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70 HP 4 Stroke backfiring

C

combahee

New member
2000 70 Evinrude 4 stroke.
Had bad to no idle and backfiring when you give it throttle.
I have service manuals and diagnostic software.
New spark plugs.
Compression OK.
Check spark OK
Found a bad IAC valve, replaced it.
Will now idle.
Gave IAC fault and injector faults.
Checked and cleaned injectors, replaced filters. Exercised injectors, OK. Ohmed tham all OK. No loose connections.
Fuel pressure fine.
Running on new fuel and portable tank.
Everything looks good on diagnostics except the IAC duty cycle want to stay low, about 10% +
Engine now starts and idles a bit high. 800-848 in the water at idle
Did a injector stop on all, 4 and 2 and 4 seemed weaker.
Did cylinder misfire and the same thing.
1 & 3 misfire or injector stop, the engine dies or almost does.
Neutral switch OK
All sensors read properly and test OK.
When I try to give it throttle big backfire in intake, runs real rough. Will not take any throttle.

I'm pulling my hair out on this. Everything seems right now with the new IAC, but just no throttle.
Any ideas?
 
Belt is fine and aligned. Everything lines up.
Starts, idles OK but when I give it any throttle it will backfire, badly in the intake.
 
Only 2 possibilities:
1: Timing (ignition/cam) is out. (check timing on EACH cylinder)
2: One or more intake valve 'leaking'
 
How could the timing be out? It's ECU controlled. As long as the cam pulley hasn't moved and it aligns it should be where it should be. So How would I change anything? I'm not arguing with you, just not getting something here.
 
In order to get the 'popping' (combustion) in the intake manifold, you must have combustion in one or more cylinder when one or more intake valves are (partly) open.
What is the exact situation will have to be tested.
1. Verify TDC and that flywheel and cam wheel are aligned and at marks.
2. Check valve lash.
3. Check timing on each cylinder. It may happen that 2 cylinders fire at the same time due to EMM error or a 'bridge' in connectors. Mark flywheel with each cyl at TDC.
4. Do a compression/leak-down test.
 
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