formula90

i have a exhaust leak in my mani. and i believe it is being picked up as spark knock by the sensor. is this right? can this happen. Also, how hard is it it take the exhaust mani off and put a gasket in?


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Andy89RS

I'd have to say no, the knock sensor will not pick up an exhaust leak as detonation. Detonation is a completely different frequency, and is also created inside the engine itself, it's not an external sound. As far as replacing the gasket, the worst part is just getting to all the bolts. Remember, after you tighten the manifold you need to start the car up, get it to normal temps, let it cool again, and retorque the bolts. Recheck torque after a couple of hundred miles, if they're all still snug then you should be good to go.

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Jester

My guess would be yeah. I don't think knock sensors are really that picky. replace the gasket just to he sure anyway.

Kevin G

Yeah, it is very possible for a knock sensor to pick up false knock from an exhaust leak... It has happened on my car. When replacing the gasket,take all the bolts out except you can leave the 2 outer manifold bolts on and just loosen them.. This will hold the manifold in place while you slip in the gasket



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zippy

exhaust leak will not be picked up by a knock sensor, but it can cause spark knock. if you want the manifold to seal, don't use a gasket.

89RS355

I had a header leak that id result in false retard that went away after repair of the manifold gasket.
It's funny that you mention "don't use a gasket" I am currently rebuilding the turbo on an 88 Merkur. When I pulled off the manifold I was surprised to see no manifold gasket. Metal to metal. I called around looking for a gasket, and finally one of the turbo guys mentioned it was made to be like that, and if I wanted it to leak, put a gasket on it, lol! Just make darn sure everything is smooth and straight.

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Eggplant Jeff

Well I'm using gaskets on my driver side manifold and no leaks. I had a leak which is why I put the gaskets on. I removed the manifold, cleaned the sealing surfaces, and reinstalled with felpro gaskets from Autozone. Worked great! I'm currently doing the same thing for the passenger side... However getting the driver side manifold off is a walk in the park compared to the passenger one.

I would DEFINITELY recommend cleaning the manifold and head surfaces (with mild sandpaper) to remove carbon deposits. No point in doing all that work just to have another leak because the surfaces weren't smooth.

Oh and the difference in work between loosening all the bolts and removing them is very small. It might take you another 15 minutes to get the manifold all the way out rather than just loosening it. The hardest part is getting the damn bolts broken loose that first 1/4 turn.

FastBroker

Retorquing the bolts after a few hot/cold cycles is mandatory, too. You won't believe how loose they'l be after a week of daily driving...

Kevin G

Well, yes it will , very simply, it causes vibrations that the sensor WILL pick up. Where are you getting your information from?? I have personally seen this many times...... causes spark knock??? explain some more can you??
Now dont use a gasket??? Again, where do you get your information....doesnt make sense.

Most engine rebuild kits come with manifold gaskets.. even thought they didnt come from the factory with them. The reason is sometime when manifolds get older, they slightly warp, and a gasket will make up the difference and seal the manifold. I have installed at least 30 different sets on cars , some of which would have leaked without them.

Matt98SS

even if the exhaust is rattling/banging somewhere it will be picked up by the knock sensor

I agree on using gaskets on headers. THe flanges to the heads are so much thinner and warp easier than the big *** cast iron manifolds.

Matt