How to do new distributor timing on Mercruiser 7.4 Gen V?

[CLi87]

I'm trying to reinstall a distributor and didn't mark the old one, what is the procedure for new distributor timing for a Merc 7.4 Gen V? I tried to look up some guides and they mention putting it in base timing mode either by shorting the purp wire or jumping the two white wires, but on my engine it only has a white/red and white/green wire that goes to some computer module mounted on the exhaust?

 

[Bt Doctur]

Do you have the flat cap and is it computer controlled?
If yes ,you install the dist with the rotor in a certain position with number 1 at TDC compression and the timing mark at 0 on the balancer and the computer does the timing

 

[CLi87]

Do you have the flat cap and is it computer controlled?
If yes ,you install the dist with the rotor in a certain position with number 1 at TDC compression and the timing mark at 0 on the balancer and the computer does the timing

MERCRUISER - 7.4L BRAVO (GEN. V) GM 454 V-8 1992-1996 - WIRING HARNESS/ELECTRICAL(MOUNTED ON EXHAUST ELBOW)TB IV | PerfProTech.com

Find your WIRING HARNESS/ELECTRICAL(MOUNTED ON EXHAUST ELBOW)TB IV diagrams at PPT using our MERCRUISER parts catalog.

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That's the diagram for my engine, the wires go to #9 which says it's an ignition module kit. What do you mean by flat cap? I have #1 set to TDC compression already, do you know which direction the rotor is supposed to be pointing?

 

[Bt Doctur]

install the dist cap to locate where #1 is on the cap and set rotor to that position slight CCW of the exact position. rotor will turn CW as it drops in to the oil pump with rotor facing #1 pin in the dist cap

 

[dubs283]

As doctor says, verify where #1 is on the cap, set distributor housing/rotor to the #1 location.

The picture you've posted shows the distributor housing clocked correctly with the sensor opening facing aft, unknown if rotor position is correct. I would highly recommend you replace the old style, exposed circuitry sensor with a new three wire sealed unit. Ground to same stud as main battery ground lead at flywheel cover

 

[CLi87]

install the dist cap to locate where #1 is on the cap and set rotor to that position slight CCW of the exact position. rotor will turn CW as it drops in to the oil pump with rotor facing #1 pin in the dist cap

Ok so just to confirm this is what I did, set #1 on TDC compression, the mark on the crank lines up with the 0 on the timing plate, I installed the distributor cover so that the rotor points to #1. Is that it and the computer takes care of the rest or do I run the motor at idle and then set it to 8 BTDC using a timing light?

 

[CLi87]

I'm waiting for my new water/fuel pump assembly since the pulley on the old one was really tight but I just tried pouring some gas straight down the carb and it's not starting, seems to actually be backfiring through the carb a bit, not sure if it's because the boat is parked facing uphill so maybe pouring the gas into the carb didn't distribute the gas evenly between the cylinders, here's a pic of the distributor completely assembled, does it look right?

 

[dubs283]

Possible you don't have the firing order correct or the distributor/rotor was installed TDC exhaust, not compression. Engine should run, albeit rough at 0 btdc

 

[CLi87]

Possible you don't have the firing order correct or the distributor/rotor was installed TDC exhaust, not compression. Engine should run, albeit rough at 0 btdc

I'm pretty sure it should be TDC compression, I turned the engine over until I could feel air blowing out cyl #1 then turned it manually until the piston was at the top, if I was 180 out would the timing mark still line up on the crank pulley?

 

[Bondo]

I'm pretty sure it should be TDC compression, I turned the engine over until I could feel air blowing out cyl #1 then turned it manually until the piston was at the top, if I was 180 out would the timing mark still line up on the crank pulley?

Ayuh,.... The timin' mark goes by twice per cycle,.,.... once on compression, once on exhaust,....

