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PCM 5.8 HO wont pass 2500 RPM's

J

Jeff19

New member
Hey Guys,
So i have a PCM 5.8 HO and have had some issues with it. Most have been fuel problems, which replacing both the pumps have fixed. Now I am stumped. Basically the motor wont run past 2500 rpms. Taking off it struggles to get up on plane and backfires a few times. Once given power, and ran at WOT, it wont go past 2500 rpms or like 15 MPH. The boat has always been babied, only fresh water, and about 300 hrs on it.
 
Any ignition system that will not offer the correct TA (total advance) will prevent WOT RPM.
We must not only set/check BASE advance, but we must also see where our TA is.

With your harmonic balancer marked off up to 30-35 degrees BTDC, strobe your timing marks as you normally would using an old school strobe type timing light.... or a digitally advancing light in Standard Strobe Mode.
(this gives us real degrees/real time)

Increase RPM and watch as the strobe indicates the advance curve and limit.
Note where it is @ 650 (BASE), 1,500, 2,000, 2,500, 3,000 and 3,200 rpm or so.
Jot this down and plot it out as though making a curve graph.

You should see nothing but BASE advance at idle or just above.
Any additional advance should not occur until just above BASE RPM, IMO.

Compare this to your OEM ignition advance curve.
Your issue may be as simple as not enough TA.


By doing the above, you will have at least elminated this as being the culprit.... or, you may find that it is the issue.
Either way, it's a good thing to do and know.


Edit:
Please...... No offense to you guys that love your digitally advancing timing lights. These do have their place.
I'm not one who is willing to place my trust in an electronic circuit board and algorithm that shows this electronically, and then trust that there won't be a margin of equipment or user error.
Two degrees of excessive TA can mean the difference between Detonation and NO Detonation for our Gasoline Marine Engines.
When we view spark ignition timing in real degrees and in real time, this greatly reduces any chance of error.
Each to his own, however. :D

.
 
Last edited:
Steve, the OP here (Jeff19), posted his first and only post April 25th. Doubt that he'll be back.
But I agree, and base line would be good as a comparison.
 
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