Absolutely frustrated with this Mercruiser engine

[Hoplite808]

This statement bothers me.



I'm not saying that it isn't in the manual, it just sounds contradictory to everything I've ever known or seen. Why in the heck would they ever throw spark at varied crankshaft positions when the engine rpm is stable? A few degrees I can understand when wear is involved.

I have seen a procedure on how to set base timing with or without the Diagnostic Code Tool, or MerCruiser Special Timing Tool but I still don't understand the reason for the instability. Don't know the sensors and controls used and what sort of feedback loop is used on this engine. Guess it's time for me to read up on it.

I don't know. That's just what it is. Took me a while to figure it out while I was trying to reset the timing after the reassembly.

 

[Hoplite808]

https://www.baylinerownersclub.org/...54-low-total-spark-advance-at-wot-gctid637982



I believe the knock sensor retarding (delaying) the spark timing has been brought up before.

Also brought up it the linked article is the possibility of a slipped outer ring on the dampener. (If equipped.)

MORE...
You could measure the voltage on the "return" (signal) output of the TPS in lew of the scan? tool.



Just things to think about.

None of the Fox Marine module readouts from the ECM showed any indication of a fault at either the TPS or the knock sensor. There is 0 knock retard and the TPS readings appear accurate based on where the throttle control actually is.

 

[JayhawkCurtis]

the previous owner is deceased. I bought the boat from his widow who had been keeping it but not maintaining it properly for a while after his death. She finally decided to sell it

I think I saw this episode of the andy griffith show, Barney fife bought a 1954 ford sedan from a sweet little old lady from mount pilot.

 

[ttmott]

I can only speak of how things were with non positive stop stud mounted adjustable hydraulic lifters years ago. The procedure was, with the engine warm and running, and after initial adjustment (both valves closed TDC) was to back off on each rocker arm adjusting nut until the rocker arm clattered, tighten until the noise just stopped and added one additional full turn one fourth turn per time (90 degrees) allowing the engine to stabilize between each 90 degree movement. The problem on some high mileage engines was when varnished plungers didn't allow for the full 360 degree adjustment so 1/2 to 3/4 turn was acceptable (180~270). The reason for the one additional turn was to center the inner plunger in the middle of it's range of travel.

Positive stop stud mounted rocker arms could be adjusted for various engine machining operations that changed the position of the inner plunger by using under or oversize push rods.

They also make pads that clip onto the end of the rocker arm where the push rod oiling hole is located in order to reduce oil "lubricating" the engine compartment.

Can't do that with roller lifters.

 

[scoflaw]

His gen 5 might not have roller lifters.

 

[PlayDate]

For the umpteenth time mechanical soundness isn't confirmed until you verify the camshaft and the valve timing. A place you haven't been.

Original owner has no insight on what might be the problem? I'd bet he knows the answer.

I agree with @scoflaw .

I get how frustrating this is and that you hoped to sell the boat as is. Now.....you are being told you will have to give it away because no one will buy it. First, you need to consider the source of the "no one will buy it". A broker is not the way to go with this transaction.

Consider a two part approach: 1) Listing it yourself 2) Continue with attempting to repair it. You may find someone who wants a project boat and you reach a deal on the terms. Certainly you lose nothing by trying to sell it on your own.

In regards to fixing it......my comments are about the history of this engine. Apparently, it hasn't worked right since you bought it. As to why.....well the guy who could answer that question has passed on which means we are back to helping you sort it out if you want the help.

Factually it either did or did not work when you bought it. If we take the view it was working .....then it has to be something that was done to it after the purchase. Either way.....you have to go back to the beginning and buy a new compression gauge and retest the engine. Almost every survey of a gas boat includes a compression test.....was one done at the Survey?

As to setting the valves......I don't believe you used the right procedure as noted by @ttmott . Since you have to have the exhaust manifolds bolted on to run the engine and the valve covers off (which can't be removed with the manifolds on) that must have been quite an effort.

I get you want to get rid of the boat and are tired of working on it. List it yourself and take a short break from working on it. When you are ready to start again.....do the compression test with a new gauge and the engine warmed up.

