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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10974
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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97 merc 0b 250hp efi- engine will not go above 2500rpm. mech

Customer Question

97 merc 0b 250hp efi- engine will not go above 2500rpm. mech says spark checks out but still sounds like skipping . changed ig ecu - did not help (expensive ouch). good water flow. lots of blue smoke at rev not idle. mech wants to pull boat to start from scratch. lost season. efi ecu problem?
JA: Sometimes boat issues seem like they'll be really complicated, but end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Is there anything else the Marine Mechanic should be aware of?
Customer: no
Submitted: 11 months ago.
Category: Boat
Expert:  Tan replied 11 months ago.

Hello. My name is Tan.

Could I get the engine serial number please?

Have you checked spark under a load with a timing light to be sure it is a spark issue?

Customer: replied 11 months ago.
mech said he checked spark twice. s# ***** other ideas?
Expert:  Tan replied 11 months ago.

You say it has a misfire? Has the mechanic checked spark when the engine is acting up? Under a load means when the engine is acting? You are the one that said it has a misfire this means loss of spark?

Customer: replied 11 months ago.
dont really know the lingo. mech said he checked spark and sequence and is ok. may have done load test too but dont know. other ideas?
Expert:  Tan replied 11 months ago.

Skipping to me is a misfire. Your description is misfire and we have to verify that we have good spark at the rpms the engine is acting up at. This has to be done with a timing light running the boat where it is skipping. Other ideas can be allot of different things. You could have a bad injector acting up.

Have you done a compression test?

You could also have a bad CDM misfiring, stator coil failing, spark plug wire grounding out.

Skipping is an ignition issue.

Customer: replied 11 months ago.
if mech says he checked spark, im in tricky position if i ask how did he do it. another example is he told me he checked, swapped, tested injectors but i dont know how or what he really did. just looking for ideas. is this a common problem with 20yo mercs or kind of rare?
Expert:  Tan replied 11 months ago.

No with the age electronic components start to fail. I have given all the things that will cause your symptoms.

If he hasn't done a spark test when the engine is acting up it doesn't tell us anything. That would be like going to the doctor and telling him you feel bad when you run and it only happens when you run. He can check all day long and if you aren't feeling bad he isn't going to find anything. So he would have to make you run till you feel bad to find the problem.

If the mechanic is checking then engine when it is running good and not acting up he isn't going to fin anything. So to find the problem the engine has to be acting up.

Saying he checked something is vague at best. When did he check it what did he check it with? I need more info than you have given to be able to tell you what the exact issue is. You have to remember I am not there doing the tests so I am getting the info second hand and it is very vague.

Does this make sense?

Customer: replied 11 months ago.
no. yes if this was a mechanics only forum and there would'nt be "vague" talk i guess. but no because I already indicated mech was stumped ("start from scratch"). I assume he did the go to fixes for this problem and not had success. that is why i tried this forum - for other ideas. you have said you "have given all the things that will cause symptoms" so thanks for your ideas. Might add that local super merc mechanic/dealer wont look at motor because its too old. figure that one.
Expert:  Tan replied 11 months ago.

You never said anything about your mechanic being stumped. All you said was he checked spark and replaced the ign ECU. If you had spark why would he replace the ECU? This tells me he is poking in the dark and just swapping parts. If he hasn't verified an issue why replace an expensive component? I can only go by what you have told me which is vague. Engine skips and spark has been checked. So that 2 things and we don't know for sure as you are assuming what the mechanic has done. To get your issue solved I have to have definite results from tests I have posted.

Has fuel pressure been checked, has the engine had a compression test, do we have spark on all cylinders when engine is acting up? I have to know test results of these checks to give you an idea of what the problem is.

Has the engine bee n checked with a Scanner or DDT? All of these are checks we do in the field to find the problem. Without results of these checks we are only guessing. Guessing doesn't fix the issue.

If you can get results of these checks I can help. I have been working on marine engines for over 40 years and there just is no way around doing the checks.

Customer: replied 11 months ago.
that he wanted to pull boat and start from scratch. the inference is that he was stumped. and like i said the super mech wont even look at 20 yo motor with this type of problem. thanks for help , if one of your ideas works out it was worth the conv.
Expert:  Tan replied 11 months ago.

He will not find the problem by pulling the boat he has to take the boat for a ride get it to act up and find the problem. Why did he replace the ECU if he has good spark? The age of the motor shouldn't have anything to do with finding and engine performance issue. All engines require the same thing spark, compression and fuel. You give me any motor and I can find out which one is causing the issue.

Has the mechanic even run the boat? In all my years of working on boats I never gave a customer a boat back that I hadn't sea trialed myself to verify the issue was resolved. I would take it to a different mechanic if he is replacing expensive parts at you expense due to his lack of knowledge.

Expert:  Tan replied 11 months ago.

Here is a direct link to me for this issue if they cannot resolve it and future issues if they resolve the issue.

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