454 MAG. BRAVO MPI (GEN VI) GM 454 V-8 1997 Crank No Spark

[JimmyD150155]

Hi hoping for some ideas direction. I am restoring a boat and done a lot of work on the engine to get it this far but cant get a spark from the coil which I replaced as thought it was the problem. Here is the condition after crawling through the service manual and testing as much as I can.

1. Ignition on I get 12v to coil, disconnected grey wire back to Tach in instruments
2. Disconnected red lead from coil and connected a spark plug tester from coil to engine earth and cranked with no spark.
3. Took out solenoid and tested independently but as I said the engine cranks ok
4. Have a diagnosis tester (Techmate) and only error code is 33 the MAP sensor, CAN THIS CAUSE A START ISSUE.? Sent for replacement but as I live in the Philippines will take over a week to arrive.
5 Started to look at the ECM and its connections and testing, The ignition relay i changed with the fuel pump relay as same part so i think ok, Checked with ignition on J1-11, J1-32 and J1-16 all have 12v over my meter (not using ECM earth.!!!). Manual fault tree analysis flowchart says the ECM ground issue or bad ECM (i am hoping not). In the ECM J1-14 and J1-30 are ground black/white wires, they disappear into my wiring harness and i cant find where they come out.!!! I did a check on both J1-14 and J1-30 and there is continuity to the cooling system water temperature sensor black. ANYBODY KNOW WHERE THE ENGINE BLOCK EARTH POINT IS FOR THE ECM EARTH.???

The manual ignition check says with key in run position Check for 1-12 Volts at WHT/RED Terminal on Distributor. My distributor wiring is different I have no WHT/RED (wiring diagram attached)



Any other advice appreciated.

 

[JimmyD150155]

sorry uploaded the wrong distributor wiring from the manual this is the correct one

 

[Bt Doctur]

My guess is your missing the main ground. examine the harness looking for any black wires not grounded to the engine block

 

[JimmyD150155]

Thank you, I will have a deep dive on the harness tomorrow

 

[alldodge]

2. Disconnected red lead from coil and connected a spark plug tester from coil to engine earth and cranked with no spark.

Removing the red kills all power to the coil so there will be no spark

Code 33 is MAP voltage high, so disconnect MAP connector and measure voltage on Lt Green and Gray. The MAP will not keep the motor from firing

Check out your distributor

 

[QBhoy]

Check the ignition sensor on the Diz. Good luck.

 

[JimmyD150155]

thanks all i will digest and get back into it tomorrow, today I did more diagnostics on the ECM and it came up clean, found the ECM ground which was on the engine block at the port side near the transom joint.

 

[Fun Times]

Found the ECM ground which was on the engine block at the port side near the transom joint.

Correct you found the correct ground wires for the ECM.:encouragement:

When you crank the engine over does the RPM gauge move to around the 350 RPM range?
Do you or a neighbor own a timing light? If so connect the timing light to the high tension coil wire that runs to the distributor cap....Crank the engine over while observing the timing light flash for near unbroken consistency during all your diagnostic work....Also at some point check a few spark plug wires too if you have spark at the coil wire.

Using the scan tool, clear the MAP code and see if it comes back.

The MAP sensor, the EST distributor sensor is all GM Delphi truck parts that you ought to be able to find at an auto parts store for more affordable testing...Look up a 1995 GM 5.7 EFI as the parts you're playing with mentioned here are the same as your stock engine model from Mercruiser.
https://www.rockauto.com/en/catalog/...ule+(icm),7172

https://www.rockauto.com/en/catalog/....7l+v8,1031443

 

[JimmyD150155]

Hi all and Fun Times thanks for the great detailed trouble shooting help, here is where I left it at close of play today:

1.ALL DODGE when I said disconnect the red cable I was unclear in my description (sorry) I did not mean the red +12V cable on the coil I meant the High Tension cable from the coil to distributor cap, with a spark plug tester and crank no spark on the tester, both cables to the coil and cables to the distributor connected at that test. My logic was if no spark to the distributor from the coil then distributor may be ok.!!!
2. I took out the MAP sensor as I saw this on the manual fault finding as it says if missing MAP sensor then the ECM uses a "normal voltage" to compensate for missing MAP sensor.
3. When I cranked in condition in 2. (MAP) sensor removed, briefly there was a single spark but happened just as the key "went back in run position" weird eh.!!!
4. I am going to try the light test as soon as the tester arrives as I ordered one but in the Philippines takes about a week to arrive. I like the idea as from diagnosis so far I think coil is bad and complicated by a bad MAP sensor, both are coming and will be good spares anyway.
5. I asked my helper (Son) who assisted me on the boat why the coil which was new would die so quickly and he told me he (as he fitted it for me) and he said after fitting that he cranked the engine a number of time but forgot to put in the coil to distributor high tension cable, he said there was a loud sparking sound from the back of the engine as he cranked but he did notice the missing cable, after replacing the high tension cable there was no life after that from the coil. Therefore I conclude the coil although was new might be kaput from that point.

Thanks again everybody I will feedback as the tests continue and the parts are replaced.

This is a great forum and I hope in the future I can help contribute to solve someone elses problem as you are all trying to do for me. I am learning a lot about this engine, I am 64 and just retired in Dec and it will be a big part of my retirement as I live by the sea.

 

[Scott Danforth]

only about 3 out of a million changed coils are actually bad.

most coil changes are from mis-diagnosis or people changing them because they did not do proper troubleshooting.

what lead you to change the original coil?


what is your cranking voltage? how are the batteries?

if your battery is weak, you may not get enough cranking RPM to actually fire the motor.

