502 not firing on all cylinders/raw fuel in exhaust
#1
502 not firing on all cylinders/raw fuel in exhaust
Had a great day Saturday, boat ran awesome. When I was idling around the ramp I noticed that the engine was idling rough, tach was bouncing 200-300rpm, and I smelled fuel. I looked back and there was a sheen on the water that's never been there before. Seems to me like I have a cylinder that isn't firing properly, but I'm not set on that because the boat ran like a top until that point. (Don't they always run great before they explode?) Loaded it Saturday night and won't be able to see it again until Weds so I'm looking to grab all the potential tools I'll need to diagnose the issue.
I'm thinking timing light on the plug wire, or pulling plug wires individually to see if I can locate a plug that isn't firing, and doing a compression check for a hung valve.
Obviously fuel is getting to the cylinder, so I don't think that's an issue.
Engine is a 502, the only modifications are the removal of the VST, it was replaced by an Aeromotive pump and Hardin reg. Not sure of the hours because the meter doesn't work, so I'll be looking for a scan tool. All the other gauges were reading normal.
Any help is appreciated.
I'm thinking timing light on the plug wire, or pulling plug wires individually to see if I can locate a plug that isn't firing, and doing a compression check for a hung valve.
Obviously fuel is getting to the cylinder, so I don't think that's an issue.
Engine is a 502, the only modifications are the removal of the VST, it was replaced by an Aeromotive pump and Hardin reg. Not sure of the hours because the meter doesn't work, so I'll be looking for a scan tool. All the other gauges were reading normal.
Any help is appreciated.
#2
Registered
Start simple. Maybe just a bad plug or wire or cap? Can hope. Those caps rust, mine was a mess. I have a 96 502.
You ideas sound spot on to me. Ignition, compression. Easy checks too.
You ideas sound spot on to me. Ignition, compression. Easy checks too.
Last edited by Pismo10; 05-19-2014 at 09:56 AM.
#5
Registered
Start with K.I.S.S.( Keep it simple stupid.)
Check fuel pressure at the rail making sure your elec pump isn't doing something weird.
Then I would start with a basic tune up. Plugs, wires, cap & rotor. It's good maintenance practise any ways.
Check fuel pressure at the rail making sure your elec pump isn't doing something weird.
Then I would start with a basic tune up. Plugs, wires, cap & rotor. It's good maintenance practise any ways.
#7
90psi in cyl 5, 112 in cyl 6. The rest fell between 138-160.
What's my next course of action? Pull the heads?
I wonder how AFR's would do? Just stick em in, run through the summer, then add a cam and the rest.
What's my next course of action? Pull the heads?
I wonder how AFR's would do? Just stick em in, run through the summer, then add a cam and the rest.
Last edited by Cole2534; 05-22-2014 at 07:06 PM.
#9
Registered
That doesn't sound good at all. A leak-down compression test would be my next step if possible. If not, check manifold vacuum for pulsations and remove oil filler cap and see if it's huffing.
Maybe the injs got plugged-up. Eng went lean and detonation took out a few ring lands??
Maybe the injs got plugged-up. Eng went lean and detonation took out a few ring lands??