Intake Manifold Gasket Vacuum Leak

[marklj]

Have a few thousand miles now on my ’88 DX since the cylinder head repair. (Had run hot and blew the head gasket)

Been running well and had a nice smooth idle. For the past week started noticing the idle was not as smooth and idle speed had dropped. Initial diagnosis indicated that the carburetor had gone very lean. Idle speed would pick up about 500 RPM when sprayed with a little carburetor cleaner. Examined every vacuum line and pinched off all lines one at a time and did not find any vacuum leaks.

Pulled the carburetor off to remove the metal plug over the idle mixture screw. Backed the idle mixture screw out a couple of turns and reinstalled it. Idle was better but still very rough. Adjusted the idle mixture screw until peak RPM was achieved. Idle speed would still pick up about 300 – 400 RPM when sprayed with a little carburetor cleaner. Checked for vacuum leaks again – all hoses checked OK. Sprayed some carburetor cleaner right at the intake manifold gasket and found it has developed a vacuum leak, seems to be worse at cylinders 2 & 3. Loosened the two brace screws under the intake manifold and tightened all the nuts on the intake manifold. (The bottoms ones are fun to get to.) But did not find any really loose and the vacuum leak remains.

So I will need to replace the intake manifold gasket. But I’m wondering about a few things.

First, how did this happen? I cleaned both the head and the intake manifold mating surfaces. Torqued the intake manifold nuts in the specified sequence and to the specified torque (16 lb-ft) while the cylinder head was still off the engine. Gasket was from a Fel-Pro head gasket kit.

Second, is there enough give in all the hoses to pull the intake manifold back enough to fit a new gasket in place?

Any other suggestions to make this a successful and lasting repair? All suggestions are welcomed.

[Dr_Snooz]

Here's what my intake gasket looked like when I took apart my LX-i.



I had blamed the last shop that worked on it for this (they did PCV work) but after the rebuild, I notice that the gasket I installed is doing the same thing, though not as bad. I too installed a good gasket according to FSM spec.

I think there are two things going on. One, the thin paper, factory gasket is not that great to begin with. Two, it is even less great after sitting for 24 years on the parts store's shelf. I'm noticing that a lot of the "new" parts I get for the car show signs of being every bit as old as the parts I'm replacing. Though I installed a good gasket on my car, it was so badly deteriorated by the time I installed it, it is disintegrating in place. I've replaced a couple of "new" oil seals too for the same reason. They just don't hold oil when they are a couple decades old, even if they were never used.

I am going to start using a lot more RTV when I put things back together.

[marklj]

Here's what my intake gasket looked like when I took apart my LX-i.

I had blamed the last shop that worked on it for this (they did PCV work) but after the rebuild, I notice that the gasket I installed is doing the same thing, though not as bad. I too installed a good gasket according to FSM spec.

I think there are two things going on. One, the thin paper, factory gasket is not that great to begin with. Two, it is even less great after sitting for 24 years on the parts store's shelf. I'm noticing that a lot of the "new" parts I get for the car show signs of being every bit as old as the parts I'm replacing. Though I installed a good gasket on my car, it was so badly deteriorated by the time I installed it, it is disintegrating in place. I've replaced a couple of "new" oil seals too for the same reason. They just don't hold oil when they are a couple decades old, even if they were never used.

I am going to start using a lot more RTV when I put things back together.

Wow. Thanks for the picture. Good idea about the RTV. I think I'll swing by the Honda dealer and pick up an OEM gasket instead of the Fel-Pro. Maybe made with better lasting material?

Also I was thinking that the machine shop resurfaced the head and I never unbolted the bottom screws for the manifold brace and maybe there was a bit of misalignment as a result. But it is probably so minuscule so as not to matter.

Still wondering if is there enough give in all the hoses to pull the intake manifold back enough to fit a new gasket in place? Suggestions?

[marklj]

Ordered the OEM intake manifold gasket from the dealer.

gasket, in. manifold
Part #: 17105-PH3-S00

$30.66 versus $4.99 for the one from Autozone. Hope it is worth the difference in price.

[2oodoor]

Snooz your's actually looks pulled some judging by the top middle stud holes.

This looks like a good cause to use two gaskets to take up the crush room from a mildly untrue surface on the intake manifold.

[POS carb]

it's hard to judge the gasket like that because it could have ripped while separating the intake manifold.
OEM (Ishino) intake gaskets are not worth $30 (I can get them for $3!). The dealership is a ripoff. I am using a felpro with no issues.
As far as the job, it is a huge PITA because it seems everything is in the way. It will not be an easy job on a stock carb. Beware of the PCV chamber hose (the one the valve sits in), it is a tapered hose (different size on one end vs the other) so you better have a spare available.
I think you are correct in assuming you have a vacuum leak. if you take off the intake leave the carb on it and don't turn it upside down, the stock carbs have issues with the floats getting stuck open

[2oodoor]

true^^^
the intake nuts are pretty hard to access, the worst ones being the two lower on the passenger side. It takes a really short, thin socket which you can either make out of a spare socket by grinding it down or you can buy those at a good tool source.
One of the things I did when I made the Egrodomy intake was cut a place clear to the hole for using a regular socket and extension.
On the EFI cars those are hard to get to even with the motor out of the car zomg...gazinga

[Dr_Snooz]

it's hard to judge the gasket like that because it could have ripped while separating the intake manifold.

This is what it looked like before I took it apart.



I had a massive vacuum leak and it ran awful. I got 26 mpg vs. the 32 I usually get.

Here's the original thread.

[marklj]

Picked up the OEM Honda gasket today. It’s orange and looks thicker that the Fel-Pro grey paper gasket. Also picked up a ¼ flex drive ,a ¼ 12 mm socket, and a tube of Permatex Sensor-Safe Blue RTV Silicone Gasket Maker.

The PCV breather hose is brand new. The original one was rock hard and crumbled when I removed it during the last cylinder head repair.

Hoping I can pull the intake manifold back enough the install the gasket without removing all the hoses. One way to find out…

[Pnem3]

Wow, my car is running like crap now with poor fuel economy and terrible idling. I'm thinking that the intake gasket is about the last thing I haven't checked. I hope it isn't too bad of a job if I have to take it on.

[Dr_Snooz]

My gasket actually started whistling at me. That's the only way I found the leak.

@marklj: Honda had a special tool for removing the intake on the '76 Accord. It was just a specially shaped box end wrench that fit down between the runners to get the two most difficult bolts. It might be worth finding out at the dealer if a special tool exists for the '88s.

What condition is your PCV system in?

[marklj]

Mission accomplished! Intake manifold gasket has been replaced, carburetor is no longer lean, and idle is smooth again.

I was able to replace the gasket without removing all the hoses. I unscrewed the metal air tube from the air valve. The EGR tube was unscrewed at both ends. To get to the bottom intake manifold nuts I removed both intake manifold braces and the oil filter. The 12mm ¼” drive socket and flex drive proved to be too tall to fit on the nuts. I was to remove the nuts with a 12 mm 3/8” drive flex socket and a 6” extension.

One trick I found was once the intake manifold had been moved about the length of the studs, you can move the EGR tube out of the exhaust manifold port and this allows the intake to move enough to clear the studs.

After carefully scraping the old gasket off and making sure both mating surfaces were absolutely clean, I used a pry bar and a block of wood on top of the valve cover to hold the intake manifold clear of the studs and position the new gasket in place.

Based on what I saw off the old gasket, I decided NOT to use any RTV. My thinking is that RTV might encourage the gasket to move during the thermal cycles. The OEM Honda gasket lines up much better than the Fel-Pro.

Links to pictures:

http://i449.photobucket.com/albums/q...11123-0912.jpg

http://i449.photobucket.com/albums/q...11123-1045.jpg

http://i449.photobucket.com/albums/q...11123-1045.jpg

http://i449.photobucket.com/albums/q...11123-1058.jpg

http://i449.photobucket.com/albums/q...11123-1212.jpg

http://i449.photobucket.com/albums/q...11123-1414.jpg

[marklj]

My gasket actually started whistling at me. That's the only way I found the leak.

@marklj: Honda had a special tool for removing the intake on the '76 Accord. It was just a specially shaped box end wrench that fit down between the runners to get the two most difficult bolts. It might be worth finding out at the dealer if a special tool exists for the '88s.

What condition is your PCV system in?

Yep, mine was whistling too.

If I had to do it again, I would try a 12mm 1/4" flex socket as the socket and add on flex was too long.

PCV system is in good shape. PCV valve is clear and rattles. Good strong vacuum at the PCV valve.

[Dr_Snooz]

I'm just finally seeing this thread since you finished the repair. I think the OE Honda gasket is definitely the way to go. That's first rate work there.