2000 Protege Fuel Trim Issues

Hey all!
So I just purchased a 2000 Protege and it has a peculiar issue.
When you start it up cold, she runs fantastic for about 8-10 minutes.Once it has been under load for about that time, it starts to misfire, rough idle, and has almost no power to accelerate. You can not even get going past 65 on the interstate full power.
My thoughts right now are that it is very possibly the o2 sensor. I have been running some logging on the obd2 port and the o2 sensor a flat line at about .1v when idling with random spikes up to .7-9, when driving, it will peg a line right at .9 and ocassionally will start running better and start doing what it should do, bouncing around between .6-7. The fuel trim is off as well, which just points more towards some issue there with the o2 IMO.

The previous owner replaced the coil packs, plug wires, spark plugs, tons of vacuum lines, and some other little stuff but said "I took the o2 sensor out and it looked fine (Obvious not an expert). I think it's pretty possible based on how the sensor looks it may not even be the right one.

Any ideas?
 
Some additional information:
-Compression tests are good.
-Bank 1 Sensor 1 O2 seems inconsistent. On idle when it's fine it's bouncing back and forth in the mid range, when its under load it's reading a constant .9v (When warm and struggling) and the idle when its struggling is a .1 steady with no movement except the occasional jump to about .7.
-I have not yet tested the fuel pressure relief bypass, but when I disconnect the vacuum line, it makes no difference. I am curious if the regulator is not stuck shut and it's flooding the injectors, causing a very rich combustion.
 
I'd be curious to know if it could run on a default strategy by unplugging that o2 sensor wire and seeing how it behaves. it would set a MIL but if it runs and does okay at it I'd look at replacing that sensor. if it failing but within range of plausible data the ecm is none the wiser and will try and account for it. worst that happens is the car acts funny or doesn't start. best outcome it runs great while it's unhooked and sets the code for open o2 sensor and you have your culprit.
 
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pcb

The Diagram Dude
:
2002 MP5
^^^ What he said.
If the O2 sensor is unplugged or there is too much misfiring, the engine is sent into "limp mode" where the ECU floods the engine with extra fuel to protect it and reduces timing advance as well as other things.

The engine will suck all kinds of gas and is completely gutless.

It sounds like your car is already in limp mode now but it should have popped a code??

The engine misfire codes are the only codes that flashes the MIL on the Protege5 (I don't know how the 2000 Protege compares?)

After the ECU has the misfiring under control by going into limp mode, the MIL stays on solid and you are in limp mode.
 
Last edited:

pcb

The Diagram Dude
:
2002 MP5
Coils can be a real PITA on the P5 and brand new ones can fail and misfire.

Hitachi coils are the best for our car.
They are the most expensive, but we'll worth it.

Screenshot_20220530-141440_DuckDuckGo.jpg
 
Thanks all for your input! The coils are working well, and it's a manual so it technically does not have a "limp" mode; So I ran a test on her this morning and logged all the sensor data for the drive. It's only doing this when it warms up so my speculation is that when it goes into closed loop it is getting bad information from one or more of the sensors.
Attached is the image of the data (Each line is a second) of the sensors. As the issue begins, the B1S1 O2 & STFT goes to 0, and pretty much stays there for the rest of the data. The MAF also seems to immediately shoot up to pver 7GPS, and goes down into the 3s.
After it starts running like crap, the exhaust out of the pipe is also very very strong. Normally you can feel some exhaust coming out, but when this is happening, it's hard blasts of air. I am assuming from the engine going extremely oxygen rich.
My guess right now is a bad o2 sensor, and it's reverting to trying to run off just the MAF which is going to result in really bad performance.

You can view the data in full here:


Let me know what you think about the data if you take a look.

Thanks Guys/Gals!
 

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I actually have messed with it's "Brain" quite a bit today. I intentionally disconnected the #1 O2 sensor to make sure it would throw a code. It's clearly not working right, so I wanted to make sure there was not something wrong with the computer. I then had a little fun, as I do every few years with most of my cars...

The SEAFOAM NEIGHBORHOOD SMOKEOUT!

What? WHAT IS THAT!?!?

Simple!

