99 silverado 5.3 lost almost 100HP after 4 months

[madprof01]

Hey guys,
I have a 99 silverado 5.3 with a STS turbo system, methanol injection, and electronic boost controller. Mods made at time of install: 42# injectors, 2 bar Map sensor, descreened and machined out MAF, Bosch iridium plugs, Taylor wires, small stall converter,
aero turbine no tail pipe, still running MAF. I think thats all! Anywho, when I tuned it earlier this spring,(before EFI University), It was running hard ;11Psi boost, Methanol, Afr mid 12's, occcasional KR of 1 to 2 deg., putting down 404RWHP(Mustang), 138,000 miles.
Just recently noticed It's not pulling as hard . I've checked everything mechanical I can think of; cats are good, O2s new, no leaks(gauge reads 11Psi still), no trans slipping( input and output speed not different enough to worry .5MPH), verified dyno calibration. when i run it on the dyno it shows 342 RWHP. Loggin shows nothing out of range or abnormal. Methanol works, although dilution might contribute, no noticable blowby or vacuum leaks. the truck runs great just not as hard.
Is it possible that the PCM has adapted? I will be switching to custom OS and SD in the near future. (couldn't make it work on my last project)
Any thought would be greatly appreciated!

One more thing: To all the guys at EFI Live keep up the superior work, Excellent product.
Eric

[TAQuickness]

have you done a compression/leakdown test? maybe you fried some rings...

Also, not sure if this needs to be a sticky?

[Redline Motorsports]

have you done a compression/leakdown test? maybe you fried some rings...

Also, not sure if this needs to be a sticky?

I agree, first thing you should do is rule out mechanical issues. I have seen a ton of broken ring lands with these motors especially after running boost. The stock pistons are great N/A but on a 138K and boost it is something to look at.

We just had a H/C ZO6 that used to make 440 RWHP come in for a cam upgrade. We dynoed the car before we put the cam in it and noticed it only pulled 402 RWHP. We shrugged it off and proceeded to pull the plugs and leaked down the motor while changing the valve springs. We found one cylinder that showed 30 % leakage and heard it hissing out the crankcase. We pulled the motor and found a broken ring land. Funny thing about this is that the owner really never felt any power loss! Based upon this if you have 2 or 3 bad pistons, the car will still run OK but could be down 100 HP.

Do a compression check first and then do a leak down. Let us know!!

Howard

[madprof01]

I'll try to get that done today and let you know. that wasn't one of my first choices for tests bexause it does run so well!
Eric

[Redline Motorsports]

I'll try to get that done today and let you know. that wasn't one of my first choices for tests bexause it does run so well!
Eric

If it runs so well then maybe you like the mid 300 RWHP! LOL!! Thats exactly the point you sometimes can't tell your down the power until it's dynoed or brought to the track. This ZO6 that I mentioned about used to tear the tires of the car in third gear, with a broken piston!

Let us know!

Howard

[madprof01]

I hear what your saying, However the truck belongs to my shop manager and he has to know why. we did not get to do the leak test today but it will be this week. along the same lines we just finished a 01 f body with the same setup and had a huge blowby problem and the car would scare you and consistently make big numbers. we ended up using a catch can that the customer has to empty periodically.
aint hot rods neat!!!!
one other question. cold start on all but one of our projects is terrible. the customer has to start the vehicle three times, on the third try it fires up sweet and idles perfectly. after initial start there is no problem.

Any thoughts????
Eric
Matthewsautomotivesupershop.com

[dc_justin]

For your cold start issue...
If you are running a 2 bar map sensor without upgrading to a custom 2 bar OS, then there is a good chance you're having issues with the VE while Cranking {B0102} table. I've been trying to work this out for quite some time myself and have decided to just live with it til I get a chance to upgrade to a custom OS.

[madprof01]

The one and only car I tuned with carputing doesn't do it (98 camaro). And the 04 Silverado I put a low boost STS sytem on doesn't do it either but I think ETC has something to do with that truck. Or it may be that the cal wasn't as radically changed and the other vehicles.
We will continue to work with it and I will let you know if I find anything.

Eric

P.S. I tried the two bar OS on the 01 camaro that I'm having the problem with. I coundn't get it to idle right without jacking up the Map offset (58). I will be trying again on the Bosses truck.

[madprof01]

well, we did the laek and compression test and 155 to 170 is great for such a high milage motor with boost. the leak down test revaled only 8% on one cylinder and no more than 3% on the rest. Then I started to think about the fuel delivery system and pulled the vacuum line off the regulator and got wet! So I will be replacing the regulator today and will let you know!

Eric

[joecar]

well, we did the laek and compression test and 155 to 170 is great for such a high milage motor with boost. the leak down test revaled only 8% on one cylinder and no more than 3% on the rest. Then I started to think about the fuel delivery system and pulled the vacuum line off the regulator and got wet! So I will be replacing the regulator today and will let you know!

Eric
Would be running overly rich due to extra fuel being sucked thru vacuum line and pressure regulator maxing out (flow rate follows injector pressure difference);
should be able to smell raw gas when this happens;
LTFT's should have showed grossly negative indicating overly rich.
Hindsight shows that looking at LTFT's would have been the next test after compression/leakdown (...or maybe the first test...).
Yes, let us I know, it improves our knowledge, we appreciate your efforts.
:)