Re: 5.7 TKS will not rev under load
Wow sorry to hear of your troubles.
new long block, new plugs wires, cap rotor, base timing set according to manual: same problem as before the new block. we replaced the block because it had very low compression on one cylinder. we thought that this low compression was causing the ecu to not let the motor run at high rpm under load. but now, same symptoms:
Runs great at an idle, and revs up fine with no load. it is a bit hard to start at times, as if timing was off, but once it starts it runs smoothly. but under a load, it will not rev above 18-1900. have tried everything! fuel flow is good, just will not push a load. ideas?
Well since your not afraid to spend money on finding the problem
I would guess/start to suspect you may have a problem with either the carburetor, The ignition sensor under the distributor, the coil, ignition control module wiring harness, (Since you probably did not get a new wire harness with the new ICU ?) Or your shift cutout switch could be either going bad or just slightly misadjusted, or weak spring on the shift plate. You could also have low fuel pressure, So check the fuel pressure at the carb. Also try running an separate fuel tank bypassing the fuel tank.
i do not want to throw another ecm at it without some kind of verification that this is the problem. i have had several "mobile marine mechanics" (aka high dollar flunkies) look at it and no one can figure it out. the Rinda diagnostic tool apparently just reads engine hours on this system- kind of useless!
Yes since this is a carburetor engine, a scan tool is useless.
Now that we have most of the guessing suggestions of what could be wrong thorn out there, The first thing you should do is verify that your ignition timing advance is moving upwards on acceleration to the mid to high 20's BTDC watching it with a timing light. Then move the timing light to the coil wire and ensuring you have a constant flashing light while under load. Then move the timing light to all 8 plug wires one at a timing again looking for a constant pattern as you accelerate.
If you did not get a new wire harness with the ICU then ensure all the wire pins connectors are clean and making good contact by pushing/wiggling wires around after pulling the connector off for inspection. The harness to the ICU has been known to be bad and I believe they have stopped sending them with the new ICU's. If their still available you may need a new one.
just paid $600 for a new ecm. now it revs to 2500 (instead of 1900), will not plane. vibration enough to shake the rails at about 1200. new block, heads, cap, rotor, wires, plugs, ecm. timed to specs, vacuum check looks good, lots of fuel flow (1/2 cup in 5 seconds). anybody have ideas?
Since you "touched" the wiring harness, I would still suspect a bad connection somehow.
I have been unable to find out if you have 1 or 2 knock sensors.
Looking at his parts catalog tells us he should have just one sensor. Item number 37,
http://www.mercruiserparts.com/Show...nbr=11741&bnbr=40&bdesc=Electrical+Components But bear in mind that this advice is not always 100% accurate all the time, it just helps give you an idea is all.
The next thing I would do if it was mine was a compression test. Have you had your injectors tested?
Once his timing advance is confirmed, another compression test would definitely be on my list. As already mentioned by the man this is a carbureted engine.
Need an expert to come in like Fun Times
I don't know about expert, One thing Don taught me was, I still have
a lot to learn.
RIP Don, you are so truly missed.
Hope this helps, Good luck.
