Code PO171, fuel consumption high?

Great old car. Feel free to share pictures. LOL I think if people had maintained those engines, they never would have gone away.

Joe

So, I got two current and one pending codes today. PO125, Toyota P1300 igniter bank 1, and PO171 pending. I have newer NGK wires on and when I lift the boot off the plug in the well #2 and #4 arc from the end of the boot to the well. #1 and #3 do not. I can also feel the spark if I rest my hand on the valve cover. When I put the wires on, I don't recall this. There's no misfire. I do only have one of the coil bolts attached. Could I not have the coil grounded enough? Also did you see my data and questions from the ECT?

Hi,

I attached the diagnostics below for the P1300. Take a look through them and let me know what you find. Note that cylinders 1 and 3 work in tandem, so if one is having an issue, the other will as well.

Also, are you certain there is no spark on 1 and 3? If there isn't, there has to be a misfire.

Let me know.

Joe

See pics below.

No, there's spark on all 4. I was saying that if I lift the spark plug boot up while the car is running the spark arcs from the boot to the spark plug well. I didn't think it was supposed to do this if the boots were good. Anyway, I went back to basics. The compression test revealed 170-175 all cylinders. Two of the fairly new NGK iridium plugs I just put in had the electrodes almost all the way worn down and two looked good. I think they may have been Ebay knock offs. I replaced all four with legitimate NGK standard V-groove gapped at .044. The only code I'm getting is PO125, but I don't think the ECT is bad. What I think is the ECM isn't receiving the reading from the ECT. What this means and how to check it I don't know. Did you see the resistance readings I listed coming out of the ECT? Also, I am wondering about a plugged Cat because there's a strong sulfur smell after driving it full throttle and shutting off. The smell seems to be more under the front of the car not out the tailpipe. By the way, for as rich as it's running the color on all 4 plugs looked ok. I'm ready to just try an ECM. It's only $20. Short of that I'm very close to paying a tech to diagnose it. I also pulled the injectors and cleaned the throttle body, which wasn't that dirty.

Hi,

The P1300 is no longer present? As far as the sulfur smell is concerned, it is usually related to the catalytic converters.

When you say the electrodes were nearly worn off two of the plugs, which cylinders? Were they cylinders 1 and 3? Also, it is normal for the spark to arc to a ground. If it was coming through the side of the boot, that is a different story.

Let me know. Also, the PCM may not be a bad idea.

Joe

Correct, the P1300 code is gone. The only one coming up right away is PO125. I tested the ECT against a new one and basically got the same numbers. I put the old one (Toyota) back in. The coolant temp is 190-200 so I know it's not that. Is there a way to check the ECT reading at the ECM? I also spoke to a Denso tech, and he informed me that because they make the O2 sensor for Toyota they cannot put their aftermarket part number or name on their aftermarket part, but it is the same specs as the Toyota sensor. The voltage from sensor 2 should be less than. 5V but it's reading .95-1.0V due to the rich fuel program. Wouldn't a bad Cat set off its own code? I'm not quite ready to give up yet. Lol #Hardheaded #Determined I've included a photo of the plugs where you can see the worn electrodes. Unfortunately, I'm not sure which cylinders were worn. But I think #1 was the first plug I pulled and noticed it. They are not shown in any particular order. Isn't one coil for #1,#4 and the other coil for #2,#3?

What do you mean #1 and #3 work in tandem?

The same coil is used for the two different cylinders.

Let me know.

Joe

Isn't it 1,4 on one and 2,3 on the other?

Yes, you are correct. Sorry about that. I messed up. At this point in the day, I have 18 hours in. The old eyes must have missed the mistake. I need to be more careful. LOL

Joe

If my scanner reads coolant temperature does that mean the ECM is receiving the ohms readings from the ECT? If that's the case, then the wiring is intact and all I can think of is the ECM is bad.

Hi,

If it reads the correct temperature, then there is a good chance it is the ECM. However, it can be sending an incorrect signal. The ECM doesn't know if the signal is correct.

Joe

I suppose the easy thing to do would be to try the used ECM. What about a weak fuel pump or dirty filter? There's no loss of power when accelerating hard so I doubt these are issues. Plugged Cat? Can't you check engine side of Cat compared downstream side with temperature gun to see if Cat's working?

Hi,

Yes, the catalytic converter can be checked with a temperature gun.

