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I have a 1999 Maxum 2300SC 5.7 Alpaha One with a bad ECU

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Guy0425

New member
I have purchased a Delco EST distributer and coil kit to replace the ECU system. I am trying to figure out if i need to leave the ECU installed do to the #7 wire in the harness that runs the Shift system interrupt switch, the #6 wire for the audio warning system and the #8 wire for the water temp warning?
Has anyone else switched over to the EST kit and if so how did you do it?
 
Which ECU do you have ? (Ideally get the GM part number from the back of the ECU.)

what is your reference when you cite "wire #x"?

Do you plan to remove the ECU or leave it (partially) connected?

FWIW, there were many configuration changes in the late 1990's due to the GM production line. Until many of the details are made explicit, there isn't a simple set of answers...
 
The ECU is 861253-1 5.7 Alpha
The wire numbers are from a wiring schematic
From a manual I downloaded.
As far as leaving it partially connected, that’s what I’m not sure about.
 
The reason why I am replacing the ECU:
The problem I have been experiencing is when I throttle up from a stand still in the water and or on land, I get an 800 rpm increase 5 to 10 seconds after throttling up to any set rpm.
I have replaced all the throttle linkage from the carburetor to the helm and put a brand new carburetor on. When I throttle up to 2000 rpm’s and watch the carburetor and the linkage, 5 to 10 seconds later the rpm’s will slowly raise to 2800 rpm’s. So now I’m being told that it looks like a bad ECU.
 
that part number is for the Tbolt V ignition module, not a MEFI-x ECU...

If you change out the originial distributor for the Delco unit, you won't need the 861253-1 module...

who published the manual you are using?
 
Mercruiser manual.
I just want to make sure that I know what to do with all of the wires that plug into the module. I have watched multiple YouTube videos on how to do it but theirs the 5.7 alpha. One of the cables that came with the kit plugs into the right side of the coil. It has one gray wire that goes to the throttle cut off switch and it has one white wire that comes out of the far right side and loops right back into the port next to it. I’m not sure if I’m supposed to cut that wire to make two separate wires or leave it looped in?
 
Questions,

Are you sure you are running a Carburetor? Or is it a Throttle body injection?
I think we still need more info on your set up, If carbed, What carb? 2BBL or 4BBL? Weber/ Rochester/Merc carb (although your year would point to Weber 4BBL if a 5.7 but you are not specifying your set up.

You really are not describing what testing has been done and really what the results were SPECIFICALLY.

The knock sensor circuit if working properly will retard timing not advance it. if it Knocks under load are typically related to fuel and/or temps and/or timing (too much advance).
So if the knock module was functioning properly one would expect a loss in RPM not a increase. If you are concerned, Unplug it at the drain plug location just forward of the starter, BLUR SINGLE WIRE. Do a test run and see what happens.

I believe the Thunderbolt V with the knock module, the shift interrupter wire lead went into the ignition timing control Thunderbolt V module to interrupt the ignition (for split second) to allow shifting OUT of gear. So if you identify that wire from the correct schematic for TB V module wiring (for Carbed engines) that would solve that wiring question.

In prior years, that wire from the Interrupter switch went to Coil - (Minus) to momentarily short the coil to ground. This was the case for point ignitions and early Thunderbolt IV's.

I think we still need more info on your set up, If carbed, What carb? 2BBL or 4BBL? Weber?/ Rochester/Merc carb (although your year would point to Weber 4BBL if a 5.7 but you are not specifying your set up.
 
Agree w/ KGHOST that the diagnostics may not have been explained in sufficient detail...

That said, assuming you are going down the path of replacing the TB-V distributor with a Delco EST kit, the directions in the EST kit are pretty clear about what changes need to be made. most of the wires that were identified in the original post will be cut and taped up...the essential change is to rewire the shift interrupt circuit as outlined in the EST Kit's directions.

If you don't have a copy of the directions, they are pretty easy to find with your favorite search engine...

Finally, I have found the original process for setting the ignition timing, using the shut to 'lock' the timing to be marginal...I prefer to set the timing to ensure max advance is reached at 3000 RPM and then live with the resulting initial value...
 
One last note,
You are referring to an ECU.

