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I have a 1994 Mastercraft ProStar Inboard boat with a 350CID

Chevy Engine. It has...
I have a 1994 Mastercraft ProStar Inboard boat with a 350CID Chevy Engine. It has a 2 barrel Rochester TBI carb and an ECM with 2 32-pin connectors labeled J1 and J2. The fuel injectors are not getting a signal to inject fuel. I have verified that they both are getting 12V when the key is on. I have verified fuel pump and system. The injector work with I pulse them with a 9V battery. I have replaced the Ignition Control Module on the distributor. About the only thing left is the ECM. I'm wondering if one of the inputs to the ECM is preventing it from activating the injectors. Is there a troubleshooting guide that I can get? Or, your thoughts?
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Answered in 12 minutes by:
10/16/2017
Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 16,289
Experience: Degree in Marine Technology. Gas and diesel marine mechanic.
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Hello my name is ***** ***** am I speaking with? I read what you wrote. Do you have a scan tool?

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Customer reply replied 1 month ago
Hi I'm Bud. I have an OBDII scan tool but the connector is different than the rectangular 10-pin connector on the boat. I'm sure it's because OBDII did not exist in '94. Is there a scan tool I can buy for this '94 ECM?

H​i Bud. OBD is a car term. In the marine world it's a different language/protocol and that language is called MEFI. MEFI is a completely different language than OBD, and OBD will not work on MEFI engines and vice versa, MEFI scanners will not work on OBD ECM's. What you likely have is a MEFI 1 or MEFI 2 ECM. For a scan tool, what you would need is either a product called DIACOM, if you want a PC/Laptop based scan tool. Or one called the Techmate, if you want a hand held scan tool. Both can be had from a company called Rinda. Click this link, this is what you would need. http://www.rinda.com/marine/marinemenu.htm

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H​i Bud. OBD is a car term. In the marine world it's a different language/protocol and that language is called MEFI. MEFI is a completely different language than OBD, and OBD will not work on MEFI engines and vice versa, MEFI scanners will not work on OBD ECM's. What you likely have is a MEFI 1 or MEFI 2 ECM. For a scan tool, what you would need is either a product called DIACOM, if you want a PC/Laptop based scan tool. Or one called the Techmate, if you want a hand held scan tool. Both can be had from a company called Rinda. Click this link, this is what you would need. http://www.rinda.com/marine/marinemenu.htm

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Customer reply replied 1 month ago
Hi Jason, Thanks for helping. Your feedback about MEFI vs OBD was helpful, as was the info about the TechMate Scan Tool. I'm not looking to spend $500, but I learned a lot from the experience, and it sent me down a very helpful YouTube and Google path that let me to learning how to read the ECM trouble codes for free with my voltmeter or a light bulb, along with a comprehensive document about my MEFI 1 ECM. I am good for now. Thanks, Bud

The problem with the test light is it's not going to tell if you if the ECM has a power or ground issue, or if the ECM itself is bad. So you might eventually have to bite the bullet and pick yourself up a scan tool if you plan on DIYing this one. I do want to make sure you are happy with my service before you go. If you had a further question on the issue by all means feel free to ask. If not, Just in case you do not understand the way the website works (and some folks do not). You do have to put forth a positive rating in order for it to credit me for helping you. When ratings are not done, the website simply keeps your deposit and they will not credit me. The ratings box is located at the top of the screen. To rate, you must select the star you wish and also confirm it. Please let me know if you run into any problems or errors when trying to do it. If you do have a problem, or if you can not see the ratings box which is at the top of the screen. Please reply back "I rate Jason's service _______" and fill in the blank.

Please note that our question sessions never close out, so if you need to come back later down the road with follow up questions to the issue, you can do so at any time, even after putting through a rating.

Thanks in advance, and good luck
Jason

Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 16,289
Experience: Degree in Marine Technology. Gas and diesel marine mechanic.
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Customer reply replied 1 month ago
Sounds great. Thanks for the guidance. This is my first time using this service and I had no idea that I had to do a rating. I'll do it right now.A thought about your feedback about a possible bad ground or bad ECM. I agree in principal and since I use my OBDII Scan Tool on my Chevy 5.7L LS1 motor in my race car, I understand the far-reaching benefits of using a Scan Tool. However, in this case, if I manually pour some gas into the carb, the engine starts immediately and all gauges, including the tach, work fine. That leads me to believe the ECM is ok. Plus, I have a spare that I connected and got the same behavior. Before I spend hundreds on a scan tool, I figured I'd see if I can read a trouble code that points me to a bad sensor input to the ECM, or something like that. I have carefully examined all the wiring, and the grounds (there are multiple grounds to the ECM) appear fine. Wish me luck, and if you can think of anything specific I should check, please do let me know. Thanks Jason, Bud
Customer reply replied 21 days ago
Hi Jason, I am still troubleshooting my '94 Indmar Chevy 350 ECM in my Mastercraft Prostar 190. It has a MEFI 1 ECM. I have thoroughly tested (ohmed out) the wiring from every pin on the J1 and J2 ECM connectors to the other end at the sensors, etc. I have verified power and ground. I have verified the TBS and the Engine Coolant Temperature Sensor are working. I have verified fuel pump operation, and verified that the 2 fuel injectors work (using a 9V battery). I have verified 12V at the pinkish red wire to each injector when the key is on. The engine runs if I manually pour gas into the TBI, but the ECM is not sending the ground pulse signal to the injectors (checked with a NOID light). Is there any known failure of the ECM with this behavior? What signals must the ECM absolutely receive to pulse the injectors? Thanks, Bud

Hi Bud. The ECM needs to see a valid MAP pressure signal in order to fire the injectors. ECM failures do happen so it's also possible the ECM itself is bad. The ECM really needs to be hooked up to a scan tool to read both the live data and check for codes.

