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454 EFI "popping" at high RPM 3500 and above

B

big cahuna

New member
have 1997 crusader 454 efi's. strb engine pops or backfires at high rpm. computer checks ok, not a lean problem, springs and valves all good, plugs and wires replced...this was the case all last season as well. HELP!
 
How do you know it is "not a lean problem"? How did you determine the "springs and valves all good"?

Condition of the distributor cap & rotor?

Which distributor do you have?
 
Boat has been serviced at same location since new. They checked for lean problem first and stated no problem. Swapped computers, replaced springs and valves, rebuilt carb replaced plugs and wires.
 
big cahuna said:
Boat has been serviced at same location since new. They checked for lean problem first and stated no problem. Swapped computers, replaced springs and valves, rebuilt carb replaced plugs and wires.
Click to expand...

No lean problems but the haven't check the anti syphon valves??

thought this was an EFI....?? Was the throttle body rebuilt? If so, what did they do with the injectors?

Have they measured the fuel pressure; if so, what were the readings?
 
You could also have a broken valve spring. THAT can be determined by pulling the covers and taking a good look.

Jeff
 
Noooo! Something else is wrong there.

Can you rev it up in neutral to 5,000 rpms without the popping? If yes, I'd keep looking. If it still pops, the camshaft could have a bad lobe (or more).

Good luck.

Jeff
 
Strikes me that there has been little diagnosis and lots of parts changing. Now they want the ultimate parts change, a new motor. Of course they could be saying "even if we manage to fix this worn out motor, you will still have a worn out motor, better to start fresh." Or maybe they don't know what to do.....

Popping could be a timing issue. Either ignition (are you sure you have the correct spark advance at high rpm?) or valve train (cam is out of time because of a worn out camshaft chain - stretched or jumped a tooth). You want to eliminate those next.

Not sure if a worn lob will cause popping as Jeff suggested but it is easy to check once the valve covers are off (as they have been many times so far). Maybe they did that already. They should have when the changed valves and springs on a hunch.
CaboJohn
 
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