Thunderbolt ignitions use a timing control module and if included, a knock module.

If I am not mistaken, only TBI (Throttle body injection) or EFI use a ECU.

can you clarify this?
 
Guy0425 said:
The reason why I am replacing the ECU:
The problem I have been experiencing is when I throttle up from a stand still in the water and or on land, I get an 800 rpm increase 5 to 10 seconds after throttling up to any set rpm.
I have replaced all the throttle linkage from the carburetor to the helm and put a brand new carburetor on. When I throttle up to 2000 rpm’s and watch the carburetor and the linkage, 5 to 10 seconds later the rpm’s will slowly raise to 2800 rpm’s. So now I’m being told that it looks like a bad ECU.
Click to expand...
I think what you are calling an ECU is the Thunderbolt Ignition Module.

Hook up a timing light and see what the total ignition advance is doing when you observe this. The TBV will keep pushing the advance until it gets "mean best timing". It keeps giving advance in small increments until the rpm stops increasing. Would think if advance is moving forward enough to increase 800 rpm then you would see it with an advance timing light.

I think the the knock module can pull out like 10 degrees. not sure if that could be influencing.... Bottom line would verify the ignition timing is moving around enough to cause this before you rip it out.

If indeed the module is no good then yes the Delco EST is the go to replacement as the TB modules are crazy cost if you can get them. I bought mine on ebay good used one and a spare for $200 a few years back
 
Ok, first of all I want to thank you both for your input and the information you have provided.

I purchased this boat brand new in 1999. Since then, I have kept it indoors and well maintained. I haven't had any issues with it until the last couple of years. The Boat is a Maxum 2300SC 5.7 350 Alpha One 250hp. It has all of the factory engine parts. 2bbl Carb. alternator and open water cooling system.

The boat still runs great but has developed an 8oo rpm surge 5 to 10 seconds after throttling up to any set rpm. The shop I took it to thought it had to do with the factory throttle cables and shifter unit. They replaced the Shifter and cables, but the surging continued. Then they rebuilt the factory 2 bbl. carburetor thinking that it had something to do with the float not functioning properly. That didn't fix it, so they rebuilt the carb a second time with a new kit, but the surge problem continued. Then they replaced the factory carb with a Sierra 2bbl Carb. Thats all that the receipt for the carb indicates for type of carb. Still waiting for the shop to get back to me on the specifics of the carburetor. The shop apparently doesn't know much about the ignition system module, because they informed me that the ignition module was the ECU and that it has gone bad, and I would need to replace the ECU with a Delco EST kit because they don't make the ECUs anymore. Then they told me that they don't get into that, so I would need to do it myself.

They showed me the Ignition module that they referred to as the ECU and the knock sensor mounted on top of it.

So, needless to say, I am trying my best to find out everything I can about how to repair the surging issue before cutting wires and replacing components. I hope that I have provided enough information for you to access the problem and help me find a solution. Is there anything else that would cause a surging issue that I should check before installing the Delco EST kit?

Please let me know if there is any more information that you need to help me with this Surge issue.

Thanks again,

Guy0425
 
Dieter said:
I think what you are calling an ECU is the Thunderbolt Ignition Module.

Hook up a timing light and see what the total ignition advance is doing when you observe this. The TBV will keep pushing the advance until it gets "mean best timing". It keeps giving advance in small increments until the rpm stops increasing. Would think if advance is moving forward enough to increase 800 rpm then you would see it with an advance timing light.

I think the the knock module can pull out like 10 degrees. not sure if that could be influencing.... Bottom line would verify the ignition timing is moving around enough to cause this before you rip it out.

If indeed the module is no good then yes the Delco EST is the go to replacement as the TB modules are crazy cost if you can get them. I bought mine on ebay good used one and a spare for $200 a few years back
Click to expand...
I will try checking the timing and let you know what I find out. Thank you!
 
Ok.
You have what is called a Thunderbolt V with knock controll. Thus the piggy back of the two modules.

The "ECU" is actually a timing control module as that is all it does.

Typically when the TCM goes bad (not always) you loose top end power as it will not advance the timing correctly.