Here is the link that explains how it is done:

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

If you question the fuel pressure, that is easy to check as well.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Let me know.

Joe

I just have to find someone with the adapter. I had made one from the end of an old fuel pipe, but I might have tossed it.

Hi,

I understand. Let me know if I can help in any way.

Take care,

Joe

What about a partially plugged fuel filter even though there's no performance loss? Is the filter for this car on the pump in the tank? I'm finding conflicting information, but I don't see one inline. Also why is my sending unit so slow to respond to adding fuel? I just want to try everything before jumping to the ECM. If live data shows 87-90 degrees C does that mean the ECT is working and sending the information to the ECM? I'm thinking the tips of 2 of the iridium plugs wore down so quickly due to the lean condition. What do you think?

Hi,

Yes, a lean mixture will burn hotter and cause damage to the spark plugs, but I would think all of them would have been damaged.

As far as the fuel filter is concerned, it is at the firewall and below the charcoal canister. See pic below.

Low fuel pressure certainly can be caused by a restricted fuel filter, but the only way to confirm that is via a fuel pressure test.

Let me know if this helps.,

Joe

See pic below.

I know that's where there's supposed to be a filter but there isn't.

Hi,

I double checked and that is the only place it is showing one. Does it appear that one may have been there at one time?

Joe

It doesn't look like it. I checked the Cat, 50 degrees difference between inlet and outlet. Here's an in tank filter. See photo.

Hi Jeff,

I found it. I had to go to the fuel pump disassembly to find it. I attached a pic below.

It appears to be attached directly to the pump.

Joe

That's what I thought also. At least Toyota gives an access port under the back seat. I'm sure it needs to be changed but I don't think it's the cause of the PO125. It could be causing the lean condition making the computer think the engine needs more gas?

Hi,

Agreed. The P0125 is specific to the cooling system. I attached a pic below of the most common repairs related to the code.

Joe

See pic below.

I just replaced the thermostat. It runs at 90 degrees C. No coolant loss. I had put in a new temperature sensor, but the results were the same, so I put my factory one back in. Fans come on normally, never overheats. The temperature stays just below midway on gauge. I traced the ECT wires and checked for continuity all the way to the ECM. The brown (ground) and white wires go to the ECM. The yellow/green one goes up under the dash somewhere. Do you know which wires is the power and which is the signal? Also where does the yellow/green wire go?

Hi,

I'm looking at the wiring schematic and it's not showing a yellow/green wire. See pic below.

As far as the power supply is concerned, it should be the brown wire.

Joe

See pic below.

It has three wires. The colors I mentioned. Brown appears to be ground. When I connect my test light to the positive of the battery and probe the brown wire it lights up. Maybe the ECT is failed.

Hi,

I just checked a different manual, and it shows the same as what I attached above. I'm not sure what to say.

I even found an OEM schematic and it shows the same. Also, according to that schematic, brown is a chassis ground, so you are correct.

Let me know.

Joe

See pic below.

I don't know what to say other than this has the three wires I mentioned and the brown and white go to the ECM directly, but the yellow/green goes under the dash? My buddy, another mechanic, said the upstream O2 sensor was failing and causing the downstream sensor to act erratically. 2008 Highlander. I'm just going to drive it and see if a PO171 code will come for injectors. Grasping at straws.

Hi,

The irony here is this. The wiring schematics show two wires. The OEM part number brings up a three pin sensor. Ugh!

Joe

I'm going to try the upstream O2 sensor because believe it or not it's listed as a heated O2 sensor not an air/fuel sensor.

Hi,

It won't hurt anything. Also, I believe it is a heated sensor as well. Let me know the results when you have a chance.

Take care,

Joe

I replaced the upstream sensor and got the CL on live data. Still waiting for the downstream one I just bought, which is a genuine Denso. Finally, I can put my dash and console back together. Lol. One of the black wires was bare and frayed, quite possibly shorting out. The gasket was blown out also so that was probably the buzzing noise I heard. I should have spotted this earlier. C'est la vie.

Hi,

Absolutely, that wire is the problem. It's an easy thing to miss. I couldn't agree with you more with the, "C'est la vie". My wonderful break from work required me to work constantly at home. LOL To add insult to injury, the upper tank on my radiator cracked and leaked.

It never ends. LOL

Take care and let me know how things work out for you.

Joe