So what I'm understanding is the ECU knows there is too much fuel going into the engine and is trying to cut back the fuel. So because of this can I assume the ECU, a/f & o2 sensors are working correctly?
That could be a possibility. I'll check.
Whoops...missed that info in your original post. Sorry. Read the sensor 1 / sensor 2 readings backwards, too. Let's see if I can do better the second time....
Hmmm...y'know, you say that the ECM seems to be swinging the A/F ratio rich, but the fuel trim number indicates the other extreme -- the short term trim is showing that the ECM is massively (20% duration) descreasing the duration of the injector firing time. The high MAF reading (which should be closer to 2.4 grams/sec on an idling 2.4L engine) seems off, too.
However the output side of the motor -- O2 sensor 1 (the A/F sensor upstream of the cat) is showing a super-rich condition (w-a-a-a-a-y above 0.45V). This is consistent with the black exhaust smoke.
So, the ECM knows that the engine is running rich, and is doing it's damnedest to try to lean out the mixture, but isn't being successful, at least according to the O2 sensor.
Of course, trim is just a correction to the basic injector duration, which is usually based on engine RPM and air volume. Engine RPM looks like it's being read OK, so that points back again to air volume (e.g., the MAF sensor). Basically, it looks like the MAF reading is way high relative to the amount of air that's actually making it to the the cylinders.
Also, you disconnect the MAF sensor (forcing the sytem open loop), the engine runs fine. This indicates that main components (such as the injectors, fuel pump, etc.) are OK, so I wouldn't suspect that the injectors are dumping in more fuel than they should for a given pulse width.
I'd start looking for more of a mechanical (clogged or broken hoses, throttle) problem in the air path. Air seems to be getting lost after the MAF sensor.
Yeah, I had a brain fart -- read the first line as the upstream O2 sensor.
There is no obstruction in the air filter and there is no vacuum leak I can find. I let the truck run for a while and noticed the Long Term Fuel Trim started to change. After a while both Long & Short term Fuel Trim maxed out at -20.3 The Load % stayed at 100 and timing was at -10 deg.
Did you look for obstructions / leaks *after* the air filter (or, more importantly, after the MAF)? It still sounds like the MAF is reading a lot higher than the amount of air actually making it to the cylinders. OTOH, I can't visualize how that could normally happen, since the whole path after the air filter is under vacuum relative to the outside air -- it stands to reason that any leak is going to result in excess air making it to the cylinders compared to the MAF reading, not less.
Hmmmm -- free-associating a bit, but is there anything strange about the pathway around the MAF itself? A MAF basically senses airflow based on cooling of something or other -- if the airflow through the MAF was somehow faster than normal relative to the entire airflow, you'd get an erroneously high reading.
Does your scan tool allow you to look at the O2 sensor plots? It'd be interesting to see the action on the upstream (sensor 1) O2 sensor, both when running open-loop and closed-loop.
My scan tool (Actron Auto Scanner) only displays the voltage of the sensors.
I can understand that if there is a leak or obstruction in air going into the engine it would cause some minor idling or driveability problems even a CE light but in my case I don't think its the problem. Could a leak be bad enough that the ecu is pulling back timing alot causing it to run very poorly? Besides if there was a leak the rpms would rise correct? Mine is actually idling lower (500rpm). When the MAF senser is disconnected the truck idles perfect making be believe there is no air leak after the air filter.
I still think the whole problem is caused by the ecu pulling back timing and I can't figure out why. I've already replaced the MAF sensor, A/F & rear O2 sensors, checked the TPS with the scan tool and it is within spec accoring to the FSM. I also checked the Knock sensor according to the FSM and it checks out. I don't think there is a vacuum leak anywhere. Is it possible it could be a bad cam or crank position sensor?
What else can make the ecu pull the timing back????
You don't need to be looking for a vacuum leak here. Vacuum leaks result in lean conditions. I really don't think you are dealing with a mechanical problem here. If the engine smooths out when primary feedback sensors are unplugged, then the problem is most likely a control issue. I still think the root of your problems go back to that calculated load line being pegged at 100%. I've been looking in manuals and the Toyota EFI theory manuals, and I haven't been able to find a definitive explanation as to how that figure is calculated. I have an idea of how its done, but it seems like you've replaced or confirmed that everything is working. Maybe we're missing something. I have a friend that works for the tech line in Cali, I'll call him up tomorrow and bounce this off him. It's a weird one. Anything else I should know about it other than the data list figures, low idle, and replaced components?
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I really appreciate everyones help & input. I just need to know where to look for a possible problem.
