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Intake Manifold Bolts

43K views 99 replies 36 participants last post by  97Concours1 
#1 ·
Check to see if they are tight!!! 6 of 10 of mine were significantly loose. A 10 mm socket, wrench, and extension. Each will be needed to get around the fuel rail at different angles.

Learned this by reading here;)
 
#81 ·
"I Stand Corrected", another member mentioned 100 in/Lbs, and I hung onto
that incorrect setting, However did mine at 100, and had NO ill effects,
but could have cracked the intake ?I believe the correct setting is 89,
but 90 would work, as the difference is NOT noticeable
 
#4 ·
Thanks for the information! I thought I was finished - I only thought to use the elbow torque-o-meter. As far as motors go I am a V8 RWD type guy...getting rarer these days. I don't know if I have the adapters on hand to step my torque wrench down to the drive that fits my metrics? I thought my project was complete, but maybe to the store.
 
#5 ·
There have been several members on the forum speak of loose intake manifold bolts so I decided to check mine tonight and 6/10 were loose. Some as much as one full turn before I hit the 10 N.m torque.

Since I was also doing a little work on my Bonneville, I decided to check it as well. I've got the LD8 engine in it (4.6L transverse mounted Northstar). It has about 111,000 km and I found every one of the 10 bolts was very loose. I initially made the assumption the torque spec was likely the same but when every one I checked seemed loose I checked the spec just to be sure. Nope, I wasn't overtightening! Hmmm, I wonder if this is a general Northstar problem or if it may be found on any GM engine with this style/type of manifold?
 
#7 ·
I believe you may be thinking of different bolts. I very much doubt these would be a stretch type bolt because the torque spec is so low. We're talking lb in., not lb ft. and to stretch, it would have to be an extremely soft alloy. Also, there is no mention in the FSM to use new bolts. Generally GM provides this when necessary.
 
#8 · (Edited)
More on this: After reading about this on here, I headed down to my high school buddy's place about 150 Miles from home.
I used 8 gal to get there, I tightened the bolts to 100 In Lbs, found ALL of them loose about 1 full turn, couldn't do the #1 or #2
bolt in the sequence as there is a pressure switch type thing facing down toward the bolt, so used a open end, and did the best
I could. Some of the indications: I noticed when pressing down lightly on the gas, it used to convert automatically from 5th (OD) to 4th gear.
before the tightening, it didn't respond well, and I blamed my less than 26 MPG on rear tires, now it converts GREAT, and I only used
6.5 Gals coming home, and the MPG avg, hit 26.6, which I have NOT seen in a long time. The transmission downshifting, usually has
what they call a modulator, used to be (Vacuum controlled), this one also must be, as it works MUCH better now !
Thanks to all who supplied the Correct info on this item, and helped me get this done.
I wanted to use LOck tite on the bolts. You would have to pull the fuel racks to do this, I NEVER have done this, so I didn't do it.:cool2::cool2::cool2:
BTW, I ONLY have 45K miles on this, you would think they are NOT loose at this point, Murphy's law got me again !
 
#9 ·
More on this: After reading about this on here, I headed down to my high school buddy's place about 150 Miles from home.
I used 8 gal to get there, I tightened the bolts to 100 In Lbs, found ALL of them loose about 1 full turn, couldn't do the #1 or #2
bolt in the sequence as there is a pressure switch type thing facing down toward the bolt, so used a open end, and did the best
I could. Some of the indications: I noticed when pressing down lightly on the gas, it used to convert automatically from 5th (OD) to 4th gear.
before the tightening, it didn't respond well, and I blamed my less than 26 MPG on rear tires, now it converts GREAT, and I only used
6.5 Gals coming home, and the MPG avg, hit 26.6, which I have NOT seen in a long time. The transmission downshifting, usually has
what they call a modulator, used to be (Vacuum controlled), this one also must be, as it works MUCH better now !
Thanks to all who supplied the Correct info on this item, and helped me get this done.
I wanted to use LOck tite on the bolts. You would have to pull the fuel racks to do this, I NEVER have done this, so I didn't do it.:cool2::cool2::cool2:

That's a good bit of information and very inspirational! My average is under 20mpg as well. Is there a step by step to gain access to the intake bolts somewhere on here?
 
