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2000 Prostar LTR Cranks Still No Start

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  • 2000 Prostar LTR Cranks Still No Start

    Hello All,

    I have started a new topic in hopes of getting some eyes on and further help with my issue that happened in July 21'; this update is also posted on old thread.
    The previous topic was , 2000 Prostar 190 - Cranks but no start, it can give a history for those who haven't seen this topic yet, but in summary, I have had a marine shop look at it for 3 plus hours and other mechanics , marine and auto and no one has been familiar enough with the setup. We have been using the Diagnosis for Distributorless setups and always leads to ICM(ignition control module ) and I/we have replaced with a cross-referenced auto part which these threads have confirmed do work but have still not made a difference. The easier checks have been doubled checked CPS,TPS,fuel, ignition switch,MAP , fuses etc.
    Larry at Indmar has said we have tried everything he can think of.
    I am hoping that someone that knows this setup or had similar issue will see this and continue helping as it would be much appreciated.


    1. I sent ECM to OBD for diagnosis; in short, it is all good, Bob doesn't see anything wrong with it. He found "one logged code - M34 MAP low and showed no run cycles without that setting". HE cleared it and ran ECM; " the injectors fired fine, all sensors and relays, IAC, IC and bypass were good.

    2. I acquired another set of CPS's as one mechanic suggested possibility that ones from Alibaba may not be good quality; made no difference.

    3. All circuit wires coming from ECM terminals have been tested for Continuity and are All Good.
    All circuit wires between ICM and ECM have continuity and have been checked that nothing adding or leaking on these wires.

    4. Some measured values: Throttle position sensor - 5.2 v key on ; MAP sensor - 5.21 v key on I believe these are correct
    Circuit 950 is 4x reference from ICM to ECM - Diagnosis Chart says value for voltage on crank should be 1-2v BUT mechanic measured 4.94v.

    5. We have double checked that CPS wires are not reversed and that they are sending spec. value to the ICM.
    We have not measured psi of fuel at rails but good pressure was at rails when schrader value depressed judging from spray force coming out.

    6. I talked to a Mastercraft dealer and the tech guy was excellent in trying to help and understood how hard these types of issues can be as these setups were not used much and for only a few years, so not many are familiar with them. He could only guesstimate that it might have something to do with a timing issue but he would have to see this setup as it has been so long since he has seen as well.

    So, without the ability to bench test the 3 ICM's I have, (including one that was working in a vehicle the week before I hooked it onto my engine) we are having a hard time believing that all three ICM's are not working but the charts still point to this being a possible issue. We have one more used auto ICM on order that we will try but we are unsure if there's still the real problem, if not the ICM, which is blowing this unit up everytime we hook a different one to the engine and crank it.
    Others who have had my exact no start issue ( TT thread - 2001 XStar LTR no ignition & $500 tow and no spark LTR 330hp Quick Help! ) have also measured higher voltage on the 4x ref. circuit from ICM to ECM as above stated in # 4. Poster JimM was trying to find a service manual that might shed some light on the meaning of this discrepancy to confirm if the ICM is then at fault, but no threads or Larry at Indmar have been able to supply the answer to this.

    Also, from research of many threads here on TT, some of the many wise posters have had good suggestions :
    1. Throttle Position sensor is not sensing properly or it is not working - We have resistance on the sensor and moved it around enough that we think we have ruled this out.
    2. Brass oil pump wear issue and /or oil pressure sending unit not working - checked for wear ;looks good and new sending unit for oil pressure installed 20-30 hours ago.
    3. Fuel pump or wire connector at fault - we haven't checked much on pump as we have pressure at the rails and not just a fuel issue as NO spark either.
    4. Engine coolant temp. sensor is faulty - we do have resistance over it but don't really know spec on that or if it would shut engine down without engine light/buzzer occuring as well
    5. CPS sensor bottom connection wire is tight and pins could be compromised somewhat - all pins on sensors checked and seem the same without issue.

