Cranks but won't fire

[whisper]

Hi guys,

tzbang please were you able to solve this problem? I'm experiencing the exact same issue. The car cranks and I can smell gasoline, but it never fires. From several tries I believe it does this mostly when engine hot. If cold, it usually starts and can be shut down, or killed with brakes, then started normally again, it runs and has full power. When hot, issues appear much more often.

I've driven over 4000 km (2500 miles) with this issue and for most part the car drives normally. Only occassionally it sort of loses all power for split second, even several times in a row, but it was always 1-2 minutes after a hot engine was started. If run for longer (few minutes or more), there are no issues.

In cases when it won't start, I can crank for ages with no results at all (battery is new). It can be push started, but it has very rough idle and dies immediately if gas is applied, like it's flooded or something. As it's running it gets better over a few minues, alternatively I'm able slowly raise the RPM with gas pedal, which in 10-20 seconds helps it to run normally afterwards and can be driven without issues. I assume it burns away the surplus fuel from cylinder walls or spark plugs or who knows.

The car has no check engine light and no error messages.
Through OBDII, I checked the following sensors' readouts, and they show reasonable values:
Coolant temperature
Oil temperature
Intake air temperature
Intake air pressure
Mass airflow sensor (MAF)
Lambda sensor (AFR)

Spark plugs are new-ish Denso ZXE27HBR8, otherwise nothing really changed on the car for 4 years... Except for replacing aftermarket UEL headers (no catalytic converters) with OEM ones, which have a cat. The OEM header's cat melted on the next track day. We emptied the remaining pieces from the "front pipe," as they were caught on the second cat mesh. Since then, the car has been completely without catalytic converters, and it seems that the following issue started occurring around that time (although it was without cats for years beforehand with UEL headers). We put in the "CEL delete" O2 sensor adapter that's usually used with UEL headers but didn't help.

Any help would be highly appreciated, as nobody I know has any idea about what could be wrong. Thank you.

[Ultramaroon]

OP hasn't returned since his last post here.

We need logs. I assume you have ecutek. Create an account with https://datazap.me/

I think it would be especially useful to have a log of all available parameters both while running normally, and while stumbling.

[whisper]

It was a bad aftermarket MAP sensor (Omni 3 bar), it sent incorrect values and ECU did not realize they were wrong (no CEL). When disconnected, it starts immediately, but with CEL. If connected, no start, but can run and be driven without CEL.