 

[CLi87]

Ok I just re-did the timing from scratch and now it seems to want to start and it'll puff puff a couple of times but won't fully run, but at least no backfire anymore. Just to confirm I did the procedure correctly, here's what I did:

1) Set Cylinder #1 to TDC Compression, I used a scope in the spark plug hole to verify the intake valve (bigger valve on the right if looking through the spark plug hole) opened and closed then manually rotated the crank until the timing mark on the crank was at 0.
2) Dropped in the distributor, this is the part I may have gotten wrong, I was reading that it was possible to drop the distributor in 1 tooth off, but how do I know if it's a tooth off? Because I can turn the distributor body so the rotor matches #1 on the cap? When I dropped the distributor in the rotor was pointing slightly past the #1 cylinder, but I rotated the body so when I put the cap on it was pointed at #1 on the cap.
3) Double checked the wire routing to make sure they were going to the correct cylinder, this part was also slightly confusing, on my distributor cap there are 2 sets of numbers, one large and one small, I routed them according to the large numbers on the cap.

 

[dubs283]

Yes, 1-8-4-3-6-5-7-2 clockwise rotation. Cylinder numbers are cast into the intake manifold, odd is port side, even stbd.

Possible the engine is also flooded. Hold throttle only wide open and crank engine til it fires, return throttle to idle when it fires to prevent excess rpm in neutral. Once running on muffs or in water you can set initial timing

 

[CLi87]

I installed the new water/fuel pump assembly and she started right up, I guess pouring gas down the carb didn't work too well.

So I did the static timing at 0 and the computer should automatically adjust the base timing and timing advance? No need to time anything with a timing light?

 

[dubs283]

So I did the static timing at 0 and the computer should automatically adjust the base timing and timing advance? No need to time anything with a timing light?

No, the thunderbolt system does not have a computer. Just a sensor and control module. You must set base timing to the factory spec on the engine tag or oem manual for your engine.

The advance curve is set in the module but it's good practice to verify full timing advance after setting initial. WAG for your engine is 8 degrees BTDC

 

[CLi87]

No, the thunderbolt system does not have a computer. Just a sensor and control module. You must set base timing to the factory spec on the engine tag or oem manual for your engine.

The advance curve is set in the module but it's good practice to verify full timing advance after setting initial. WAG for your engine is 8 degrees BTDC

How do I lock my distributor into base timing mode? I don't have the 2 white wires or the purp wire, all my wires go to some type of control module.

@Bt Doctur said to just set the timing mark to 0 at TDC and the computer does the rest?

 

[Bondo]

Ok so just to confirm this is what I did, set #1 on TDC compression, the mark on the crank lines up with the 0 on the timing plate, I installed the distributor cover so that the rotor points to #1. Is that it and the computer takes care of the rest or do I run the motor at idle and then set it to 8 BTDC using a timing light?

Ayuh,...... Yer motor don't have a 'puter, if it's got a carb,.....

 

[dubs283]

How do I lock my distributor into base timing mode? I don't have the 2 white wires or the purp wire, all my wires go to some type of control module.

@Bt Doctur said to just set the timing mark to 0 at TDC and the computer does the rest?

Your 454 doesn't have thunderbolt 5, it's a 4 that has no base timing mode. Someone referenced an mpi style which no 454 came with.

Just set the base timing to 8 btdc and you're set. And do check total advance, not a huge deal with the 454. It can handle up to 43ish naturally aspirated with no consequences

 

[tpenfield]

I believe the first 454's with MPI were the Gen 6 in 1996-97 (which I had 2 of them in my Formula) They used the MEFI-1 controller . . . Neanderthal by today's standards. Looks like your engine (distributor) is old school . . . no computer.

As stated 8˚ BTDC and you are good to go. . . and . . . You will want to get the timing in the ballpark so the engine will start. It is a matter of putting the engine at #1 TDC and catching the mating gear within the engine as you install the distributor so that the rotor points to where the #1 plug wire is/will be on the dist. cap once the distributor is full seated. The rotor usually turns about 30˚ as the distributor is seated.

 

[CLi87]

Your 454 doesn't have thunderbolt 5, it's a 4 that has no base timing mode. Someone referenced an mpi style which no 454 came with.

Just set the base timing to 8 btdc and you're set. And do check total advance, not a huge deal with the 454. It can handle up to 43ish naturally aspirated with no consequences

Cool thanks! And is there a set idle rpm I need to be at when setting the timing?

 

[Bondo]

Cool thanks! And is there a set idle rpm I need to be at when setting the timing?

Ayuh,.... standard idle is 650/700 rpms,....