spark advance ?

[jwkoehn]

96 gm 5.7 tb5 ign system I reset timming to 8 deg btc also disabled spark advance during timming and reconnected it when done engine starts good took it on the water runs great wot was 5000 rpm and maxed out at 45 mph the question is the spark advance stays at 8-12 deg adv even at 3500 rpm is this possible

 

[Don S]

Re: spark advance ?

disabled spark advance during timming and reconnected it when done

By your discription, it doesn't sound like you put it in base timing properly. could you explain "EXACTLY" how you put it in base timing. That alone could be your problem.

 

[jwkoehn]

Re: spark advance ?

with engine off i hooked a ground wire from what i think is the ignition groud lead {the white bluish purple lead that is in the wire harness on top of the ign manifold under the carb} to the block /next i started the engine idled it to 600 rpm and set the timming @8 deg btdc shut off motor/ disc the lead restart motor check timming still @ 8 deg btdc took engine to 3000 rpm advance appears to only pick up 5-10 deg I m guessing. Is it possible I grounded the wrong wire?

 

[Don S]

Re: spark advance ?

Sounds like it was set properly, did you check the advance by just throttling up and letting back off? If so, hold the rpm steady up around 3000 rpm and see if the advance comes up.

 

[jwkoehn]

Re: spark advance ?

Itook it to 3000 held it there /it appears to stay at aprox 12 deg btdc

 

[John_S]

Re: spark advance ?

Which model Mercruiser engine do you have? A number of the 5.7l's with T5 have a base timing of 10 degrees BTDC. Thats not causing your advance issue though. I would expect around 20-24 degreed advance for a total of 30-34 degrees. Most advance curves are fully in by 3500rpms. Depending on your model, you may have a knock sensor and module that retards advance if it detects detonation.

What doesn't make sense is your wot data. If your were not getting any advance, I don't see how it could be running so well.