1999 MerCruiser 50 EFI electrical mystery

"New at this - sorry, my first

"New at this - sorry, my first post was in the wrong section.
I have a 1999 Regal - 5.0 EFI MerCruiser / Alpha one.
The boat has less than 100 hours on it and has been used very little over the last 3 years - has essentially been summerized and winterized.
The first time out this summer it seemed to run okay for 1/2 hour or so and began "popping". The sound to me was like a backfire. Long story short, the shop has done almost everything trying to figure it out, to no avail. As far as symptoms go, the tach appears to act irregular, MOST of the time the boat pops. I will add it it doesn't always make the popping noise but certainly seems to lose power simultaneously with the noise or the tach spiking(5000+). The boat idles fine and that's about it. Under any load it will most certainly pop/backfire. I can sometimes get it to run without popping, usually at a constant speed of around 19-24mph.
The boat has been scoped or scanned and zero codes come up.
The following has already been tried
1) Tach changes - 3 times
2) New batteries
3) New alternator
4) New plugs
5) New wires
6) New ignition module
7) Gas changed - at least twice with fuel additive
8) Valve cleaner / injector
9) recently two of the three wiring harnesses have been changed - the third is back ordered
10) New fuel pump
11) New distributor cap / distibutor... and maybe some stuff that the shop/mechanic hasn't discussed with me. To my knowledge this has been discussed with Merc and they are at a loss. The shop has advised me they have reviewed the shop manuel in detail and gone through every test Merc has told them to perform.
I only bought the boat this spring and the prior owner(friend) tells me he has had no problems, i believe him because he is dealing with the repairs.
I initially thought it was a fuel problem but that does not appear to be the case, i know the shop even piped it direct to the motor to see if fuel was somehow limited - and it was not.
Everyone seems to think electrical - i know the shop made up a set of guages to bypass mine to see if somehow one or more was causing a problem - the same symptoms continued.
I think the only thing not changed is the throttle unit???? and the third harness on back order.
Not sure how i can better describe the symptoms, continuous under any load, appears to be linked to a tach reading which does not appear to be in sync with the actual engine rpm.
This is getting unbelievably frustrating and costly with no one being able to pin anything down. All comments are most appreciated. Thanks."

Remove injectors & have th

Remove injectors & have them tested for fuel flow. There is a machine made just for this test.

Check gaskets on throttle body

Check gaskets on throttle body and all tubing. Any loss of intake manifold vacuum can lead to those symptoms except for the spiking tach reading. Just an idea i didn't see mentioned above.

Sorry about the short reply I

Sorry about the short reply I was running late.
If the injectors aren't letting enough fuel in at higher rpm it can cause the sounds you hear.

But I must say that I can't tie this to the tach problem unless the engine missing is causing some type of electrical pulse affecting the tach.

If the boat has been sitting & was not serviced for a long time storage period the injectors can have crud in them just as a carburetor gets in the jets.
The system can have all the pressure & fuel in the world piped to it but it will not get through a dirty injector or one that is not staying open long enough.

Tune-up in a can is not going to remove this deposit if it is there just as it will not remove it from carb jets.
If you can't locate a flow testing machine try spraying carb cleaner & WD40 into the intake at the same time when the engine starts to act up. If it runs any better it is running lean.
Only do this long enough to tell if running lean is the cause. If so the injectors need to be sent to a place that can test them.
Reason for the WD40 is to protect the engine from damage from the carb cleaner. Reason for the carb cleaner is WD40 is not a good enough fuel on it's own(like running diesel).

With all you have listed this is about the only thing that comes to mind as the cause.

Can the shop check the fuel flow through the computer? Most injection systems have a way to check the fuel flow.

If you already tried this sorry for wasting you're time it took to read this.

"I have spoken with the shop.

"I have spoken with the shop. They have not tested the injectors (do not have the machine referenced) but also do not feel that it related to them. The reasoning presented is that it doesn't necesssarily "pop" from the same side / bank of cylinders. Also feel it is not injector related because occasionally it will run okay, just not under load.
Regarding the vacuum, there are no vacuum lines in this throttle body - the wiring harness for the throttle is the last one to be replaced - on back order...
Shop is still at a loss..."

"What did the laptop tell them

"What did the laptop tell them? Is the engine going into knock retard? The computer gives you much more information than just fault codes. There must be some information indicating the problem. Also, have you checked for leaking riser gaskets which could allow water back into the cylinders?"

"No fault codes what so ever.

"No fault codes what so ever. I know they have a specialty Mercruiser computer/laptop - i have been told no fault codes are coming up at any time, even when it is popping.
I can't see there being any water in the cylinders, they have had the plugs out on more than one occasion"

"If you think about it,if the

"If you think about it,if the injectors were lean it would fail more under load when the engine needed more fuel. If you keep listening to the people you have working on it you should cure the problem soon enough.
At the rate you are going you'll soon have a complete new engine.

Any shop that just replaces parts on a guess is a freaking joke.
That is not how it is done. Find a real shop with the proper test equipment."

"Fraser:

Troubleshooting

"Fraser:

Troubleshooting rule number one: make a slow and deliberate visual inspection first for the obvious. Parts replacers can't see the individual tree when they are looking at the whole forest. You can also wriggle and tug on the wire harnesses one at a time. Looking closely will find the problem. A bad ground connection is a number one electronic failure. It may look good but it needs to be tested with an ohmeter.

The jumping tach is telling you that the RPMs are running wild--loose ground? This condition can be due to the module or a component in the computer failing. I had a intermittently failing solid state voltage regulator that made the gauge pointer vibrate and jump all over the place.

Are there any tiny sealed relays in the fuel circuitry? They can work one minute then quit right now. Have the tech. use a light weight long screwdiver and start tapping lightly, using the handle end, on every electronic module, the computer, injectors and every component on the engine. I watched a TV repairman find a bad module using that method. Backwoods test worked!