 

[rustybronco]

None of the Fox Marine module readouts from the ECM showed any indication of a fault at either the TPS or the knock sensor. There is 0 knock retard and the TPS readings appear accurate based on where the throttle control actually is.

The disadvantage of not having read the entire thread.

I would still verify that the TDC marking on the dampener corresponds with the #1 piston being at TDC. should be easy enough to do with just a stiff wire.

 

[Skybolt]

@Hoplite808 It doesn't look like you have pulled the timing chain cover and checked the cam timing. This was mentioned back in post #23, but you have wasted so much time and effort so far, seems like the it's time to do this.

 

[rustybronco]

His gen 5 might not have roller lifters.

Looks like that is the case for a 1996 gen V. Lifter p/n 811583 shows as a flat tappet style.

Nope... 1996-97 7.4LX shows roller. p/n 850467

 

[km1125]

With how they designed this set up the only way to get a reading of the timing with a timing light is to put it into maintenance mode. Otherwise the timing light flashes will not make any sense with the mark on the crank. It’s an over complicated design that was made early on when Mercruiser was adding electronic ignition systems and fuel injectors and they moved on from the design apparently very quickly. I don’t like it, but it is what it is.

It's got nothing to do with "how the system is designed". You can ALWAYS use a timing light to CHECK timing. You ECU is really no different than those going back to the mid-80s. Pretty basic and just trying to get spark and fuel to the right cylinders in the right amounts and right time. Adding the knock sensor is really the only "complicated" part.

Don't give the ECU too much credit. It's not that complicated, especially regarding spark. It's a pretty basic spark map and just uses manifold pressure and RPM. At IDLE, MAP can bounce around a bit quickly as each cylinder ingests air, so spark could be bouncing around a bit. RPM may also move around a little as the ECU manages RPM with the IAC. But spark should still be in a reasonable space, just not so consistent that you can use the measurement to SET the timing.

Remember... the timing light is telling you exactly WHEN the spark is firing. If the spark advance is really "all over the place" then that means the spark plug(s) are really firing "all over the place". That might really mean you DO have timing chain issues, as the slop in the timing chain is translated into the distributor movements. That doesn't happen with coil-on-plug ECUs because they're just using a crank sensor for timing.

You might want to pop the distributor cap off and then move the crank both directions to see how much slop you really have. That could tell you A LOT.

 

[Scott215]

If it's not a roller cam. Is there a possibility of a or several flat lobes. But I don't understand the 2000 rpm cieling it seems very odd

 

[PlayDate]

I'm curious.......this is from the OP May 10, 2022 (I decided to reread the previous thread):

"I was getting zero pressure in the #7 cylinder when I was testing all the cylinders. It had 150 according to my notes before the rebuild."

Yes. I know this was in the middle of finding out your head rebuild had problems. Still, I am focused on that 150 number and the 120 number you started this thread with. Am I to understand that you started with 150 and the cylinders are now 120?

 

[370Dancer]

Looks like that is the case for a 1996 gen V. Lifter p/n 811583 shows as a flat tappet style.

Nope... 1996-97 7.4LX shows roller. p/n 850467

marineengine.com using his serial number shows 811584, flats

 

[Hoplite808]

I'm curious.......this is from the OP May 10, 2022 (I decided to reread the previous thread):

"I was getting zero pressure in the #7 cylinder when I was testing all the cylinders. It had 150 according to my notes before the rebuild."

Yes. I know this was in the middle of finding out your head rebuild had problems. Still, I am focused on that 150 number and the 120 number you started this thread with. Am I to understand that you started with 150 and the cylinders are now 120?

Sorry typos happen. Most of this is being typed on my phone.

 

[Ericinmich]

This statement bothers me.



I'm not saying that it isn't in the manual, it just sounds contradictory to everything I've ever known or seen. Why in the heck would they ever throw spark at varied crankshaft positions when the engine rpm is stable? A few degrees I can understand when wear is involved.

