408w running poorly
 

Just finished installing the Edelbrock Victor Jr's on the 408 last week and have been trying to get it to run right this week. The car ran good before the install (boo too me), but did not have the power the owner wanted.

I am in the process of timing it, and also should have some vacuum readings within an hour or two. I know until I have the timing down, all this could be hard to diagnose, but humor me here.

When I took it for a drive, the darn thing felt real sluggish. So much, that I turned right around and parked it. It will be idleing at 1100 rpm's and jump up to 2100 all on its own. It will stay there for 5-10 secondse, then come back down to 1100. If you are trying to feather the throttle, the 1st quarter of throttle feels dead. That first quarter feels like it does nothing, unlike before the head swap. Give it more then a 1/4 throttle, and she revs right up, but seems to be slow at coming back down.

Standing at the rear exhaust, I swear I can hear a miss in it, but have checked the firing order several times, the plug wires are on good, and the plugs are brand new.

Checked the oil, looks and smells good. Tried spraying w/d 40 around the intake and carb gasket areas....made no difference. I am really thinking I have a gasket leak, most likely at the intake. Any guesses?

408w, 750 double pumper, msd all around, Comp Cam #35-250-4 , Weiand Stealth intake, shorties to 2.5 out the back.
Thanks as always guys.....I am really begining to hate this 408!
Ryan

Re: 408w running poorly
 

Did you check for vacuum leaks? It's sounds as if you have one.
Unplug a vacuum source(creating a vacuum leak). If the idle picks up then you have a vaccum leak somewhere.

Re: 408w running poorly
 

Timing is set to 5 degrees BTDC, vacuum gauge read 6.5 - 7 inches vacuum. Fluctuated very little to none, basically just between 6 to 7 inches.

What would be an acceptable vacuum source to unplug? The brake booster? That is about the only thing I can think of on this that runs off of vacuum.
Ryan

Re: 408w running poorly
 

Add some more advance. I would start at 10* and go in 2* increments until vacuum reading is maxed out at idle.
You have the next step up cam that I have. I have the 274XE cam.
That cam, in that 408, should have tons of torque through the rpm range.

Yes, you can disconnect the brake boost for a leak test.
Here is a helpful link to diagnose possible problems by using a vacuum gauge: http://www.tradervar.com/Engine%20Pe...um%20Gauge.htm

Re: 408w running poorly
 

disconnected the brake booster....killed it out every time..instead of picking up. got mad, used a can of brake cleaner over the #7 and #8 intake runner near the head, every time I sprayed it there the car would idle great. After a few seconds, it would start to run crappy and I would spray it again....smoothing the idle out.

I am 99% positive it is an intake leak, now here is the next issue. I have never used torque wrenches on intakes. I am thinking I should have with aluminum to aluminum, can I lossen these up and retorque? Or, should I just pull it and use new gaskets and RTV the crap out of them this time? Anyone know what they should be torqued too?

82GT- The car has always had gobbs of torque, just never has revved as we feel it should.

Ryan

Re: 408w running poorly
 

you can try loosening all the intake bolts and find the right order and torque them down and see if that'll help but best way would be to use new gaskets and you don't need to go wild with the rtv either.

Re: 408w running poorly
 

I dont want to go wild with the RTV, but I have never had one leak on me before...kinda makes me not so happy
Ryan

Re: 408w running poorly
 

Yes, loosen and re-torque the bolts. I want to say the specs are 24# but not positive. It's also important you torque them in the correct pattern. What gaskets are you using? I'm a big fan of Fel-Pro blue. I only use RTV on the front and back of the intake instead of the two cork pieces....about a 1/4 inch bead.
If you want, I can dig out my book with the correct torque specs...

BTW, 5*BTDC is still not enough advance. I would shoot for between 34-38* total advance after you get your leak fixed.

Re: 408w running poorly
 

One more thing. I had to re-torque my intake bolts several times before they were seated good.

Re: 408w running poorly
 

I used the Printo -seal gaskets by Fel pro, FPP-1262 with a 2.100 port height and 1.280 port width. I used the tightening procedure in my haynes maual. I am gonna get a torque wrench tom and retorque them. If that dont work, I am gonna redo them. If I still have a problem, I am gonna suspect the used heads. Thanks guys
Ryan

Re: 408w running poorly
 

I realize 5 degrees is not enough, but the way it is right now, timing seems to not help it any (more advanced). Once I get the thing running better, I am gonna bump it up to 10 - 12 initial...and see how it likes that.
Ryan

Re: 408w running poorly
 

I just checked my book for the intake torque specs and it says between 23-25 ft/lbs.
When I did mine, I went 17# on the first round and then 24# on the second pass and then re-torqued them 3-4 times again after that.
Buying used heads is a risky chance unless you know the person very well that's selling them.
I hope it ends up that it's not the heads and that all you need is to re-torque.

Re: 408w running poorly
 

yeah, very risky indeed. Good thing I did not buy them, yet I end up workin on this car...how did that end up that way? Guess we will see after tomorrow.
Ryan

Re: 408w running poorly
 

Aluminum intakes on Aluminum heads are a pain in the arse. I torgue them (in the correct pattern) starting at 10#, do that like 2 or 4 times until they're ALL at 10#. Once you work your way out to the ends, the middle ones are no longer at 10#, with me? Then up to 15#, do the same thing, then on to 20#, do the same thing, then on to 24#. Be VERY careful on the end bolts!!! There's not alot of meat out on the end of the head for the intake bolt to hang onto. Our 333 is fine, but our 347 I actually had to use longer bolts just on the 4 corners. Sounds like a pain in the ass, and it IS! But that method works really well, and should kill your leak. After the engine gets some heat in her, kill it and retorque. You'll be SURPRISED how loose those bolts are!

Re: 408w running poorly
 

I would be so happy not have to pull that darn thing again...I still gotta re-pull mine for the trick flow cam I am ordering :)
thanks guys,
Ryan

Re: 408w running poorly
 

I KNOW what you mean! Bent 2 valves, broke a guide plate, 2 pushrods, 2 rockers up at Fun Ford. Fixed all that over the course of 2 weeks, took the car for a 5 mile test drive, all was well. VERY well! Washed the car, took a shower, heading out to a car show. Car shut off in the driveway. Long story short, the pin came out of the cam gear. Bent 12 valves, 6 pushrods, 1 rocker. Not even 5 miles later, off come the heads.........

Ain't cars FUN???!??!?? ;)

Re: 408w running poorly
 

That sucks! :eek:

Re: 408w running poorly
 

Jester,
Thanks for putting stuff into perspective...now I dont care as much about the leaky intake:)
Ryan

Re: 408w running poorly
 

Not having enough initial timing will cause the idle problem you are talking about. Set your baselines with atleast 10 degrees initial..

Re: 408w running poorly
 

Bumped the timing up to 10 degrees, ended up at 12 at the end of the night. Loosened the bolts, re torqued them to 10, 20, then 25 ft lbs. Went over them tons of times. Surging idle is gone, carb acts like it is a little stumbly off idle, but runs tons better.
Took it for a test spin, not bad. Gonna let it sit over night, check the intake bolts again, then put the g-tec in it and get a ball park figure as to where we are.
thanks guys,
Ryan