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My 97 has thrown p0300 for ever and I've been chasing it for just as long. Adam over at revlimiter knows my pain...or did.
Anyways got the car back on the road recently and it threw a 02 code while I was driving along with the p0300. It was a pending code due to the reset that morning and I couldn't catch if it was up or down stream. I replaced the from one last year so I figured it was the rear. Here I am minutes after installing the downstream and it threw the random misfire again...****. So I turned off the car and just pulled the front one off the Jackson headers....hot no touchy... well try not to. So here's my question is this ****** burnt up or what?
I've replaced the crank angle sensor at the crank, I've swapped the coil pack, new wires, new plugs, new red injectors (smooooth), new fuel filter. So the only things I have left are the cam angle sensor, the fuel pressure regulator, and the ecu. What say the more knowledgeable then I?
Oh and the ff data says 835 rmp. Something something something.... basically no load. But I have seen the cel start flashing at wide open in 5th around 5500 rpm which I'm thinking might be fuel related. I took the hardtop spoiler off the top I got and I don't have any buttseching stickers on my car so I don't think I transgressed against the Miata gods but maybe I missed something.
The joys of having a day at the lab as a project manager.... easy to step out for 15 minutes and it's pretty normal to see me round here cover in grease taring into something.
Looks like a used 02. They usually have a light white soot to them. Rear 02 (on NA/NBs anyway), is for cat efficiency monitoring only. No changes to fuel trim, or anything else. Misses can throw 02 codes, rare, but the incomplete exhaust charge can confuse the computer before it hits open loop.
Do you have access to ANY ODBII diagnostic tools, with live data capability? That would make finding your issue much faster. A flashing CEL means a misfire determined to be strong enough to damage a catalytic converter. The OBDII NAs use that crank sensor exclusively for misfire monitoring, actual timing cam/crank signals are still created by the CAS on the exhaust cam. In theory you should be able to have the car run without the crank sensor at the crank pulley, the CAS simply wasn't accurate enough for misfire monitoring via OBDII requirements, thus the extra sensor.
#1 - Is the air gap between the crank sensor and the trigger wheel within spec? (it's adjustable to an extent on NB cars) You also need to confirm the trigger wheel is clean and in decent condition. Mild rust is okay, tons of rust changing the shape of the teeth is not okay.
If you have some sort of live data available, try to use that to check misfire counters. MAF in G/S at idle should be approx. equal to displacement, so 1.8-ish, 1.5-2.1g/s. I'd be more than happy to give you basic expected readings from sensors if you have live data.
EDIT: When you pull the p0300, what freeze frame data points do you have? P0300 is the only listed fault code?
I do have a scan tool and I will pull live numbers off it tomorrow at idle and freeway.
I re gapped the cps today from .022 to .03, no rust anywhere in the car except the oxidation on the exhaust flanges that's it. After cleaning the egr I also cleaned the maf with maf spray. I noticed my the k&n filter on my racing beat intake was pretty nasty so I pulled that off as well and didn't put it back on. I noticed some oil residue at the front of the intake, looks like its coming through the tube from the valve cover so I wiped it out of the intake cross over and put a new OEM pcv I had sitting in the box o crap- figured it couldn't hurt. I did all that cleared the ecu and took it for a five mile canyon run after it sitting in the driveway running for 10 minutes. Taking it easy, running hard, going down the hill, flat out through some flat curves and under hard vacuum under decel into the tights. No codes.
Something I did notice is still there is a bit of hesitation at acceleration. Kinda lags then starts pulling good. I'm going to see if I can grab my brothers snap on tablet this weekend and see about pulling a full data log. In the mean time I just need to have the ecu read ready so I can smog the bastardy Miata!
If cleaning the MAF worked to improve it, it likely needs a MAF. The cleaner just cleans up the hot wire, but never gets it properly back to original condition. Intake air temp is also something to check for accuracy.
This is after I got back to the lab at 1pm started it up and plugged in the scan tool. Some over lap in screens to show all information. By no means the best scanner but seems like it has a halfway decent refresh rate.
116 coolant temp means the engine isn't all the way warm. If the gauge says it is, that's an issue.
Short term trim is normal,long term is way out of wack. 3.9ST and 14.8LT is an effective 18.7active trim. WAY too high. The car is adding 20% more fuel than the base map says it should, when it is in closed loop operation. Long term moves around to keep the short term around 0, switching back and forth.
4.5 is the equivalent g/s of the lb/min reading of .60. Too high as well
Bank 1 upstream switched between your last two pictures, so it is working somewhat. .745 is rich, .050 is lean. The 02 is switching, but I would not expect it to be switching with 20% added fuel.
Your fuel trim says the engine is running lean, and has air entering the intake stream behind the MAF. Without graphing 02 voltages, it's hard to be sure it is telling the truth. Being that it is switching, I'd be inclined to say it is. If you crack some propane into the airbox with the car running, you should be able to watch the front 02 go pig rich, sit there, and the return to normal switching with the propane removed. Much easier if you can graph the data.
IF the 02 is telling the truth, and the engine has a lean condition. You have a vacuum leak (or sticking open EGR, idle air, etc), or the MAF is telling the engine it is getting more air than it actually is, and the computer is dumping fuel to compensate for the huge amount of air the MAF says is going down the intake tract.
IF the 02 is lying, then it will need replaced before moving forward.
