Idle Oscillates and Engine cuts out at speed

[Robbabob]

1995 VP 5.0 Fi
model 50FAPHUE
Serial T01285465
VP SX outdrive 2868157

1.) Engine starts fine, idles around 600 or so, then begins to oscillate rpm up to 1500-2000 then back down. This continues until it drops too low and dies. Start it again, problem continues. Ran blower for extended periods, but the problem remained. Noticed this June 4 and again June 5.

2.) During planing speed, engine loses HP for about 1 second, then kicks up again. Happened twice on June 5 Never happened before.

I assume the 2 issues are related. Fuel filter, bad gas, water separator, Fi system, O2 sensor, TPS? Purchased gas at our same marina all season, thus far. I am not a motor or gear head, so our preference is to have the marina perform the servicing (unless super easy to access and perform).

Your input is appreciated as I want to get a feeling for what we're up against. B.O.A.T. or easy fix

Thanks in advance!

 

[Robbabob]

Re: Idle Oscillates and Engine cuts out at speed

Marina mechanic says a tune-up should cure what ails it; that and change the water separator. Estimated at $300 to have them do it.

Think I'll research what it takes to do this!

 

[Robbabob]

Re: Idle Oscillates and Engine cuts out at speed

Is there anything difficult about changing plugs, wires, rotor and cap?

Can't be that difficult, right?

 

[thejetman]

Re: Idle Oscillates and Engine cuts out at speed

Shoot, I will drive to your boat and do it on your boat for 250!

 

[thejetman]

Re: Idle Oscillates and Engine cuts out at speed

It really not that bad,
Spark plugs- 5/8 inch socket, maybe an extension, swivel.
If you do em one at a time, its really hard to mess it up!
Fuel/water seperator......7 bux from walmart.
Do yourself a favor and get some dielectric grease, and some grey moly assembly lube
spark plugs dont need alot of torque.

Make sure you have set the gap on each plug to manufactures recommended specs.
Put a dab of dielectric grease in each end of each plug wire.
Put a dab of moly paste on the THREADS of the new plug.
Do one wire/plug at a time.
Marinas charge 50-80 bucks an hour. If your handy, it will cost you 20 bucks, and maybe an hour or so worth of your time.
If you wanna get really serious about it, look at every single plug. make a note of how it looks.
Oil=Bad
Soot/blackened=normal
No electrode= bad

spark plug condition is a good indicator of engine condition.......

 

[Robbabob]

Re: Idle Oscillates and Engine cuts out at speed

Thanks, Jetman,

I didn't think it would be much different than my car/truck. Know what you mean about doing it one wire at a time; saves in having to research firing order to trace each to its home.

Take care,
Robb

 

[thejetman]

Re: Idle Oscillates and Engine cuts out at speed

No problem.
I am a mechanic by trade, just new to the whole boating thing!

 

[Oddle]

Re: Idle Oscillates and Engine cuts out at speed

Robbabob,

I am having a similar problem, if you are able to figure it please let me know. my post is here http://forums.iboats.com/showthread.php?t=472830

Thanks!

 

[Robbabob]

Re: Idle Oscillates and Engine cuts out at speed

Well, I am troubled that iboats doesn't have plug cables for a VP OMC Cobra 5.0FI 1995. This fix is not way up on my priority as I am traveling a lot right now and will have to figure it out when I have more time. Give me a week or two. Figure to start with 1 thing at a time and test from there, so I'll have a clue what single thing it might be.

Will update as I go!

 

[thejetman]

Re: Idle Oscillates and Engine cuts out at speed

You should be able to get away with wires from your local Automotive store. Anything for Ford 5.0 should work. You can get a nice set for about 30 bucks.

 

[Robbabob]

Re: Idle Oscillates and Engine cuts out at speed

You should be able to get away with wires from your local Automotive store. Anything for Ford 5.0 should work. You can get a nice set for about 30 bucks.

I don't mean to contradict anything you say or know. However, as I am trying to learn about this, I came across information stating the marine wires are copper, not metal as in automotive. Something about the lower operating temps due to less resistance. Might have something to do with lower chance of a spark outside the insulation (?????). I dunno bout this stuff.

Again, thank you for the input!

 

[thejetman]

Re: Idle Oscillates and Engine cuts out at speed

Well it all depends on how much you wanna spend the copper ones are gonna be more than just your plain ol metal ones. All you gotta do is look inside the wire end Its more of a corrosion thing than anything else. It comes down to how much you wanna spend really.

