1999 Mercruiser 4.3L EFI "ping" above 2,500 RPM

[Daddy O]

Re: 1999 Mercruiser 4.3L EFI

Re: 1999 Mercruiser 4.3L EFI

Have you looked at the TBI? The shaft can wear and cause the TPS to get a bad reading, and give bad map readings. Also the TPS itself might be bad. Which can cause the engine to sputter, and go lean. This is all from car experience, not boat.

 

[Reel Poor]

Re: 1999 Mercruiser 4.3L EFI

Re: 1999 Mercruiser 4.3L EFI

Ok, no codes present, except for the MAP sensor, and we understand that one. Fuel pressere ok. Ignition system ok.

It's very possible that the injector(s) are not allowing proper fuel flow ie, glogged or defective, causing lean mixture backfire.

A couple other ideas here. While running under a load chek the ignition timming with an, adjustable degree wheel timming light. Make sure timming is advancing and retarding as it should be, and not operating fixed, at any one setting. With the engine at a high idle (while in neutral) you can also rap on the engine block with a small hammer (while watching the timming) and it should retard the timming if the knock sensor and control module are working properly.

Do a compression test and a cylinder leak test. I say this because you said this problem (spark knock/detonation) has been apparent and has progressivly gotten worse with time, since you installed the engine 3 years ago. The spark knock can cause mechanical problems with valves and seats as well as pistons. It very possible that you may have a valve and seat problem raring it head at the higher rpms. Its also possible that an exhaust valve is not opening enough to let the exhaust escape under heavy throttle (possible came lobe worn).

I would lean toward faulty injectors, but what do I know, I'm just an arm chair mechanic. d

 

[rowndman]

Re: 1999 Mercruiser 4.3L EFI

Re: 1999 Mercruiser 4.3L EFI

Thanx guys for more input.
TBI & TPS seem to be good - there is no wear or slack on the moving parts, and when the "Techs" were fooling with the machine a couple of weeks ago, one of them mentioned that their scan tool was showing good, correct readings for the TPS. They also said that the timing was spot-on at idle (saw them check that), and that advance through increased throttle position seemed normal. They weren't too sharp, but I gotta believe they could read their tool reasonably well (wish I had one of those). Faulty injectors could be, I guess, but I don't think so - if you don't mind reading another long story, here's why I'm convinced that the problem is electronic . . . and between the distributor & the coil.

I bought this engine & outdrive Brand New in 1999 to replace the Mercruiser "470" that was in it (that I installed in this boat in 1978 to replace the original Volvo Aquamatic 100 that it came with when it was bought new by my father in 1962). Anyone that has, or had, a 470 knows why (another good Merc/Kiekhaefer idea that didn't work-out in the long run), but I guess 21 years ain't bad. It was a running take-out, but I was sick of dealing with the continuous electrical problems with it. Anyhow, designed, built, and installed new motor mount foundations and installed this engine with complete new instrumentation & controls (Quicksilver). The old 470 ran a 21" prop; that's what I had, so that's the first test wheel I tried - engine maxxed-out on the rev limiter (4950 rpm). Next tried a 23 - same thing. Next tried a 26; it also maxxed-out on the rev limiter, but it was real close. Finally found an SS 26 cup that would peak light-loaded at 4850 - 4900 rpm - Perfect! That's what has been on it since (the same wheel; I'm careful with this thing). Boat absolutely performed well beyond my expectations - would make 54 - 55 mph (according to a good GPS) when light, and can routinely plane-off & run in the high 40's with 10 full grown men & a couple ice chests aboard.
I don't really need to, or want to, go that fast, so this rig spends most of its life at around 3,200 - 3,500 rpm. Everyone's comfortable, and the engine is loafing. She ran flawlessly for about 2 1/2 - 3 years.
Somewhere around this time I noticed the tachometer would occasionally "blip" up about 200 - 300 rpm higher than the engine was running, then it would drop back to normal. Engine was running fine, so I figured my new tach was going bad & didn't really sweat it; when it finally broke I'd get a new one. As time went by, this phenomenon occured more often & the blip would get higher, 400 - 600 rpm; engine still running fine. One day my son asked me if I had noticed the engine pinging, which I hadn't. We were on a run to our camp off Lake Pontchartrain & I had opened it up for some reason; he was sitting in the back by the engine & heard the faint pinging sound. I couldn't pick it up at the helm. We swapped places & sure enough there was a light ping at WOT. Whenever the tach would blip, the engine would ping. We both noticed this. Crack the throttle back (to 4,200 rpm or so) and everything is lovely again. Since I don't need to run WOT, and it didn't always do this, figured I'll just live with it cause it doesn't effect anything at my normal operating speed. We DID try a couple of tankfulls of premium fuel, but that made no difference.
As time went by, this phenomenon began to occur at lower & lower rpm and more consistently, until its reached the point its at now. One thing that has been notable through this saga, is that the engine has much less tendency to do this on a cold (40 - 50 degrees), dry day. Interesting, but we don't get many days like that in south Louisiana.

