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Exhaust leak |
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ducane 
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Joined: October-01-2020 Location: utica ny Status: Offline Points: 6 |
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 Topic: Exhaust leakPosted: October-01-2020 at 10:16am |
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Original owner of 1991 Excel with about 1250 hours. PCM 351w Ford. Boat has been trouble free until this summer. Ran fine in the beginning of the summer but about a month in it developed a tick which I first thought might be a valve tap. Ran the boat with valve covers off and no sign of looses rockerrs or pushrods. However shortly after I discovered very high concentrations of CO in the engine compartment. Deadly concentrations. Pulled both manifolds and riser elbows which were in perfect condition. Gaskets were fine. Compression check showed 134 to 136 psi in all cylinders except #1 which showed 120 psi. No sign of water in the oil although there did seem to be more than usual smoking or condensation from the exhaust.. Before I pull the heads which i'd rather not do, any suggestions would be appreciated.
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ducane
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Posted: October-01-2020 at 2:52pm |
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a revision. The #1 is 141 all the others are 150 on the nose
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11059 |
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Posted: October-01-2020 at 5:51pm |
Does this mean the riser gaskets and the exhaust manifold to head gaskets were all fine. I don't think I've ever taken off an old exhaust manifold to head gasket and had it be "fine" Same for the riser gaskets. Especially 29 year old gaskets.  As a start, I think I'd make sure all the sealing surfaces are clean and put the manifolds and risers back together with new gaskets and then reinstall them on to the engine with new gaskets and see if the tick is still there If you have all that CO build up while it's running I'd be checking the ventilation hoses, vents into and out of the engine compartment because there should be plenty of fresh air flow through there while the boat is moving.
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ducane
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Joined: October-01-2020 Location: utica ny Status: Offline Points: 6 |
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Posted: October-02-2020 at 1:59pm |
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That's exactly what it means. Gaskets and manifolds, risers all perfect. CO level was measured at 800 PPm at dock. The tailpipe exhaust from my car is only 200PPm. After tearing it down as far as the intake manifold I found a black oily deposit on the intake , the carb spacer and the brackets that supports the sky pylon. This would appear to suggest that the leak is related to the intake manifold either a crack or a leaking manifold gasket. In the beginning of the summer I replaced the carb due to some issues with the old one. I know that the new one was running rich. That would cause higher co but not a leak. At this point I'm about to remove the intake manifold to see what's happening there. Thanks for the reply. BTW I've removed and reinstsalled the exhaust manifolds and risers three times so there not the problem. Also the CO was measured with the sun deck opened.
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SNobsessed
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Joined: October-21-2007 Location: IA Status: Offline Points: 7102 |
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Posted: October-02-2020 at 3:01pm |
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Well, if there is an intake manifold leak, that would be sucking gases in, not expelling them. So that doesn't sound like a plausible CO source to me. Is it possible you have a leak further downstream in the exhaust system? Maybe if it is in top of muffler it wouldn't spit much water. Another possibility could be the PCV hose leaking. |
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“Beer is proof that God loves us and wants us to be happy.”
Ben Franklin |
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ducane
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Posted: October-02-2020 at 3:37pm |
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That's what I thought too but a mechanic friend said it's possible that internal engine pressure could force it out of a crack or bad gasket. Removing the intake soon so will know before long.
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11059 |
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Posted: October-02-2020 at 4:16pm |
Here are a few things for you to think about You have a v drive and the hatch was open sitting at the dock. People have gotten sick and or died from CO poisoning sitting in the back seat of an idling inboard...........the same spot your engine is sitting. With your hatch open, and a rich idling engine, those gases can curl right around and into the boat and give you false indications of a leak from the engine. Just 'cause I was curious I took a portable CO detector out to the boat and set it on the back deck, started it up and the detector alarmed within a few seconds and kept climbing till it got to 999 ppm which was as high as the detector can read. It didn't take long at all to hit that 999 either It was a good actual check of the detector Since you're tearing further into the engine on the intake side, it's probably too late to say "put it back together and check the levels of CO with the hatch closed. If your EGR system is working right, there's no internal engine pressure. Like SNObsessed mentioned, with vacuum on the intake when the engine is running a leak would be into the engine, not out. Since CO is a byproduct of combustion, it's kinda hard for it to get in through the intake side of the engine. I guess I'm assuming your engine runs good, hitting on all 8, and just has a tick, since you didn't say anything else about other problems Maybe your "tick" is from something bolted to the engine like an alternator or water pump with a ticking bearing unless maybe you've checked them and didn't mention that |
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Gary S
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Joined: November-30-2006 Location: Illinois Status: Offline Points: 14096 |
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Posted: October-02-2020 at 4:29pm |
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Ken you also didn't mention that the co level of a 1991 Excel is going to be way different than a fuel injected O2 sensed catalytic equipped car - unless he's still driving something from the 60's early 70's ;)
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ducane
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Posted: October-02-2020 at 5:15pm |
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Thanks for the advice. the reason that I checked the CO level in the first place was because of the extremely strong odor of exhaust in the boat which we never had before. The ticking was almost certainly indicative of an exhaust leak. I checked for lifter problems. Even ran the boat with the valve covers off. No problems there. I had a friend who is an automobile mechanic come over and ran it for him. He was pretty certain it was and exhaust leak. He also smelled the exhaust. The sooty carbon deposits on the intake manifold need to be accounted for as well. Thanks again.
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8122pbrainard
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Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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Posted: October-02-2020 at 5:16pm |
The smell?
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ducane wrote: