1990 3.0 Mercruiser DDIS no spark/start

[J&J Speed Shop]

Boat: 17 ft Larson
Engine: 3.0 L Mercruiser
Ignition System: DDIS

Problem: Out with the family on Memorial day and the boat started and ran just fine. Lake Erie was a bit choppy got into the throttle and up on plane when I started to hit some decent waves. Hit one wave and landed and the engine studdered a bit (RPM drop) then caught again. Next wave completely killed the boat dead in the water. Checked all the fuses and finally got towed in. Back at home looked over everything and verified that I have no spark.

I already have the MCM 3.0L DDIS Wiring Diagram and the DDIS trouble shooting guide. Got the multimeter out and found that on the Purple wire no. 5 I only have 9.48-9.50 volts with the key on. I checked this reading at the eletric choke connection, the connector to the ignition amplifier, and the alternator. In the DDIS troubleshooting guide it states:

2. Engine Harness to Amplifier Power Supply - Disconnect engine harness from amplifier and measure voltage between harness connector terminal #2 (Figure 2) and amplifier mounting bolt. Approximately 12 volts.

Does the Ignition Amplifier need 12 volts to function properly? Why am I only getting ~9.5 volts. I also checked under the dash on the ignition switch. I have a constant 12 volt on a red/yellow wire and in the run position I have 12.5 volts on the purple wire there. I also checked the shift interrupt switch on the top of the valve cover and it seems to function properly (only providing ground when microswitch is depressed). I also checked the motion sensor and it read 169-172 ohms. I am going crazy here and the weather is warm. HELP

 

[Reel Poor]

Re: 1990 3.0 Mercruiser DDIS no spark/start

Does the boat have a safty lanyard kill switch? If so it could be faulty or have bad connections. Also need to check for wire chaffing on the purple wire between the ignition switch, kill switch (if equiped) and the main engine harness connector (terminal #5).

 

[J&J Speed Shop]

Re: 1990 3.0 Mercruiser DDIS no spark/start

Does the boat have a safty lanyard kill switch? If so it could be faulty or have bad connections. Also need to check for wire chaffing on the purple wire between the ignition switch, kill switch (if equiped) and the main engine harness connector (terminal #5).

there is no safety lanyard kill switch only the key switch. Is there anything in the shifter?

 

[Reel Poor]

Re: 1990 3.0 Mercruiser DDIS no spark/start

Only the neutral safty switch but that is in the cranking ckt, not the ignition ckt.

 

[J&J Speed Shop]

Re: 1990 3.0 Mercruiser DDIS no spark/start

Only the neutral safty switch but that is in the cranking ckt, not the ignition ckt.

Yeah boat turns over fine. Just has no spark. Looks like another day of fun

 

[Don S]

Re: 1990 3.0 Mercruiser DDIS no spark/start

Check your voltage on the ignition switch purple wire and see what the voltage is there, also check the red wire on the switch (they should be the same voltage)
If the voltage is ok at the switch, disconnect the round plug on the engine and check the voltage on the inst. panel harness side to check the voltage on pin #5. Should read battery voltage.

 

[J&J Speed Shop]

Re: 1990 3.0 Mercruiser DDIS no spark/start

Check your voltage on the ignition switch purple wire and see what the voltage is there, also check the red wire on the switch (they should be the same voltage)
If the voltage is ok at the switch, disconnect the round plug on the engine and check the voltage on the inst. panel harness side to check the voltage on pin #5. Should read battery voltage.

Don S glad you jumped in feet first to help.

I just came inside from a little multimeter fun.
On the purple wire I have 12.6 volts when I first test it, then it seems to drop to 8.5 - 9.5 volts after a bit. I read about a resistor in the wire somewhere?

Now onto the DDIS check. When the ignition amplifier is connected and I disconnect the ignition coil and check the voltage there I only get 0.50 volts. Also when I plug the coil back in and leave the amplifier plugged in a check the voltage at either the alternator (purple wire) or the choke thermostat (purple wire) I get 0.50 volts. In the troubleshooting it says if the voltage between the 2 spots vary by .5 volts the ignition amplifier is defective. I have the same voltage but the ignition amplifier seems to be drawing a good amount of power. My first through is the ignition amp is defective cause I have checked everything else like the coil, motion sensor and voltage just about everywhere (key switch). The only thing that confuses me is the drop in voltage on the purple wire from 12.6 to ~9 volts.

Any more ideas?

Thanks
Jay
jason@jandjspeedshop.com
(716) 830-0506

PS - it is going to be 80? today and this boat is driving me nuts

 

[Don S]

Re: 1990 3.0 Mercruiser DDIS no spark/start

On the purple wire I have 12.6 volts when I first test it, then it seems to drop to 8.5 - 9.5 volts after a bit. I read about a resistor in the wire somewhere?

The resistor wire is ONLY in the wiring of a points type ignition, NOT the DDIS
Where did you get the 12.6 Volts at?
Disconnect the electric choke and see what the voltage does.

 

[J&J Speed Shop]

Re: 1990 3.0 Mercruiser DDIS no spark/start

The resistor wire is ONLY in the wiring of a points type ignition, NOT the DDIS
Where did you get the 12.6 Volts at?
Disconnect the electric choke and see what the voltage does.

I get 12.6 volts at the electric choke wire. I have had it disconnected during this whole troubleshooting phase. I also have the alternator off the engine currently and I get 12.6 volts at both the red and purple wire. Then the voltage in the purple wire seems to drop.