With all that history, and many parts changed along the way (plugs, cap, rotor, wires, numerous fuel filters, temporary fuel supplies from outboard tanks, MAP sensor, knock sensor,etc, etc,), I have to believe that whatever is causing the tach to "blip" (it will now swing over 1,000 rpm higher than actual) is the cause of my problem. Occasionally, I can "sneak-up" on it and get-up to 3,400 rpm with no problem, but after 3 or 4 minutes the tach will blip, then it starts pinging. If it blips 800 - 100 rpm, I'll get backfire. Crack the throttle back to below 3,000 rpm, and the tach stops blipping & the engine is smooth as silk. Something is giving the coil (and the tach) bad information, or so I believe.

 

[calwldlif]

Re: 1999 Mercruiser 4.3L EFI

Re: 1999 Mercruiser 4.3L EFI

Ignition control module

 

[Don S]

Re: 1999 Mercruiser 4.3L EFI

Re: 1999 Mercruiser 4.3L EFI

When you went to the 4.3, did you change the wiring harness that went up to the instrument panel? and install new gauges etc?

 

[rowndman]

Re: 1999 Mercruiser 4.3L EFI

Re: 1999 Mercruiser 4.3L EFI

Yep! New instruments, new harness, new throttle/shift control box, and new throttle & shift cables (length was wrong because of the different shift/throttle set-up on this one vs. the 470). Only thing that stayed was the Teleflex steering.

Calwldlif:
Any way that you're aware of that the ICM can be checked / tested before replacing? That's a $110 word you wrote.

 

[calwldlif]

Re: 1999 Mercruiser 4.3L EFI

Re: 1999 Mercruiser 4.3L EFI

I wish there was. I couldn't find one.
I did read a similiar thread, and the guy
said an auto parts store had a machine.
It was a limited test.

I agree it is a high ticket item.
In my limited testing of them, I was successfull
in repairing issues they caused by replacing.

Your symptoms are enough for me :%

I can only stress the proper system testing, using
flow charts, to eliminate other parts, will leave this
part as defective.(although it will check ok)
it is a gut type call. I find the rpm and symptoms
your having.....................................leave the ICM.
The heat issue you discribed would leave me to
first re-heatsink and test.

When I first read the entire thread I found many good
testing items, and didn't get the impression you
did as instructed................I felt you Poo Pooed
and tested your own way :$

I am not privy to your personell testing, or the
engine. I have been wrong, ask my wife

I will agree the price of the part did motivate me
to test and retest, I still gulped hard when buying
a new one. BUT it did fix the issue........................

 

[johnbo]

Re: 1999 Mercruiser 4.3L EFI

Re: 1999 Mercruiser 4.3L EFI

After reading your recent posting of the history of your setup, a couple of questions popped up. I'm definitely not the expert here, just an electrical engineer trying to avoid some work at the office, but here goes:

1) How is the tach connected to the engine? More specifically is the tach just monitoring the coil trigger or is it an output from the engine control?

2) In either case, if the tach is misreading and we aren't looking at bad grounds in the harness or something trivial like that, then it would mean that the tach is indicating that the engine is 'thinking' that its running faster than it is. I'm trying to think of what could cause this.

