awilson40

I dont know whats up but after doing the oil cooler seal job including changing the oil and coolant the car doesnt 'feel' as fast. Boost still hits 16psi at around 3300 rpm buts seems slower to build. I didnt undo anything in the intake or exhaust tract it just isnt as quick. I did some Gtech runs last week so I did some again and it shows the same thing. Down on power and TQ. What would cause the car to be down on power but still build the same PSI boost?
The car runs great otherwise, no other problems at all.

Heres a Gtech plot that shows last week vs this week.

Tom M'Guinn

Are you sure you did not knock a vacuum line loose somewhere? What did you remove and replace, and what is nearby?

awilson40

I have checked and rechecked. Idle vacuum is still the same and I'm still hitting the same max boost.
I didnt have to remove any vac lines or exhaust items to change the cooler seals. This is too weird.
I also cleaned the engine bay but am sure nothing got knocked loose and only used low pressure water to wash off the degreaser. I checked the diverter valve also just it case it ruptured.

fast951

Andy, few things to check just in case you haven't already.

- Dry distributor cap & rotor
- Plug wires
- Spray clean the AFM connector.
- Of course pressure test the intake system.

If nothing found. I'll start looking at the exhaust side for any leaks...

awilson40

Thanks, I'll start on the list.
Wouldnt water ingress also cause rough running??
I will probably also do a compression check just to see if I have lost a cyl.

fast951

Let's hope not! While checking things, check if the knock sensor is operating properly.. While at idle, tap on the engine, see if the idle changes some..

awilson40

Well John, I think I found it. Everything checked OK, compression good at all cyls.
While replacing the oil cooler seals I went around and snugged all the exhaust bolts within reach.
I noticed a very 'loose' exhaust manifold stud at the #2 cyl so I snugged it about 1/2 turn thinking all is well. Today I pressurized the exhaust and found lots of air leaking around the #2 flange. I checked the stud again and it was loose...really it was broken and my tightening it just finished breaking it.
So now what...its broken at the head with no room to drill the the stud out.
See the shiney and dull part of the stud...looks like it has been cracked for some time.

awilson40

So , not to be one to give up and I'm sure not going to pull the head at this time so
I fabricated a bridge clamp to let the #3 stud also clamp the #2 flange.
This one is made of 1/4 in flat stock. and it works great. I have no more leaking around the flange.
Still a couple of minor leakes under the heatshielding but not the huge amount I had before.
When I get to work I'll fab another out of tool steel and heat treat it.

fast951

It sucks that the stud broke off.. Hopefully your temp fix will work for a while.. As long as there is no leak, you are fine. If leaks develop, you'll have to fix it or risk buring a valve.

awilson40

Yep, Thats what had me worried. I will keep an eye on it.
Thanks for the help.