maybe just a tad rich, but nothing serious.

[mckrishes]

I used some seafoam through the brake booster to attempt to clean the combustion chambers. I did this a few months ago without success. I am waiting on the endoscope to come in so I can see what it looks like in there. I may have to soak the pistons. I might try some berryman for soak. I heard it was pretty good. I am going to check the fuel pressure again with a new kit since the Harbor Freight kit I bought had some issues. Not sure if I can trust their stuff. I bought a multi-meter from them that I had to return for erroneous readings. I tested my coil and it was out of spec. Was gonna get a new coil, but I decided to verify with a meter at advance auto and turns out it was ok. I was listening to my fuel injectors the other day and it seemed like injector 4 was clicking faster than the others. I’m not sure if it was my imagination. Gonna repeat the fuel test and see what I get.

[mckrishes]

I think I am getting somewhere. I repeated the fuel pressure test. I’ve got good fuel pressure at 31psi. The fuel pressure regulator checks out fine at 40 psi unplugged and clamped. On shutdown I noticed a 3 psi drop within 5 minutes and a 10 psi drop in 30 minutes so I know I have a leak somewhere. Fuel lines aren’t leaking so it’s either my pump or injectors. I’m having a problem. In Eric’s video he was to clamp the return line and the supply line. Problem is my supply line is metal so how do I get around that?

[mckrishes]

The supply line that goes from the filter to the rail is rubber. The fuel pressure gauge is attached to the filter and before the hose. I was able to pinch the supply line and I noticed a 2 psi drop in about 20-25 minutes at 27-28 psi from 30. Upon releasing the supply line, the pressure went down immediately to 20-22 psi. I am thinking the fuel injectors are leaking. I am going to pull the rail so I can see first hand if this is the case.

[James P Grosso]

Plugs look a bit rich, but I was expecting them to be oily too?
Any oil entering the combustion chamber has very low octane rating and can cause knock, but that does not seem to be the issue?
High engine temperatures, and high air inlet temps can also cause engine knock, but it sounds like engine temps are normal, and I assume using the stock air filter assembly?
Sounds like ignition timing is OK too?
I don’t know Honda engines, but the compression ratios look OK, except #3 wet at 190 seems high to me? and looks to be 30-40 higher than the rest?
Could there be excessive valve lash or cam wear on that cylinder (closing the intake valve sooner than the other cylinders?)

[mckrishes]

I am using the stock air cleaner system. I will have to investigate the valve lash on that cylinder. I got my endoscope in and I was able to inspect the cylinder heads. There is hardly any combustion deposits on the cylinder. There are very minimal deposits on the side of the cylinders. Definitely not enough to warrant increased combustion chamber pressure.

The problem with the fuel test is that the pressure gauge attaches directly to the filter. The supply line before the filter is made of metal so I can’t clamp it. I am able to clamp the supply line from the filter to the rail. I am going to try to find an adapter that will let me connect to the rail so I can perform a more accurate test. If not I will have to pull the rail and test the injectors that way. Would rather not do that because I don’t want to disrupt the injector seals and cause unnecessary leaks, but if I have to I will.

[mckrishes]

I went to the junk yard today and picked up a fuel hose and 4 injectors from a newer model civic. I removed my fuel rail and observed the fuel injectors. There was no leaking. I removed the injectors and they were very dirty. The housing was very dirty as well. I cleaned the new injectors and the housing and put it all back together. I cut the fuel hose in half and put a t-split on it with a schrader valve. Now I can clamp before the fuel pressure gauge and get a more accurate test. Here are the results of the test:

Unclamped = After 30 minutes = 11 psi drop. After an hour it’s a 12 psi drop.

Supply line (before fuel pressure gauge) and return line clamped: After 40 minutes = 2.5 psi drop

Supply line clamped (after fuel pressure gauge) : After 40 minutes = 4 psi drop

Return line clamped: After 30 minutes = 4 psi drop

Supply line clamped (before fuel pressure gauge): After 30 minutes – 1.5 psi drop

[Author]

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