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5.7 vortec problems

 
Fireman696
I love my Chevy Chevette!
Posts: 4
Joined: 12/12
Posted: 12/16/12 04:10 AM

i have a question i hope someone has a anwser my 98 silverado 5.7 vortec pulls extreamly hard till about 4500 rpms then is like it runs out of balls ive checked the fuel pressure it has 64 psi under a load (from what the gauge says) all of the ignition system is all good Im running out of ideals  kinda thinking it might be the valvetrain  Confused  

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tuffnuff
Moderator
Posts: 272
Joined: 01/10
Posted: 12/16/12 08:49 AM

Sounds like your valve springs are cycled out.,. time to replace them.

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When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

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68scott385
I have an SS396 tatoo
Posts: 325
Joined: 07/09
Posted: 12/16/12 09:06 AM

How many miles on the vehicle? Is it completely stock? Did this just start happening?  
68scott385 68scott385 68scott385

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Fireman696
I love my Chevy Chevette!
Posts: 4
Joined: 12/12
Posted: 12/16/12 01:46 PM

the engine is has less than 100k on it yea its complety stock  

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Fireman696
I love my Chevy Chevette!
Posts: 4
Joined: 12/12
Posted: 12/16/12 01:47 PM

its been doing it sence i got the truck  probly 6 months  

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waynep71222
My first time was in a Chevy
Posts: 218
Joined: 04/12
Posted: 12/16/12 01:52 PM

+1  

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pepsi1
Big Block power for the win
Posts: 940
Joined: 03/11
Posted: 12/16/12 02:54 PM

+1 Tuff

  I agree with Tuff it's time,for a valve spring change.That engine is a Pulling (Torque Type) 5.7 engine, when used in a truck.  
  Just a little FYI. The longer you let it go. The valve springs will start losing more and more pressure. Your MAX RPM will get lower.
  If they are the BEE-HIVE type. I would Just plan on replacing them. You can replace they with a little more on the seat pressure. While your in there have the valve seals replaced too. GM has a nice replacement kit for them.
  If you need any more help as you can see we are here. Good Luck..
One retired Fireman to another....
MERRY CHRISTMAS and HAPPY NEW YEAR..
Bob  

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Fireman696
I love my Chevy Chevette!
Posts: 4
Joined: 12/12
Posted: 12/16/12 03:53 PM

thanks for the good advice thats what i was thinking bout the valvetrain anyone out there have any suggestions bout cam kits im thinking something kinda lopey but still have a little number gains  i know it wont be a massive gain sence every thing is basicly stock                 happy holidays to yall to  

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pepsi1
Big Block power for the win
Posts: 940
Joined: 03/11
Posted: 12/17/12 08:37 AM

Unless your willing to have the ECM Modified there is really not much you can do for a bigger cam. Your engine controller is OBD2 that thing will not tollerate any big changes in engine performance.
  The best thing you can do now is replace the Valve springs. You have 100,000 miles on it. Making sure the lower end can also tollerate any performance improvments is also another consideration. Now your talking about replacing timing chain.
  Unless one of my GURU partners have something up their sleeves I don't know I hope they chime in! I want to know also.

Bob  

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tuffnuff
Moderator
Posts: 272
Joined: 01/10
Posted: 12/17/12 09:45 AM

I'm a long ways from being a Guru on this forum.,. I still maintain that the springs are tired and should be replaced.
"IF", the valves are lashed down 2 turns it could also limit revs.
Try 1/2 turn and see if it improves things.
Springs are easy to change and the tool is cheap.

AlltradeTools - Catalog - 648546 Valve Spring Compressor
648546 Valve Spring Compressor
Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

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tuffnuff
Moderator
Posts: 272
Joined: 01/10
Posted: 12/17/12 10:07 AM

There is some good info on valve springs at Chevy High Performance.,. check it out.

http://forums.chevyhiperformance.com/70/9347319/car-engine/looking-for-some-thumbs-ups-or-downs-on-my-selecte/page4.html

Click on the above link.

Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

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pepsi1
Big Block power for the win
Posts: 940
Joined: 03/11
Posted: 12/19/12 07:27 PM

+1 Tuff.
  If those lifters are adjusted to tight it will also limit top engine RPM. But I believe as you said the first time tired old Valve Springs...Doo.Dah..

Bob  

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Ravoll
V-6 Camaros rule!
Posts: 85
Joined: 02/12
Posted: 12/20/12 04:29 AM

Hi Guys,
I'm not questioning ya'lls diagnoses,but I was just wondering why in the world would a 1998 chevy's valve springs be worn out with under 100k miles,when much older chevy's with many more miles on them are still going strong? Confused


I had the same thing going on with my daily driver (Opel omega / caddy catera). Turned out that the ECM detected a problem (crank speed sensor)and went into the backup mode.The backup mode limits the engine to a max of 4500 revs.And since the bulb that lights the check engine lamp was burned no one knew the ecm was running on backup.
Also found out recently that if I run low on oil or water,the same thing happens,4500 rpm max.
I've been in Europe for the last 22 years and my knowledge of modern US vehicles
is limited,but I think that GM uses pretty much the same system across the board.
If so ,I would check to see if the check engine lamp lights up when the key is on and the motor is off,to make sure the bulb is good, and we're not in backup mode,then go from there.Sounds stupid, I know,but I can say ,"It happens",and it was very frustrating. Grin  
The older I get,the faster I was.

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Ravoll
V-6 Camaros rule!
Posts: 85
Joined: 02/12
Posted: 12/20/12 04:51 AM

And what if the ECM "is" in backup mode,and someone disabled the check engine lamp to hide the problem so they can sell the vehicle?
Before I changed any mechanical parts , valve springs,or otherwise,I would go and let someone read any codes that are possibly stored,just to make sure.Can't hurt.  
The older I get,the faster I was.

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