Merc 350 Mag Distributor install

[Texas22]

2003 350 MAG While replacing the cap, one of the screws broke off in the distributor. I had to pull distributor completely out to remove broken screw. I thought I put it back in exact same position. Not so lucky. Engine does not start at all now. So I want to find TDC and reinstall distributor correctly. Not sure how to do this.

 

[Alpheus]

Re: Merc 350 Mag Distributor install

Pull the #1 sparkplug. Put your finger over the hole and have someone bump over the engine. When you feel air pressure blowing your finger off the hole stop. Line up the mark on the harmonic balancer with the 0 mark on your timing chain cover. This is TDC. Your cap only goes on your distributer one way and it should be marked. while noting the position on your cap set the distributer down in while making sure the rotor is pointing to your #1 position marked on your cap. Set all the way in and tighten up the yoke so the distributor can still turn by hand. Install your cap and install your plug wires on 1-8-4-3-6-5-7-2 .(rotor spins clockwise) Install timing light,start engine and time to manual. Tighten up yoke...

Here is a link to download the service manual. This will help you get the job done. Good luck...

http://www.4shared.com/document/XC08xfct/Mercruiser_Service_Manual_31_2.htm

 

[Fishermark]

Re: Merc 350 Mag Distributor install

The only thing I would add to that is instead of lining up the mark at the 0 TDC -- go ahead and line it up to the mark it is supposed to be timed at. Whatever that is - 8 degrees BTDC for example. It'll just be a little closer when you time it.

 

[FreeBeeTony]

Re: Merc 350 Mag Distributor install

MIght want to ask which ignition he has.........TBIV or TBV?

 

[Bondo]

Re: Merc 350 Mag Distributor install

MIght want to ask which ignition he has.........TBIV or TBV?

Ayuh,.... Good point, but stabbin' a distributer is stabbing a distributer....
It'll matter when setting the timing though...

 

[Texas22]

Re: Merc 350 Mag Distributor install

Thanks for replies. I was able to line up the mark on balancer with timing cover grove. Checked #1 piston head to verify position. Distributor droped right into place with rotor pointing to #1 point on cap. Engine starts as it did before any changes were made. Idel is great. Lake test has same result. Very low power from dead stop....does not run over 3500 rpm...Adjustments to distributor location does not affect timing. Does cpu set this? Also have checked compression,(180psi x8) and running on auxilary fuel tank to rule that out.

 

[Don S]

Re: Merc 350 Mag Distributor install

Here's the problem, you have a MAG MPI, you can not adjust the timing, and shouldn't even be trying. You need to look at the OEM manual linked to earlier and get the timing set like it should be. Then you need to start troubleshooting instead of changing things. You may very well have a fuel issue, not ignition timing. But until you check pressures and do a lot of other tests with the proper equipment, you aren't going to know for sure what the problem is.

 

[Bondo]

Re: Merc 350 Mag Distributor install

Adjustments to distributor location does not affect timing. Does cpu set this?

Ayuh,... It has to be jumper wired into base mode, set the timing, then remove the jumper wire...

 

[Aloysius]

Re: Merc 350 Mag Distributor install

If that's the crank fired ignition, there's a cam position sensor in the distributor. Literally all the distributor does is distribute spark. If it has a pulse pickup in the distributor, there's a "spout" wire that is disconnected or grounded to set base timing.

Idle speed is adjusted by the computer..it will never change.

 

[Texas22]

Re: Merc 350 Mag Distributor install

Here's the problem, you have a MAG MPI, you can not adjust the timing, and shouldn't even be trying. You need to look at the OEM manual linked to earlier and get the timing set like it should be. Then you need to start troubleshooting instead of changing things.

Well thanks for solving my problem buddy. Thats just why I posted up here to get told what I should not be doing.

Originally a simple tune up was done to this engine. Plugs, wires, cap and rotor. This cap is the style with torx screws. One broke. I had pull distributor to extract broken screw. It would seem logical to worry about timing at this point.

I read the ignition section of the manual. It does not read how to put it in base timing.

7. Install the rotor onto the shaft. If the engine is at number 1 cylinder TDC, the tang must be aligned between the two marks.

