Mercruiser 5.7 New Day - New Problems

[mutiny]

Working on a 1996 Mercruiser 5.7 with Thunderbolt ignition. Starts up and runs really rough. Found that after doing the basic tests I have some oddities going on. I have 190 lbs in cylinder #4 and all the rest are at 160 lbs. Weird.

The spark test came back interesting as well. The engine is running on 3 cylinders. It does NOT have spark on 1-2-3-4-8 and is running on 5-6-7. The mechanic before me did a tune up last season before winter with a new cap, rotor, plugs, wires, and pickup coil in the distributor. I checked all of the distributor parts to make sure that it has all v-8 ignition components, changed the plugs and have the same issue. Anyone else have this same problem or one like it? I am planning on changing out the cap and rotor tomorrow. My concern is... will the ignition control module allow some spark and not others? In my experience it is either working or NOT working. I've done the coil resistance tests and all seems to be fine. Any experience on this subject would be great. Thanks.

 

[Watermann]

I would recheck what the work the mechanic before you did. It's hard to imagine he sent it out the door running on 3 cylinders expecting someone to be happy with that. Sounds to me like like the cap could be on **** eyed causing the 4 wires going to 1-2-3-4-8 not getting the fire from the rotor.

 

[mutiny]

I would recheck what the work the mechanic before you did. It's hard to imagine he sent it out the door running on 3 cylinders expecting someone to be happy with that. Sounds to me like like the cap could be on **** eyed causing the 4 wires going to 1-2-3-4-8 not getting the fire from the rotor.

I thought that as well. I opened and checked and rechecked the cap several times. Still scratching my head

 

[tpenfield]

check for water (or other liquid) in cylinder #4. That can bring higher compression. Maybe compare the resistance of the wires for the 'good spark' cylinders versus the 'no spark' cylinders to see if it is a bum set of wires :noidea:

 

[Watermann]

It would be a good idea to go ahead and test the plug wires with your multi meter set to ohms. It's pretty much standard at 10k ohms resistance per foot of plug wire.

 

[mutiny]

Couple of questions. I did the testing procedure for checking ignition problems and am running into a road block. Here are the test results.

My first question, when testing the white/red wire in step #1, am I supposed to test it disconnected or connected between the distributor and the amplifier?

#1 - Connect your voltmeter neg. lead to the engine ground and pos. lead to the white/red wire terminal at the dist and it should read 12v.
READINGS - 11v while connected (tested at the connection) 0v disconnected and to the distributor, 11v disconnected and to the amplifier.

#2 If 12 volts is present, remove the coil spark wire from the distributor and connect it to a spark gap tester to ground. Remove the white/green lead from the dist. terminal turn the key to on and strike white green lead to ground. if there is a spark replace the ignition sensor in the dist.
RESULTS - No spark from the coil to ground when striking the white green/wire from the amplifier to ground.

#3 If there is no spark, change coil and retest. If no spark replace ignition amplifier
RESULT - Changed coil, still no spark.

#4 If there is no voltage in step 2 disconnect the white/red wire and check it again for 12v if 12v is present replace the ignition sensor inside the dist cap. If no 12v is present with it disconnected, replace amplifier.
RESULT - This is where I need to know how to test properly in step #1. If I am supposed to test between the disconnected white/red wire to the amplifier then I am getting 11v. If I am to test between the disconnected white/red wire to the distributor then I am getting 0.

My battery is testing good on a load tester and reads 12.5v across the terminals. It reads 11v at the white/red wire going to the amplifier.

I am getting a crazy flurry of spark from the coil thru my tester to ground while actually cranking. it has a momentary pause then back to the crazy sparky jidders. Almost as if I am getting double spark on a rotation of 8 then a pause, then back at it again. Any possibility that the tachometer can be bad? Not sure how to test the tach.

 

[Bondo]

Not sure how to test the tach.

Ayuh,..... Disconnect it's lead from the coil's (-) terminal,.......