I would also recomend never going to that shop again. Throttle cables do NOT cause your issue unles broken. And rebuilding a carb twice then replacing it also says to me they dont have a clue.
This is also a condition of new technology, if they cannot hook up a laptop to diagnose they are dumbfounded.....

I agree, carefully watch your timing marks.
You should be about 8* btdc at 650-750 rpm. By 3000 rpm you should see full advance which i would say would be about 32* btdc. That is 8* initial + 24* advance =32* total.
I dont have my manual as i am typing from my phone so those numbers are close but may be off a couple of degrees.

Once you confirm this, bring it up to 1000 rpm steady and check timing and pay attention to any movement.
It shiuld stay in one place +/- a degree or two.
Try that and report back.
 
Ok, I reinstalled the timing module and the knock module, checked the timing at 750 rpm and found that it was at about 2* BTDC. I readjusted the timing to 8* BTDC @ 750 rpm. At 750 rpm it seems to bounce by 1* up and down. Then at 1000 rpms it drops to 2* BTDC and holds. At 2000 rpms it bumps up to about 24* BTDC and at 3000 rpms it runs around 32* BTDC. At the 2000 and 3000 marks it tends to jump up and down a degree or 2. Also, it is still surging 800 rpms and I have to keep backing off on the throttle to get it to the 2000 or 3000 rpms.
What should it be reading at 1000 rpms?
 
I looked up your part number, Ignition control module.

What I see is the module is controling timing. Although the 1000 rpm 2* doesnt make sense.

1. Have you pulled the spark plugs to see if any are running lean or rich?
2. As I suggested, if the knock sensor is telling the knock module it senses a knock, it will retard the timing. How much I am not 100% sure.

Can you retry but pull the Blue wire off the knock sensor and hang it away and see if that has any impact on your results?

One other question, who winterizes your engine and how is it done? Do they pull the drain plugs on each side of block?
If so, has the knock sensor been moved from its upright position?
I am not suggesting this is your issue but the knock sensor when it detects a knock will cause the timing to retard.

Thats all i have for now.
If I have time this afternoon i will look at the manual and see if I can find more info.
Also if anyone else has experience troubleshooiting the knock circuit please chime in!
 
May be worth the effort to get a vacuum gauge and make sure that there are no leaks....

And 2X the recommendation on the service shop used previously...
 
Guy0425 said:
Ok, I reinstalled the timing module and the knock module, checked the timing at 750 rpm and found that it was at about 2* BTDC. I readjusted the timing to 8* BTDC @ 750 rpm. At 750 rpm it seems to bounce by 1* up and down. Then at 1000 rpms it drops to 2* BTDC and holds. At 2000 rpms it bumps up to about 24* BTDC and at 3000 rpms it runs around 32* BTDC. At the 2000 and 3000 marks it tends to jump up and down a degree or 2. Also, it is still surging 800 rpms and I have to keep backing off on the throttle to get it to the 2000 or 3000 rpms.
What should it be reading at 1000 rpms?
Click to expand...
you need to put it in base mode to lock the idle advance before setting timing. The attached merc doc shows how to set base and approximately what the ignition control module will do as far as advance. I think the knock module has to supply 9 vdc to the ignition module to keep it out of retard mode. you could measure the voltage on that wire to see if it is intermittently retarding timing.

I would lock it into base and set the base at 10 * BTDC which is spec for a Vortec. in base mode it should stay at 10 until you remove the ground to Purple/ white wire.

If you have a steady 24 to 32 * BTDC at 2000-3000 rpm it is not the module. If you rev it up to 3000 get 32 degrees, go back to idle and rev it an get a different advance at same rpm then yes It could be the module, but otherwise the advance numbers you give are right on the money, a degree or two is not going to make it surge 800 rpm .

As mentioned I would look for a vacuum leak at the carb and intake manifold. I hope you still have your original carb as some of the cheap aftermarket ones are just that cheap...

In addition to the above - what do the spark plugs look like and what is your fuel pressure?

Agree find another mechanic as the are wasting your money.
 

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Dieter said:
you need to put it in base mode to lock the idle advance before setting timing. The attached merc doc shows how to set base and approximately what the ignition control module will do as far as advance. I think the knock module has to supply 9 vdc to the ignition module to keep it out of retard mode. you could measure the voltage on that wire to see if it is intermittently retarding timing.

