Good Cranking But wouldnt Start

[milkyway]

Mercruiser 1998 5.0 Alpha 1 220 2 Barrel Carb TV ignition

Last week i replaced the spark plugs but did not check timing., Idle seemed off but had no time. PCV pressure was about 17 psi on the valve tester. Boat ran ok but not excellent.

Last weekend, I changed the oil and oil filter. Removed the throttle cable. Ran the motor warm it up so i could set the correct idle speed and timing. After 5 minutes or before reaching normal temp, motor died. Primed the carb and Restarted twice with good cranking but did not start. Switched battery. Primed the carb , good cranking but no start. Checked battery cables and that end of the positive on the starter, all good and solid. Both batteries read 12.7 or 12.6 on my digital voltmeter.

I also connected the 2 wires on the fuel switch and the fuel pump did not run when i turned the key. Strange. But the fuel on the carb with the priming should be enough to start the engine and unitl for 30 seconds. "" That seems a different issue" from the starting problem.

So tomorrow I will test the ignition coil for spark and see if its good. Where else should i check?

Thanks.

 

[Don S]

Re: Good Cranking But wouldnt Start

Primed the carb and Restarted twice with good cranking but did not start.

Did it start when you primed it or not?

Check coil voltage on the + terminal. With the key on, you should show voltage on the purple wire at the coil, the alternator, and the oil pressure switch.

If you don't have any power on the purple wire, that would explain why jumping the wires together on the pump didn't work and why priming the carb didn't work.

 

[milkyway]

Re: Good Cranking But wouldnt Start

did it start when you primed it or not? ----- it did not start.

Check coil voltage on the + terminal. -- is this with engine cranking or not?

With the key on, you should show voltage on the purple wire at the coil, the alternator, and the oil pressure switch.--- will check.

If you don't have any power on the purple wire, that would explain why jumping the wires together on the pump didn't work and why priming the carb didn't work.

- i thought it would start as long as you can prime it with the throttle even if the fuel pump is dead.

 

[milkyway]

Re: Good Cranking But wouldnt Start

sorry for the wrong reply format. but here are the answers:

it did not start.

when checking the coil voltage on the + terminal. -- is this with engine cranking or not?

will check tomorrow on the voltages on the purple wire at the coil, the alternator, and the oil pressure switch.

i thought you could start engine as long as you can prime it with the throttle even if the fuel pump is dead.

 

[Don S]

Re: Good Cranking But wouldnt Start

when checking the coil voltage on the + terminal. -- is this with engine cranking or not?

No just key on, engine not running.

will check tomorrow on the voltages on the purple wire at the coil, the alternator, and the oil pressure switch.

This what is the key to all your troubleshooting right now. Gas is not the problem, ignition is.

i thought you could start engine as long as you can prime it with the throttle even if the fuel pump is dead.

It will, if you have gas in the carb, and spark. But if you don't have spark the engine will never start no matter how much gas you prime it with. When you jumped the purple and the purple yellow wires together and the pump didn't run when you turned the key on tells me you either have a dead pump, or you don't have power to the purple wire.
It's a lot cheaper (Free) to check for voltage on the purple wire than it is to throw a new $200+ pump on it and find it still doesn't work.

 

[Failproof]

Re: Good Cranking But wouldnt Start

You cant "prime" with the throttle if the carb is empty. If no power at coil, oil pressure or alt (purple wire) then that is issue. You could prime by squirting fuel in the carb throats.

 

[milkyway]

Re: Good Cranking But wouldnt Start

Thanks, Don. I hope to identify the problem tomorrow.

 

[milkyway]

Re: Good Cranking But wouldnt Start

Good morning., Here are the reuslts of the test, wit the key on run position:fuel switch - purple wire has 12.6 volts and started when jumped.alternator - purple wire has 12.6 voltsignition coil - purple wire has 12.6 s with black lead of tester connected to engine ground. however, 0 volts with the black lead connected to the negative lead of the ignition coil. what do you think is wrong?

 

[Don S]

Re: Good Cranking But wouldnt Start

wit the key on run position:fuel switch - purple wire has 12.6 volts and started when jumped.

Jumped to where? Did the pump start or the engine start?

Did you have spark?

 

[milkyway]

Re: Good Cranking But wouldnt Start

i did not start the engine at all. its the fuel pumped that ran after i jumped the wires. i will now check for spark in the ignition coil...

 

[milkyway]

Re: Good Cranking But wouldnt Start

connected the ignition coil to a spark plug tester and there was spark.started the engine, and it started and it ran for 10 minutes and reached normal op temperature. vacuum is 17 psi on idle and moves up to 24 when revved up. idle speed is 675. looks perfect.so what happened?was it the fuel pump? the pump did not energize when i jumped it last time but it did energize this time. loose connection? but the fuel pump is supposed to be working while the engine is runing (and without the aid of electricity) . so why did the motor die in the first place after 5 minutes and wouldnt start again? stupid question- could i have lost vacuum when i connected the pcv valve to the vacuum tester prior to running the getting the engine warm?wondering what casued this incident to avoid being strranded.

 

[Don S]

Re: Good Cranking But wouldnt Start

You probably have a bad (loose or corroded) connection somewhere.

 

[milkyway]

Re: Good Cranking But wouldnt Start

thanks Don for all the testing tips!! will double check conenctions.