Do the propane enrichment test first. And confirm the numbers you pulled at 116 are generally the same at 100% warmed up temp. Fuel trim, 02 voltage, and MAF volume being the 3 important ones.
Being that the 02 switches with 20% fuel trim, I'd say unmetered air is entering the intake behind the MAF.
P1170 - bank 1 sensor 1 fixed, ie slow response. On the 02 sensor plug, there will be 4 wires. Unplug the sensor from the loom, and identify the two wires of the same color. That is the heater circuit. You should have continuity between those 2 pins on the 02 plug. If you don't, the heater is bad. Regardless, you likely need to replace that 02. IME, if the computer is unhappy with 02 performance and sets a CEL code, you need an 02. The OEMs do a damn good job on 02 self testing.
Basically, if the heater is bad, the 02 will react slowly on start up and low-load situations. If it is biased or lazy, it will lie to the computer, and throw off all other diagnostically significant data points.
When you replace the B1S1 02, unhook the battery for 30 min or so. That will wipe the fuel trim numbers. I'm curious to see if fuel trim stays sky high after the 02 replacement. Basically, swap the 02, then re-check fuel trims. If it's still high, you have another issue.
Oh, and just a word to the wise. If the literal OE part is available, always use that when replacing 02s. It's not as critical on this older stuff, but cars are getting really picky about 02, AFR, Lamda sensors.
I'll try to look up the actual OE part, if my system lists it, tomorrow.
That was a cheap sensor from the interwebs. I just swapped the Bosh back in and cleared the codes. Should I still unplug the battery and put my foot on the break to drain charge?
Just unhook both terminals. zip tie them together if you really want be 100% drain everything dead. As soon as power/ground are gone, most everything should be wiped. Try it for 2-3 min, go to start the car, check where long term trim is at. If it isn't low (around zero) at start up, you didn't disconnect the computer long enough to set the learned fuel trim numbers back to zero.
Dumb question, these are plug and play sensors, right? None of that "crimp the plug on from your old 02 onto this generic 02" nonsense? The upstream is an actual 02 made for this car? Been bitten by that a few times when I was chasing a funky 02 number. Idiots crimped those nonsense generic sensors in.
Oh yeah no solder stuff going on. Straight plug and play. Bosh o2 plug was from Napa with proper connector.
So just to spoon feed me here. What should the St and lt number read? In relation to each other or otherwise at idle fully warmed up.
Second I'm running the racing beat intake- it's what was on not when I got it....and loud. I took the propane torch and gassed straight into the inlet. No surge, change in idle or any other change. Checked with gas around the stock cross over tube- same result. Checked around all vacuum hoses, pcv valve, egr, and all around intake. No change what so ever.
OBDII cars have 2 operational modes, open and closed loop. Open loop is used for cold start, full throttle, and a few other instances. Open loop means the ECU is running 100% off of the fuel "map" mazda wrote when they built the thing. Open loop means no feedback, or adjustments. The computer sees X air, adds Y fuel, doesn't check the result afterwards. Closed loop is sometimes called feedback loop, and that is where the oxygen sensors come into play. The computer sees X air, adds Y fuel (per the fuel map), and then checks the result.
So, for X units of air, Y fuel is added in closed loop. Obviously nothing is perfect, but the ECU tracks the output of the combustion process via the 02 sensors. The ECU notices that while it is injecting fuel at the prescribed amount according to the fuel map, the 02 sensor consistently says rich. Now the ECU knows it is adding more fuel than required to meet the AFR target (not always 14.7), so it adjusts fuel as a percentage of the original fuel map value.
These adjustments are the fuel trim. Each bank of cylinders (which is monitored by its own 02 sensor) has two trims, short and long term. Short trim is the "live" number. It bounces around, say at idle, +/- 5%. So the 02 is checking the result of combustion, and adding or subtracting 5% off of the original fuel map. If short term trim starts climbing in one direction or another, Long term trim compensates. The ECU wants the ST number about zero, +/- 5% basically. You're at 3-4%, totally normal. Your long term is the issue. The ECU is adding 15% more fuel under basically all conditions (long term), to keep sort term trim in the normal range. Long term typically is in the 3-4% range, usually negative, although the early OBDII stuff usually ends up closer to 0. Long term moves to make short term dance around zero, going positive and negative as the engine runs.
So, if your short term is at 3-4%, long term is at 15%, the effective total trim is 18-19%. Add ST and LT, you want +/- 10%. If you had a single cylinder miss, with 18-19% total trim, I'd say you had a bad injector.
The propane test only work with live monitoring of the 02 activity. Unless you have a giant vacuum leak, the engine will likely not respond.
Don't bother back-probing with a meter, use the scanner to watch 02 numbers. When you crack the vacuum line, it will drop lean, ST numbers will climb, LT will then climb to allow ST to come back to the +/- 3-4% area. When you crack the propane, the 02s will go rich, and ST will go negative, pulling fuel. After a moment, long term with swing negative, bringing the ST trim back to its happy place.
Happy to help. p0300 without individual cylinder misfire counts is a PITA on older cars.
OK de energized the car last night, started it up this morning and with the old OEM Bosh o2 the ecu is happy and the St and lt are not jumping all over.
09-26-2017, 08:39 PM
chasing p0300's ..... burn up O2 sensor
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