    Another couple of questions I have after review of some previous posters comments:
    1. mtajpa - said " You did say you checked the fuses on top of the ECM, there should be 3 of them. This would be a common problem if MEFI main fuse is blown." - at first thought one of the 3 was a MEFI fuse but they are for Fuel pump, ECM/Bat., and Injectors. IS there a separate main fuse for the MEFI as you mentioned? we haven't been able to find any other fuses except the ones under the dash which are all good.

    2. Mikeg205 - said " ICM is easy to source" - I don't think this is reference to a new part as I've understood it is discontinued and when checked with Tech Services, theirs was a used part as well. If you happen to have a source for a known good ICM part other than TS, please let me know , but will check again with TS to see if theirs are refurbed or known to be functioning properly.

    Still really no further in finding the real issue without known good parts or better insight of how the system works; I'm trying to source a service manual for this engine.

    Any further help with this would be awesome as have run out of options.


  • #2
    So, without the ability to bench test the 3 ICM's I have, (including one that was working in a vehicle the week before I hooked it onto my engine) we are having a hard time believing that all three ICM's are not working but the charts still point to this being a possible issue. We have one more used auto ICM on order that we will try but we are unsure if there's still the real problem, if not the ICM, which is blowing this unit up everytime we hook a different one to the engine and crank it.

    have you taken this ICM and put it back in the vehicle that it worked in and validated it works? if it does then your not blowing it up.. if it doesn't you know something is causing an issue.


    • #3
      Thanks for your reply curver900

      Unfortunately, the vehicle was from an auto wrecker and it was already torn apart when I purchased the ICM. I was thinking the same way about trying to find a vehicle still on the road that would match but that seems to be a long shot as well. Still at a dead end except for some unknowns of the larger voltage on the reference circuit from ICM.
      Another unknown; when testing coils, I could not get the pulsing of test light, one would expect if firing sequence was given from ICM and do not have pulsing at injector connectors as would expect as well.

      Thanks for anything further.


      • #4
        Flybird - In your previous post your said "Also, no fuel in cylinder as after cranking the spark plugs are still dry."

        What's the scenario for how a bad ICM would prevent fuel from going to the cylinders ? Wouldn't a bad ICM just prevent spark ? Wouldn't no spark and no fuel point to something upstream of the ICM ?

        I have this same engine so I'm trying to understand what's going on in case I run into the same thing.
        2000 Prostar 205V


        • #5
          i don't know if you pulled the spark plug and see if it is firing?
          also you can pull the throttle body and see if it squirting gas or even look and see...
          you hear the fuel pump prime right?
          the ICM can stop just about any and everything.. you need 3 things spark, fuel, air... you can pull a sparkplug and see if it is arching, you should be able to determine if gas is getting out of the throttle body.. the rest is easy...

          what participated the problem? i.e. what did you do before it quit working? no accusations here, but this is where all trouble shooting starts..

          what is your battery standing voltage?

          I don't know how you got to the ICM as being the issue. IMO you should start back at ground zero..
          1. spark?
          2. fuel?
          3. battery?
          4. Lanyard?
          5. what changed?
          Last edited by curver900; 02-14-2022, 03:45 PM.


          • #6
            Thanks for the replies,
            To begin, I must admit I wasn't much of a mechanic at the start of this, could get by but not deep knowledge but I have learned a fair amount and know a lot more, at least on this engine, however I will not always follow some of the more tech stuff. The problem is, that most I've spoken with, don't know this particular setup very well either and although Indmar gave me a fair amount of insight they are now saying they can't help further. So, when it comes to knowing what is happening and why, its kind of a shot in the dark. I am in process of calling marine shops to find out if they have intimate knowledge or have a mechanic who has worked on these older beasts, before sending into shop again for a last resort.

