Intake bolts loose

olddog · #1 (**permalink**) 10-01-2007, 07:56 PM

5.0 SB Ford with Edelbrock performer heads and an Edelbrock Victor Jr intake (modified by Mass Flow - injector bungs welded in for EFI). Engine has about 2500 miles on it. I think the engine was first assembled with a carb, and the EFI intake installed later. It had 1500 miles on it when I bought the car.

I have been having a poor idle when cold, and I have been sorting out the EFI. However the problem was getting worse not better. I noticed that the fuel pressure was unstable when cold, and the fuel pressure regulator varies based on manifold vacuum. I threw a vaccum gauge on it and started it up cold. The vacuum was all over the map and dropping to zero. Vacuum was random, that is there is no pattern like a certain cylinder causing a drop. The vacuum drop leads the rpm drop. Once the engine was warm , the vacuum was steady, and the idle was steady as well (which is why I didn't find it earlier). Additionally my oldest son was ridding with me Sat. and said he thought he heard the squeel of a vacuum leak at a certain rpm.

My first thought was that if the leak is mostly sealed up when warm then it is likely do to aluminum heads and intake expanding. So I checked the intake bolts. With torque wrench set at 16 ft-lb, I got about a 1/4 turn per bolt. I pulled the throttle body and you can definately see where it has been sucking in oil. No water has leaked into the oil.

So here are my questions:
1) Should I put it together and see if this fixes it, or should I pull the intake and replace the gaskets? I'm leaning toward giving it a whirl.

2) I would like to clean the oily mess up inside my intake, ports, valves. It's a single plane so it is open to the valves (end cylinders are curved enough you cannot see the valves). Carb cleaner would clean it, but I'm concerned about spraying that much into the cylinders and washing all the oil away from the rings. How best to clean this up?

Pete Munroe · #2 (**permalink**) 10-02-2007, 09:21 PM

I had the intake manifold gaskets fail on my engine, iron 289" with aluminum heads and aluminum intake at about 2500 miles.

While the engine was running I squirted oil at the intake/head joint and could see where entire chunks of gasket, 1/4 to 3/8 had broken off and the vacuum had sucked it right in. Made the gap was obvious to see. Duh.

Upon removing the intake manifold, the Fel-Pro gaskets looked like they had been tortured...squirming around the intake/exhaust ports...have some pictures if I can find them.

I do not care what common wisdom dictates...they need to be retorqued...OFTEN...in my case often is every few thousand miles.

Anyway, I replace the gaskets...used the same Fel-Pro hiperformance whatever but have retorqued the bolts every 1000-2000 miles since...a few, usually bolts up front, squeak, creak and take another 1/4-1/2 turn to hit 22+/- ft/lbs...the others just sit there.

I am now at 13000 miles, about 6 weekend track events and no problems.

Next time the intake comes off will be to put in a hotter roller cam.

Oh, use more silicone than you may think to seal the front/rear of the manifold when you replace the manifold.

VERY HELPFUL...use four studs on the heads for alignment as you lower the manifold onto the heads...still be carefull the intake doesn't pull the gaskets "down" from alignment...but helps me immensely to align the intake and get a good seal.

Pete

Rwillia4 · #3 (**permalink**) 10-03-2007, 10:07 PM

I had to pull the intake of my new build to install the engine. I purchased felpo gasket and they were WAY thinner that what I took off. So I called the builder. I was told if you haven't had your block planed then you need the thick gasket which is about 1/4" thick (two felpro's didn't even match the thickness).

To install the gaskets with good success I was told to use weather strip black sealant (from your local automotive store) which is much thinner than RTV or silicone. Put the sealant around the ports on the bottom sides of the gaskets, align them onto the heads visually. Push into place, the sealant will have enough tack to hold them. Let it dry for a few hours (read: go get lunch and let it dry), this will allow you to be able to put the intake on without having the gaskets move. Put the sealant on the top of the gaskets, install the intake. Let dry overnight and startup in the morning. No it is not a quick process but you only have to do it once (other then re-torqueing the bolts).

Tom Wells · #4 (**permalink**) 10-04-2007, 07:00 AM

Be sure to get the correct gasket for street use if you don't want to replace them often. See this thread:

http://www.firstcoastcobraclub.com/v...c.php?f=8&t=13

The non-reinforced Fel-Pro Print-O-Seals are NOT intended for long term street use. You need the newer steel shim reinforced Fel-Pro or Victor Reinz gaskets. This applies to FEs, 385s, Windsors and all.

Tom

olddog · #5 (**permalink**) 10-08-2007, 06:37 PM

Well since there is only a couple weeks of driving left, I decided to re-torque the intake bolts and put off changing the gaskets until winter. I cleaned the intake up with carb cleaner and a rag as best I could. I found the throtte body wasn't opening up all the way - the ball the throttle cable snaps onto had threads going through too far - but I digress.

The vacuum is now steady, when rpms are steady. It was (before re-torquing) erratic and jumping to zero, when cold. However the cold idle still wants to drop down to about 200 rpm - where the vacuum is about 2". If I hold the idle up to 900ish (by ear - I could not hold throttle and see tach and vacuum gauge all at the same time) the vacuum cold is about the same as hot - around 14".

So I'm trying to understand is the vacuum being low causing the low idle speed when cold, or is the low rpm when cold causing the low vacuum? The cam at 0.050" lift is 236 intake and 242 exhaust duration, resulting in 19 degrees of overlap. It would seem to me that such a cam would run less vacuum as the rpms go down, but I'm not sure.

Do I still have a vacuum leak?

By the way as soon as the O2 sensors heat up and the ECU goes into closed loop control the idle is perfect.

When I tighten the manifold down, the first time around I got about 1/4 turn on the bolts, second time a little over an 1/8 turn, third time some moved a little, fourth none moved. I set the wrench on 16 ft-lb per Edelbrocks instructions (16-18 ft-lb).

Rwillia4 · #6 (**permalink**) 10-08-2007, 07:21 PM

Do you have the ability to see what corrections your EFI is cranking in to get your idle to smooth out. I would turn off your O2 correction (unplug it) get the idle setup see if the vacuum corrects itself, then plug back in the O2 sensor. This would minimize the "work-load" on the EFI.

olddog · #7 (**permalink**) 10-08-2007, 07:27 PM

Quote:

Originally Posted by Rwillia4

Do you have the ability to see what corrections your EFI is cranking in to get your idle to smooth out.

No. ECU is factory - late 1980s to early 1990s mustang 5.0. All I have is OBD1 scanner that will test and flash the codes. I assume the idle air control valve is opening up, to bring the idle up once in closed loop, but maybe not.

It seems like it is buring rich until it goes into closed loop, by smell. The fuel pressure is supposed to drop 1 psi for every 2" of manifold vacuum. With this cam, the idle vacuum is only 14" where a stock 5.0 would be up closer to 20". So the fuel pressure at idle is 33 psi where a stock engine would be more like 30 psi. So I can see where the open loop fuel map is going to be wrong. Then when the idle drops lower and the vacuum drops off more the fuel pressure goes even higher toward 38 psi. I think it is like a snow ball rolling off a cliff.