#13 ·
I can't comment on a change in fuel economy just yet as I haven't driven enough since tightening the bolts to know. I can say that the first time I drive each day, or after the car has sat for several hours and cooled off, the car hesitates a little as I accelerate and I need to back off a little. Since tightening the intake manifold bolts, this appears to be resolved. I've also noticed a smoother, more powerful acceleration anytime I'm driving. Overall I'm happy with the results of a very simple maintenance procedure.
 
#17 ·
This whole thing had me curious...so over lunch I ran home and checked. To my astonishment, 9 of the 10 bolts were loose, with one almost ready to fall out. (pictured 2nd from firewall on drivers side) Auto part Car Vehicle Automotive exterior Engine


My STS is an 07 with shy of 98k. I couldn't believe these could come loose in less than 5 years.

Amazingly this 5 minute fix immediately solved a number of issues.
Rough idle and startup after car sat overnight.
Hesitation in lower RPM. 700-1500
Erratic shifting patterns, rough shift.

I highly recommend everyone checks this out...should almost be sticky. Thus the beauty of an enthusiast forum. :)
 
#19 ·
Thanks for the advice, mkmarsilio, ddalder, and everyone else! I checked mine today and found they were very loose! I could tighten them with my fingers, if I had twisty little long skinny fingers. I have to go out tomorrow and find something like an articulating 3/8" extension, because I didn't have enough clearance to get my socket on most of the bolts. Harbor Freight is an hour away, but I'm sure they will have something, and I could use a motorcycle ride.

Once again, very nice job to the forum members. Shame on Cadillac.
 
#20 ·
What do you know... 06 STS Northstar, 57,000 care-free miles. Checked the intake manifold bolts and had 10 out of ten loose to real loose. Tough to get to. Needed 10mm socket, flex adapter, and open end wrench. 10 minutes, and all better. Runs smoother now. :bouncy:

How can Government (was the General once) Motors build them so sloppy? Perhaps this is one of reasons they had to use my money to bail them out. :hmm:
 
#21 ·
Its only been a few days, but I have had a noticeable improvement in gas mileage. It was around 13.5 average for city - suburb driving, but now I am around 19.5. Next would be a road trip. My last on in August averaged 21 miles to the gallon. :thumbsup:
 
#22 ·
I did this as well last weekend to try and fix a stalling/misfire during off the line acceleration. The car does not stall now but does a funny acceleration like this... RUMM RUMM RUMM RUMM RUMM when going halfway on the pedal. Once I let off if smooths out. It is a little peppier and gas mileage has improved. I still need to have that checked. Other members suggested a clogged catalytic converter and/or bad/clogged fuel pump/filter...
 
#25 ·
Just tightened the bolts on our '06 STS N* with 54k miles. All 10 were loose. Done in 10 min. Runs and shifts great now. This is a must do. I am going to check them every 10,000 mi or so.

I could not get a socket on bolt #1 per diagram, so I used an open end 10mm wrench which is not ideal. So I will buy a crow foot wrench, or else remove the fuel rail. The other 9 bolts were easily reached with a 1/4" socket (10mm), with a std universal, then a 6" extension to my torque wrench.

It might make sense to use an appropriate Loctite product. I wonder if there is a technical bulletin on this??
 
#31 ·
Finally checked mine, and yep, all ten were loose. At least three weren't even finger-tight.

Tip: You have to have either a 10mm crow foot or 1/4" socket/u-joint/extension for this to get under the fuel rail. A 3/8" drive isn't getting under there.

I could not find my 1/4" u-joint, so I'm getting another. The crow foot wrench worked, but a 1/4" drive would have been SO much easier and quicker.

I can't believe they cover up such a pretty engine with plastic. I'm sorely tempted to leave it off.
 
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