            dpb185 - You are thinking the same as we are that ICM only controls spark /ignition and charts tell us that it is in control of everything while in crank mode and then at 3-400 rpm the ECM takes over once it starts, so we believe that the ECM isn't allowing fuel to get past prime of rails as it detects no spark and won't let gas flood the engine and create more issues. Yes, the charts lead to the ECM being at fault if the ICM is good but I have sent to OBD in California as in first post and it is good; also went to great lengths to ensure the CPS are proven to be good. If you look further back in my original thread, you will see electrical schematics and if you google Distributorless Diagnosis for Indmar LTR, it should lead you to the charts we have been using. I can attach next time if can't find easily. I've come to conclusion that had I known what I do now, before I bought, I wouldn't have bought it with this setup; I was actually looking for a corvette engine.

            curver900 - I've tried the old standard way of pulling plug to ground and have had a couple mechanics test with proper spark testers and threw gas in throttle body to see if anything would fire and nothing for all. The pump can be heard running and have pressure in rails by test of schrader valve at rail; not proper test but lots of pressure and mechanic said its good.
            If you look back at my previous thread ( 2000 Prostar 190- Cranks but no start) it will give you all the history of what was tried and all the obvious and more basic stuff that has been tried and tried again but I hear you, could be something overlooked or that I haven't found that is simple. Mechanic and I spent 5.5 hrs going through a lot of it from scratch, just last weekend.

            The original issue happened after I had started it up after a two week rest and let it warm up more than I normally do, say 15 minutes while I cleaned up the boat. I reversed off the dock and then changed gear forward and headed out at a slow pace as usual and can't recall for sure but think I was just throttling up when it shut down like someone turned the key off; no sputter or hesitation and then would not start up ever since. Of course, I thought of the lanyard and fuses and ignition switch and then on and on.
            Battery is 13.6 ish and is 1 1/2 yr new. you've seen above that I am using Diagnosis charts that were supplied to me by Indmar and they're the same ones as the shop was using to tell me that they believed it was the ICM after double checking the crank position sensors.
            At Indmar suggestion, and one of previous responders, I disconnected the boat from the engine and used starter button to crank; nothing changed. There has to be a nugget of info to do with how this system works that may explain why it is doing this but maybe just crappy luck that all ICMs are not good or like I said, the real issue keeps blowing these units. I have not torn apart all wiring harness as sections that I have seem to be in good shape, but may have to start that very time consuming task.

            Hope I've answered fully and provided picture of where this is at which near end of frayed rope for me.


            • #7
              thanks for all of that in your response that does help. So in reading the above
              1. you sent the ECM and had it looked at and it was found to be good
              2. Circuit 950 is 4x reference from ICM to ECM - Diagnosis Chart says value for voltage on crank should be 1-2v BUT mechanic measured 4.94v.
              what is the disposition of this ?
              3. ICM you have 3 of them one from a working car. did you use it to do the test above? or the other two?

              IMO which is free of course, stick with one thing till it is fixed then move to the next thing if it doesn't fix it. Be careful of the shotgun approach it rarely provides for a solution...

              My personal experience with something like this ended up being a wire connector under the helm.. it worked great till it finally pulled apart enough to stop it.. dead.. but everything else worked and it took me a while to find it.. i started with a volt meter at the key and worked my way till i found it... it took a long time but luckily it was on the lift!

              My recommendation is to go and trace wires and look at every connection under the helm unplug them look inside for corrosion mark them so you know you looked at them and they are good then make sure they are put back together. This may be a long shot but it worked for me with similar issues...specifically the red wire coming out of the key switch

              I'll keep pondering it... good luck


              • #8
                I had a similar problem a couple years ago. It’s a different engine, 2004 MCX, but the diagnostic approach may help. It’s a long, technical read (62 posts) but hopefully there’s something in there that could help you. In the end, it was my ignition coil.

