jstand22

Hey guys, I'm having an issue with idle and low speed in gear. It seems voltage related....at idle my voltage is erratic, between 10-12. It seems to be causing the engine to stumble and eventually it just dies. Its always idled fine until now. Also in gear at low RPMs it wanders 800-1000, and has trouble getting into gear. Would a bad battery or alternator cause ignition problem? It doesn't appear to be carb related.

wingnit

OK. You didn't say what power you were running, but I'll take a stab at this.

Generally, if a battery has enough voltage to turn the starter, it should be OK. If this is an EFI motor, they tend to be more finicky about voltage. First check the main harness plug to be sure there is a good connection. Have you checked the alternator output at the battery with a volt meter? If the problem continues, the next thing I would do is disconnect the positive wire from the battery while the boat is running. If it stalls the alternator isn't charging.

jstand22

Crap, I'm sorry, I posted this in a haste while anchored in the boat. So It's a 1997 5.7L 2bbl (Serial 0K026165) mated to an alpha one Gen II, Alternator is the older type (55 amps if I remember correctly, but it's a serp belt setup).

Now there have been some developments since I posted this. I couldn't hear it at first, but the engine is definitely missing. At idle rpms vary and vibration is high, it doesn't respond to small throttle increases until that cylinder kicks in at like 2000 rpms and the miss seems to go away. So I've got a miss to chase.

Here's more information: I just changed the cap/rotor (quicksilver) and wires (united marine), and plugs (regular NGK). The new wires were a bit longer than factory and I had alot of trouble keep them separated (had to buy a whole bunch of extra looms). Cylinder 7's wire is very very close to the alternator harness where it cuts in back of the engine (it is wrapped). There could be an arc somewhere, but I would think that would still be pronounced at higher RPMs. No water in the oil, and exhaust manifolds, risers are brand new. I'm going to pull the plugs later on to see if one is fouled.

Any other input would be appreciated; sorry I didn't give enough info before.

wingnit

Get a pair of spark plug wire pullers and pull each plug wire off at the plug one at a time. If there is no change to the idle, put the wire back on and move to the next one. That would be the easiest way to find out which cylinder is missing.

Did the problem start before you changed all those parts or after. The firing order is 1-8-4-3-6-5-7-2 in clockwise rotation.

SB

97 has (should have anyway) Vortec heads which require different plugs (same thread pitch, same heat, but much longer than) older style heads. A plug for an older head will not even put the electrode in the Vortec's combustion chamber.

If you have the correct plugs, you could have screwed the pooch with putting your wires on wrong by mistake. Happens a ton ! Don't say no - go recheck them !

Edit in, if ignition issues are from alternator, typically it won't effect idle (carb) if battery didn't need a jump start but will as rpm/load goes up.

The Vortec spark plugs a reach of approx 17.5mm
The older style heads have a reach of approx 11.7mm.

Huge difference.

FIXX

he might have one of those chokeless carbs that merc was toying with way back then..? that would be affected by voltage..

SB

Never heard of them...but....I don't work on 2bbl stuff.....that's my disclaimer. LOL. I am serious though. Stock 4bbl is the lowest performance I touch and that's hard for me to do. He, he.

jstand22

It's a 1997 5.7L 2-barrel (Mercarb) with electric choke, and non-vortec heads, 232 hours mated to an alpha gen II...even though it's a 2bbl, it's all the boat needs; it's an 18 foot bowrider and it sprints to 60 in a hurry Even the extra 30 ponies from the 4bbl might be too much.


Anyway, I think I'm dealing with two separate problems - but there's a small chance they're related. I noticed the #3 plug wire is resting against the alternator harness and 7 is close as well (wires are new United Marine 8mm). Even though the alternator harness is wrapped and jacketed I wonder if it could still be arcing.

I'll let you guys know what I find; thank for the help!

Edit: Checked the wires 3 times (once after the miss started), they're all on the correct terminals and associated plugs.

SB

Prove to me it doesn't have Vortec heads. LOL.

jstand22

Haha, sure, but you'll have to tell me how to post pictures. It's asking for a URL and there's no browse computer option.

Otherwise, I posted the engine serial number in the original post....give it a run on the merc parts site.