It looks like all your problems are being caused by the calculated engine load being pegged at 100%. You need to concentrate on what is causing that reading to stay at 100%. If you have the factory service manual you may want to look at the wiring diagrams and start checking sensor voltages by backprobing the sensor connectors. You would be looking for an out of spec voltage reading or a short to power or ground. I haven't found a good description of how the system works online but I would be looking at the MAF and TPS. They would both have the ability to tell the ECU that the engine is under load. From the wiring diagram I found online, the TPS and MAF use some of the same wires so a problem with one could affect the other. Another possibility is that you have a bad ground somewere. This could be as simple as a loose ground wire or a broken wire in the harness. Another thought, does this engine use a MAP sensor?
One other problem I noticed is that on your post that showed all the sensor values. You state the engine is fully warmed up and shows a coolant temp of 170 - 180 degrees. You should have a 195 degree thermostat so your coolant , fully warm, should be at least 195. This would not be the cause of the 100% engine load but it would indicate a thermostat that is sticking open.
Another thing worth mentioning is my truck didn't come with a tach so I installed an Autometer tach shortly after buying the truck in 02. I ran the tach signal wire off the gauge cluster harness and it worked fine up until now. It suddenly stopped working. It was still working when all my troubles started. I first suspected the tach went bad so I tested it by connecting the signal wire to the RPM signal wire going to the ecu and the tach works just fine. It seems that the ecu is still getting an RPM signal (The scan tool shows the correct RPM) but the gauge cluster isn't. Do you think this is related to what is going on?
Well, the advice from the california tech line was to look to the TPS. I don't know what you can look at with your scan tool, but in ours there is a data line called "CTP". It stands for closed throttle position. On these newer ones, there aren't physical contacts in the TPS to tell the computer when the throttle plate is shut and the engine is idling. Rather, there is a 'learned value' by the computer as to when the plate is closed. So, if the computer is not reading that the plate is closed and the engine is at idle, it will want to do all kinds of things like add fuel. Anyway, the CTP line is an on/off value. It should read 'on' when the engine is idling.
My scan tool reads it in (%). When the throttle is closed it reads 11% and at WOT it reads 78% (within spec according to the FSM). This is when the truck is idling normal when in limp mode with the MAF unplugged but come to think of it when the MAF is plugged in and the truck is idling poorly the scan tool reads the TPS at 15% when closed. Do you think the problem lies with the TPS?
Yeah, what I'm saying is forget about the reported % value. The TPS should be reporting to the computer at some point that the throttle plate is closed and the engine is idling. In our factory scan tools, there is a data line that reflects this. It is called CTP. You might not be able to see it depending on what kind of scantool you have. If the ECU isnt being told by the TPS that the engine is idling, all kinds of crazy stuff can happen. Based on all the info you've given, I'd say its the next place to go.
I'm going to replace the TPS and see what happens.
Thanks.
I've read all these posts and some people seem very confused. I agree that the MAF reading is the culprit. The Maf reading is the main sensor for fuel trim on a dynamic basis. You show 100 load so the MAF must be reading a huge airflow at idle which would be like if you have the throttle way open towing a trailer and going up a mountain. But your airflow reading is probably way above that even. Your computer has a fuel delivery table for open loop (not listerning to oxygen sensor). So your computer when it goes into closed loop will listen to oxygen sensor which always reads rich which is correct for MAP reading. So computer subtracts and subtracts fuel trying to get sensor to go lean which it never does, but computer will only subtract up to a certain limit. So either your MAP sensor is bad, MAP wiring is Bad, or maybe Power supply or ground to MAP is bad (supply probably comes from computer) or computer is bad. Best way to determine is voltage readings at computer harness with truck running, best if you use a digital oscilloscope and know which computer terminal is which and what voltage signal to expect. It is always fastest and best to look at signals on a running vehicle because so many things can go wrong.
I replaced the TPS and the problem still remains. I think at this point its safe to assume its a wiring problem.
My Actron scan tool can show the I/M READINESS which is defined as a snapshot of the operations for the emission system. When the scan tool shows the results of the test the Oxygen Sensor Moniter & Oxygen Heater Sensor Moniter comes back as incomplete. Is this an indication that something is wrong with the A/F sensor?
The A/F sensor being the culprit sounds consistant with that fact that the truck runs normal when the MAF sensor is disconnected and the ECU is running in limp mode which doesn't use any feedback from the a/f sensor. Since I've already replace the A/F sensor do you think the problem lies with the wiring harness?
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