Hey all,
So I am having an issue where the car will randomly start running on what sounds like 2 cylinders and throttle input won't make the car accelerate.
This seems to only happen when the car is warm but there doesn't seem to be much of a rhyme or reason for when it happens.

My setup is speed density using the fuel temp sensor for IAT, stock frame FP red, ID 1700x, a double pumper and S2s.
I had a COP setup and thought that was the issue but when I placed my stock coils back on the car, the problem still showed up.
The other strange part is that while trying to limp the car into a parking lot on 2 cylinders, it will go back to running totally fine, like nothing ever happened. This has me leaning electrical.

Any ideas?
I was thinking maybe one of the cam sensors coming and going?
Crank sensor?

I haven't been able to get a log of it yet but I am working on it.

 

Can you data log? That will tell you if a sensor is bad.
What's your AFRs when it goes bad? Maybe it's a loose ground. It's really hard to diagnose over the Internet. We'd probably need more info.

 

Thanks for the response kaj.
The afr shows rich when it's happening which leads me to spark and not fuel being the issue.

I have checked the ground on the cam sensor and the one near the battery. Any others you can think of?

Also while logging, how could I tell if a cam sensor or crank sensor is bad? I'm really leaning cam sensor at the moment.

 

Data logs will show inconsistency in certain parameters that won't make sense, which could let you know which, if any, sensor is bad. It's not very common for them to stop working. It's been a while since I've messed with my car but I remember a mass of grounds near the fuse box, one on the transmission, then there should be one from the engine to the body of the car. It's been so long since I've worked on my car, I can't remember
Hopefully someone who knows for sure will chime in.

 

Alright thanks for the tips I'll look around at grounds tonight.

One other thing is that yesterday after a drive, it started acting up and got to the point it wouldn't even start. Let it cool til this morning and boom, fired right up like nothing was up.
Super odd problem

 

Didn't see anything with the grounds.

In a fun turn of events, the problem has worsened. When the car is warm now, it will stall and refuse to start until it cools. This pointed me back towards a cam sensor.
As a test, I got a spare set of cam sensors and a MAP sensor. I replaced the exhaust cam sensor and it didn't help. I'll be trying the intake cam sensor and MAP sensor tonight but I am doubting it will help.
It also threw a P0121: Throttle position sensor voltage low code this last time it died. I ran threw the range with a meter and didn't see any inconsistency in the voltage.

At this point I am thinking maybe the TPS or a CPS but I'm open to other ideas.

 

When you say it cools, do you mean like below operating temp? So it's giving you trouble when it goes into closed loop? That would be a good clue that it's a sensor somewhere. Then you just need to data log to hopefully find another clue to which. Could also be wiring and not the actual sensor.
throwing random parts at it is a long, grueling, process. And expensive.

 

Yea Kaj. It seems to be worse when its at operating temp for sure.
I after I replaced the intake cam sensor and MAP sensor with my spares it ran and drove fine again for 1 ride home from work and I haven't tried to drive it again since.

I have tried logging and can't seem to find any inconsistencies to point at a specific sensor. Its really frustrating.

My plan is to put the original sensors back in and then use a heat gun while the car is cold to heat each of the sensors up individually. Ideally, this would allow me to single out what sensor is acting up when it gets hot.
Going to start with the TPS and MAP sensor and work from there.

 

So after swapping back to the original sensors, it appears that a failing ONMI 4-Bar map was causing most of the issue. The car acted up with the original one again and when swapped for a new one, runs much better.
In another turn, while the car is running and idling better, I have started to get a P0011-Cam A Timing over-advanced. From what I can tell on here, that generally means that the oil control valve, solenoid or gear isn't working right. I will be pulling the solenoid to check that and going from there.
I will update this thread with whatever I find to hopefully help someone in the future.