If the coil is being triggered at inappropiate times, in addition to the normal trigger points, you'd be seeing sparks at awkward times. The extra sparks/triggers would cause the tach to rise, afterall, all it is doing is integrating the sparks per unit time. (Sorry, engineering speak). But, these early sparks, if it can jump from the rotor to the plug terminal will essentially cause an early ignition, which is exactly what a ping is, but caused by different things.

One thought: Now trying to come up with a reason for the speed dependancy... Since there is only a certain degrees of rotation of the distributor rotor where a proper spark could make it to a plug, this might be a function of engine speed, if the source of the extra sparks is not tied to the engine speed (thinking about a random trigger source). This would imply that a distributor rotor with a narrow contact would make the engine run better than a rotor with a wider contact.

Question: what is the source of the spark trigger? Is this the distributor or a crank angle sensor and a engine control unit?

A test: This is going to depend on your ability to find someone with a engine oscillscope. If you could look at the coil trigger wire or the high voltage coil wire, you should normally see a nice sequence of evenly spaced sparks or triggers. As you run the engine up to speed, the distance between the sparks should decrease linearly. My guess is that at some point, you would see 'extra' triggers.

The problem is that you are going to need to find someone who really knows how to use their scope to look for this. It would only take a few 'extra' triggers to cause a pre-ignition that would sound just like a knock. So what you would really like to do is to trigger when the pulses are too close together, which is common in electronics test equipment, but may not be in an automotive scope.

I used to design and build oscilliscopes for the electronics industry and what you trying to look for is possible, but it might take some luck to find someone who has a good enough scope, knows how to use it, and how to get it into your boat.

Another (simpler) test. If you could mark the harmonic balancer with 6 equidistant marks aligned with the timing position at the problem RPM. Now watch the results of the timing light when connected to the coil wire. In theory, you should only see the marks that you created all lined up under the timing pointer. If their are extra (or misplaced) sparks/triggers, would see the marks disappear or shift.

Maybe all of this (long) discussion will trigger someone else's thoughts that might be more relevant to this setup.

Later,

johnbo

 

[rodbolt]

Re: 1999 Mercruiser 4.3L EFI

Re: 1999 Mercruiser 4.3L EFI

the index test will only work with plug wires, if you use the coil wire you will see a few at once.
however thats the easiest way to look for spark scatter.
make 5 more marks from the TDC mark at 60* itravels. label them in a ccw rotation starting with the balancer mark as 1 and the rest follow the engine firing order to number.
then run it at the problem RPM and move the timing lamp pick up from 1-6 and see if any number other than the wire your on shows up.
this is a tried and true method.
we used it on the older jonnyrudes with the 4 coils mounted on top as well as the amplifier type systems as they were notorios for cross fireing. it works on about any ign driven setup.
there are a few siamese coil setups its tricky to use as both plugs fire at the same time.
if its crossfireing or a cylinder or two is firing early you will see it.
but like I said, the causes of preign/detonation are few. eliminate each engine subsystem as the cause and your problem will be solved.

 

[johnbo]

Re: 1999 Mercruiser 4.3L EFI

Re: 1999 Mercruiser 4.3L EFI

My inexperience may be showing here, but I think that monitoring the coil wire would be what you want. In a normally working system, the coil would fire for each plug, which should flash as each index mark went past the timing mark. An extra flash would hopefully show an index mark that was out of place. <Edit> Note that I'm looking for a flash that doesn't appear at a normal timing mark, like 10-20* early.<End Edit> This extra flash might not appear if the spark didn't make it across the rotor to plug connector gap in the distributor, but would show up at the coil.

Side Note: If this was happening, I could imagine that the coil would be quite unhappy about this, as this would essentially leave an open circuit for the coil at the point that it trys to fire without a load. I seem to remember that this is bad news for coils and ignition circuits.

Also, I think that I (and rodbolt) made a mistake about the indexing of the crank. This is 4 cycle motor, so on a V-6 you'd get 3 sparks per revolution. I believe, but can't prove, that the firing point for the 'opposite' cylinder would be at the same spot. Therefore, you'd need to add two additional marks to the pulley/balancer, 120* apart.

