Can Anyone Make Sense Of These Numbers?

[benro2]

I did have a thread going overe here but it seems no one can be bothered looking all the way to the end, so I've started a new thread here and reposted my last questions If you can answer anything, it may pay to just glance over my problems in the linked thread for details.

A general rundown of my problems are:

- Car is grossly underpowered when it's cold.

- Rocks lightly at idle, in neutral, once warmed up.

- "Surges" on an off the power every couple of seconds under load (usually only top gear going up a hill when ambient temp is >30C), kind of like R&R.

I've bought one of these from ebay (scroll down to view). Great little unit, the guy who sells them was really helpful and shipping was extremely quick - received it the next day!

Anyway, these are the readouts I'm getting, bearing in mind I've only been driving with it for 20 mins so I may have remembered them wrong...

These are the readouts at a constant 110km/h:

- kph = 110km/h

- rpm = ~2800rpm but is jumping around by 100-200rpm

- battery voltage is ~13.5V when running

- fuel consumption is 9-10L/100km on the flat, also jumps around a bit

- INJ (injectory duty cycle) is about 6-8% on the flat (I think! I set the injector size to 370cc)

- ignition timing is ~ 30-40 deg B on the flat, probably a fairly constant 35

- AAC (is this the same as the Auxiliary Air Control valve?) reads about 50-60 on the flat

- O2 is jumping around from 0.15V - 0.85V all the time under constant load on the flat. This doesn't seem right to me. When the ECU shuts off the injectors it reads 0.00V.

- Water temp is ~80-85C

- AFM is ~2.500V on the flat (I think)

- TPS is 8-10% on the flat - I had to change this from a voltage to %age readout. I think the voltage range was ~0.3V - 4.3V - sounds about right?

A few notes/thoughts:

1. The fuel consumption seems a bit high, although the average it calculates seems to be about right compared with what I work out myself, so I think it is accurate, meaning my car's actual fuel consumption is bad. I've heard a bad O2 sensor will do this, however people with good O2 sensors report about the same fuel economy as me (400-450km out of 50-55L). However I drive the car like a granny most of the time and it just won't go any lower than this. Can I improve this with a new O2 sensor?

2. The ignition timing is 0 deg B at idle with no electrical or A/C load. The A/C puts it to about 10 deg B. Very light throttle (1-3% maybe) makes it go to 40-50 and most normal driving (5-15%) makes it go to 30-35. Is this normal? I did my load test up Lapstone Hill and when it was surging, under a constant throttle of maybe 30-40% (still in top gear) the ignition timing was moving around a bit, maybe in a range of 5 or so. At other times it seems to be relatively constant.

3. AAC goes down to ~40 when the car is at idle. Seems to increase with throttle. What is this reading anyway?

4. The O2 sensor has me worried a bit. I would have thought a fairly constant readout at constant throttle would be expected but mine is jumping wildly all the time. Never reads over 1V (0.9 was the maximum probably) but interestingly, still reads 0.00V on injector shutoff on overrun. Could this be busted?

5. Is the AFM readout about right? I didn't look at this too much other than on the highway so I can't remember what it was at other times.

6. The rpm readout jumps around a bit, maybe by 150-200rpm @ 2800rpm, less at less rpm. Would this indicate a faulty crank angle sensor?

7. Just out of interest, on injector shutoff the fuel consumption readout is still ~1.5L/100km, yet the O2 sensor reads 0.00V. What gives??

[Bozz]

o2 sensor 0v = lean, 1v = rich. You have a narrowband sensor, for all intents, there is no 'inbetween'. The ECU responds only to swings from side to side and finetunes mixtures that way. The quicker it swings, the more responsive your o2 sensor is. IIRC, the ECU considers anything under 0.3v as 0v, anything above 0.7v as 1v.

The other thread someone mentioned to check the ignitor pack. You dont have one, its a series 2 rb25det

the o2 sensor sounds like its working. At idle it should swing once every second or two, under load and revs, it should swing many times per second. If it does, it's probably OK

Your symptoms sound like the variable cam timing solenoid is broken or there's no power to it. It gets the same power feed as the o2 sensor heater wire. With the ignition on but engine off, check you have 12v on one of the three wires at the o2 sensor and the same color wire at the VCT solenoid.

Start the cold engine and let it idle. Verify you have 0v (or close to 0) on the other non signal wire at the o2 sensor. This should go to 12v after 2-10 minutes when the ECU switches off the o2 sensor heater.

Dont look at the throttle as a percentage, go back to voltage and get used to it that way. 0.45v should be closed, just under 5v should be WOT. The VCT solenoid should make a distinct 'tick' as you crack the throttle just off idle and back again. If it does, it's most likely OK.