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Customer reply replied 21 days ago
Checking the actual MAP sensor signal output to the ECM is next on my list. I was wondering about that, but I was hoping that during cranking, the ECM used a default value to drive the injectors until the engine started, regardless of MAP sensor input. I did read the DTC (codes) from the ECM and there aren't any. It just keeps repeating 12.

12​ means that there are no codes stored. The way the ECM works is it expects a certain range of values from each sensor. If it doesn't see those expected values, it flags a code. A sensor can still be out of range but as long as the value is acceptable to the ECM it will not flag a code. Typically if a sensor is shorted or disconnected, it will flag a code. But if it is reporting a bad value the ECM will still accept it and not flag a code. For example, the MAP sensor. Atmospheric pressure is 14.6 psi, which is what the ECM want's to see. However technically speaking 1 psi would also be an acceptable value. If the MAP sensor was reporting atmospheric pressure of 1 psi, there would not be a code and the engine would not start. You can try disconnecting the MAP sensor and seeing if the engine will start. When the actual sensor shorts or is disconnected the ECM will replace the MAP sensors input with an assumed value. The other thing you want to look at is to make sure there is continuity between the ECM and the ignition module. If there is a break in the harness there the ECM will not get a trigger signal from the ignition. I am going to upload the flow charts for you for diagnosing the issue. See attachments.

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Customer reply replied 20 days ago
Thank you!!! for the diagnostic flow chart. That is exactly what I was hoping / looking for. Where would I normally get such a document? I've been searching the web and Indmar's site but could not find anything like this. You mentioned "make sure there is continuity between the ECM and the ignition module." Yes I did that. In fact, I literally checked continuity from every single conductor at the ECM J1 & J2 connectors to the other end of the harness, wherever that may be (TPS, Injectors, IAC, MAP, Knock Sensor, Ignition Module, EFI relays, etc etc. Every single path checked out perfect, including grounds. I also disconnected the MAP sensor with no luck. I actually did that for the ECT (Engine Coolant Temp) Sensor, the Knock Sensor, and the TPS. Nothing made a difference, and doing that did not result in the ECM throwing any codes, which I think might be a red flag. When a sensor is disconnected, shouldn't the ECM store a code for that? Anyway, I'll use the flow charts this weekend and I have a few other checks to do also. Thanks man. Really appreciate this discussion. My best, Bud

The documents all come from the service manuals, which you would buy from the dealers if you wanted one. The engine will start and run to a degree without a functioning TPS, IAC, knock sensor.... But it will not start without a functioning MAP.

When a sensor is disconnected, shouldn't the ECM store a code for that?

Yes it's supposed to.

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Customer reply replied 17 days ago
Jason thanks for sending me the above link: 0b04d721-4fc9-4883-a5c3-ada3b410e281_diagchart.pdf
Are you certain that these pages are for 1994? I ask because the page with 'Chart A-3 (3 of 4)' states “check the resistance of the injectors. Should be 12 ohms +/- 4".My injectors both measure the same at about 1.4 ohms. They work perfect when I check them with a 9V battery under fuel pressure. What I’m worried about, is that the low resistance means they will draw more current from the ECM. I’m wondering if they have been pulling too much current and this has blown the injector drive circuitry in the ECM.Bot***** *****ne: Is a resistance of ~ 1.4 ohms ok?Thanks, Bud

Hi Bud. It's a misprint in the manual. The injectors should be 1.2 ohms +/- .4.

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Customer reply replied 16 days ago
Ah. Thanks.
Customer reply replied 15 days ago
Thanks again for our interaction Jason. Everything is pointing to a bad ECM. I verified proper 5V being supplied to the MAP and the TPS gray wire, and I verified proper "in range" voltage back to the ECM from both of those sensors. I also verified the wiring and proper signal range (in ohms) from the temperature sensor (ECT) to the ECM. So the ECM is getting the correct inputs. I also verified the presence of 12V on the pink wire to both injectors with key in ON position and CRANK position. The injectors also work perfect with a 9V battery, and I verified the blue and green wires from the injectors to the ECM. The last thing I'd like to verify is this: Does the ECM need to see any specific signal from the Ignition Control Module on the distributor during cranking, in order to pulse the injectors? I'm thinking not, but just want to be sure. Thanks, Bud

HI Bud,

The last thing I'd like to verify is this: Does the ECM need to see any specific signal from the Ignition Control Module on the distributor during cranking, in order to pulse the injectors?​

Yes it does. That signal is how the ECM knows the engine is spinning over. That being said, when the ignition control module is bad there will be both no spark and no fuel. But your engine does have spark so that means the module itself is at least working. This is why I said to verity that there is continuity between the control module and ECM harness wires just to make sure there isn't a break in the wires and to make sure the ECM is not not seeing the control module because broken wires.

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Customer reply replied 15 days ago
Thanks Jason. Yes, I verified continuity for every conductor on both the J1 and J2 ECM connectors. The wiring harness has no faults. I verified I have spark at 1 spark plug. And, when I crank the engine, the tachometer in the dash shows about 200 RPM.Assuming I end up replacing the ECM, do you know if a MEFI 2 ECM will work in place of my MEFI 1? That will give me more flexibility when purchasing a replacement unit. I'm hoping to get one used. Speaking of that, other than Google and eBay, do you know where I can buy a used or refurbished/tested ECM?

Mefi 2 will not work, the connectors are different. Try calling this company and see if they can help you out with an ECM - https://www.obd2allinone.com/mefiecms.asp

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