1) Buy your self a bottle of regular ol SeaFoam.
2) Then take the brake booster vacuum line off, but do so slowly so your engine can adjust to the vacuum loss.
3) Then, slowly start pouring SeaFoam at the open vacuum line, it will suck it right in. As it is combustible, your engine will increase in RPM. Pour maybe a few ounces in.
4) Put the vacuum line back on.
5) Rev the engine up to about 3000 RPM for about 10 seconds, then back down to about 1000 for 5 seconds. Repeat 10 times. Don't mind fog that you have created throughout the entire neighborhood.
6) Stop the engine.
7) Using a funnel, or whatever you can make work, dump a few ounces of SeaFoam directly into the brake booster vacuum line inlet. This will allow the seafoam to go into the manifold and coat the bottom, the heat left from the engine will cause it to vaporize which will cling to all the carbon deposits in the intake.
8) Wait about 20 minutes.
9) Start the engine and immediately go to about 3000 RPM, then down to 1000 RPM, and go back and forth between the two about 5 times.
10) Now, from 1000 RPM, take the revs up to about 4500 RPM and hold for 20 seconds. This is where you are likely going to see so much smoke you would swear your engine is melting and while doing so caught all the houses in the neighborhood on fire. Nah, That is all the deposits in your engine burning up and coming out the exhaust. The more miles on your car, especially if this has never been done, the more smoke it will create.

DISCLAIMER: This should NEVER be done with newer cars OR cars with turbo chargers as you can damage vital components. Really, 2010 is about the latest I have seen cars where this is USUALLY safe. Consult with your local mechanic to make sure. If your car does not have a brake booster line, do NOT try and get SeaFoam in your intake through any other method. I learned this method from a mechanic friend years ago, and it has always done a good job at smoothing out the idle on most of my cars by clearing out the carbon deposits that have collected in the intake, on the injectors, on the valves... Even on the pistons. The other thing you need to be aware of is... If you have never done this and you car has high miles (>100k), there is a moderate chance that you WILL foul your o2 sensor. If not done right and you have chunks of carbon that leave your engine, you could clog your cat.

After I did this today, I finally got the #1 o2 sensor to fail completely. It caused the heater circuit to short out, rather than just provide terrible signals back to the ECM. So now, there is a rough idle all the time and still a lack of power, but not as bad. The o2 sensor failing actually caused the ECM to finally realize.. Hey... The MAF sensor is bad, too (Since it fails over to the MAF only if the o2 fails). So now I am running on 200k mile engine on a default fuel map which is obviously not the best performing given the wear on the engine.

Oh well, a new o2 sensor, MAF sensor, and speed sensor get here today (Speed sensor because the speedo does not work.)

I will let you all know how things go after replacing all those. I may even post my more recent drive's logs if you want to take a look. Hopefully all this helps someone else fix their issues.
 
I guess I shoulda mentioned, IF the map/maf are working right you'd run fine. 😂 Man that reminds me of diag on another car, a Buick LeSabre years ago, that had a failing maf but I didn't know the map was also bad. Tried to start w/o the maf and it ran like sheiitt I hadto seal that one up, that got me to work and back the next day while I got a maf and map replacement.
 
Hey all!
So I just purchased a 2000 Protege and it has a peculiar issue.
When you start it up cold, she runs fantastic for about 8-10 minutes.Once it has been under load for about that time, it starts to misfire, rough idle, and has almost no power to accelerate. You can not even get going past 65 on the interstate full power.
My thoughts right now are that it is very possibly the o2 sensor. I have been running some logging on the obd2 port and the o2 sensor a flat line at about .1v when idling with random spikes up to .7-9, when driving, it will peg a line right at .9 and ocassionally will start running better and start doing what it should do, bouncing around between .6-7. The fuel trim is off as well, which just points more towards some issue there with the o2 IMO.

The previous owner replaced the coil packs, plug wires, spark plugs, tons of vacuum lines, and some other little stuff but said "I took the o2 sensor out and it looked fine (Obvious not an expert). I think it's pretty possible based on how the sensor looks it may not even be the right one.

Any ideas?
To follow up, my issue was a bad coil pack.