Missing under boost after valve spring change

[89mulletbird]

I changed my valve springs this weekend to 100# springs, now my car is really bogging bad under boost. In 1st gear it happens after about 5# of boost, the other gears it happens all of the time under boost.

I was able to go WOT in 3rd gear for a bit and my 02 and knock seemed normal but it felt like I was running on about 4 cylinders.

The car runs perfectly when not boosting.

The only thing I can think of is did I not properly place a pushrod or two when putting them back in? Is it easy to get them incorrectly placed on the lifters?

I am probably going to have to pull my valve covers and look at rocker arm operation to be sure all the exhaust valves are opening.

How does a car behave if one of the exhaust valves is not opening?

Thanks!

 

[tom h]

100 # springs seem awfully strong, stock springs are around 75# @ 1.7" height. here's a pessimistic thought- could one or more cam lobes/lifters have been prematurely flattened by the strong springs? cranking, or briefly running, the engine with valve covers off should provide a direct visual indication.

 

[89mulletbird]

How fast can you wipe a cam lobe?

 

[tom h]

I've never re-built an engine, but most people caution that if a 20-30 minute break-in is not done correctly, you can flatten lobes. It can happen very quickly.

I could be completely off-base on this hypothesis. Best to see if other ideas are presented before getting too worried.

A number of people do run these 100lb range springs, apparently without problems -- but I'm chicken and would not do it on an otherwise stock valve train. Exmple, a number of pictures have been posted over the years, showing broken ends of rocker shafts -- very strong valve springs and higher RPMs can lead to unanticipated problems.

 

[89mulletbird]

I just drove the car around some and noticed the following things:

1. It idles at 1500rpm
2. The boost gauge seems to build prematurely. It will appear to spool up with very little throttle.
3. You can hear a small "turbo chatter" sound when letting off the throttle without even building boost.

I'm inclined to believe that the intake valve is not closing all the way, or the exhaust valve is not opening. I used a temp gun on the headers and they all seem to be around 800F. I'll remove the valve covers tonight and see what's going on inside.

 

[Vega v-6]

sounds simply like a vacuum leak

sounds like a vacuum leak the way you discribe your prob. probably when you had the valves covers off ( if you replaced the springs with the heads still on that is) if you had the heads off theres a number of things that may of went wrong, you might have a vacuum line off or misplaced giving you a lean mixture that the computer can't make up for giving you the funky ride quality. 100# springs don't sound very heavy at all...wiped out a lobe...I doubt that too.
Good luck

 

[tom h]

When re-checking for loose/cracked/leaking vacuum lines, don't overlook the wastegate tubing & electric solenoid.

 

[89mulletbird]

I'm inspecting vaccum lines. I took the valve covers off and no problems with the valves or cam

I did replace the EGR solenoid because a fitting broke off. I wonder if the new one could be defective...

 

[VadersV6]

So all you did was replace springs with the heads on the car? Did you replace any seals? Did you make sure every pushrod was seated when you tightened the rocker shafts back on?
Theres a really big deal here that many people overlook, and then wonder why their rocker shafts cracked. If you tighten the rocker shafts down on one end where a valve isnt opening, bottom it out, and then tighten down the shaft on the other side where it is opening a valve, the preload from that lifter pushing the pushrod up, will put a TON of sideload on the shaft and WILL damage it. You need to always begin tightening the shaft down, right over the areas where a valve is opening/a pushrod is pushing up...pretty obvious when one is sitting higher than the others. Then gradually tighten the other ones, making sure the entire time that the rocker shaft is perfectly level and not cocking. Overhead cam guys will do this and crack cam towers. Then they blame it on the car and not their own stupidity or inexperience or common sense...*cough*ricers*cough*
Take the valve covers off and look for rocker arms not sitting where they should across the length of the shaft, from the lifter buttons not being there anymore. Look for cracks. Look for spring retainers not sitting correctly because of missing or cocked keepers. Make sure all those keepers are in there and sitting how they should. make sure every pushrod is sitting in the rocker how it should. Unbolt the connector from the ignition module, then have a friend crank the engine over while you watch each and every rocker rock back and forth.

 

[bison]

Did you happen to crack a spark plug when removing it or replaceing it? If so you will get a miss like you say.

 

[89mulletbird]

I just inspected the rockers and they look OK.
I just changed all the plugs also, thanks Bison! I took much care while installing them as I've had a cracked plug cost me hundreds of $$ replacing the coil pack and ign module.

I noticed if I grab the bottom of the EGR valve and press it up, my idle goes to where it should be. When I let go of it, the EGR valve springs back and the idle goes back to 1500rpm. Maybe the EGR valve or EGR controller is bad?

 

[bison]

I just inspected the rockers and they look OK.
I just changed all the plugs also, thanks Bison! I took much care while installing them as I've had a cracked plug cost me hundreds of $$ replacing the coil pack and ign module.

I noticed if I grab the bottom of the EGR valve and press it up, my idle goes to where it should be. When I let go of it, the EGR valve springs back and the idle goes back to 1500rpm. Maybe the EGR valve or EGR controller is bad?

I had a problem once where somehow one of the plug gaps got closed down to .010 and the car would misfire like crazy. Took me a whole day of BS to find that. All i can think is i gapped the plugs and one must have fallen off the bench onto the floor and got picked up by someone else. Not knowing this i never rechecked before installing them. What a PIA!