280DA 4.3MPI's won't rev over 2400rpm under load after ignition tuneup

[Gunn]

So I'm asking for advice to see if I may have done something incorrectly or overlooked something...though I know where to begin. Always helpful to bounce ideas off of all of you!

At the end of last season, my starboard engine was having a hard time starting. So before I ran it this season, I purchased all new Mercruiser ignition system parts: New AC plugs, new wires, new distributor cap, and new rotor. I did this for both engines.

After installing everything I fired them up. They did take a bit of coaxing to get running, but once they were, they seemed to run very well and smooth at idle. Revving them up in neutral they sounded fine. So we went out for a spin...when I pushed throttles to full, they went up to about 2400rpm and sat there. I couldn't get any more out of them. No alarms or anything. I went back to neutral, gave a quick burst of throttle and they revved fine over 4k easily. Tried again, but no luck. Drives were tucked in, tabs up, everything as usual. Nothing else changed on the boat. After warmed up and shut down, the engines fired up instantly.

So...anything obvious I should look for? I am thinking I may have one or more loose plug wires that did not fully seat on the plugs themselves. Because for a couple of cylinders, they are a pain to install and push on!! The distributor cap is numbered with terminals on the left and right side (and the common high tension terminal on the right-rear); the left side shows 2 4 6 and the right side shows 1 3 5 (1 near the bow, 5 at the stern). #1 cylinder is on front (bow) port side of boat followed by #3 and #5 on the port side. The rotor had two T15 torx screws and seems to only go on one way. I'm stating the obvious here, but if anyone catches something out of place, be sure to yell at me!

I gapped each spark plug to 0.060" as the manual stated; they were pretty much there right out of the packaging. They were same spark plug number of was taken out (AC 41-993 I think...).

I placed a dob of dielectric grease within the spark plug boot before installing, then I pressed on. I did not use dielectric grease on the distributor cap. The manual said to use some on the outside of the coil terminal, which I did.

I couldn't find any timing information on the MPI engines. I'm assuming it's all computerized. But I have a timing light and could check it, but couldn't find out anything as to what to look for. I'm not even sure if there is a timing tab or mark on the crankshaft! But surely I couldn't have messed up the timing changing the rotor and distributor cap...I did NOT remove the distributor.

I've searched online and found others with my problem, but most of the posts are a dead-end with no fix noted.

One of the questions I had...if one engine is having trouble, would this prevent the other from reaching it's max rpm? I would assume so, because this boat needs both engines running at rpm to get on plane and stay on plane. I'm assuming I only have issues on one engine, and that engine is not allowing the other to rev up because of the load. Reasonable to assume? I mean, I could have an issue with both engines (because I did the same thing improperly, twice), but this is a basic job.

Anyway, any advice or ideas? I'm going to feel around and reset all the wires on the plugs tonight or tomorrow and see what I find as a first step.

Tom

 

[Gunn]

dielectric: A dielectric material (dielectric for short) is an electrical insulator that can be polarized by an applied electric field.

Hmmm...so I am now thinking when I placed some dielectric grease into each spark plug boot that I used too much...thereby insulating the conductor from the spark plug!?!?

 

[nickdcj7]

the dielectric grease keeps the electricity inside the boot, and if you have the wires pushed on properly it wont hurt anything. i would start by double checking the wires both for location and being pushed all the way on. It could also be a timing issue. Is there any chance you accidentally rotated the distributors when you were installing everything? Checking and setting the timing would be my next step.

 

[BillK2632]

dielectric: A dielectric material (dielectric for short) is an electrical insulator that can be polarized by an applied electric field.

Hmmm...so I am now thinking when I placed some dielectric grease into each spark plug boot that I used too much...thereby insulating the conductor from the spark plug!?!?

Possible if you put a lot on, a small - very small - amount is good, it seals the boot connection to the sparkplug, keeps out moisture and prevents the boot from sticking to the plug. Any small amount that gets on the plug itself basically squishes off the top of the plug when you put the boot on and does not affect the connection. If you put a glob on each one, it could cause a problem and it would not hurt to clean it off. The correct way to use dielectric grease on spark plugs is to apply a small amount to the inside of the spark plug boot, not the spark plug itself.

Try the simple things first:

Check and recheck the work you have just done:

1. Clean off the dielectric grease except for a small amount on the inside of the spark plug boots.
2. Check, double check and triple check the spark plug wires to make sure you don't have two crossed. CLEAN, TIGHT, and in the right ORDER.
3. Check the ignition sensor - the bottom of the rotor has "teeth" on it, they pass through the ignition sensor, kinda of like the modern version of ignition points. They can go bad, especially the older ones with exposed connections on the back, and cause all kinds of strange ignition behavior, they are cheap and easy to fix. A first step would be to make sure the contacts are clean.
4. Fuel filters? Always check fuel filters - although seems odd both engines and considering the ignition system parts you just replaced.