I would lock it into base and set the base at 10 * BTDC which is spec for a Vortec. in base mode it should stay at 10 until you remove the ground to Purple/ white wire.

If you have a steady 24 to 32 * BTDC at 2000-3000 rpm it is not the module. If you rev it up to 3000 get 32 degrees, go back to idle and rev it an get a different advance at same rpm then yes It could be the module, but otherwise the advance numbers you give are right on the money, a degree or two is not going to make it surge 800 rpm .

As mentioned I would look for a vacuum leak at the carb and intake manifold. I hope you still have your original carb as some of the cheap aftermarket ones are just that cheap...

In addition to the above - what do the spark plugs look like and what is your fuel pressure?

Agree find another mechanic as the are wasting your money.
Click to expand...
A bit more about the knock sensor function,

The 8 volts comes from the ICU. The knock sensor is a 'single wire' and presents either a high resistance or a low resistance to the ICU. When a detonation event occurs ('knock') the sensor resonates at the frequency of the knock and it's resistance drops. When the ICU sees that resistance drop, it retards the ignition timing until the resistance goes back up.
 
kghost said:
A bit more about the knock sensor function,

The 8 volts comes from the ICU. The knock sensor is a 'single wire' and presents either a high resistance or a low resistance to the ICU. When a detonation event occurs ('knock') the sensor resonates at the frequency of the knock and it's resistance drops. When the ICU sees that resistance drop, it retards the ignition timing until the resistance goes back up.
Click to expand...
I was talking about the signal from the knock module to the ignition module. Yes there is a single wire from sensor to knock module. I think it is in the engine manual , pretty sure the knock module sends a voltage signal to the ignition module. I was looking into adding it to mine when I did a repower seemed stupid to require having 9V to keep it from going into retard, seemed over engineered...

I'll look when I get home maybe my memory is off
 
Dieter said:
I was talking about the signal from the knock module to the ignition module. Yes there is a single wire from sensor to knock module. I think it is in the engine manual , pretty sure the knock module sends a voltage signal to the ignition module. I was looking into adding it to mine when I did a repower seemed stupid to require having 9V to keep it from going into retard, seemed over engineered...

I'll look when I get home maybe my memory is off
Click to expand...
I totally agree, TB IV is the best design.
It does one thing, advance the timing only!!
If I ever were to buy a newer boat with TBV i would swap it backwards.

I have several good timing modules in my personal stock!!
 
kghost said:
I totally agree, TB IV is the best design.
It does one thing, advance the timing only!!
If I ever were to buy a newer boat with TBV i would swap it backwards.

I have several good timing modules in my personal stock!!
Click to expand...
Heres a couple more snips from the manual talks about the knock module and voltage signal.

Not all TBV use a knock module. Both the original 4.3 and the base 5.0 that I repowered with do not use a knock module. Not sure if it was just the 2 bbl carb models or what . I have had zero issues with my TBV . I did pick ups used spare module off eBay a few years ago
 

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Based on what he is describing, and the info posted from the manual I see the most likely issue is something in the knock sensor circuit.
It could be an actual knock that he doesn't recognize/hear,
It could be a corroded pin/socket connection at the knock module,
It could be a bad knock sensor or incorrectly installed, (does not appear like the picture in the prior post images) or its loose,

Based on the troubleshooting in the prior post documents, I think, if the Knock module pins and socket are confirmed NOT to have any corrosion, then disconnect the BLUE wire connection at the sensor and retest to see if the timing retards. Absent of the connection the knock module will not change the 8-10 VAC signal to the timing module thus NO timing retard. If pins and socket are clean and with the knock sensor disconnected and the timing does not retard then it would be a knock sensor or Blue wire issue.

It does note to keep Blue wire away from Ignition wires as the high voltage could create a false knock detection.

Opinions?
 
This is all great information. I want to thank you all for your input. I will take the information you have given me and give it another try. I will be on vacation for the next week so when I get back, I will get right on it and send an update on what I find out.

Thanks again,

Guy0425
 
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