Later,

johnbo

 

[rowndman]

Re: 1999 Mercruiser 4.3L EFI

Re: 1999 Mercruiser 4.3L EFI

Thanx again everyone for your input. Lots of things here I can try this weekend, and I sure appreciate everyone's thoughts - ideas - hints - or personal experience. If anyone has felt "poo-pooed", I certainly did not intend that at all, and am sorry if I gave that impression. I am a hard-headed old cuss; my wife reminds me of that frequently.
When I was in high school and college, I worked for a local Evinrude & Mercury dealer, first as a floor sweeper, then floor sweeper & boat rigger, then more. The mechanic in this shop was one of the VERY best ever, a legend in these parts, and I learned (an awful lot!) at his side - he gave my young self a whole new outlook on what "do it right" really meant. Did this for 6 years, and was a pretty good country boy mechanic when I graduated from college & started a "real" job. This was in the 60's, when Carl Kiekhaefer was the King, and Thunderbolt Ignition first came on the scene. Good old days, those. Anyway, a lot of what I try is based on those old experiences, what (somewhat limited) tools I have at my disposal, and degrees of relative ease with which some things can be done (I'm not as flexible as I once was). Please, no one take any offense at anything I write, 'cause certainly none is intended.
New Chapter:
Yesterday afternoon was finally able to make contact by phone with the "diagnostician" that I mentioned on Sept. 6. Turns-out he's been in the hospital for several days - just got out & he's gonna be OK. Had a long conversation with him, and after he listened to all the symptoms and asked a few questions, he reckoned he knew what it was but would need to bring all his diagnostic equipment to the boat & check it out thoroughly. Exactly what I had in mind, but since he's been out of commission for several days, he's Waaaay behind in his work and won't be able to get to me for about 2 weeks. Talked a little more, and was able to coax his diagnosis out of him:
He suspects the ignition coil is arcing between the secondary output & the "tach" lead end of the primary ckt. That's the source of the "blips" on the tach and the misfiring. Says he's caught a couple of these coils doing that over the years. Told him I'd looked the coil over pretty good looking for signs of that & didn't see any; he said that didn't matter; he had found one doing it internally. His theory sounds very good; would account for all the symptoms. I'm very tempted to swap the coil myself & try it, then pay him a consulting fee to his satisfaction if he's correct.
Messing with this engine all the time is interfering with my beer-drinkin'; know what I mean?

 

[rodbolt]

Re: 1999 Mercruiser 4.3L EFI

Re: 1999 Mercruiser 4.3L EFI

yor right, the 4 stroke 4.3 will only need 2 additional marks and they will show up twice per complete cycle.
however at 3000 RPM the human eye is not going to focus fast enough to use the coil wire as its going to fire every 120 degrees.
thats gonna mean the marks will be jumping.
the dist on the 4.3 rotates at 1/2 crank speed. means 120 degrees of crank rotation to bring up the next ign pulse to fire the next piston in the fireing order.
what your looking for is a steady flash with the mark at the correct position to the reference point.
if the coil is arcing and you light is attached to the plug wire the mark will not be steady.
while the human eye may not refocus fast enough to see the number it is fast enough to see if the flash is steady or not.
but go back to the cause of detonation in a 4 stroke.
there are not many and they can be eliminated as a culprit rather easily.
it can be caused by ign, easy to use a timing light. it can be caused by poor quality fuel. easy to eliminate with a known good fuel source, it can be caused by excessive compression for the grade of fuel used, again easy to test.
it can be caused by excessive combustion pressures due to an overloaded engine, a bit harder to test.
it can be caused by excessive heat due to a lean air/fuel mixture, use a large volume squrit can and spray fuel directly into the intake tract to test.
this is what I deal with on a daily basis.
we get boats in that we have no history of,the customer is only sure its not running correctly but cant tell us anything more.
we have to accuratly diagnose and fix it.
most of the time a careful analysis of the spark plugs will tellme whats going on.
which is why I hate it when they put brand new plugs in it just before I get it .
but if that plug has been firing in that cylinder a long time it will tell me what is going on, it will show excessive heat,lean fuel rich fuel and many other issues.
the biggest problem with looking at spark plugs is the time and amount ya have to look at to figgue it out.
thats the one area thats all but impossible to teach or look in a book.