I have seen a procedure on how to set base timing with or without the Diagnostic Code Tool, or MerCruiser Special Timing Tool but I still don't understand the reason for the instability. Don't know the sensors and controls used and what sort of feedback loop is used on this engine. Guess it's time for me to read up on it.

At idle it's typical for spark to be moving around with those vintage of controls. In the early 90's (long before ETC) idle was control by a slow IAC valve/pintle but some smart controls engineers refined the controls to get more stable idle by using idle spark control. A set amount of bias would add or subtract to the target spark and you could hold idle very stable and also target a lower RPM (which in cars helps FE). Typically the base spark would be a bit retarded for desired so that would you could add or stubtract without causing missfire. It was pretty cool the first time we put it in! I summary, spark control would be the fast reaction while the IAC motor would catch up with air as needed. Turning on AC (cars) was alwasy the tough situation until the AC systems went to stroking compressors.

So yes, there had to be a way to put it in a diagnostic mode to look at spark timing that didn't move around.

 

[Ericinmich]

https://www.baylinerownersclub.org/...54-low-total-spark-advance-at-wot-gctid637982



I believe the knock sensor retarding (delaying) the spark timing has been brought up before.

Also brought up it the linked article is the possibility of a slipped outer ring on the dampener. (If equipped.)

MORE...
You could measure the voltage on the "return" (signal) output of the TPS in lew of the scan? tool.



Just things to think about.

The knock system should never be active at idle, I'm sure it's not calibrated to be active. That vintage of knock system used a resonant sensor, basically a big bell that hung on the side of the block that would light up when it with the target frequency. At idle, various engine noises can ring the bell... so it's ignored.

I did have a friend with a slipped dampener on a late 80s small block, it took years before someone firgured out why it ran like crap. But it was more of an odd misfire, not a flat low on power.

And as far as TPS reading dropping, that isn't showing up on the data from this boat.

 

[km1125]

At idle it's typical for spark to be moving around with those vintage of controls. In the early 90's (long before ETC) idle was control by a slow IAC valve/pintle but some smart controls engineers refined the controls to get more stable idle by using idle spark control. A set amount of bias would add or subtract to the target spark and you could hold idle very stable and also target a lower RPM (which in cars helps FE). Typically the base spark would be a bit retarded for desired so that would you could add or stubtract without causing missfire. It was pretty cool the first time we put it in! I summary, spark control would be the fast reaction while the IAC motor would catch up with air as needed. Turning on AC (cars) was alwasy the tough situation until the AC systems went to stroking compressors.

So yes, there had to be a way to put it in a diagnostic mode to look at spark timing that didn't move around.

Would ISC be a feature on MEFI-1?
Also, wouldn't an off-idle condition (say, raising the RPM to 1500-1800) be enough to get out of the ISC control?

 

[Ericinmich]

Would ISC be a feature on MEFI-1?
Also, wouldn't an off-idle condition (say, raising the RPM to 1500-1800) be enough to get out of the ISC control?

Since I long ago tossed the sw listing I can't say for sure, but I think so. We did an early version on the 90 l98 Vette when it went to speed density (89 was mass air flow) and it was a game changer for idle stability during load transients. And yes, getting out of idle mode disables it. On cars you would blow the emissions if you bounced spark around as much as isc did.

 

[Hoplite808]

Due to the comments that were made suggesting I improperly adjusted the valves I decided that would be an easy enough thing to check while I wait for the pickup coil to arrive. The last two days I’ve been going down to the boat to work on this for a bit before I have to go in to the work that pays the bills, and the last two days I show up and blue skies all around and once I’ve opened everything up and start to wrench the sky let’s loose and heavy rain that wasn’t on the forecast starts dumping on me. So I have to hurriedly cover everything back up. But of course once it’s all closed the rain stops and if I open it up again the rain starts again. Either I’m being punished by God at this point or the Devil has possessed the boat and is trying to make sure I’ll never fix it. Anybody want to come help with an exorcism? At this point I don’t think it would hurt.

 

[Nater Potater]

Anybody want to come help with an exorcism? At this point I don’t think it would hurt.

It sounds like you might need two exorcisms! I'd love to come help you, but anything I can think of has already been addressed.