Timing Issues on Merc 5.7 Thunderbolt 5

[rpdwyer]

Hello all.

I have two 1997 Merc 5.7L 2 Barrel motors with Thunderbolt 5 ignition. Timing wise I have one dialed in nicely at around 8 degrees and advancing correctly to about 32-34 degrees at 3500 rpm's. The other one has been troublesome. When in Base Timing mode, I set it to 8 degrees at an idle of around 650. When I startup again out of base timing mode, the engine sounds fine...idles fine, but the timing is around 18 degrees. Furthermore, there is only about 5 to 8 degree advance in this state. Both engines have new caps and rotors and new plugs.

Yesterday I took the ignition module that is on the outside shaft of the distributor and swapped those. Problem stays with the engine. I then swapped the module that is inside the distributor. Problem stays with the engine. Even swapped coils... although I didn't really expect that to do much. Same result.

There is no knock sensor on this engine so it's not that. Also the amount of up and down play in the distributor shaft with the caps off between both distributors is the same... which is a very tiny bit...maybe a 1/16 of an inch.

Any ideas on what could be the cause? Both engines were run on muffs as I am not in the water yet.

Thanks,

--Rick

 

[MikDee]

Re: Timing Issues on Merc 5.7 Thunderbolt 5

Is your Dizzy spinning in a perfect circle, or is there a worn bushing, or part that is causing sideways play, and it's spinning out of round?

 

[rpdwyer]

Re: Timing Issues on Merc 5.7 Thunderbolt 5

Is your Dizzy spinning in a perfect circle, or is there a worn bushing, or part that is causing sideways play, and it's spinning out of round?

No sideways play at all. Just a 1/16 up and down. I can have my son hold the key over while I look down at the top with the cap off.

--Rick

 

[achris]

Re: Timing Issues on Merc 5.7 Thunderbolt 5

Check that the distributor has a ground wire from the engine block (or in the wiring harness) going to it.

 

[MikDee]

Re: Timing Issues on Merc 5.7 Thunderbolt 5

No sideways play at all. Just a 1/16 up and down. I can have my son hold the key over while I look down at the top with the cap off.

--Rick

Have you physically tried to wiggle the Dizzy shaft? I had this happen to me, but I couldn't tell till I tried wiggling the Dizzy shaft. Any movement here would throw your dwell, & timing off.

 

[achris]

Re: Timing Issues on Merc 5.7 Thunderbolt 5

Have you physically tried to wiggle the Dizzy shaft? I had this happen to me, but I couldn't tell till I tried wiggling the Dizzy shaft. Any movement here would throw your dwell, & timing off.

Actually, on these ignitions, it won't. The dwell is controlled completely in the electronics module, and the timing might vary about half a degree, not enough to notice, even with an advance timing light.

 

[MikDee]

Re: Timing Issues on Merc 5.7 Thunderbolt 5

Is it possible the Dizzy is off one tooth? I would set the crank on TDC, it does not matter if it's Cyl. #1, or Cyl #6. Take off the Dizzy cap, and look at the reluctor wheel. It should be dead center of a tab on the wheel (window closed) sending the spark to the rotor, coil, & plugs. If it's off one way or the other, I would think it would affect the timing. If so, you should pull out the Dizzy, line it up to whatever direction it has to go to match everything up, then drop the Dizzy back in. Then snug it up, and try retiming it now. If all is lined up the way it's supposed to be, move on to other things.

 

[rpdwyer]

Re: Timing Issues on Merc 5.7 Thunderbolt 5

I believe (and I could be wrong) that you cannot be off a tooth on these distributors. I could insert the distributor any way I want since I can then rotate it so it comes into spec on the timing light. If it reads 8 Degrees... it's 8 Degrees regardless. Anyway, it's position is nearly identical to the other engines distributor position so I believe it's in the correct position.

HOWEVER, update, last night, I went down to the boat and this time I was able to get it to time correctly. In both base timing and out of base timing it is currently around 8 or 9 degrees... and appears to be advancing correctly. So what gives? What could possibly cause it to run 18 degrees or so but idle fine and then when checked a day or two later, I was able to reign it in? The day it was off, I tried toying with it for several hours and always the same. 8 degrees at base would jump to about 18 out of base at same idle... and little to no advance. Now, a day or two later, in base, I set it to 8 degrees and out of base it stays around 8 and advances just fine. Nothing changed between the two days except time.

--Rick

 

[MikDee]

Re: Timing Issues on Merc 5.7 Thunderbolt 5

Your Dizzy has little spaces on the reluctor acting like open, or closed windows. Apparently it's some type of beam, maybe infrared? that gets interrupted by the window, then fires. As soon as the window stops the beam, it fires. IMO, if the window was off a little bit, (like one tooth) it would fire a bit advanced, or retarded, changing your timing. I know, it's just a theory I have, but I've had an old Chevy points (circa 1974) Dizzy that was off so much due to factory tolerances, that I had to put a bolt through the vacuum advance arm to move it forward, so that the points would open exactly on the high point, and when the rotor was on #1. Good thing I looked, it blew my mind? At the time I was putting an advance kit in the Dizzy, so I didn't need the vacuum advance, but needed the breaker plate to be where I wanted it. Then I could set the initial static advance, & let the kit do the rest!

