2007 Yukon Denali Intermittent Crank No Start

[Fless]

You should look for the MAF reading in g/sec at hot idle. It should be very close to the engine displacement in liters.

You may also want to look at the intake air temp (IAT) and the engine coolant temp (ECT) to see if the readings make sense. Either one of those being incorrect can cause over-fuelling.

You could also have a leaky injector or a purge valve that's stuck open (or intermittent) causing excess fuel.

 

[Fless]

my Yukons efficiency/mpg stayed good without a relearn.

Although it's normal to not notice any issues after changing either the cam or crank sensor - or both -- sometimes the relationship between the two can get skewed. The CASE relearn is quick and easy and will rule out any issue with the cam-crank correlation. That's why it's a suggested procedure.

 

[Maxpower_454]

You should look for the MAF reading in g/sec at hot idle. It should be very close to the engine displacement in liters.

You may also want to look at the intake air temp (IAT) and the engine coolant temp (ECT) to see if the readings make sense. Either one of those being incorrect can cause over-fuelling.

You could also have a leaky injector or a purge valve that's stuck open (or intermittent) causing excess fuel.

ECT and IAT are both on the attachments I posted... They're good.

 

[Fless]

The MAF reading on the graph is a frequency. Can you correlate that MAF frequency into g/sec (that's grams per second) which is an easily understood and relatable value?

 

[Maxpower_454]

The MAF reading on the graph is a frequency. Can you correlate that MAF frequency into g/sec (that's grams per second) which is an easily understood and relatable value?

Higher the frequency, higher the mass flow. Really no need to convert. It will just be a calculated value anyway.

 

[j91z28d1]

new maf you say? what brand.


so the point of looking at the maf in g/sec is because you can tell if it's actually reading the correct amount of air flow. at warm idle it will read about what the engine size is. kinda wild, but it works. it's a good way to check if the maf is reading correctly.

it's not as simple as just reading a freq for airflow. these gen 4 ecm's do everything ofd airmass. timing and everything is off the maf signal blended with other stuff. I have a log before and after cleaning the maf and it's running in a different part of the timing map based off the airmass reading change just from some maf cleaner in a q tip.

but yes, 3ms injector as idle sounds high and having to use clear flood mode to get it to start is classic flooded with fuel..

did you check the alcohol %? I don't remember.