Timing being off is unlikely and especially in both engines at the same time and special tools and procedure is required for EFI engines - that might be something for the dealer to check if it gets to that point.

 

[CliffA]

I just tuned up a 4.3 vortec in a 2005 truck I recently bought....i am assuming that engine is very similar to your engines....I may have read your post wrong so sorry if I did, but it sounds like you have the #1 plug wire attached to the first distributor cap terminal on the port side....I am pretty sure the #3 wire should be the front one followed by the #1 and then the #5........

I am going from memory which is dangerous but this diagram sort of backs me up....

again this is assuming you have the same distributor as my truck engine.....

cliff

 

[Gunn]

Thanks guy for the input so far.

I think I'll feel around for a loose wire and if nothing obvious, pull them all, clean the dielectric grease from them, then properly coat the inside of the boat lightly with dielectric grease using a q-tip, then re-install. This is actually my 1st time using this grease, and I basically put a small glob, covering the entrance to the boot and then installed. Never realized it was actually an insulator, and the reasoning behind using it!

Here's what the distributor cap and rotor looks like on the 4.3MPI; notice the rear left side (in this view) is the main ignition coil lead, and in front of that coming forward are the numbers 6, 4, 2. This is the way it would be installed as I'd be looking at it from in front of the engine. It's nearly foolproof, compared to the circular caps of yesteryear...

 

[CliffA]

Thanks guy for the input so far.

I think I'll feel around for a loose wire and if nothing obvious, pull them all, clean the dielectric grease from them, then properly coat the inside of the boat lightly with dielectric grease using a q-tip, then re-install. This is actually my 1st time using this grease, and I basically put a small glob, covering the entrance to the boot and then installed. Never realized it was actually an insulator, and the reasoning behind using it!

Here's what the distributor cap and rotor looks like on the 4.3MPI; notice the rear left side (in this view) is the main ignition coil lead, and in front of that coming forward are the numbers 6, 4, 2. This is the way it would be installed as I'd be looking at it from in front of the engine. It's nearly foolproof, compared to the circular caps of yesteryear...

That is the same distributor cap I have....the #3 plug wire should be first (towards the bow of the boat) on the port side (right hand side of your picture) of the distributor cap then #1 and then #5.....I think you may have #3 and #1 wires crossed at the distributor cap....

 

[Bt Doctur]

http://ww2.justanswer.com/uploads/ggrote1/2010-03-25_153617_4.3_firing_order.gif

 

[Gunn]

...but it sounds like you have the #1 plug wire attached to the first distributor cap terminal on the port side....I am pretty sure the #3 wire should be the front one followed by the #1 and then the #5........

Cliff, you were spot on! I actually missed your first post; it came within minutes of me typing my 2nd update. And sure enough, I knew that was the problem immediately. For some reason, I guess I saw the 6-4-2 on the left side and saw the other odd numbers and just assumed they were 1-3-5. But NO! They were indeed 3-1-5.

And that fixed the problem; as soon as I fired it up I could tell it was smoother and actually started immediately (as it should have). The reason I did all of this in the first place was because the starboard engine was hard to start. The distributor cap was very corroded on the terminals underneath.

It's amazing that these V6's can run as good as they do on 4 cylinders.

Thanks guys for reading my post carefully and spotting my problem!

Tom

 

[Quint4]

You owe Cliff a soda and candy bar.

 

[CliffA]

Cliff, you were spot on! I actually missed your first post; it came within minutes of me typing my 2nd update. And sure enough, I knew that was the problem immediately. For some reason, I guess I saw the 6-4-2 on the left side and saw the other odd numbers and just assumed they were 1-3-5. But NO! They were indeed 3-1-5.

And that fixed the problem; as soon as I fired it up I could tell it was smoother and actually started immediately (as it should have). The reason I did all of this in the first place was because the starboard engine was hard to start. The distributor cap was very corroded on the terminals underneath.

It's amazing that these V6's can run as good as they do on 4 cylinders.

Thanks guys for reading my post carefully and spotting my problem!

Tom

glad it was something simple......the reason I suspected you had reversed the #1 and #3 wire at the distributor is because I did the same thing on my truck engine.....:grin:.....

this is also a perfect example of a poster giving the group enough information up front so we can start to troubleshoot in the right direction.....often posters just do not give us enough info to be of help in an efficient manner...

cliff

 

[Gunn]

You owe Cliff a soda and candy bar.

Yes, at least!

Sent from my SM-G900V using Tapatalk

 

[CliffA]

I like 'Mountain Dew' sodas and 'Baby Ruth' candy bars.....:smt001......

cliff