4.3 merc misses at 4000 rpm or above

[KCChris]

I recently purchased a 1988 VIP w/4.3 merc 6 cyl. Only got to take out once during the season. Noticed engine misses consistently at or above 4000 rpm's. Cruises at 3000 to 3500 rpm's great! WOT 4000 to 4500 misses. New plugs, wires, etc. Other than timing anything I should check.

 

[hondon]

Re: 4.3 merc misses at 4000 rpm or above

Fuel quality is the first thing to check.If you have a water separator ,change it ,and dump the contents of it into a clear vessel.Lots of water ? BINGO!If you do not have the water separator, then you will need to get the fuel sample at the fuel pump.An outboard primer bulb will help you here.

 

[karayj]

Re: 4.3 merc misses at 4000 rpm or above

Timing or if you have it vacum advance

 

[Capt. T]

Re: 4.3 merc misses at 4000 rpm or above

I had the same problem 3000-3500 rpm 4600 rpm ok 4000 rpm minor miss/stumble <br /><br />Could be you have a moisture problem in the wiring - I did. If so, go through and clean and reseat all the connectors and liberally coat with diaelectric grease. (This is an inexpensive fix that should be done in any case)<br /><br />On a more expensive note: have you checked the alternator? I replaced mine after only five years. According to a local shop, the alternator model on mine, a '91 4.3L, was a piece of junk, not worth rebuilding... <br /><br />Welcome to iboats! You'll find lots of good info and products.