Installation
1. If the engine was completely disassembled, verify that the engine is at number 1 cylinder TDC. Verify that the rotor tang is in the proper location as shown above.
2. If only the distributor was removed, align the rotor, the housing and the intake manifold
using the scribe marks.
3. Slowly lower the distributor (with gasket) through the intake manifold and into position.
If the distributor shaft will not drop into position, turn until it drops into position.

 

[Don S]

Re: Merc 350 Mag Distributor install

You line it up as stated in the manual, there is no base timing. All you are doing is getting the distributor in a close position so the computer can do it's thing.

 

[Aloysius]

Re: Merc 350 Mag Distributor install

Just looked up that engine..it's the same ignition/engine management as late '90's vortec truck I had. Like Don says..the distributor MUST be installed as specified. There's a cam position sensor in the distributor that tells management system which rotation of the crank the engine is on so it fires the appropriate injectors. This cam position sensor MUST be with 15 degrees of specs, or it will set a code. Those "crab" caps are junk, and can crossfire internally. don't run heavy engine oil like 20w-50, or you will destroy the distributor drive gear.

 

[Don S]

Re: Merc 350 Mag Distributor install

There's a cam position sensor in the distributor that tells management system which rotation of the crank the engine is on so it fires the appropriate injectors.

That may be in trucks, but not in Mercruisers. That sensor does nothing, it just comes with the distributor.

don't run heavy engine oil like 20w-50, or you will destroy the distributor drive gear.

Odd, wonder why Mercruiser isn't having problems? They use the heavier oil? I suppose that's another truck thing?

 

[Aloysius]

Re: Merc 350 Mag Distributor install

You're probably right about the sensor they don't do "sequential" injection on the marine/industrial application..no O2 sensor either. Thinking about it, the timing on marine stuff probably runs off the default advance...strictly rpm related, unless the knock sensor interacts.

Oil..the bronze(?) distributor drive gear used against the steel billet roller cam will wear excessively with heavy oil..too much pumping load from the oil pump. I've seen 'em worn thin. takes 50,000 thousand miles or more IF it happens..that's like 1500 hours of running in a street vehicle. most marine engines haven't racked that mileage yet.?? As long as the engine is nice and hot, and the oil is thinner, it's probably not a problem.

Isn't Mercruiser oil a 25w-40?

In any case, the distributor is REALLY just a distributor of spark, and turning it does nothing but move the relationship between the rotor and plug terminal when the spark fires.

 

[John_S]

Re: Merc 350 Mag Distributor install

The stock gm distributer gear for roller cams is melonized, not bronze.

 

[Aloysius]

Re: Merc 350 Mag Distributor install

I know it's different that the standard iron gear. That distributor also uses a different size shaft that most GM distributors.

 

[John_S]

Re: Merc 350 Mag Distributor install

The T4 and latter the T5 distributers from mercruisers started using them in the late 80' and early 90's. Mercruiser started using them in '88 for V6 roller and non-roller. http://www.boatfix.com/merc/Bullet/88/88_18.pdf

I don't think merc ever used a bronze gear. Aftermarket performance parts, yes.

 

[Aloysius]

Re: Merc 350 Mag Distributor install

That "crab" distributor cap tells me it's a stock distributor in some form, or a Chinese replacement. The problems with that lousy unit are pretty well known in the street world, but since they're not alot of them (relatively) in the marine world, the information hasn't transitioned yet.

The replacement caps are junk. The rotors are junk. The threads in the distributor body strip out. If they aren't clocked properly, the spark will jump to adjacent cylinders. This can cause serious engine damage on one cylinder (can't remember which) because it lights off 90 degrees advanced.

GM has come out with a revised plug gap spec to help reduce the firing voltage required, thus reducing the likelyhood of spark scatter. I found that going from 0.065 to 0.035 on the gap didn't affect performance, and eliminated alot of problems.

 

[Eric 3.7LX Alpha 1]

Re: Merc 350 Mag Distributor install

The only thing I would add to that is instead of lining up the mark at the 0 TDC -- go ahead and line it up to the mark it is supposed to be timed at. Whatever that is - 8 degrees BTDC for example. It'll just be a little closer when you time it.

That's the way I like to do it too.

 

[Alpheus]

Re: Merc 350 Mag Distributor install

Doesen't say in the manual what the timing is. I guess you get it close and the computer takes over...