 

[rowndman]

Re: 1999 Mercruiser 4.3L EFI

Re: 1999 Mercruiser 4.3L EFI

FOUND IT !!!!

Put a new coil in it - no change. Had a 3-day weekend at my disposal and was determined to get to the bottom of this if I could. Sat down & drew-out my own schematics so I wouldn't have to keep flipping pages back & forth in the manual to see both ends of a circuit, and everything in between. Then started checking all grounds in the system - everything was lovely. In the process of drawing things, it finally dawned on me that the shift interruptor is in the signal circuit between the ECM & the ignition module. That being the case, this thing needs to work very well, not just work, for it to do its job correctly. Had checked the interruptor before with my meter on Rx1000 and it showed working fine - opening & closing every time. However, that ain't good enough for the circuit it's in. Set the meter to Rx1, and found about 1-2 ohms resistance across the switch in the closed position. If I put my finger on the body of the switch and squeezed it a little against its mounting, the resistance would go up to around 6 - 8 ohms. A little side pressure on the switch's probe, or jiggle the rocker that the shift cable connects to, and resistance would dance around fro 4 -16 ohms. Hello! - that looks familiar. Since the signals involved here are low voltage, that much resistance would make a whale of a difference in the conversation between the ECM & the IC. Made a little jumper out of some 12 gage romex & fitted it to the plug, then took off for a trial. Engine ran perfectly - 4500 RPM & not a missed beat. Let 'er run for about 15 minutes at WOT (first time that could be done in over 2 years) and not a whimper. Ran the rest of the weekend with my jumper in place (you can shift it if you're very careful, patient, and not doing any delicate maneuvering) and not a moment's trouble.
New shift interruptor ordered today ($25.15).

To Newport Dave, who first recommended this check, and to Don S & rodbolt who brought it up again (thank goodness) - my heartfelt thanks. To anyone who reads this thread & has a similar problem, be sure you check the shift interruptor with your meter on its lowest range so you get the real story, and don't follow my stupid (and expensive) example.
Thanks again everyone for all your suggestions & ideas.

Still planning to have the "diagnostician" referred to above come & check everything, & make sure there are no new codes set and all is as it should be.

 

[Don S]

Re: 1999 Mercruiser 4.3L EFI

Re: 1999 Mercruiser 4.3L EFI

Glad you found the problem.
That same shift interrupt switch causes a lot of problem with outboards as well.
The reason I say disconnect it is because of the flakey readings you can get using a ohm meter.
Disconnect it completely and test. If it works replace the switch. Those switches are really JUNK.
For anyone with older engines, it a particular type switch and causes problems because it connects to the ECM, not directly to the ign. system. Here is a picture of the switch that causes the problem (#18 )

 

[blackmouther77]

Re: 1999 Mercruiser 4.3L EFI "ping" above 2,500 RPM

Re: 1999 Mercruiser 4.3L EFI "ping" above 2,500 RPM

I have the exact same problem going on with my new boat I just bought 3 weeks ago. I have been to 3 mechanics and spent 2200 dollars. I finally joined this forum and when I posted to this discussion I found the second page. I am going to test this tomorrow and if it works you are the man

 

[DMeyers]

Re: 1999 Mercruiser 4.3L EFI "ping" above 2,500 RPM

Re: 1999 Mercruiser 4.3L EFI "ping" above 2,500 RPM

I have the same problem that I have been fighting for the past 5 years. I have changed every component except the ECU. I have spent untold dollars fighting this problem and no-where did anybody offer the shift switch as a possible issue. I jumper it and all problems are solved. Thanks for posting to this site. I have placed a PM in your box and would like to mail you a gift since you avoided my next purchase of the ECU for $1500 that would not solve anything.

 

[Farmer 2]

I have the same problem since I bought the boat and was told first the motor was bad replaced that same symptoms. Then all electrical was replaced same symptoms. Came across this article about the Shift interrupter and made me a jumper wire . Now when you unplug the shift interrupter the boat will shut off remember this is all tested on the water. After unplugged you put the jumper wire in the ECM side of the plug then you start the boat and very carefully you put it in gear. Than when your out in open water put the hammer down. I want to thank all my boat ran like a new boat. I ordered the switch. Thanks!