2001 21v Merc Mag MPI - Sputters / Cut's Out Under Heavy Load

[chopper515]

When surfing with full ballast, it will occasionally cut out or sputter. Any ideas? I've only been running non-e fuel for the last 2 summers.

Replaced in the last year
fuel pump
fuel filter
plugs and wires
distributor cap and rotor
distributor sensor (3-wire)
coil
fuel tank anti-siphon valve
fuel injectors

Planning on testing
MAP sensor
fuel pressure regulator

I found a couple of pretty good videos on how to test these.

https://www.youtube.com/watch?v=fGQa...V3OFz-gz72NB0n

https://www.youtube.com/watch?v=DWtEmYBoS4g

[chopper515]

I tested the MAP sensor and fuel pressure regulator and they check out. However, I got a new fuel pressure gauge (I didn't feel my harbor freight model was giving me accurate readings) and low fuel pressure might be my issue. It's running at around 22-24 psi with the regulator vacuum attached and it jumps to 32 psi when I remove the vacuum which tells me the regulator is doing its job. I need to be at 32 psi or so with the vacuum connected. Since the fuel pump and anti-siphon valve are new, I'm going to check the voltage drop to the pump. If that's OK it almost has to be a clogged fuel line.

[chopper515]

Gumby,

I've read a few different posts that mentioned 30 plus or minus 2 psi. If I had 28, I could rule out fuel pressure.

I didn't find any specs. I just confirmed that the voltage dropped when the vacuum increased. So it's functioning but I suppose it could be out of spec. I guess I assumed if it was a bad sensor, it would be obvious and wouldn't fluctuate at all.

I just checked the voltage drop to the fuel pump and it's only around 0.2 volts on each the positive and negative sides. Well within spec. I was kinda hoping for a large negative voltage drop so I could just fix the pump ground. Oh well, I guess I have to pull the cool fuel system and blow out all of the fuel lines which is the only thing really left to check.

[chopper515]

Well everything checked out. All the lines seemed fine along with the tank vent. While I had the cool fuel system out, I decided to throw the old OEM fuel pump back in. I recently replaced the OEM pump with one from fuelpumpfactory.com while chasing another issue with the engine randomly dying. The OEM pump shows the same pressure. I guess we'll see how it runs next weekend.

[chopper515]

Well, after I put the old OEM fuel pump back in, it ran perfectly. Problem solved for now.