Can a rich o2 code be caused by FPR?

Hello!

I'm currently working on fixing my new '04 Taco to stock and still have a check engine light on.

Code is high voltage on A/F oxygen sensor (bank1 sensor 1)

I already changed both o2 sensors, changed all thermostats, temperature sensors, spark plugs(oem stock ones, not iridum or platinum), changed timing belt, air filter, fuel filter, cabin filter, pulleys, gaskets(it was leaking oil in the head gasket), water pump, suspensions, lower ball joints, steering rack, oil, tires.

Stats:
88,000 miles on the clock.
2004 PreRunner - 2wd double cab
I only fill the truck with E10 juice.

Last work on the truck: The Transmission temperature sensor was unplugged, we plugged it again, and code was erased.

Still getting a code for o2 running rich.

We already know there is an issue with the fuel pressure regulator since the truck has hard starts from time to time (independently of weather). Where I live is always 95 F to 100 F. So weather is not the issue.

Since it is all that is left, can the faulty fuel pressure regulator be the cause of the truck running rich and triggering the o2 sensor code?

Thanks in advance!

 

Welcome to TacomaWorld
Could be counterfeit sensors from eBay or Amazon. Use only genuine DENSO a/f and O2 sensors.

 

I bought all my parts from the dealer. Denso OEM o2 sensors

 

If the regulator is leaking into the vacuum port or fuel pressure is too high it could cause a rich condition.
How did you determine the regulator is bad?

 

Did you install the A/F upstream and the O2 downstream?

 

Yes, both installed. The previous ones seemed to work well it seems. Tested with a multimeter, but changed them anyways. Previous owner neglected a lot of things and kinda want my truck to be as good as new. Just my preference

 

The regulator seems to be leaking a little (personally I don't know if it is oil or fuel). My mechanic works on the truck. He told me it definitely seems the fuel pressure regulator could be the issue since the only symptom is long cranks before starting. It doesn't make a difference whether it is a cold start or after 30 minutes of the truck being parked. Sometimes it just takes a few cranks to start. Sometimes is worse, sometimes it starts after a couple tries, sometimes it starts right away. It never starts after one second of cranking, at best after two/three seconds max. It's not out of this world, but it indicates an issue of pressure. Alternator, battery, and starter got tested as well. Everything works fine, so not an electronic issue. Really worked on the truck properly and we are ahead of most things. As I said, only the fuel pressure regulator seems to be left and just wondering whether that could cause the rich condition on the o2 sensor. Also read that it could be just moldy wiring or short of the o2 sensor somewhere in the harness, but that would be my last resort if a new pressure regulator doesn't solve the issue. Just looking for some insight if someone has the same issue. From reading posts here I know a lot of people had the same issue, but don't mention the fuel pressure regulator. There aren't any videos about it on 1st gens on youtube. Might be a good idea to make one for everyone to be aware that it could just be a bad fuel pressure regulator

 

@04TacoPyR
Have you tried pulling the EVAP Purge feed hose off of Throttle body/intake manifold and running it like that?

 

You need to do a little more thorough diagnosis, for which you need a scan tool with live data capability.

1. What are your short-term fuel trims?

2. What are your long term fuel trims?

3. Is the A/F sensor responding but peaking above the code-set criteria threshold?

4. Is the A/F sensor stuck at a specific voltage and not responding?

It could be a faulty sensor (new parts, even OE, aren't always good parts) right out of the box, it could be a wiring/connector/harness issue, or a fuel-delivery issue.

 

Would a stuck open PCV cause rich mix?

 

How do you know you're running rich? The P0132 code does NOT necessarily mean a rich condition; it can, but it's not a certainty. This is why I recommended getting some additional data, but FWIW, a malfunctioning PCV can cause a rich condition, yes.

 

Will do, my mechanic has the scanners, but he doesn't share that much detail unless I ask. Some customers don't want to know the details I guess. I like knowing how to fix my own vehicle, so I keep asking and helping him diagnose the issue.

I'm working on purchasing a scanner for myself. When I do it, I definitely will look into the fuel trims myself, I know they are a key part of the diagnosis. Thanks so much for replying will keep you guys posted

 

Increased fuel consumption, never getting up to temperature, smell of gas inside the cabin(no leaks what so ever), no black smoke at all, no white smoke, no blue smoke, nothing else.

It was partially due to thermostat in water pump being cut(we found it like that, previous owner/mechanic must have cut them. It was not the only temp related sensor/unit that was cut. Also the temp sending unit. So engine temp gauge was always down and engine was trying to warm it up constantly, that plus the o2 sensor code (which is not the sensor itself now that we ruled that out) lead to increased consumption. Engine was running extremely rich.)

MPG's were all over the place when I got the truck. Once I got 3.78 MPGs. Always being consistent with the fuel I pump(E10) and the station that I go.
P.d.: I don't have any modifications on the truck. It is not lifted, not modified with a bunch of steel plates, not with big tires, nothing that might affect the mpgs like that. Everything according to stock specs and all parts from toyota. Everything stock

Once thermostats, and sending units were all replaced. It stabilized way more and engine now runs way more quiet and smooth. Once it gets up to temperature(1/2 minutes max) it lowers rpms to 700. Before it always idled at 2,000 rpm trying to warm up the engine.

Haven't really used up my tank since all the temperature issues so I can't really give a figure of how much my truck is consuming now yet, but I can tell that is working way better since I haven't had to fuel up the truck yet and is lasting me way more miles than before. Before I had to pump every three/four days max. It was eating up the fuel.

That is all that was going on with the truck. Once o2 sensors were replaced, no code for o2 sensor, just the transmission temp sensor (which was unplugged, who knows why. As I said before, seems previous owner just didn't care about keeping up with the truck and sold it once it started to eat fuel for breakfast. I'm gonna be working on the input you guys gave me and then I will update on what worked.

Thanks a lot!

 

Does a ScanGauge have such abilities? To take live readings, I mean.

 

I don't know to be honest, I set mine up to monitor specific things (Oil Temp, Trans Temp, Water Temp), but never looked that far in to it. I wouldn't expect that it can, but a scan tool with live-data capability isn't terribly expensive.

 

@tirediron i got the scanner and checked the fuel trims.

Short-term fuel trim was -14%
Long-term fuel trim was -20%

Both constant, minor variations (within .5%)

Took it to my mechanic today. Changing that fuel pressure regulator. Hope it works. What else can it be if not that?

 

You're definitely running rich; interesting that the ST wasn't pegged out, or at least higher... as for what else... could be a bunch of things, but I like the FPR as a first step. Based on the parts you've already changed, it's sort of hard to say. This is a 'stare at the live data and wait for something that looks out of place' scenario I think.

 

Well, just keeping this thread up to date.

Changed that fuel pressure regulator and seemed to be working way better than before. No more codes. Truck starts right up now, no hard cranking what so ever. Now I'm almost hitting that 3,100 mile mark and the p1702 code crawled back again. Reset it with my scanner to see if the code would go away and it came back after 20 miles.

Since I already did both o2 sensors Imma try cleaning the maf sensor and if nothing works gonna change the thing.

My short term fuel trim at idle is now 1%/-1% so it got fixed

But my long term fuel trim is still at -20%.

Any guesses or input on the fuel trims?

My mpg improved from 5mpg to 16mpg and now it is at 11 mpg. Been moving stuff with the truck so added weight might be the culprit there.

 

Can you post your x-gauge codes for oil temp and h2o temp? Thanks!