Here is the background:

I previously jacked a thread dealing with code 43, and I decided to start a new one so nobody else is confused. This Christmas I replaced the O2 sensor with an aftermarket one from TAS Auto due to a Code 41 (Heated O2 Sensor) which was constantly on. It had an OEM connector. There was an open circuit in the original sensor. About a month or two ao, I got a code 43 (Either O2 Sensor or Fuel Supply System) periodically. I noticed this especially when it is cold. I have no other Check Engine light coming on.

The Symptoms:

I have been getting terrible gas mileage in the city (~20 mpg), but on the interstate I can go about 450 miles without having to fill up. The car runs rough when going from ~1500-3000 rpms. I shudders but I would say that it doesn't lack power. Sometimes I will hit the gas and the engine hesitates for a second then accelerates with a slight shudder.

What I have done so far:

I cleaned the connections for the O2 sensor and the connection at the shock tower. I replaced the coil with an old working one, and still have the problem. Changed the spark plugs (OEM NGKs always). Compression tested the engine (118, 110, 115, 115). When I did the compression test, I saved the spark plugs and the fuel pump fuse. I put a picture of them below. The plugs are ordered if you were looking at the engine from the bumper (4321). #1 looks normal. Going from 2 to 4, the electrode gets progressively worse with a white crust on the center electrode and the arm. I also noticed that the fuel pump fuse was getting pretty corroded (replaced).

What are your thoughts on the abnormal spark plug and Fuel pump fuse wear?

I am waiting for an OEM fuel pressure gauge to test the fuel system. Hopefully something becomes obvious with the fuel supply.

How can I test the O2 sensor while the car is running? I don't have a test harness.

Is there anything else that I am not thinking about?

Thanks for reading such a long post and your help.


[IMG]local://upfiles/5767/EEFEA28579784CB18558E314F4EA3A96.jpg[/IMG]

 

How many miles/years on those sparkplugs? Lotsa short trips or hiway miles? The variation in theplugs doesn't look outrageous to me.

The one blade of the fuse looks shiny right where thesocket makes contact. Corrosion on the rest of that blade probably didn'tcause your problem.

Can you figure out a way to back-probe the O2 sensor plug? That means finding some kind of pin to slide in alongside the wire, in the back of the plug. You want to measure the signal WHILE it is connected with the engine running. Maybe at the ECU since that's not a waterproof/sealed plug.

The comman way for an O2 sensor to fail is to get sluggish. Not really to give a flat-out WRONG signal. Find the signal wires, not the heater wires.

You'll want an analog voltmeter (yes, a NEEDLE). Or many good meters have a bar-graph alongside the digital display. (I love my Fluke for that.) Most inexpensive digital meters won't update fast enough for this test. If you can get your hands on an oscilloscope that would be awesome.

With the engine fully warmed up & running, the O2 sensor signal should flutter somewhere between 0.1 to 0.9 volts. You're not so concerned about the actual voltage, but you want to see it swing up & downquite a few times per second.

 

Those plugs are about a year old. They have ~15K on them. 75% of my driving was in town. I just noticed that there is a coating of brittle white crap on the insulator of the electrode and on the arm. 4 is the worse. I can flake off the outside layer pretty easily. Plug 1 has none of that. If they were all the same, then I wouldn't worry too much. But the plugs are different from each other.

I was just hoping someone would tell me that the spark plug condition was caused by a rich or lean mixture.

I'll have to check my volt meter to see if it has the bars on the side. I will have to backprobe the ECU to get a good reading. I just want my fuel pressure gauge to arrive, so I can figure this out.

Thanks and I'll keep you posted.

 

Yeah maybe theycould be lean, but it's a little hard to tell from the photo (as opposed to seeing the plugs directly firsthand).

Somewhere on ngk.com I've seen some nicephotos of sparkplugswith deposits fromvarious problems.

 

Your compressions are all on the low side, belowminimum spec value of 135 psi. How did you measure them? Cold engine, warm engine, hot engine? You should measure the max compression after 4 compression strokes w/ a warm engine. It they were measured warm or hot, I would suspect either leaking valves or seriously worn compression rings. A "leak-down" test" may be indicated to determine valves or compression rings are causing loss of compression. Note, this would account for your low gas mileage also.

Check the fuel pressure regulator vacuum reference line for a strong smell of gas. If yes, the diaphragm in the regulator is ruptured, which allows unmetered gas to enter the intake manifold and will seriously depress gas mileage.

good luck

 

I have done the vacuum test on the fuel pressure regulator and don't smell raw fuel. I am hoping the fuel pressure gauge comes in soon, so I can verify the status of the fuel system.

I noticed earlier that I was below the minimum of 135 psi. For some reason, I thought that anything above 100 was good.

I drove the car for 40 miles on the interstate and did the compression test immediately when I pulled in my driveway. So I am guessing that my engine was hot. I couldn't find the procedure in my shop manual.

 

"How can I test the O2 sensor while the car is running? I don't have a test harness. "

Use a wire splice to establish a good contact w/ minimumdamaging to O2 sensor wire. I have tried backprobing at connectors and it's difficult and unreliable. I believe the O2 sensor wire is near the RH shock tower. Use a good VOM, and watch for voltage shifts. You should get 1-2 per second at idle, and increased rate at 2000 rpm, perhaps 2-3 per second. Voltage should reach 0.1-0.2V on low side and 0.8-0.9V on high side. Avg. should be abou 0.45v. Note, w/o an oscilloscope it will be very difficult to extract the above information. You should be able to see highs and lows at idle w/ a good digitial VOM. A analog VOM won't be able to track voltage at speed above idle and digital will be switching all the time. A 1 megaohm or higher VOM resistance is necessary to avoid loading the circuit (output of O2 sensor is very low amperage).

Compressions suggest a possible engine problem. I would repeat the compressiontest w/ wide open throttle and enough compression strokes to allow pressure to stabliize (no further increase). If compressions stay this low, the engine may need an overhaul to perform better.

good luck

 

Yeah, I am an idiot. I forgot to hold down the gas pedal while doing the compression check.

The only way (hopefully) air can get in there was through the breather tube and the air control valves.

 

Yeah, closed throttle should make a big difference. Do it again with wide-open throttle. Don't feel bad, you didn't do any damage. (Except maybe embarassment...)