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Old 07-14-2020, 04:50 AM   #1
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Default 5.0 305 1999 3200 scr

Hey all,

Went ahead and did a tune up on both my motors, cap, rotor, plugs and wires with a buddy who knows a bit more than I do when it comes to motors. We attempted to get the idle down and took her out for a run. Port motor died after roughly 15 minutes of running WOT. When I let off the throttle she died and would not turn back on. Have done a compression test on almost all the cylinders except 1, back left. All around 125-135psi. I believe he did mess around with the timing, or atleast checked it with timing light.

She's getting fuel, and spark, but will not start up. Any ideas?

Thanks
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Old 07-14-2020, 11:19 AM   #2
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First WOT (wide open throttle) ~4400 rpm is a test rpm to ensure the engine is running good and proped correctly and should only be operated at for a few minutes. Running at this rpm for extended time can damage the engine.

When ever ignition parts are replaced the timing should be checked. Since itís not running you canít check timing now but you can set the engine to TDC and verify the rotor is pointing at cylinder one post on the cap.
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Old 07-14-2020, 11:25 AM   #3
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Forgot to mention being Thunderbolt V ignition you need to install a jumper to set base timing, the procedure is in the Mercruiser manual #24 which can be found under Documents of this site.
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Old 07-14-2020, 11:45 AM   #4
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Quote:
Originally Posted by mmwjr View Post
First WOT (wide open throttle) ~4400 rpm is a test rpm to ensure the engine is running good and proped correctly and should only be operated at for a few minutes. Running at this rpm for extended time can damage the engine.

When ever ignition parts are replaced the timing should be checked. Since itís not running you canít check timing now but you can set the engine to TDC and verify the rotor is pointing at cylinder one post on the cap.

My mistake, I meant we were running her full throttle. Would not installing a jumper allow us to adjust timing and have the engine turn over only to have it stop once the throttle was let off?
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Old 07-14-2020, 02:04 PM   #5
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Not installing the jumper to set base timing probably isnít the reason sheís not running but it is the proper procedure to set base timing. This system uses electronic advance. If you have fuel and spark the only other components for combustion are compression and timing.
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Old 07-14-2020, 04:04 PM   #6
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Went did the compression check on the last cylinder. They all range from 120-150. Most round 120, being said I pulled the oil cap and smelled a mix of gas and oil, upon pulling the dip stick I noticed its level is almost halfway up the stick. Smells of oil and gas. So thats not making me feel good. Checked the other other motor and its fine. Oil is at the correct level. I pulled the stick roughly 5 times just to ensure what I was seeing was correct.

After letting off the pressure from the last cylinders compression test the tester was coated with gas. Dunno if this helps at all either but figured cant hurt. Again thanks for the help.
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Old 07-14-2020, 04:43 PM   #7
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Being a 1999 it should have an electric fuel pump and not a mechanical one. The mechanical ones could have a ruptured diaphragm and allow fuel into the oil but they are double diaphragms to minimize this. Is this a carbureted engine? If so sounds like the carb is dumping fuel down its throat when the engine is off. Typically the float level being to high will cause this, may need a rebuild of the carb.

Sounds like a lot a fuel in the oil, this is an explosive situation and the oil needs to be changed ASAP!
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Old 07-14-2020, 05:32 PM   #8
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The fuel pump is electronic I had to replace it this time last year. Lots of gunk in there, gelled ethanol etc. I will drain the oil out asap, and replace. Recommendations on carb rebuild do it yourself or have a pro shop do it?
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Old 07-14-2020, 06:31 PM   #9
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Quote:
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The fuel pump is electronic I had to replace it this time last year. Lots of gunk in there, gelled ethanol etc. I will drain the oil out asap, and replace. Recommendations on carb rebuild do it yourself or have a pro shop do it?
That depends on you skill level. If itís a 2 bbl it rather easy while the 4 bbl carb requires a higher skill level.
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