Hi all,
I wanted to share my recent experience with the replacement of intake manifold gaskets on my 91 LB9 TPI M5 formula.
I bought this car last February from a guy in northern Iowa who used to drag race the car. Not long after I noticed that I was loosing coolant. I checked all of the obvious places for coolant leeks, heater core, water pump, thermostat housing, hoses etc, until I noticed a small antifreeze leek at the point where the intake manifold meets the driver side engine head, just below the thermostat housing. Since no coolant was getting into the engine oil, I added some bars stop leak, and drove for about 7K miles, until the leek started again. Thus, I decided that it is time to fix the problem.
I took the car to a reputable shop to do the job, and they estimated that it would cost $650 to get it all done, including coolant flush, fresh oil change, and new thermostat. It sounded just fine.
It took the shop two whole days to do the job. Apparently the old owner had put his hands into the intake and had broken two bolts that hold the intake runners to the lower intake manifold near the back of the block. The shop I had my car at struggled in the small space back there to remove the bolts, so that they could disassemble the intake.
So $850 later I have my car back, and it seems to run OK. However, I have a noticeable exhaust leak from the pipes that are going into the two catalytic converters.
How much of a loss in back pressure and low and torque would such a leak cause on a 305 LB9?
The car feel a little bit sluggish after the repair, and I wonder if that might be contributed to the exhaust leak, or some other problems with the intake.
Any help is much appreciated.

 

Honestly, I think there is something else wrong here. I have a small exhaust leak on my LB9 aswell. But I'm not sure where mine is. I'm not sure if its on the passenger side header, or on the header flange. But eitherway, I have not noticed a decrease in performance, just the loud ticking noise produced...
good luck

 

The leak was there before it went to the shop correct? Removing the intake shouldn't have affected the exhaust at all. If it feels like it's down on power its probably timing related since they had to remove the distributor. It's possible that they didn't set the timing correctly.

 

I'm not sure what the factory base timing spec is for an LB9 but 10BTDC sounds about right.. It should be on a sticker under the hood. It's possible that the guy you bought it off of bumped the timing up a little to give it a little bit more ***** and shop simply set it back to the factory spec..

 

The leak was there before the repairs, however it was much less. I think that when they put the car on the lift to rotate the tires and replace the fuel filter, they accidentally worsened the exhaust leak. Now you can hear a bit of ticking sound coming from the pipes before the cats while the car is cold. When the car warms up in a few minutes, the leak becomes less apparent.
Top end power does not seem to have been affected much, low end torque seems a bit lower.

 

it is possible that it's the problem and you gotta fix it anyway so fixer up and let us know if it solved the problem

 

it sucks u paid 650 bucks to do it, the intake on tpi is NOT bad to do

first time i did myn it took me less than an hour to take it of.

 

Well,
I have bigger problems now. After the shop replaced my intake manifold gasket, I have been losing both coolant and oil. I can see oil dripping near the back of the block, near the oil filter. I don't see where the coolant is going, but I have had to add a quarter of a gallon in the last 80 miles. Prior to deciding to fix my leak I only had to add 1/4 of a quart every 3000 miles. Looks like they not only charged me 850 but did not do the job right.
I just dropped the car off at their shop, but there is nobody there, and I don't know if there will be somebody there tomorrow. Maybe Wednesday after Christmas would be the soonest they would be able to get back into it.
I am worried that these people are incompetent to do the repair properly. I will let you know how this whole ordeal turns out.

 

they must be pretty bad if they can screw up something as simple as intake gaskets..

 

I would take it to a gm dealer ship and have the shop pay them.

or do it your self and get a refund

 

The GM dealership is a good suggestion. I will see what the shop says when they take a look at the car. I hope the GM dealership still has people that know how to work on engines this old. I have not had the best of experience before with GM Goodwrench.
The people I took my car too pride themselves on quality. They are called A to Z auto in St. Louis. I have used them before for service on my other firebirds. They used to have a very good mechanic that rebuilt the heads on a 3.1L v6 firebird I used to have a long time ago. He did a great job. Unfortunately that mechanic left, and I have not had any experience with the new mechanics at this shop.

 

So I think the problem with my intake is finally resolved. The oil leak that I was having was coming from the oil filter. The filter was defective, and was not sealing properly, causing oil to leak. The coolant disappearing problem was caused by large air pockets in the engine that finally got themselves worked out.
The people at the shop did a coolant die test, that looks at the presence of combustion bi products in the coolant, and everything seemed fine. I took the car for a nice long drive today and it ran fine. Hopefully things will stay this way.

 

I'm glad you finally got the issue resolved...as you might have feared, it would have been a big PITA if it indeed was a botched job...

I agree on the filter. I've had that fear before. There was oil "residue" on the back bumper and spoiler, I thought it was a faulty oilpan, or oilpan gasket, but thankfully it was only a crappy fram oil filter...now I just pay extra for the K&N...

 

The filter I was having problems was Fram. I didn't know that K&N made oil filters. Where do you get yours from and what to they run?

 

most autoparts stores carry em, Advance Autoparts, O'rileys, Auto Zone, Etc. They're good filters, kinda overkill, about 10 bucks for the big 1. Mobil 1 filters and good ol AC Delcos are also good.

 

yeah, they usually do run $10-$12 at an autoparts store, but I figure if they make their oil filters as good as their air filters, then its worth it. Optimum lubrication is always a plus... I'm pretty sure filter number is 2002 for our cars...