Could be the knock sensor giving faulty readings. I dont recall the value (it was something like 22k or 220k) but remove the plug off the knock sensors and fit a resistor in place and try driving again but only for a short period of time. If the symptoms go away, it may need the base timing set by someone with a timing light, or a faulty knock sensor (or two) replaced.

On injector shutoff, the fuel consumption should be zero. You can easily tell injector shutoff by holding a low gear while moving, closing the throttle while revs are above 2000rpm or so. If you have an aftermarket exhaust, you'll hear it pop/fart etc for a second then the exhast sound will be smooth down to about 1200rpm when fuel comes back on. You can also feel a very gentle tug like you've just touched the accelerator or your GF has released the handbrake after driving 15km.

[blind_elk]

O2 sensor is working just fine. On injector shutoff on overrun, there is no fuel being supplied, so the mixture goes ultra lean (air only). That is why the O2 sensor reads 0V. Now don't freak out about the "ultra lean", no damage can be done to the engine because there is essentially no load on the engine (and I suspect Nissan, and many other manufacturers, would not do this if it risked the life of the engine).

Essentially, you really should not be able to determine the power of the engine while it is cold. You should be grannying it until it is up to temp.

What mods do you have - they may be contributing to the symptoms you are suffering.

[benro2]

Thanks very much for the detailed replies, guys. Will definitely get around to those tests ASAP... they sound like likely candidates too.

Regarding the injector shutoff, I suspect this is just an error somewhere in the calcs as the O2 sensor is reading exactly 0.00V. I've looked at other cars' trip computers and sometimes they will do the same thing - read 1 or 1.5L/100km when they should be reading 0.

the o2 sensor sounds like its working. At idle it should swing once every second or two, under load and revs, it should swing many times per second. If it does, it's probably OK

Yes, it's definifely doing what you say. However, I've always wondered about whether it's reading correctly? The reason why I ask is because ever since I've had the car, no matter how I drive it, the fuel consumption is the same! I've been calculating my consumption in L/100km for 4.5 years and it is *always* about 12.7L/100km, as I tend to do the same sort of driving. I've driven like a total granny for a whole week and it turns out the same. Sometimes I'll have a bit of WOT in there and it's still the same. In other cars, even driving slightly differently gives different overall averages, sometimes by a few L/100km. Could this be the O2 sensor or something else?

On injector shutoff, the fuel consumption should be zero. You can easily tell injector shutoff by holding a low gear while moving, closing the throttle while revs are above 2000rpm or so. If you have an aftermarket exhaust, you'll hear it pop/fart etc for a second then the exhast sound will be smooth down to about 1200rpm when fuel comes back on. You can also feel a very gentle tug like you've just touched the accelerator or your GF has released the handbrake after driving 15km.

The car is an auto, so I can't feel it cut in that easily. However, looking at the O2 sensor and injector readouts, under about 1500rpm I can see them increase. It's unusual that under say 50km/h on overrun, I don't think the injectors have cut out! It's obvious it's just the way the transmission/ECU is programmed, as they probably weren't thinking so much about fuel consumption as car manufacturers are today.

Essentially, you really should not be able to determine the power of the engine while it is cold. You should be grannying it until it is up to temp.

LOL, yes, I'm still driving like a granny while the car is cold. However, in my other thread I have detailed what happens. This is what I said:

A few months ago (meaning on both stock coilpacks and the Splitfires) my car started suddenly losing power when it is cold. I seriously have to go into 1-2 psi boost to get any useful acceleration under 60km/h! Even on the flat at a constant 50km/h, the boost gauge needle is almost on 0! It is very sudden, almost like the A/C compressor has turned on, but saps about 3x as much power (it's not the A/C comp, I've checked), pretty much instant loss of power, like a switch has been flicked somewhere! I also swear I can hear a "click" when I lose power too, but that may just be my imagination

- On the water temp gauge, it happens only from just above cold to about 2/3rds normal operating temp, after which point it's fine.

- Straight after I start the car, it will hesitate for a second or two the first time I give it gas, then suddenly take off like it should.

- Occasionally, when I start the car, the revs will drop really low (like 400-500rpm) for about 5 secs unless I give it gas for a couple of seconds, which seems to get the revs back to normal.

What mods do you have - they may be contributing to the symptoms you are suffering.

The car is basically stock except for a K&N panel filter. I have previously messed around with the boost solenoid so now I'm only getting wastegate spring pressure (~5 psi on a cool day, ~3 psi on a hot day!), however I am going to put in a Jaycar IEBC and DFA soon so I'm not fussed about getting it back to normal until all these problems are fixed. It's probably best I'm running on low boost while I have potential engine problems anyway!