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HELP 5.3 Turbocharged Compression?

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Old Mar 17, 2015 | 09:46 PM
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Default HELP 5.3 Turbocharged Compression?

I've been having problems with the car since purchase about a month ago.

Just did a compression test.

#1 - 162
#2 - 165
#3 - 160
#4 - 170
#5 - 165
#6 - 160
#7 - 150
#8 - 166

What do you guys think? I'm still in the tuning process as well.
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Old Mar 17, 2015 | 09:55 PM
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Not horrible. Maybe a little low with a stock cam. Give us more info on the combo!
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Old Mar 17, 2015 | 10:00 PM
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04 5.3 stock bottom end
243 heads stock
arp studs
ls9 head gaskets
comp cams dual springs
custom grind boost cam 114lsa
mpt70 turbo .96 ar
KY turbo kit 3in down pipe
50mm bov
41mm waste gate
80lb injectors
fast fuel rails
ls6 intake smooth and painted
performabuilt 4l60E stage 2
3600 edge converter
sphon front k-member solid motor mounts
sphon torque arm and sway bar
Founders panhard bar
sphon 1.5 drop
stock 10 bolt 3:37 gears from motive
e85 twin granatelli 340 fuel pumps in tank
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Old Mar 17, 2015 | 10:03 PM
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Depending on where the cam is degreed, it could lead to those compression test results. Should be more around 175-180 typically. However, most don't degree cams and just throw them in and run em. What kind of problems are you having?
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Old Mar 18, 2015 | 08:04 AM
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When I first got the car it would run fine around town, but when it would hit boost it would just fall on its face. Now I know a lot of that has to do with the tune, and I'm getting that worked on now.

Last week it really started acting up. Barely idles, dies a lot. Rpm is really jumpy.
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Old Mar 18, 2015 | 09:26 AM
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Log it to see what's going on. Verify pcm inputs good/stable as expected.
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Old Mar 18, 2015 | 03:09 PM
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Odd the #7 is so low too. Shouldn't have a 20psi spread between numbers.

My 2008 5.3 was 190-200 cranking compression with 243's and ls9 gaskets. With the Isky tripple 12 cam about a 1/2* advanced form the card.

Threw it in "dot to dot" the first go around and I saw very low compression and poor performance like your seeing. My crank key was way off. When I put the degree wheel on I was almost 8* retarded from the card "dot-to-dot"

This was also on a cheap harbor freight compression tester so who knows how accurate those numbers really are. I'd say your on the low side for cranking compression though. Did you do the test with the eng warm and TB open?

Last edited by Forcefed86; Mar 18, 2015 at 08:39 PM.
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Old Mar 18, 2015 | 03:53 PM
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Typically a "mechanical" problem like a difference in compression tests are not going to come and go like you say. Check your fuel pressure and flow volume. Sounds like it might be sub-par.
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Old Mar 18, 2015 | 05:08 PM
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I wouldn't sweat those compression numbers. If it's bugging you, warm it up good and do it again. I bet it comes out different.

Read the plugs too. Might tell something.

But as was mentioned, you need to data log the car. It should be very revealing
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Old Mar 18, 2015 | 05:25 PM
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Originally Posted by Forcefed86
Odd the #7 is so low too. Shouldn't have a 20psi spread between numbers.

My 2008 5.3 was 190-200 cranking compression with 243's and ls9 gaskets. With the Isky tripple 12 cam about a 1-1/2* advanced form the card.

Threw it in "dot to dot" the first go around and I saw very low compression and poor performance like your seeing. My crank key was way off. When I put the degree wheel on I was almost 8* retarded from the card "dot-to-dot"

This was also on a cheap harbor freight compression tester so who knows how accurate those numbers really are. I'd say your on the low side for cranking compression though. Did you do the test with the eng warm and TB open?
I did the test on a cold engine with the TB open.
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Old Mar 18, 2015 | 05:26 PM
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I've logged the car, but know nothing about tuning. I'm having it tuned by someone.
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Old Mar 18, 2015 | 08:18 PM
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I tested the fuel pressure. The gauge only goes to 60, and it was pegged past that.
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Old Mar 18, 2015 | 08:42 PM
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Oops!
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Old Mar 18, 2015 | 08:49 PM
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Originally Posted by RonSSNova
Oops!
What?
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Old Mar 18, 2015 | 09:52 PM
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Well, if that is way too high, then it will cause rich running.
I guess you need a gauge that goes higher.
And ask your tuner where it is supposed to be set.
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Old Mar 19, 2015 | 02:57 PM
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If your fuel pressure is way to high your injectors on the lowest pulse width they can do, may still be too much fuel.
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Old Mar 19, 2015 | 03:06 PM
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Does it have a boost referenced fpr?
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Old Mar 19, 2015 | 08:27 PM
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Originally Posted by mkvamso
Does it have a boost referenced fpr?
Not sure.
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Old Mar 19, 2015 | 08:28 PM
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I adjusted the fuel pressure to 57. It was probably around 75.
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Old Mar 19, 2015 | 08:41 PM
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Well if it was tuned for 57 and shot up that high that would make any car run like crap. How much did it help?
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