 

[achris]

Re: Timing Issues on Merc 5.7 Thunderbolt 5

Your Dizzy has little spaces on the reluctor acting like open, or closed windows. Apparently it's some type of beam, maybe infrared? that gets interrupted by the window, then fires. As soon as the window stops the beam, it fires. IMO, if the window was off a little bit, (like one tooth) it would fire a bit advanced, or retarded, changing your timing. I know, it's just a theory I have, but I've had an old Chevy points (circa 1974) Dizzy that was off so much due to factory tolerances, that I had to put a bolt through the vacuum advance arm to move it forward, so that the points would open exactly on the high point, and when the rotor was on #1. Good thing I looked, it blew my mind? At the time I was putting an advance kit in the Dizzy, so I didn't need the vacuum advance, but needed the breaker plate to be where I wanted it. Then I could set the initial static advance, & let the kit do the rest!

MikDee. Please learn about the Thunderbolt system before trying to advise people on how they work. It is not a beam, it's a reluctor, works by sensing the metal of the rotor. As for being 'one tooth out', the OP is correct in that if the engine is firing at 8 BTDC, then it matters little about the actual position of the distributor drive gear. The only thing that would effect is the lay of the spark plug leads from the distributor cap.

They is absolutely no point in comparing these systems with an old Kettering system (points). There are no advance weights and springs, they is no vacuum advance.

OP... This is sounding very much like a grounding issue, did you check for a ground wire on the distributor body?

Chris......

 

[Fun Times]

Re: Timing Issues on Merc 5.7 Thunderbolt 5

Nothing changed between the two days except time.

Did you physically reset the timing a few days later? You may have had a bad grounding at the distributor or possibly at the Ignition control module due to possibly a wire starting to back out of the wire connector to the ICM. Something of that nature.

Also if engine idle speed is just a bit on the high side, you will see the timing advance. Be sure you idle speed is fluctuating between 643 -648 RPM for best results.

 

[rpdwyer]

Re: Timing Issues on Merc 5.7 Thunderbolt 5

Did you physically reset the timing a few days later? You may have had a bad grounding at the distributor or possibly at the Ignition control module due to possibly a wire starting to back out of the wire connector to the ICM. Something of that nature.

Also if engine idle speed is just a bit on the high side, you will see the timing advance. Be sure you idle speed is fluctuating between 643 -648 RPM for best results.

Yes, yesterday the timing was reset physically by moving the distributor while locked into base timing...same as I had done over and over for nearly two hours the day before. But this time, when out of base, it stayed around 8* while at idle while the previous day it would have jumped up to 18* at idle. Definitely grounded, but next time down I will cleanup up the area the ground bolts to the block to make sure I am getting good contact.

Thanks for all the input.

--Rick

 

[MikDee]

Re: Timing Issues on Merc 5.7 Thunderbolt 5

MikDee. Please learn about the Thunderbolt system before trying to advise people on how they work. It is not a beam, it's a reluctor, works by sensing the metal of the rotor. As for being 'one tooth out', the OP is correct in that if the engine is firing at 8 BTDC, then it matters little about the actual position of the distributor drive gear. The only thing that would effect is the lay of the spark plug leads from the distributor cap.

They is absolutely no point in comparing these systems with an old Kettering system (points). There are no advance weights and springs, they is no vacuum advance.

OP... This is sounding very much like a grounding issue, did you check for a ground wire on the distributor body?

Chris......

The Thunderbolt 4 ignition might be electromagnetic, but from what I read, the Thunderbolt 5 is a photoelectric style ignition, using a hall effect sensor.

and Yes, there is no vacuum advance used on a boat.

 

[achris]

Re: Timing Issues on Merc 5.7 Thunderbolt 5

Umm... Photoelectric using a hall effect.... So, which is it? Photoelectric means using a beam of light. The 'Hall effect', named after the man who discovered it, is a voltage produced by a magnetic field.

Thunderbolt IV and V both use the same sensor in the distributor... Same part number in fact... And it's a reluctor, sensing the metal tab as it passes. The sensor electronics has 12v going in (wht/red wire) and switches the output (wht/grn wire) between 0 and 5v as the window passes each time. The electronics in the amplifier module uses that as the signal to start the timing process based on engine revs (calculated by the frequency of the window passing the sensor). When the appropriate amount of time has past, usually just a few milliseconds, the module fires the coil, producing a spark....

BTW, Merc has never uses a photoelectric cell (in any engine), and most electronic systems don't. More than 90% are of the reluctor type.

Chris...

 

[Limited-Time]

Re: Timing Issues on Merc 5.7 Thunderbolt 5

The Thunderbolt 4 ignition might be electromagnetic, but from what I read, the Thunderbolt 5 is a photoelectric style ignition, using a hall effect sensor.

and Yes, there is no vacuum advance used on a boat.

Hall effect sensors utilize a magmatic field to trigger them. They are not photoelectric.