I am able to make about 14-15 PSI of boost with my stock, except for AIS filter, 2002 Excursion .

My understanding is that it should be closer to 20.

I've tested the intake side with a boost leak detector. I found a few minor leaks, but fixing them didn't change the boost readings.


The MAP sensor seems ok. The EBP sensor seemed ok too, but it was clogged. I cleaned the tube and sensor but that didn't change anything either.


Here are some stitched together WOT runs. All but the last are with the red wastgate line off and plugged.



I've visually inspected the exhaust side of the turbo and found no leaks. I also removed the EBP sensor and injected air (Low PSI) there. I wasn't able to hear any leaks. I taped a garbage bag to the exhaust and I was able to fill it full, like a balloon. The compressor is a York automotive AC compressor with only a 1 gallon tank, so the CFM isn't super high.

Next, I installed the EBP sensor and pressurized the system from the exhaust side. The only leak seemed to be in the muffler. We would pressurize the system, let it bleed down a little and then pump it back up.

You can see below that when pressurized from the exhaust the EBP is not "noisy" like it is when doing a WOT test.




Are there any other things that I can check before I start throwing parts at this?

For example could the wastegate be opening too much too soon or could the turbo just no longer be at 100%?

I have AutoEnginuity, but I could not find a way to measure the duty cycle for the waste gate solenoid, did I just miss it, or can we not monitor that?

 

I haven't used my AE in a few years so I may be leading you down the "garden path" but if I recall correctly you want to monitor "manifold gauge pressure (MGP)" not manifold absolute pressure ( MAP).

MAP is MGP minus atmospheric pressure.

Or did I just make that up?

 

I use MAP when comparing with EBP, but MGP is the same thing with BARO in the math. I suppose it's possible he has a bad BARO reading high, so doing the KOEO test is appropriate.

Key On, Engine Off: Log Manifold Absolute Pressure, Manifold Gauge Pressure, Exhaust Back Pressure, and BARO (Barometer). We can see if the sensors make sense.

I haven't ruled out a turbo or sensor problem. Based on my own experience, I'm leaning on a missed intake leak - but don't yet break out the hammer, chisel, and stone. I fought my leak for a while, but it wasn't until I had a good look all round the intake plenums with Simple Green that I finally found the sneaky bass turd.

 

i have never seen more than 17 lbs boost on a stock engine.

 

Yes - 17 is stock, unless one has capped off the red line to the wastegate.

 

Thanks for the correction. Seeing 15 of 17 seems much less bad vs seeing 15 of 20....


Shoot, I didn't log gauge pressure. I'll do one of those next chance I get. My cleaning of the EBP sensor and tube did something. The sensor reads high. Originally I was going to say it fixes itself when it warms up, but that's not really the case.



Here's some more info:

have a file from Jan 2011 with these KOEO readings:
EBP: 14.61
Baro: 4.64 (14.83)

And from Jan 2015:
EBP: 15.33
Baro: 4.62 (14.76)

Here's a drive cycle from cold to warm. I stared KOEO and finished KOEO:




Here's a drive cycle from yesterday. I can't say for sure that I got KOEO at startup, but I did at the end. See how the EBP is now close to MAP KOEO. I assumed it just needed to be warmed up to behave, but the chart above proves that's not the case:





At this point it seems that the EBP sensor needs to be replaced even if it's not the source of the low boost. Agreed?

 

I have not given up on looking for leaks and I'll probably order and EBP sensor on Monday. I'm still trying to get a good understanding of the inputs to making boost. There's the air side and the fuel side.


There must be some relationship between fuel and boost(air). In the chart below as RPMs go up from 2500-3200 rpm, it appears as if ICP Duty Cycle, Injector Control Pressure, and Injector Pulse Width are all heading down until the shift at time ~40.

I do understand that the bouncy EBP readings suggest an air leak, but do these other sensors back that up or say something different.

I'm pretty sure that shift at time ~40 in the chart is the torque converter locking up in 3rd gear.

 

boost is not regulated by rpm, boost is regulated by load. an engine with no load will make very little boost, and engine pulling 15,000 lbs up a 17º grade will make maximum boost.

 

I understand the basics. The above chart is after fixing a few minor air system leaks leaks. I'm going up a small hill, trying to load the truck as much as possible without having to go hook up a trailer for testing. It's obvious that the EBP "noise" is not improved. It seems like boost has peaked at the same point as before the fixes. However, I'm not sure if I'm getting faked out because the engine isn't being loaded enough.


Here's an example of the same truck before any leaks were fixed towing 8,000 lbs. The boost is about the same, but the fuel curves don't descend (RPM is lower too).

 

EBP is problematic. I can do KOEO and get values from 13.5 to 16.5 or so. I'm not sure what causes the difference. At first I thought it needed to be at operating temp to be stable, but now I don't believe that's the case.

 

i can not help you with that because being color blind i don't know what the graphs represent. it is just a bunch of lines to me.

 

Here you go. A simple chart. Boost has flattened out. Mass fuel desired is going down. Is this an example of what people refer to as defueling?

 

the easiest way to explain defueling is simply where the MAP sensor sees over 24 lbs boost and shuts the fuel off.

 

KOEO on a cold truck, that's what is needed to be seen before anything. You've gone above and beyond without starting with the basics. We need the readings of MAP, BARO and EBP. Get those and go from there.

EDIT: I only seen 15 psi on my truck when it was stock too. Come to find out I had a big boost leak on the bottom of my spider at the Orange boot but didn't find it until I was tuned

 

Post 10. Why cold?


I still could be missing a leak. It would have to be one that hides itself pretty well. I found two "hiders" yesterday. One was the red tube for the wastegate at the turbo pedestal. If I shook it it would bubble some. I fixed that for now with a zip tie.

The other was the hot side of the cac tube at the turbo. If I wiggled it it would hiss/bubble a little. Fixing things didn't have any impact on max boost though.

I still could be missing an air leak. It would have to be one where seeing soap bubbles is not easy and it does not hiss when energized with air.

I think it would be really easy for such a miss on the exhaust side.

I have taken a cell phone on a stick and taken photos of the back of the turbo and the the exhaust connection to the turbo looking for soot spots with no luck.

Pressurizing from the tail pipe is possible (actually easier than the intake side - using the same PVC plug ) but listening for hissing is more difficult because the muffler seems to be a noisy leaky spot.

Also, when doing the intake side yesterday I hooked up a battery charger and left koeo and used the map sensor to monitor PSI. This threw a code for a low EBP sesnor value. I assume the PCM saw the pressure increase at the MAP sensor without one on the EBP side.

Are there any other side effects of leaving koeo for a long time?