350 MPI Horizon Base Timing
 

I'm trying to wrap my head around the information I'm finding online. I realize it is rare, but sometimes things you find online aren't accurate. lol.

My engine is a 2002 model I believe. 0M634400. It appears that this engine does not utilize the hall sensor in the distributor. There is nothing plugged into mine, and the OEM manual says "no connection". I also read that there is no timing adjustment allowed or needed on these motors. That the ECU does it all. That's fine, but I would think that without a hall sensor to tell the ECU what the timing actually is, that we would need to set base timing. Some people say yes, some people say no. WTF. The manual makes no mention of it at all, but the distributor certainly has the ability to be rotated. I found the below information on Performance Product Technologies website. Is this something I need to verify? Do these motors need base timing or does the ECU really just handle it all without ANY input. If it used the hall sensor, then I could understand that the ECU now knows the position of the rotor and can make those adjustments but theoretically I could rotate this distributor and the ECU would have no clue I did anything. I would love to hear some input from smart people. I do have the diacom software if that will help me out. V6 and V8 EFI Models (EFI Ignition)

Two items of test equipment are required: an inductive pickup timing light and one of either a Scan Tool, Marine Diagnostic Code Tool or MerCruiser Special Timing Tool (Quicksilver 91-805747A1).
1. Connect timing light (91-99379 or similar) to No. 1 spark plug wire. Connect power supply leads, if applicable, on light to 12 volt battery. Refer to Specifications – “Engine Rotation and Firing Order,” for cylinder numbering and location.
2. Connect a shop tachometer to engine.

NOTE: Before starting engine make sure the timing tab and mark, or marks, on crankshaft damper are clean. Chalk or white paint on timing marks may help visibility.

NOTE: If NOT Using MerCruiser Timing Tool: With engine running, set the scan tool or Marine Diagnostic Code Tool to the SERVICE MODE and follow manufacturer’s instructions. On 350 Mag MPI Model, engine RPM will automatically increase to a higher RPM. You do not have to increase it manually, as stated in the following steps.

3. Connect the Timing Tool (or appropriate tool, as listed above) to the DLC connector (in the electrical box or on the electrical bracket) of the wiring harness.
4. Start the engine. Allow it to reach normal operating temperature.
5. On all models except 350 Mag MPI: Manually adjust the engine throttle to 1800 RPM.
6. Aim timing light at timing tab, located on the timing gear cover and crankshaft torsional damper. Check the timing. Refer to “Specifications.”
7. Loosen the distributor clamp bolt enough to just be able to rotate the distributor with some resistance.
8. Aim timing light at timing tab and recheck location of timing mark. Slowly rotate the distributor clockwise or counterclockwise to adjust the timing to specified degrees.
9. Aim timing light at timing tab and recheck location of timing mark. Repeat Step 8 until timing is correct. Torque distributor hold down bolt to 30 lb. ft. (40 N.m).
10. Manually close the throttle to bring engine RPM back to idle.

IMPORTANT: Be sure to disconnect MerCruiser Special Timing Tool from the DLC connector, or set the tool to NORMAL MODE if using the Scan Tool or Marine Diagnostic Code Tool, before attempting to resume normal operations. If the MerCruiser Special Timing Tool is left in pace or the setting of the tool remains in SERVICE MODE, the ignition system will operate only in the “Service Mode”. This means that the additional timing advance features would not function.

11. Disconnect the MerCruiser Special Timing Tool from the DLC connector. If using the Scan Tool or Marine Diagnostic Code Tool, set the tool to NORMAL MODE. Disconnect the tool.
12. Stop the engine. Turn ignition key to OFF position.
13. Remove timing light.

Is this your distributor ?
If so, Mercruiser tefers to it as the HVS style. Do search on this. few people have outlined how to do it. If you can't find them, i’ll help find’m.


https://cimg7.ibsrv.net/gimg/www.off...0f08b6524.jpeg

Or this distr ?
GM Merc Voyager / EST

https://cimg1.ibsrv.net/gimg/www.off...55687e4ed.jpeg

Basically, yes. I have "the crab" and I did read that term as being "high voltage switch". I'll look specifically for that info.

So I'm fairly certain I've discovered what I need to do, and in the same time have come up with another question.

To index the rotor, I set the motor to #1 TDC using the marks on the balancer. Then rotate the base of the "distributor" until the pointer lines up with the rotor. Per pic below. Correct?

The additional question now comes about plugs and their gap. I replaced plugs in the fall with NGK ITR4A15 with a gap of .060. I've read that with the crab cap I should not be above .038 gap. Is that good information?


https://cimg7.ibsrv.net/gimg/www.off...7ca0cfe0e6.jpg

Yes. Great info. My honest belief is the dumb .060” gaps are responsible for the crab cap issues. Causes too much voltage demand.

We don’t have to deal with the emission police. Keep your gaps to .035” - .040”. No more than that.

You understand now why the HVS distributors don’t effect timing ? Sounds like you may.
Rotor to cap phasing is not ‘timing.”

I do understand, but I guess you could argue that it's a fine line between base timing and phasing. To me, setting "base timing" is giving the ECU a benchmark from which to determine timing. It seems like phasing also does this, but differently. Essentially the ECU has no idea what the actual timing is. It knows what it wants it to be and assumes that we set the distributor properly to give it that benchmark.

