Gen 6 - 454 / 7.4 TBI Timing Procedure?

[douglee25]

Can someone tell me what the correct way is to time a 1997 Gen 6 - 7.4L with the TBI setup? I only see directions for carb or MPI, neither of which mine is.

I believe I need to need either ground or unplug some connector? Again, it varies and I can't seem to find anything remotely similar to what's described.

Thanks again.

 

[PlayDate]

I need to rummage around to find it but it is more about the Thunderbolt Ignition than anything else. You either have a IV or V and the timing method is different for both.

I believe you have a V but I would need the engine serial number to confirm it.

 

[douglee25]

Serial OK189466

I'm almost positive after a little more research that it's the same process as the MPI motors using the DLC connector. The two pins get jumpered or you use the scan tool to put it into Service mode.

 

[PlayDate]

It should be this procedure for the V.

https://www.perfprotech.com/blog/articles/mercruiser-engine-timing

 

[douglee25]

I looked it up and it has an MEFI 2 system, not thunderbolt. I was able to cross reference it from the parts diagram.

Did the serial numbers lead you to believe it has a thunderbolt ignition?

 

[PlayDate]

I looked it up and it has an MEFI 2 system, not thunderbolt. I was able to cross reference it from the parts diagram.

Did the serial numbers lead you to believe it has a thunderbolt ignition?

Your serial number resolves to this:

https://www.perfprotech.com/mercury...gnition-components/assembly/2358/90?model=307

If you look through the parts associated with it you will see it is a Generation VI engine. The distributor is part number 805222A1 which is also known as a Thunderbolt V distributor (Mercruiser just renamed the GM distributor). The MEFI 2 is the ECU that manages the TBI and the distributor.

 

[scoflaw]

That's the EST not a TB5 setup. Puta paper clip between pin 1 &2 at the DLC. Hold rpm's on a warmed up engine between 16 and 1800 rpms

 

[PlayDate]

That's the EST not a TB5 setup. Puta paper clip between pin 1 &2 at the DLC. Hold rpm's on a warmed up engine between 16 and 1800 rpms

This is from the link I gave him....are you proposing something different than this?

 

[scoflaw]

On my 99 with the EST the directions are slightly different, not at idle but 1800 rpms and the pins are clearly labeled 1 &2. Your picture looks correct, my timing also says 8 degrees not 10. Doubt 2 degrees will matter or rpm's. I also have a Mefi 3

This is a GM distributor that came on many vehicles from the 80's. Every part can be bought at a local NAPA dealer. Echlin parts are high quality and their caps have brass terminals

 

[douglee25]

The diagram you posted is correct, but that's not a thunderbolt setup. It's definitely an mefi 2 setup. Thanks for the help both of you. I was able to set the base timing at 8 deg base. While fully under load at WOT I was seeing 32-34 deg at 4k rpms.

I am chasing what I feel is a low rpm situation at WOT. The cover on the flame arrestor says WOT is 4000 - 4400 rpm. I verified compression and also did a leak down test. All numbers are within spec for a boat with almost 1200 hours. Timing is in spec. New plugs. Wires are 2 years old and so is the cap and rotor. Oil and filter changed. New fuel filters. Two independent fuel tanks. The port side can maybe muster another 100+ rpm over the starboard (port was 4000/4100 and the starboard was 3900/3950 - the sync gauge shows a slight bias to the port motor as well). The bottom has also been scrubbed. I'm at a loss. It must be a prop thing at this point. I think they pitch this thing to put it in the sweet spot at 3400-3600 rpms. If they allow the motor to spin up higher, it will put it out of the power band.

Any other thoughts? Good where it is? Motors run smooth. No issues.

 

[douglee25]

I looked it up on the power boat guide specs.... Says WOT is 30 knots or 34 mpg. I think I hit 32 or 33 mph on the GPS. I also confirmed on the cruisers board that most hit 4000 - 4100 rpms from the factory. So maybe there is no issue. Sounds slightly over-propped from the factory.