BUIZILLA

Hi all, wierd things yesterday while running my Formula with a '98 454-310 MPI.... launch boat, starts right up after 2 month hiatus, after about 30-45 minutes running perfectly, came off a plane at a harbor, and the engine choked and died without warning. Several attempts restarting, as soon as it starts, it die's immediately, like you turned the key right back off. Finally got it started, jammed it in gear and took off, won't run below 3800 or it try's to shut down, above 3800-4000 it runs okay... got back to channel for ramp and had to keep throttling it to keep it idling 1/4 mile to get to the dock, where it stalled approaching the dock... yup concrete doesn't move, dinged the front rubrail..... local gendarme's not amused.. wouldn't re-start there, starts and die's immediately when trying it. Get it home and it starts immediately, and idles somewhat okay, but hunts 200-300 rpm for awhile, settles down, and the fuel pump is screaming (new pump and filter and injector service 15 hours ago) Remove the anti-siphon ball from tank fitting and the fuel pump quiets down somewhat.. but the idle speed surge stays there.. sometimes.

question.. 1) what exactly does that vacuum triggered pressure regulator/damper at the back of the fuel rail do?? the actual fuel pressure regulator is on the fuel cooler/pump combo down below.
2) I noticed at WOT and sometimes cruising, the tach would jump up about 500 rpm for no reason, never does this at idle, just upper rpm, never an engine miss or sputter when it does this. Maybe the ignition switch or distributor module is crapping out? but what would that have to do with the idle surge?
I am going to change the fuel filter again today, and stick a fuel pressure gauge on the rail tap for checking the pressure stability. I never cut corners on maintenance, so i'm a bit stiffled..

any input appreciated, I don't have access to a Merc scanner for codes.
Jim

Edward R. Cozzi

If your fuel pressure is too high it's usually because of the little screen getting clogged that's under the regulator mounted over the fuel pump.

If the fuel pressure is too low, then check water separator.

Scan the ECM for possible IAC trouble too.

Dave_N

The regulator/dampner on the fuel rail is to smooth out the pressure drops/spikes caused by the injectors firing. The abnormal pump noise is usually a sign of a supply problem, checking the fuel pressure is a good place to start. A scan tool may be helpful, but might not tell you anything in this case.

Dave

BUIZILLA

thanx guys, I did notice an audible surging sound yesterday in the fuel rail when running, and that you could feel when touching the rail itself, hence my question about the dampner. I disconnected the vacuum source at the dampner, and nothing changed. I'm thinking it's IAC setting, and fuel starvation. Out to the backyard now for filter change and pressure testing, will report later.
Jim

BUIZILLA

ok... key on-engine off I get 68# fuel pressure ?? engine idling it bounces from 66-72, creeping to 75# at 1200 rpm. Doug Russell parts site says the regulator should be 43# ?? the regulator holds rock steady at 38-40# key off. I have no black smoke, nor does it even smell rich ?? transom is spotless clean..
Also I have a Merc filter #35-802893T black filter on it now, book says to use a 35-802893Q white filter ? what the hell is the difference other than one is white and one is black ?? supercession ??

Anybody know offhand what the fuel pressure(s) should be static?? and idling??

thanx guys, Jim

Dave_N

Key on, engine off, the pressure should be 34 to 38PSI. Based on your fuel pressure and symptoms, I would think the engine is flooding. But, I would think you would be smelling gas and have a ton of black soot on the transom. I didn't think the fuel pump could even develop that much pressure with out a total blockage of the fuel return line. Something is not right there.

I am guessing that you already checked that the vacuum line to the regulator is connected and receiveng a vacuum signal.

Dave

R Addiction

Look for a vacuum leak........Go to the basics first. My fuel pressure on a 502 mag is 38-40.

BUIZILLA

I removed the little screen from the regulator outlet and it frickin' PURRRRRS... now I have 50-51# idling, and it's never sounded this good, been this responsive, or been this smooth. I also changed the fuel filter again. It had 43-44 when I started it back up, then slowly creeped to 50-51 and is steady as a rock right there. Still seems a little high, as I would think with vacuum disconnected it would be 43, and connected it would be 38 or so... fuel pump sounds normal now, typical whine... vacuum source is/was on and tight. What a ***** getting those two little regulator screws in and out though... DAMMMMMMMMMMMMMMMMM, little blood on that move. It's 74* right now and sunny, may be a boating day still ??
Thanx guys, your the best.

Jim

R Addiction

Buizilla, Is this motor stock? Any add ons?

cuda

It's stock John.