Hey everybody,

Backstory: Late 2019 I was at the drag strip. I had successfully run a few 11.9xx's running a GS350 diff in the back and I was trying to do the same again after putting my stock ISF diff with OS Giken TCD back in. I was consistently running 12.0's and 12.1s then after maybe 10 runs the car felt a little sluggish and I ran a 12.5. I called it quits for the night and trailered the car back home. For both those times at the drag strip I had the catback exhaust removed from the X pipe back (due to needing room to get the diff swapped). The ISF had been sitting in the garage on a trickle charger all winter and when I drove it I got a bunch of codes (bank 1 and 2 lean, MAF sensor code, and a misfire code). I checked and couldn't find any intake or exhaust leaks. I cleared the codes and tried idling around my neighborhood, but lean banks and MAF codes came right back.
A few days ago I drove the car to the Toyota dealership only a few miles away to have them take a look (I just had shoulder surgery and wasn't about to mess around with trailering it somewhere farther). Below is their diagnostic notes:

Codes in system for too lean bank 1 and bank 2 (P0171, P0174). Reading data list at 39% fuel correction. Correction on list needs to go negative. All data check at idle. Check for air leaks with throttle/starter fluid and reading data list, no correction on data list while spraying intake. Plugged intake at PCV inlet and no correction on data list. Plugged inlet at purge VSV for intake, no correction on data list. Checked MAF, flowing at 4 grams per second at idle (good). Cleaned MAF sensor, no correction on data list. O2 sensors and AF sensors are reading and mimicking bank to bank in voltage and current. Pulled fuel sample, fuel looks and smells okay. Told by customer that gas in tank is approx 6mo old. Can not condemn gas at this time due to not testing fuel.
With no air leaks, no bad check valves or VSV, and MAF good. Condition is being brought upon by just bad enough fuel or low fuel pressure. Recommend, due to tuned vehicle, upgrade fuel pump with fuel drain and refill with fresh gas.

The recommendation of replacing the fuel pump and draining gas sounds plausible to me (I always fill with 93 octane so fuel type shouldn't be the issue, just fuel degradation possibly). Does anybody else have experience with this or suspect anything else of being the issue? I wasn't sure if there was something else that might cause different components to miscommunicate with each other with the vehicle being tuned and having o2 SIMs with the headers. Thanks in advance.

 

What are all of your mods? Stock intake? Air/Oil seperator?

 

RR-Racing intake box and tune, JoeZ intake pipe, Sikky headers w/O2 SIMs, Borla catback exhaust. I purchased an air-oil separator, but have never installed it.

 

I let my ISF idle for a bit this morning and took some readings.

 

What's the battery voltage when running? Is it getting to 13.3 vdc or is it higher after idling for a bit? I've noticed at full charge the system voltage is 13.3, but if the battery is down it's higher. Battery issues cause all kinds of weird things with these cars. I'd start there since it was working fine before, you didn't change anything other than let it sit, and now it's mad about something big time. Sulfated battery wouldn't be any surprise to me at all.

 

Unrelated, but you can ditch the O2 sims now that your tuned.

 

I only have an analog multimeter, which is reading roughly 12.5V while idling and 11.5V with the engine off. When looking at the data I can see from OBDII scanner, the only voltage I can read are OBD Volts and ECU voltage. Both those were reading approx 13.4V with the engine idling and 12.8V with the engine off.

 

My ISF had been parked on my trailer for quite a while as I didn't have time to troubleshoot the issue, tuner shops around me didn't have availability, and other shops didn't want to mess with a modified vehicle. I found a local Toyota tech who has been troubleshooting it in his spare time. He replaced the fuel pump, drained the fuel tank and cleaned the fuel injection system. That made the car more responsive, but the codes still came back (P0171 & P0174 - System Too Lean Banks 1 & 2 / P0101 - Mass or Volume Air Flow Circuit Range/Performance / P1170 Fuel Performance/Port Injector) and the car feels like it's lagging/limiting power on throttle from idle as well as when it gets to the mid/high 3k rpm range. The tech went through 19 diagnostic checks to figure out what the issue could be. He said he was able to rule out everything and narrow it down to Direct Injection Fuel Rails issue or ECM problems. The fuel rails parts-wise are the cheapest. Does this course of action make sense? Thanks in advance.

 

What leads him to believe the rails are the issue? Problems with the pressure sensor? That's the only thing the rails impact because you can't buy the sensor separately.

Have you been running a high volume of alcohol in your fuel or just sticking to regular pump gas?

Did he swap batteries? I know it sounds silly, but I'd try that before replacing the fuel rails.

 

I swapped batteries before bringing the car to him. I've just been using pump 93. I assume he thinks it's a pressure sensor issue in the rails because based of his text he was saying the issue was isolated to the fuel rails. The way I understood it is the injectors are working properly and the issue is either the regulator isn't working properly or the ECM isn't sending parameters correctly. I wish I had time to do more research.

 

There isn't one regulator. Each of the HPFPs has a check valve to set the pressure. There's a real chicken and egg here - if one of the check valves in one of the HPFPs is bad or leaky, it could cause the whole thing - assuming fuel pressure is the issue. It should be easy enough to datalog with Techstream and see what the fuel pressure sensor is sending to the ECM. If there is a problem with a spill valve, you could also have the same issue, and the spill valves are both controlled by the ECM.

 

In addition have you attempted to remove the tune to see if the behavior(s) continue???



Personally I wouldn’t throw new parts at this unless I know my ECU programming is back to STOCK.

Joe Z

 

No technical info to share - but I do remember reading of a similar issue that was caused by the RR intake box (with larger maf tube diameter). FWIW - RR was unable to figure out what about the airbox caused the issue.

If you can, swap back to the stock airbox and tune - it might be that simple.

EDIT: found post I was thinking about, looks like KCLV was impacted and there was drivability issues too.

https://www.clublexus.com/forums/is-...sound-etc.html

 

I would have put the stock airbox back on and flashed it back to stock tune as one of my first troubleshooting steps if I could. I don't know where my tuner is...in fact I don't remember even having one. I know Rafa flashed it for me at an ISF meet with a tune for the stock airbox. I installed the RR Racing intake when it arrived a little later and must have had a tuner to update the tune for the RR Racing intake, because I ran the car for 1-2 years with no issues with the RR Racing intake before this whole mess started. I'm just not sure how it vanished off the face of the earth though. This is just another chapter of my headache in all of this. Maybe I should put the stock intake back on, trailer it up to RR Racing, and have them flash it back to stock for me to see if that magically fixes it.

 

Can RR do that? I thought your car would be “married” to that specific handheld device.