Spark, fuel, and air right???

[cdre]

For some reason I can't get my mercruiser 5.7 to start.<br /><br />Background- It started life as a '91 5.0 and I upgraded to a 5.7 when I rebuilt it (new short block). Saltwater cooled, 4 barrel carb, A1 outdrive, Thunderbolt ignition.<br /><br />It was stalling whenever I shifted, so I tried to adjust the idle speed on both the carb and the cable(not yet knowing of the shift interrupter switch). I got it running well enough to shift into forward and head toward the dock at a few RPM above idle (no wake zone).<br /><br />About 5 minutes later, it started sputtering. I pushed on the throttle in an attempt to keep it running, and it kept it going for a few seconds before it died. I tried to start the engine, but my battery was completely dead. <br /><br />I'm guessing I need to check my alternator, but I cant get the thing started again. <br /><br />I charged the battery and the engine seems to be turning over pretty well, although maybe a little bit slow. I tore down and cleaned the starter, but the engine is still turning a little slow... should be fast enough for it to start though. Turns over very well when I put my battery switch on "Both," so I am assuming my batteries are dying a slow death. <br /><br />I have a good spark (as indicated by my spark plug tester light and the good jolt I got while holding it). Air is good. And I believe fuel is good (I changed my filter and checked the check valve on the tank). I removed the #2 spark plug and put my finger over the hole to feel for pressure with good results (I dont have a compression tester). I didn't see any water in the oil when I pulled the dipstick. While trying to start it, I sprayed both carb cleaner and starting fluid, but I couldnt get so much as a sputter out of the engine. <br /><br />I am assuming the starting fluid should have been a good substitute for fuel to at least get a stutter (assuming I had a problem with my carb or fuel delivery). I also tore down my fuel filter to check for tears in the membrane, and it was good to go. <br /><br />I can't thing of what else might keep it from starting. Any suggestions?

 

[tommays]

Re: Spark, fuel, and air right???

it sounds like you tried eather(starting fluild is pretty hard on the motor)which means you dont have ignition or the motor is cranking over much slower than you think<br /><br />if the batterys are weak its really hard to have good spark<br /><br />i am not sure of the things you have done but i would check the spark more carefully because the starting fluid should have given some sign of life<br /><br />if you adjusted the cables the shift int stops spark if out of adjustement<br />tommays

 

[cdre]

Re: Spark, fuel, and air right???

Thanks for the quick reply, Chief.<br /><br />The lack of combustion with starting fluid blows me too. I bought a little spark tester (the one you put inbetween the sparkplug and the wire) and I was watching the light flash like it should when I sprayed the fluid in the carb, so I am not too sure of what is going on. <br /><br />Is it possible that some kind of internal damage could cause a problem like this?

 

[Don S]

Re: Spark, fuel, and air right???

I would pull the plugs and check for water in the cylinders. If there is, when the water gets on the plugs they won't fire. Period.<br />During all your work, were the manifolds and risers check and where the gaskets surfaces in good shape (Shiny metal, not black).

 

[qaztwo]

Re: Spark, fuel, and air right???

I would pour some gas down the carb and crank. If still no good. Would pull the dist. cap and verify that the rotor is pointing to the right terminal. If thats all good would pull a spark plug and run a jumper wire from the spark plug to the engine, or hold it to the engine and visually confirm that the spark plug is indeed producing a spark.<br />Good luck.

 

[cdre]

Re: Spark, fuel, and air right???

Hmmm... water in the cylinders sounds like a reasonable solution. I pulled a few of the plugs and they were a bit wet, but I was thinking it was from unburnt fuel. When I rebuilt the engine, I sandblasted the exaust risers. Now I am thinking they may have failed on me. Hopefully I havent caused any serious hydrolock type problems. <br /><br />Is there any way to be sure it is water and not just fuel? I guess I could try to burn it off of the spark plugs with a lighter...<br /><br />If I do have water in the cylinders, what is the best way to ensure they are clear and ready to go again? Just pull the plugs and maybe shoot some compressed air?<br /><br />Anyone know of a good source for exhaust? I assume buying used ones from my local boat junkyard is a waste of time.<br /><br />Thanks for your help, so far, Chief. As a SWO, I learned pretty quickly that you guys tend to know what you are talking about occasionally.

 

[Don S]

Re: Spark, fuel, and air right???

It's really easy to check the plugs for water, especially if your hands are oily. Just pull the plugs and tap the electrod on the palm of your hand....water will bead up, gas will spread out an soak in.<br />Even if it's gas on the plugs, I doubt you would get the gas to light.<br />Risers and manifolds are really expendable items and have a normal life of 5 to 7 years with normal use. Used ones are there for a reason....they were replaced because someone knew they were close to the end of their life or the engine died for unknown reasons....may even be water in the cylinders. Would you trust them?

 

[steve n carol]

Re: Spark, fuel, and air right???

Cdrec, you wrote;<br />

when I rebuilt it (new short block).

It's possable that water may be entering your engine from other areas. <br />Before you pull the manifolds you may want to read what 'tommays' posted on mercruiser bulletn about this. search his posts and read it. (in the last month or 2)..sl

 

[deputydawg]

Re: Spark, fuel, and air right???

First thing you need to do is make sure you are getting full power from the battery. It is very hard to make a good daignosis with a weak battery. <br />next make sure the plugs are firing. Sounds like you tested the wires, now check the plugs. While at it do what is said here and look for signs of water intrusion. If that is good, then check timing. Timing should never just go out of range far enough to kill the engine like you said. But check it anyway, just in case.<br />The holding the finger in the hole compression test, although it can be fun really means nothing. Cpmression leakage will take the path of least resistance, which would be around the finger.<br />If you verify good spark, good engine cranking, good timing, then verify you are getting the right amount of fuel.