7.4L Merc wont start

mBurns

Cadet
Joined
Apr 7, 2016
Messages
26
Was out on the water, got about 3/4 mile from the dock, throttled down to pass a little fishin boat, (from about 3000 RPM to about 800). went to throttle up - usually to around 1200 (quicker idle with minimal wake), and I looked over at my RPM, and it was at 0.

Turned the key, and crank, crank, crank, crank... no fire. pulled the top of the carb off, and I saw fuel when I opened the throttle, so it's getting fuel. checked the main line on the distributor, got spark.. pulled the plugs, they looked ok.. little bit of carbon, (consistent with ~1 year old plugs).. hooked up my portable jumper to boost cranking current, still nothing. There was a disconnected wire on the port side of the block, near the bilge, 1 of the guys onboard said it might be an oil switch? anyway, we hooked it back up, and when i turned the key, I got an alarm. alarm was solid until I turned the key off. 1 thing I'm curious about - with the key in run, oil pressure was at 0. maybe a bad oil pump? or do I only have pressure when the pump is running?

anybody have any ideas on what else to check?
1995 7.4L Merc w/ Bravo 3 - (not the MPI)
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
42,587
As a carb 7.4 there are three things that can give you a solid alarm, oil pressure low, drive lube low, and over heat temp.

In most cases when the key is turned to ON, you will hear the alarm first thing before the motor is cranked. This is caused by the oil pressure switch is at 0 psi. Once started or after a bit of cranking the sound will stop from turning over.

Could be the wire disconnected was the pressure switch and now it's working like it should. Either way I don't see the oil pump being the issue.

Need to see if your getting spark
 

mBurns

Cadet
Joined
Apr 7, 2016
Messages
26
little bit of corrosion in the distributor cap - changed it, fired up right away - absolutely terrible idle, little bit of knocking, stalled out after a few seconds. Did it 2 more times. Then decided to check compression. 110, 60, 0, 95, 0, 105, 125, 30.

^ ^ lovin' life right now..
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
42,587
little bit of corrosion in the distributor cap - changed it, fired up right away - absolutely terrible idle, little bit of knocking, stalled out after a few seconds. Did it 2 more times. Then decided to check compression. 110, 60, 0, 95, 0, 105, 125, 30.

^ ^ lovin' life right now..

Ouch, that's a bummer
 
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