[Tuckmac15]

I was working under my 1992 GTST and found what looks to be a crack in the lower intake manifold. No matter where I look I cannot find a replacement manifold like OEM. Is this a big problem? Could this be what's causing the car to lose torque and sputter at high RPM?

Thanks

 

[sparkso]

It looks like a crack but also follows the casting mark perfectly so could be a casting mark

If it is a crack then yes, a boost leak like that will give all manor of strange problems, stuttering and missfire like symptoms can all stem from a boost leak.

Does the car idle high as though it is drawing in air?

 

[Tuckmac15]

It looks like a crack but also follows the casting mark perfectly so could be a casting mark

If it is a crack then yes, a boost leak like that will give all manor of strange problems, stuttering and missfire like symptoms can all stem from a boost leak.

Does the car idle high as though it is drawing in air?

I don't know if it idles high but I don't think so. Everything sounds and feels great until I hit around 5000 RPM

 

[Dan92]

I'm not sure it's cracked. If it is, you can have it repaired - just find a shop that repairs aluminium. I would be concerned about the oil in that area (intake manifold only has air and coolant passages). You need to find the leak (possible head gasket issue).

 

[Tricky-Ricky]

That could easily be oil from another source, have you tried spraying carb cleaner or WD40 on it while running and see if the idle changes or if t gets sucked in?
If there is no change in the idle and you're only getting miss after 5K RPM do you see a drop in boost pressure when on boost at this RPM as if it was a crack it would leak as the manifold is pressurised...or off boost its less likely to leak on open throttle as there is less depression off boost .

 

[Tuckmac15]

That could easily be oil from another source, have you tried spraying carb cleaner or WD40 on it while running and see if the idle changes or if t gets sucked in?
If there is no change in the idle and you're only getting miss after 5K RPM do you see a drop in boost pressure when on boost at this RPM as if it was a crack it would leak as the manifold is pressurised...or off boost its less likely to leak on open throttle as there is less depression off boost .

I don't think that boost pressure actually drops now that I think about it. I haven't driven it in a while because I pulled the transmission and then caught COVID so as soon as the transmission is put back in I will test it to see if the idle changes.

 

[Tricky-Ricky]

Hope you're feeling better...sounds like you got away lightly from this nasty virus.

 

[Tuckmac15]

That could easily be oil from another source, have you tried spraying carb cleaner or WD40 on it while running and see if the idle changes or if t gets sucked in?
If there is no change in the idle and you're only getting miss after 5K RPM do you see a drop in boost pressure when on boost at this RPM as if it was a crack it would leak as the manifold is pressurised...or off boost its less likely to leak on open throttle as there is less depression off boost .

It idles at around 700-800RPM. It only starts feeling weird at 6000RPM. I also don't think that the fluid is oil. And when I cleaned the fluid with brake cleaner it does not come back until I drive for about 10 or so miles. The only time it losses power is when the manifold is pressurized.

 

[Tricky-Ricky]

So the staining comes back after a short drive? Have you checked to see if it's coming from another source? The trouble is coil pack breakdown also shows up when the engine is under load, so it might be worth checking or changing the coil packs before thinking about removing the manifold and getting it welded.