I was on a backroad doing some WOT tests and for some oddball reason when I shifted from 3rd to 4th the car sputtered at WOT. I let off the throttle and floored it again and it was fine. Looking at the datalog at the time this happened I noticed the the BPW was at 2.8ms at WOT with a commanded AFR of 14.9. Normally it's at 8.5ms at WOT with commanded AFR of 11.8. There was no knock at the time this happened. Has anyone come across this issue before? What would cause the BPW to go that low at WOT? This has only happened twice in the last 1000 miles. I'm using saujpv4 7730 $8d.

 

Were the MAP, TPS, and RPM readings OK?

RBob.

 

The MAP readings were 41kpa and TPS was at 100%(4.59v). RPM readings were actual around 4900rpms when it happened.

 

With the MAP at 41 KPa that is why the PW went so low. Most likely caused it to drop out of PE mode.

I can relate to one item that may have happened. The intake duct work collapsed which caused the MAP reading to fall. If you were data logging the fuel pressure see if it too fell.

RBob.

 

When the engine starts to misfire like it did wouldn't the MAP drop down anyways or would it stay around 100 kpa? As far as your intake boot collapsing, how did you go about finding that out other than removing the hood and visually seeing it? Also, how do you datalog the fuel pressure? Tunerpro Rt only has fuel pump voltage which didn't change from 13.5v during the misfire.

 

bump

 

Only if there was a restriction put in the intake path. "Vacuum" is just measuring the restriction of air to get into the intake manifold or cylinders. Look at key on engine off MAP reading, It should be around 100 KPA, no miss fire, or anything of the sort, but the MAP reading is high due to no pulling of air into the cylinders against the restriction of the intake, being the closed the TB in this case. The only reason the vacuum would go "high" (low number) is because something blocked or restricted the intake path.


There's no correlation between pump voltage and fuel pressure, well not in the way I think you're thinking. You'd have to add a pressure transducer of some sort (I have ideas) and add a channel or change a channel in the ALDL datastream to display the feed from the sensor correctly.

 

I asked if the fuel pressure was being data logged as it would back up the MAP reading. If it too dropped then the MAP reading would be verified as correct.

On the '90-'92 TPI Camaro's the collapsing intake is common. There is a length of convoluted rubber duct between the TB & air cleaner. It tends to collapse and cut off the air flow.

The fix is to cut both ends out of a coffee can and shove it into the duct.

RBob.

 

That's awesome info rbob. I will do that and test it again.

 

I always get confused and get it backwards. Thanks for the info