A hairline circuit board crack or bad solder joint will show up that way. They also will appear all of a sudden due to heat expansion of the circuit boards. There is an electronic COOLING spray that can be sprayed on one part at a time to check for a heat related component failure. Works when its COLD and fails when it heats up.

Check all the electrical plugs carefully (use a magnifying glass)for pins that are spread open to far or pushed back some in the plug head. Push and pull on each wire. Engine vibration can cause them to work one minute and not the next. A telltale sign of a loose pin is a dark or burned spot on a pin tip caused by arcing.

New doesn't mean it works. Saw it too many times in military SAM radar units. New parts right out of the box were defective.

For what you have needlessly paid for so far, I'd have the technicians ride in the boat with their diagnostic computer hooked up so they can see it in action. Drive it out to the middle of the lake and don't take them back until they fix it. Let them swim!

An old fashioned oscilliscope can show the spark pattern and tell you if its spark or timing (computer) related.

I agree with Charli--parts swappers are shooting in the dark at your expense--test, test, and retest. But first you need to have the knowledge of the electronics and components.

My favorite useless computerized gadget is the computer battery tester at WalMart. It says good or replace but doesn't tell you a darn thing about the battery's condition. Same goes for the laptop. It only shows the current conditions unless it can record a period of time.

Guy"

"Fraser:
It just dawned on

"Fraser:
It just dawned on me. Connect a digital voltmeter to the alternator output set on A/C volts scale. If there is AC voltage there replace the alternator--one of the diodes is shorted and allowing AC voltage wreak havoc on the electronics, hence the oscillating tachometer. Guy"

"I have the same engine/outdri

"I have the same engine/outdrive and year w the same problem. Mine seems heat related, not overheated but hot weather and at least a 1/2 hour plus running time. Engine temp always about 172. Im thinking electrical as a fuel problem would likely exist at cold temps, runs fine cold. It does not say you have replaced or tested your coil, just curious about that?"

"Hey, where did you guys go? I

"Hey, where did you guys go? Im still trying to figure mine out, seems to run fine but much cooler weather now. I have a long trip this weekend with a bunch of guys. Any advise besides take plenty of fuel for the kicker motor?"

"Guy- if the bridge was bad, i

"Guy- if the bridge was bad, it would probably discharge the battery, right? I didn't see this as a symptom but it is a possibility. I agree, AC does weird stuff to DC electronics, though.

I would be doing the wiggle tests all over this motor. Also, the shop should stop replacing parts until they prove to be bad, as others have said. They should put a noid light on each injector plug and see if/when it goes out. I would include the safety switch in the testing, too. They cause a lot of issues if the lanyard is on the switch all of the time and the sun softens the plastic. Plus, there have been some problems with switches.

"Backwoods test worked! "

I believe that's called "percussive diagnostics". Yeah, the simple ways often work for this kind of problem. When I was at training for Mastercraft, we were told to verify the problem, do a visual inspection and then do a wiggle test. If those didn't find anything, then hook it up for diagnostics. Had a customer call to tell me that their boat died after a hard turn and wouldn't restart, so I should look at that while I was changing the oil. Low voltage on the screen of the Tech 1, so I went right to the grounds on the block and saw the ring that hadn't been slid over the stud with the others. Thsi one could be that simple, too.

Fraser- make sure the boat plug is connected fully- they had some problems with that in '98-2000. Also, there were some fuel line issues and I think '99 was included. Call Regal and ask for Customer Service to get any pertinent info if the shop that's working on it isn't a Regal dealer. Make sure the shop has/gets all of the service bulletins for your model year from Regal and Mercruiser, including the years surrounding yours.

Where are you located? Is your boat a 1900LSR/1950LSR/2100LSR/2150LSR?"

"Guys:
We need to put our h

"Guys:
We need to put our heads together and get this issue solved. Since the weather has cooled off it is running better--it has to be a heat related problem! Electrical is still my first suspicion. But what about a heat related vacuum leak? Or a heat expansion problem with a fuel delivery part? Did anyone check the intake manifold or heads and retorque the bolts? If it was ever overheated, warping could have occurred on these parts.

Now that it is cooler out, you can make the problem show up while running on earmuffs. Use a 1200 watt hair dryer on low heat and high fan. Cook suspect parts from about 8 inches--keep the dryer moving so you do not melt a plastic part.

Do any of the harness plugs have electrical grease embedded in them to prevent corrosion? Too much of it is not good. GM put gobs of the sticky grease on lamp sockets and multiwire plugs
only to drive mechanics insane. Cleaning out 99% of the goo solved many electrical problems.

"Everyone seems to think electrical ...shop made up a set of guages to bypass mine ... the same symptoms continued" Where were they connected? If they were connected at the engine, that would seem to suggest the problem is @ the engine. If they were connected at the dash, the harness is still suspect. If the dash is a module similar to auto dashes, moisture may be affecting it.

If the connection to any dash part or computer component is a "FLAT" connector that presses onto the circuit board, remove the connector and inspect the wires one by one--look for a poor push fitting where the wire is just pressed onto a u-type connection that it cuts the insulation to make contact.

Next, take a pencil eraser and clean (erase) each part of the male connector on the circuit board (looks like a piano keyboard). A cold (dull looking) solder joint on the circuit boards or harnesses can be affected by heat--hot it expands and your problem shows uo. Cold--problem disappears. Every solder joint should be bright and shiny like polished silver in appearence. A frosted or dull look is "a cold" solder joint doomed to become a nuisance.

Are there relays in the electrical system other than the starter circuit? After 7-8 years they are going to fail as the contacts slowly burn from use; only relays within a vacuum do not burn the contacts."