4.8 4l80 7875 8.8 fox ...troubleshooting
 

Fox
Gen 3 2001 4.8
stock Ecu with deka 80’s
aeromotive a1000 pump
sloppy stage 2 cam
4l80 hd2 with circle d converter
8.8

Hi guys I blew up my last junkyard 4.8 after 3,000 miles of pure fun. I am now having some issues on this new Sbe 4.8 that I swapped in. ( I swapped my pac1218 springs onto the new 706 heads too)

the only changes I’ve made is the new 4.8 sbe. And I replaced the 3/8” fuel lines with 1/2 AN fuel lines feed and return.

the car feels very sluggish and is acting like there is a boost leak at part throttle driving. (8psi) Very lazy taking off from an idle. (To sum it up, car feels like it’s down 150hp). Compression test on the motor was good, I’ve verified dot to dot marks on the cam.

There is no boost leak I’ve checked over all the couplers and reclamped many times. It is running 16:1/15:1 at idle even though HP tuners is commanding 13-14:1 idle. (Same tune as the previous engine which was not running as lean).

when I roll into boost AFR is 11.2-11.3 ( fine but again feels like it’s down 150hp)

I squirted carb cleaner all over the vacuum lines and all around the intake with no changes in engine RPM. Fuel pressure at idle is 60psi. The BOV is open at idle. I believe that is normal.

any thoughts ? Tips for trouble shooting ? Thanks just struggling a bit getting this thing back together.

On a turbo car the BOV is CLOSED at idle.

Spraying carb cleaner on a EFi motor isn’t going to show rpm jumps like a carbed motor as the EFI will compensate accordingly, unless 02s are shut off.

Did u verify the 706 heads weren’t the castech version? Just be aware the early 2000s the 706 castech heads were prone to cracking under the covers around the head bolts due to core shift.

Is the 15-16:1 at idle open loop or closed?

When's the last time you calibrated the WBO2?

What's the timing like at idle, part throttle, and full throttle?

Are you hitting your commanded WOT boost?

Fuel pressure under boost verified?

Also, BOV's shouldn't be open at idle. They open when there is a pressure difference (boost in the intake pipe and vacuum at the reference port).

And if all the simple suggestions fail, you may want to verify cam timing with a degree wheel.

Strange that it would be off that much in power, seems like you have checked all the boxes.
Only thing that could pop out is what was your lifter preload. If to much you could have a valve
open and bleeding off comp, might not show up on a comp test since they are not pumped up
with the engine not running. Machining from one engine to the next can be off, milling, valve
grinding, etc, can all lead to making a PR to long.
As far as the blowoff valve, I have always run them open, as long as they are shut at WOT
(no vac) they are working, but I guess in the turbo world things are a little diff. You could
always pull the line and cap it, try it, just don't go WOT.

Did u verify the 706 heads weren’t the castech version? Just be aware the early 2000s the 706 castech heads were prone to cracking under the covers around the head bolts due to core shift.The heads are actually off a 2004 4.8 Gen IV motor.
Is the 15-16:1 at idle open loop or closed? i believe closed loop, engine was still hot after a long drive...
When's the last time you calibrated the WBO2? It's an AEM wideband, they supposedly don't need open air calibration
What's the timing like at idle, part throttle, and full throttle? , I did not get to check this.
Are you hitting your commanded WOT boost? yes
Fuel pressure under boost verified? no I don't have a gauge visible in the car...I may have to get one

Next I will check the intake gasket & verify rocker arm's are all torqued to 22ft/lbs...

my aem x series wideband did.....

Sounds like you're not logging. You really need to log to see whats going on.....and verify the BOV setup as a couple of us stated it shouldn't be open at idle.

I’ll get my friend to log it on hptuners and come back to you guys with more info. Thanks for all the suggestions I know it’s literaly shooting in the dark with minimal data.

thanks

Don't you mean, it should be open at idle? It's under vacuum. The BOV will close under boost, which pressurizes the intake tube and opens when you let off the throttle, relieving pressure.

The BOV relies on a pressure differential. Vacuum and no boost don't open the BOV at idle unless the spring is too weak. They typically are closed at idle and open right after a boost even when there is still pressure in the charge pipe and vacuum at the intake manifold.

https://www.nukeperformance.com/faq-blowoffvalve.html

I guess my understanding is incorrect as well (as mine is open during idle). Sounds like the spring is too weak.

Doing a search there are a TON of opinions on this lol. I've always been in the camp of closed at all times unless you let off the throttle. Posted a link corroborating this idea as well. I guess as long as OP's is closing when he presses the pedal and isn't a boost leak it should still be ok.

Mine is open at idle but it is pre-MAF. It works as it should, otherwise.

bypass open at idle is every factory turbocharged vehicle

All bypass should be placed as closed to the turbo as possible and before any heat exchangers

open at idle is preferable if the bov is routed back into the pre-compressor inlet

where it conserves kinetic energy which was originally imparted to airmolecules from compressor

when properly implemented improves economy(regains *only* energy originally spent, returns some of what was used accelerating the air, this doesn't "add" any fuel economy) and response, a higher transient impeller speed will be noted in logs

on to the problem:
All suggestions above are fine but specifically emphasis on
1. perform boost leakpressure test from compressor cover through engine, use air pressure to expose leaks, every leak no matter how small is crtical

2. check plugs (gap color quality), fuel quality, accuracy of sensors (use two gauges for everything) basics, compression test, &c
3. If using a maf sensor and turbo, the maf should be placed before the turbo and the bypass needs to be recirculated after the maf. The maf also has it's own list of subtle requirements. #3 is highly recommend removing the maf. Use only MAP sensor for simplicity.
4. disable closed loop until tuning is complete. don't rely on any computer correction until you are ready to sell the car or totally done tuning (never). Use wideband logging and fine tune the engine properly while you drive through all conditions. If you didn't bring the laptop just remember where it needs tuning later. The designers implement closed loop to account for myriad wandering conditions because they themselves would not be sitting in the car with a laptop and tuning software while the owner is driving to make minute corrections. Which is exactly what you are there for. So the only reason to be using closed loop is to make sure it works right then shut it back off to finish tuning the car.

Is the cam the same cam that was in your old 4.8? As said, you may want to degree it in if you can't find anything. Matt Happel went through this on Fairmont 5? I believe. If I remember correctly he sold the car and the new owner fixed it.