If this ignition amplifier is defective what is the best solution to the problem. I know they are very expensive. How good are they or will I be buying one again in the near future. This boat has very low hours

 

[J&J Speed Shop]

Re: 1990 3.0 Mercruiser DDIS no spark/start

UPDATE: At the alternator wire red/purple I get 12.5 volts, at the alternator purple - choke purple - and ignition amplifier connector purple wire (all the same wire right?) I get varied voltage readings. When I just checked with the key on it was 10.5 volts. I cranked the engine over a few times and it dropped to ~8 volts then to around 6 volts. This boat is really starting to give me a headache and I can't have a beer until noon

 

[Don S]

Re: 1990 3.0 Mercruiser DDIS no spark/start

If you are getting 12.6 V and it drops to 8 or 9 volts in a few minutes, then you have a bad (loose, corroded, ????) connection somewhere.
When you are trying to start it, there is even more draw on current and probably less voltage.
Check your voltage on your purple wire while trying to start the engine and see what it drops to.

 

[Don S]

Re: 1990 3.0 Mercruiser DDIS no spark/start

Well, I was typing while you were posting.
Since the alternator wires and choke wires all stay high and only your ignition wire is dropping, I would say the wire is bad, or where the wires are soldered together in the wiring harness on the engine.

 

[J&J Speed Shop]

Re: 1990 3.0 Mercruiser DDIS no spark/start

If you are getting 12.6 V and it drops to 8 or 9 volts in a few minutes, then you have a bad (loose, corroded, ????) connection somewhere.
When you are trying to start it, there is even more draw on current and probably less voltage.
Check your voltage on your purple wire while trying to start the engine and see what it drops to.

I did check the voltage while cranking the engine and it drops to around 6 volts. It might drop even more if I continued to crank the engine. Would it be a good idea to hot feed a power wire directly from the battery into the electric choke wire to try to pinpoint if my ignition system works or not. It would be very easy to do with a length of wire and a crimp on blade connector

 

[J&J Speed Shop]

Re: 1990 3.0 Mercruiser DDIS no spark/start

Well, I was typing while you were posting.
Since the alternator wires and choke wires all stay high and only your ignition wire is dropping, I would say the wire is bad, or where the wires are soldered together in the wiring harness on the engine.

According to my wiring diagram the:

1. Purple feed wire to the ignition amplifier
2. Electric choke wire (purple wire)
3. Alternator voltage excitation wire (also purple)

are all connected (the same wire) which is my #5 wire (purple) at the engine boat connection. In the wiring diagram that is my ignition wire and that wire drops voltage after time or when cranking the engine. The red/purple wire at the alternator stays at battery voltage (12.5 volts)

Could the problem be in the wiring on the boat or maybe up under the dashboard? My understanding from reading the diagram is the power goes up to the front (dash) via the #6 pin to the keyswitch and then a purple run wire off the keyswitch goes back to the #5 pin to power the ignition wire (purple) on the engine harness which is connected to the voltage reg on the alternator, the electric choke wire, and also power for my ignition amplifier

 

[Don S]

Re: 1990 3.0 Mercruiser DDIS no spark/start

Would it be a good idea to hot feed a power wire directly from the battery into the electric choke wire

It wouldn't hurt anything, but the problem is, if the wire to the DDIS is bad and the wire to the choke is good, it tells you nothing.
Where were you testing this voltage at?
What's the voltage show at the battery when cranking? and while the voltage is low on the DDIS wire.

 

[Don S]

Re: 1990 3.0 Mercruiser DDIS no spark/start

According to my wiring diagram the:

1. Purple feed wire to the ignition amplifier
2. Electric choke wire (purple wire)
3. Alternator voltage excitation wire (also purple)

are all connected (the same wire) which is my #5 wire (purple)

They are the same circuit, not the same wire. There is a connection in the engine wiring harness where those wires are soldered together. It could also be the #5 pin or socket on the main plug that is causing the problem. Could even be and slightly corroded fuse under the dash that feeds the purple wire.

 

[J&J Speed Shop]

Re: 1990 3.0 Mercruiser DDIS no spark/start

It wouldn't hurt anything, but the problem is, if the wire to the DDIS is bad and the wire to the choke is good, it tells you nothing.
Where were you testing this voltage at?
What's the voltage show at the battery when cranking? and while the voltage is low on the DDIS wire.

I was testing the voltage at 3 spots which should all be the same wire/circuit:
1. Purple pin feed to ignition amplifier
2. Purple wire to choke thermostat
3. Purple wire to voltage regulator/alternator

During cranking the voltage on the battery drops a bit then quickly recovers like it should. I did check all the grounds and they all appear solid, tight, and not corroided

They are the same circuit, not the same wire. There is a connection in the engine wiring harness where those wires are soldered together. It could also be the #5 pin or socket on the main plug that is causing the problem. Could even be and slightly corroded fuse under the dash that feeds the purple wire.

Yeah you are correct. I said same wire, I was thinking circuit. Checking the ignition fuse wouldn't be a bad idea. If I find a corroded fuse I will kick myself directly in the behind but I will be happy that I don't have to spend big dollars on an ignition system

 

[J&J Speed Shop]

Re: 1990 3.0 Mercruiser DDIS no spark/start

First off I would like to thank Don S for all the help.

I finally figured out my problem. It was the purple ignition feed wire on the back of the boat's tachometer. The stud on the Tach was loose and caused the voltage to drop when the key was turned on or any load was on the system. I don't know why a boat manufacture would wire a boat like this. I mean to take the purple wire off the key switch and go through 4-5 gauges before going back to the engine compartment just seems stupid. I mean if I am out on the water far from shore my gauges not functioning correctly isn't that big of a deal as long as I can get home. On the other hand a broken gauge or loose connection that has me sitting like a dead duck in the water is stupid. I fixed the problem by adding another ring terminal and extending the purple wire that goes to the back/engine directly to the key switch.