 

[Justin Kennedy]

Re: Idle Oscillates and Engine cuts out at speed

I have the same VP 5.0Fi engine and have had the opportunity to go through all this stuff over the years. First of all, the wires, cap and rotor are definately not available. The auto cap and rotor work fine however, the wires are not the right length and will not work. Even the Sierra aftermarket marine wires are incorrect although the book says they are. You have to buy wire in bulk and cut to length, install new wire ends. Summit Racing has it. Changing the plugs is very difficult because the exhaust manifold obstructs the access to the plugs. Ive always just taken the manifold off, which requires new gaskets when reinstalling, more time and expense etc... Its more time consuming than you would expect. As far as your idle surge problem. Make sure your low pressure pump, right above your fuel filter is working properly. It should come on for 2 sec after you turn the key to run, make sure its not hot or making loud noises. It will buzz a little but thats normal. If its good, check your fuel pressure. If you dont have a guage, they're about $45 at Autozone. Hook it up to your fuel rail schrader valve near the right front of your lower intake manifold. It should idle around 32psi and hold it for at least 60 sec after shutdown. If your pressure is good, then you may have an air leak, dirty throttle body or EEC/sensor problem. If your pressure is low, then you probably have a fuel problem. Check filter, fuel line, pick up tube, anti siphon valve, pumps, vapor separator. I just fixed this same problem with mine, idle between 600-1200, then at speed, it was like someone turned the key off and then back on. Turned out to be intake gasket air leak. In the process, I really learned a lot about this particular engine. If you're sure its not a fuel issue. Then check sensors and IAC system like this. If it idles fine just after cold start up for a min or two, then starts to occilate. You have an issue with maintaing the proper air/fuel mixture. Whats happening is that your temp is going up so the EEC is leaning the mixture to run more efficiently. In the idle position, this is done by opening the Idle air bypass controller. If you have an air leak, the EEC cannot detect that, so what happens is it starts to occilate, now the EEC gets a signal from the distributor that the engine is shutting down, so the EEC closes the IAC to enrichen the mixture to keep it running. Because the EEC cannot detect the additonal air coming from the leak, it cannot overcome this problem and the engine eventually dies. Compounding the problem is the elevated engine temp( because of the lean mixture)confuses the EEC even more. Air leaks are hard to find because one, the engine wont stay running long enough to find them and two, the big upper intake manifold gets in the way. Its really not too big a deal to just replace the intake gaskets. They are all available at Autozone or NAPA. Just watch the lower gaskets. The auto ones are blocked off on one end and you need to be sure they go to the blocked end of the intake. Good luck.

 

[Robbabob]

Re: Idle Oscillates and Engine cuts out at speed

Hey Justin,

thank you for the detailed information. that is exactly what I was hoping to hear (details anyway). Hate to hear the work involved as I am not an engine guy. Perhaps the $300 is looking very good at this point, considering the intake must come off and the gasket will be replaced; something that might cure the oscillating.

~kinda~ Happy camper....

 

[Don S]

Re: Idle Oscillates and Engine cuts out at speed

Moving to OMC forum. This is not a Volvo engine. Identical, but it is an OMC and belongs in that forum.

 

[RIDEPATE]

Re: Idle Oscillates and Engine cuts out at speed

The IAC-Idle Air Controller is probably dirty. Very easy fix. Just needs cleaning. It's a known problem with 5.OHHH's in the mustangs and boats. No need to go spending all that money just yet. Go get a 5.00 can of Throttle Body cleaner, an 8mm 1/4 drive socket, remove the IAC from the throttle-body, clean all the black-stuff out/off, re-install. A 5.00 dollar fix.....The manifolds do not have to be removed to change the plugs, BTW. And you can go buy a set of 8mm wires for a 90's Mustang, they will work perfectly.

 

[Robbabob]

Re: Idle Oscillates and Engine cuts out at speed

Thanks, Don, for the move.

and Thank you Ridepate for the information. Seems well within my ability.

Fight on!

 

[Robbabob]

Re: Idle Oscillates and Engine cuts out at speed

Update....

Went ahead with the marina performing the tune up as time and availability were not my friends. They performed standard replacement of parts and (guess what?), the engine idle still oscillates. No real surprise there! Been over 2 years since last tune up so it was due no matter.

When the idle was still ill for them, they found the fuel filter was clogged during their initial investigation. They added some sea-foam for some reason (we already did it 2 tank fulls ago, but they didn't ask us). Anyway, they say she now idles and runs great, WOT at 4600 running 50+.

Can't wait to get her out this weekend, double check the speed via GPS, and let her idle like a kitten again.

Although we used the Marina for the service, thanks to y'all I was able to talk like I knew something about the problem and relate to them with a certain level of confidence and understanding.

Thanks again!

 

[whodey]

Re: Idle Oscillates and Engine cuts out at speed

Thanks for posting your resolution to the problem, so many people don't. It helps others people to get their issues resolved

 

[Robbabob]

Re: Idle Oscillates and Engine cuts out at speed

Out both Saturday and Sunday. No signs of the oscillation and the engine ran as smooth as the marina service department mentioned. Did not compare with GPS speed since so much traffic and chop prevented from anything near WOT.

Tuck this learning experience away until someone asks about a similar event!