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Discussion Starter #1
hello I need help I own a 93 Sentra with the ga16de. I'm having an issues where the car cant get over 85 mph and when I push it to that speed for a long period of time like on an interstate or running on a track the exhaust manifold where the o2 sensor sits and about half of my manifold pipes and my downpipe gets CHERRY RED HOT. everyone is like "oh your cats clogged" well that'd be a great fix except I don't have one the exhaust is straight piped except I do have a muffler. timing is perfectly spot on. fuel pressure was a little weak so I changed the regulator and no change. I'm afraid that if the manifold continues to get red hot like this it will do some serious damage to my block. temp gauge never moves from normal operating temp so if anyone has any idea what to do or what to check for next that'd help a crap ton

car has 130k miles and is all stock expect for a CAI and the straight piped like I mentioned
 

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Sup Mod keeping the peace
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The engine is probably running with an extremely lean mixture which might indicate that there's a major vacuum leak in the intake system. To check the intake system for a vacuum leak, attach a vacuum gauge to a full vacuum source. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be 21 InHg. If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.

What was the fuel pressure reading? The readings at idle should be as follows:
- with vacuum hose connected to the fuel pressure regulator: 36 psi
- with vacuum hose disconnected from the fuel pressure regulator: 43 psi

If you replaced the pressure regulator with no change, then the fuel pump may be marginal. Also the fuel filter may be plugged up.
 

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Sup Mod keeping the peace
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Well if the vacuum reading is around 20 InHg, then there's no vacuum leak. Other things that can cause a lean condition are a restriction in the exhaust, restricted/plugged up catalytic converter or a retarded ignition timing condition.
 

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Discussion Starter #7
Well if the vacuum reading is around 20 InHg, then there's no vacuum leak. Other things that can cause a lean condition are a restriction in the exhaust, restricted/plugged up catalytic converter or a retarded ignition timing condition.
timing is perfect and don't have a cat
 

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NF Mod/Nissan Master Tech
2006 Pathfinder LE, 2003 Frontier SVE
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I once worked on a Nissan years ago that had the baffle plate inside of the muffler rot off inside and fell to the back of the muffler, blocking the exhaust flow out of it. I had another where apparently someone didn't like the guy and they jammed a potato about 12" up his tail pipe. Just because it has straight pipes, doesn't mean it can't be restricted. It wouldn't hurt to do an exhaust back-pressure test to be positive that it's not the problem. If you can get access to a scan tool, looking at oxygen sensor voltages and fuel trim would probably give some clues. GA16DE engines also had some issues with the upper chain tensioner guide failing causing timing to jump. If you hear any chain rattle at the upper chain, it may be worth taking a look at, or at least do a compression test.
 

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Discussion Starter #11
Back pressure is fine and so is timing and no chain rattle plus when we straight piped the car the baffle was broke in the muffler it rattled like crazy so we replaced the muffler the weird thing is the car runs great! Amazing in fact! Got all the punchy little low end power and the engine loves to rev! It's just got little to no power after about 83 mph the needle just wont move and then the manifold gets red hot I'm stumped i dont know what it could be ?
 
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