I really appreciate your input on this.

After further reflection (my brain needs to know how things work) I retract what I said about phasing being similar to base timing. Moving the distributor body tiny amounts in either direction wont effect timing at all, just the ability of the spark to get to the cylinder. Too far either direction and the spark cant make the leap. The timing would remain the same though, as long as the spark gets through. It could be that I'm slightly out of phase and it is very hard for the spark to make the jump. The closer to exact alignment, the better chance of a successful firing of the plug without building up so much voltage that it jumps internally within the stupid crab cap. Am I starting to get it?

Yup. You got it. :)

As far as plugs, merc uses the platinum plugs because that’s what gm installs in them before shipping to merc.

The copper MR43LTS (you have vortec heads riight) are cheaper, last long in time because who drives there boat 30k miles anyway ? Platinum good for 70k and higher. Lol.

The LTS come gapped at .044”, therefore not far to bend (close) to .035”-.040”. Less current going thru the cap/rotor will give beter chance of not running into cap problems.

I don't know if I have vortec heads or not. Whatever they would have put on a 350 MPI Horizon in 2003. The plugs I have are the NGK Laser Iridiums and I think they came gapped at .060 and I'm sure I checked them as well. I have a gap tool that should make it easy to get them to .038. Current plan is new cap/rotor/wires. Check phasing. Re-gap plugs. The unfortunate part is that where I boat is 2 hours away and when I go, I'm there for at least the weekend. Hopefully this solves my problems. Last weekend was a bit miserable being stuck on an island in 35-40mph NE winds and not knowing 100% if the boat was going to run well to get back to the mainland. lol.

Vortec heads used from approx 1996 and up. Easy to identify. Intake is held down with 8 bolts (4 per cyl head) at a straight down angle. Earlier heads had 12 bolts (6 per head)) at angles holding intake to the heads. Those used MR43T plugs.

1st pic Vortec (note straight up and down bolt holes. Their are none in middle positions unlike earlier heads)

https://cimg0.ibsrv.net/gimg/www.off...bea8e5283.jpeg





2nd pic earlier sbc heads


https://cimg8.ibsrv.net/gimg/www.off...02b365f1c.jpeg

Playing around with this, I discovered that it is quite a bit off. So much so, that I don't think the housing will rotate far enough without interference. Does this mean that its off a tooth?

https://cimg4.ibsrv.net/gimg/www.off...42721a2b46.jpg
https://cimg6.ibsrv.net/gimg/www.off...389eceab77.jpg

If turning dist and there is interference, dist is prob off a tooth. Prob someone who didn’t move oil pump pushrod a hair (need long flat blade screwdiver) and just dropped it back in.

You ever put a chevy dist back in ? If so, this is piece of cake.

You know the history on this ?

I've never done this. My experience is on smaller imports etc. The history that I know of is that the PO had the same issues I'm having. Hard start etc. One time it actually just stalled. He found the distributor loose. He rotated it to the point that it ran and left it. I don't know if he may have removed it to try and tinker or not. Or if his mechanic may have. I know he had trouble finding people to work on his boat and took it upon himself a lot. Some of his work was good, some was less so.

Lol.

Any ways. Dist is easy. Loosen clamp first and see if it turns enough. Recheck alignment when you tighten clamp. It can move a few degrees as the dist and cam gear are helical.

I'll give it a shot. just looking at it, it looks like the housing will hit the intake manifold before it gets to the exact right location. I bet I can get it close. One fun thing would be if I had to remove it. I may or may not have enough room to get it out of the boat. Perhaps I could pull it up, rotate it, drop it, and turn the engine by hand to line up the oil pump?

No no no. I’ll give you my cell in a pm. I mumble so put your good ears on. Leave engine at tdc. It’s easy.

if the phasing is off it will run like crap and cut out i use an old cap cut open to get it right

On this, you don't need too. There is a little pointer if you will on the distr that the rotor will point too. It's about an inch or so up from where his rotor is in that pic. And by his pic, his dampener is at TDC.

Well we got there. Just moved it one tooth and its good. I spoke with the original owner. He swears it was never removed. I could have gotten it close without jumping the tooth. Probably about half of what it was out. My guess is that at Mercury it was installed "close enough" and it ran for a long time like that. Thanks SB! I'll let you know how it runs tomorrow. The black flies were killing me tonight!

https://cimg0.ibsrv.net/gimg/www.off...33b0cbcb19.jpg

…..

Don't think close enough is correct but that's just me
Can get it precise by building the gadget in the file starting on page 15

Good info.I had to build something similar years back for another engine that escapes me. Was near last years of radio shacks being around.

You and Bup had other good info here too:
https://www.offshoreonly.com/forums/...on-timing.html

Apparently close enough was good enough to get it to run for many years. However, I'm not a good enough kind of guy. It is now spot on per the merc manual 31. I'll see how it goes. If it's not running right then I plan to follow that TSB and build the tool. Seems easy enough.

Holy thread regurgitation!!
 

Basketcase - I know this is a cobweb covered thread from the dark, distant past, but was your problem solved?? I have the same issue of hard starting, it'll even run backwards for a couple seconds when I turn the key off. Once it starts and warms up it starts great the rest of the day. With a timing light hooked up to #1 and the engine warmed up the timing mark is off by about an inch before the timing mark.