 

[JimmyD150155]

Hi Scott, thanks, the original problem started more than two years ago when in a freak stork at 2:00am the boat mooring broke and it washed up on the shore rolled over and was water logged for a day before I could get it out with a large crane, Long story but since then the engine was overhauled and was running with all new components so that was about 1.5 years ago. It was never happy in the water after that as I had overheating (impeller rubber broke in pieces and blocked the cooling path), steering became incredibly stiff as salt water no good for anything, fuel gauge not reading and....... so it lay for more than a year until I am now retired and able to spend most of my time fixing it, long answer to a short question.

 

[JimmyD150155]

Battery voltage showing 12.3V on most checks except ECM of course where I see reference voltages. If you mean while cranking I have not measured that but will do and perhaps share a video

 

[alldodge]

Battery voltage showing 12.3V on most checks except ECM

If your meter is good, the 12.3V is barely on the good side, and a bit low. Should run if it ever starts

 

[Fun Times]

Next time you're at the boat we'll need to know if the RPM gauge is moving when you crank over the engine.

3. When I cranked in condition in 2. (MAP) sensor removed, briefly there was a single spark but happened just as the key "went back in run position" weird eh.!!!

When this happens it's sometimes an indication that the ignition key switch may be failing internally possibly due to moisture corrosion issues from either the boat sinking or rain water, etc.. Try bypassing (jump) the wires of the key switch to see if it helps also try starting the engine at the main wiring harness plug connector such as this,
https://youtu.be/NUoXFIo2Ab8

Charge up your battery and if possible ensure you have enough Cold Cranking Amps with a battery type analyzer such as something similar to this device, https://www.harborfreight.com/digital-automotive-battery-analyzer-66892.html

Though you'll need to recheck things out... If there really was loud sparking sounds from the coil wire removed then it sounds like there may have been spark but maybe not enough to start the engine due to low battery volts when cranking.

 

[JimmyD150155]

Here we go, had sometime on my own this morning to follow up on your ideas and here is what I found, I took some videos of cranking and RPM gauge on crank and will post soon as they are too big for normal mail to send from my Iphone to computer.

1. Cranking does seem slow (video to follow) but similar to what I see in this youtube video https://www.youtube.com/watch?v=wVa82dV52m0, thought it was because the engine has not started and might be stiff, that said i can turn the engine by using a wrench on the fwd crankshaft wheel so cant be that stiff.
2. Took video of RPM gauge while cranking and first indicator mark is 2 RPM, the needle twitched to 1 RPM when cranking.
3. NEW (PIC ATTACHED): I noticed that because I had to leave the boat immediately I disconnected the battery.THE THICK MAIN POSITIVE RED LEAD WAS HOT, It goes as you know to the battery switch box but BOTH thick red cables coming back to the the engine were COLD. The battery switch box as you know is hidden and I have never got in there to clean and check as I did everywhere else, looks like I have a bad connection at the switch box. Will check that out on Monday.
4. I did bypass the ignition switch as recommended shorted across yellow/red and red at run position, did not make a difference. It was a good thought as during all of this testing over the last weeks on three occasions when i turned key to run position i got no buzzer therefore I believe no 12v to purple.

If correct the full amps are not getting to the engine as you guys have been indicating therefore could be root cause.???

Many thanks

 

[QBhoy]

Hi
If it’s anythjng like my MPI...the battery needs to be total strong condition. Any slight sign of weakness (like 12.3v at rest) would trouble my MPI. It would turn it over but not fire it, due to the load taken by the starter. This occasionally means the ecu doesn’t get enough juice to fire the engie. Worth a thought at least. The old thinking of if the battery turns it over, it should be fine...doesn’t apply to the MPI.

 

[JimmyD150155]

Thank you QBhoy, I took out the battery Isolater box and terminals looked ok, cleaned them of and cranked again same issue no spark, main cable to battery still felt hot after cranking so I bypassed the switch box and bolted the cable from the battery to the cable going to the engine directly, same condition after crank where cable is hot near the battery connection,.

Could there be a short circuit on the engine, I need to check the voltage drop when cranking as a next step and try a different battery as you suggest with a better voltage.

Thanks

 

[JimmyD150155]

Hi just wanted to give an update as its been a week of holidays here in the Philippines but back to working on the boat last Monday.
After stripping down the distributor assy which I thought was further up the no spark problem chain after the coil I went back to mercruiser manual study and did a better job of understanding how the whole system works and realized that the IC Module and Pick Up Coil are controlling the spark from the coil to distributor cap. When I tested the pick up coil it was shorted hence no pulse signal back to the coil to open and close the primary circuit.
New pickup coil on its way and relatively small cost and I packaged it with a new IC Module as a probably much needed maintenance replacement.
I will update when new part installed as I see many problems raised on the forum but some just stop dead with no "this fixed it".
Many many thanks to all who have supported me this far as I did see the pick up coil mentioned in one of the comments by AllDodge and was slow to "pick up" (sorry for the pun) on its importance in the ignition sequence.

 

[JimmyD150155]

Hi all quick update the pickup coil arrived finally from the US and I fitted this morning. Delighted to say I have spark all the way to the plugs. Engine did not fire as fuel line just opened for the first time in a while. I have put batteries on charge as they were getting low and will try a full test in a few hours

 

[JimmyD150155]

Here is the damaged pickup coil