3.0 idles on 3 but great on WOT. HELP..

[gdbechtold]

3.0 runs great at WOT or anything above idle, but runs on less than 4 cylinders at 1500 rpm or less. Thoughts appreciated.

 

[sqbtr]

Re: 3.0 idles on 3 but great on WOT. HELP..

Start with a compression test.

 

[Maclin]

Re: 3.0 idles on 3 but great on WOT. HELP..

You might also post what the recent history of this is, like did it just start doing this? Was it recently tuned up? Was this the first run of the season? info like that.

 

[gdbechtold]

Re: 3.0 idles on 3 but great on WOT. HELP..

problem is intermittent, so compression is out as option. runs same temp consistently. tune up is probably due as i just bought boat with about 400 hrs at which time compression check was done and all good). ran fantastic first day on high and low rpms. has since developed a habit of running great at all rpms until running at higher (3k plus) rpms for a bit. It then tends to "miss" a cylinder at low rpms, but still runs fantastic at any rpm over 1500. Has been through one complete tank of fuel (93 octane). Thinking carb or general tune up, but looking for other ideas in case.

Thanks

 

[Maclin]

Re: 3.0 idles on 3 but great on WOT. HELP..

Have you looked at the sparkplugs? They can be read just like a sensor. See if one is not quite the same as the rest.

Many times low rpm misses are ignition related. Lower rpms are actually harder conditions to light the mix in. Cap/rotor and plug wires are factors. A plug wire may be arcing. The plug can try to foul at the lower rpms then clear up later.

You did not give the year or model number, so not sure if this is points ignition, but improper dwell or points in bad condition can "pick on" just one cylinder sometimes, especially if a wire is arcing or the cap is cross-firing, things like that.

By the way, you should not need the higher octane, 87 (R+M/2 method) should be all it needs. I am not saying this is the problem but it could be a factor.

 

[gdbechtold]

Re: 3.0 idles on 3 but great on WOT. HELP..

cleaned fuel filter, changed plugs, inspected ignition, cleaned air filter, fresh fuel, still same issue. then went to carb. cleaned carb. Still issue. examined holley 2 barrel and made adjustments to set screws. Now purrs like a kitten.

Thanks