                2004 X-30 5.7L MCX


                • #9
                  Thanks for the replies,

                  curver900- no one can tell me what the extra voltage means or is caused by ( thinking a faulty ICM). But again, I have tried the known good one and all others including my recent purchase of another ICM which all show the over voltage situation. I have had contact with Technical Services and they have agreed that I have good CPS's and I'm waiting to see if they can comment on the voltage on CKT 950.
                  We have been using the Diagnosis Charts and have gone through in detail step by step as you mention and we agree but have come up with no change to issue over and over. I believe the last step, though very rigorous will require the wiring check as you say; and not sure when you mention the helm but believe you mean the control panel with ignition etc. If so, I have checked in a broad way, all the wiring external to the engine by disconnecting the circuits that run to the helm or anywhere that isn't specific to running the engine. Using alternator as source of power and a starter button to crank, we have ruled out the external circuits being a cause for the issue as the engine still did not start, so must be something on the engine. We are going to have to take all harnesses apart to check for damage and hence short, but so far nothing from ECM or ICM shows an issue as continuity, so this is where I'm not sure how whole setup works to know what might be inflicting on the system to cause issue.

                  Soder- I will look through to see if any tidbits but from what I have understood, these setups are unique, but may offer a tip to look at, thanks for your solution as well; all my coil packs 4 x 4 ICM units have proper resistance and mechanic has ruled them out as the issue. Even if some were faulty, would get sputter or rough fire etc. but we get nothing.


                  • #10
                    under the helm is the wiring harness from the ignition switch, I traced all those wires and my plug was in a real awkward place.. IIRC it was a 6 or 8 pin connector...These are the hardest issues and i certainly feel your pain.. hopefully we can provide you with the answer...


                    • #11
                      Thanks for the help to all.
                      Soder- I had seen that thread before but didn't go through in detail once I saw it was a different setup and distributor but it has very good generic ideas we can check; already tried the disconnect of ECT which hadn't thought to try before.
                      I will be checking engine harness next and may take a few days to a week as life gets in way, but will let you know what I find when done with an update.


                      • #12
                        Maybe I missed it, but did you say you isolated and eliminated the neutral position switch and lanyard?

                        Also, I'm sure you've seen this, but if you haven't, attached is the LTR wiring diagram / troubleshooting manual?
                        Attached Files
                        Last edited by osmonet; 02-17-2022, 07:40 PM.


                        • #13
                          Thanks for your reply osmonet.
                          Yes, the marine shop checked those, and I have also isolated not only those two common culprits but the whole boat side with its wiring harness which rules out any of those type issues.
                          Thanks for those charts, I was given them in parts at different stages of this process and they are the diagnosis charts that I have mentioned .


                          • #14
                            Originally posted by osmonet View Post
                            Maybe I missed it, but did you say you isolated and eliminated the neutral position switch and lanyard?

                            Also, I'm sure you've seen this, but if you haven't, attached is the LTR wiring diagram / troubleshooting manual?
                            To the OP. I bought an LTR powered project boat back in the day that was a crank no start. Luckily mtajpa sent me the above diagram/troubleshoot manual. It was quite an ordeal to check every circuit for ground, continuity, etc. but this is the process any good tech will take. It will take time, patience, and some decent troubleshooting tools. {specialty tools needed are in the full manual) My issue was a bad crank position sensor but I also had a break (no continuity) in one ECM circuit. Good luck.


                            • #15
                              To Bouyhead, thanks for the above comments; it's good to hear these can get resolved as beginning to doubt this one but like you say, time and patience.
                              Can you elaborate on the specialty tools as I don't have the full manual; I have a fairly decent DVOM, and a test light although I should get an LED test light. Also have some back probe pins and hookups. Can you tell me any others that were helpful to you or that the manual suggests.
                              mtajpa gave me part of the schematics to work through as well but wasn't comfortable back then as now with trusting I was doing checks right so concentrated on where charts were taking me to ICM etc. Now, have to concentrate on all wiring; although nothing unusual found yet. The 4.94v on high ref line was found to be ok.

                              Thanks for anything further.