spark advance problem Thunderbolt IV

jbt1

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Well time to find some expert advice. I have a 1986 Chaparral with a Alpha One Mercruiser 200 V8 small block in it. Thunderbolt ignition system. I went to do a tune up as I was missing on two cylinders and plugs were 10 years old.....NEW plugs, cap, & rotor were in order. The screws for the old cap would not come off in the boat......so, I had to remove distributor. On the workbench, 3 of the 4 screws snapped off. Decided it would be easier just to update to a newer distributor with an electronic sensor instead of the older style (87-91019A3) ignition sensor. Found a working one on ebay for reasonable price. Installed distributor in engine lining up timing marks and rotor to #1 position of cap. New cap, rotor, & plugs installed. Fired boat up, idles great but no power at throttle up....... almost like no spark advance at all. Is it possible the newer version sensor is not compatible with my ignition module?? I moved timing 10-15 degrees either way by rotating distributor thinking it might be an initial timing set point issue......but don't really see much difference except if you go too far either direction with timing, even the idle dies....which one would expect. I am at a loss.....please HELP. Thanks! Jeff
 

Fun Times

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Decided it would be easier just to update to a newer distributor with an electronic sensor instead of the older style (87-91019A3) ignition sensor. Found a working one on ebay for reasonable price.
Hi there, welcome to iboats!:)

Do you have a photo or link to your new distributor and sensor?

You may want to try using a timing light to see if your getting any advance.

Did you ground the ignition sensor black wire to the battery ground stud at the rear of the engine?

 

achris

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The sensors are exactly the same, no difference. The advance is done in the module (the one mounted on the exhaust elbow). I would do a few things. First, check that the timing is advancing (I suspect it is), then I would check, double check, and triple check the plug wires for the correct order. Have a lot of threads here about exactly this, especially after any ignition work. Engine idles great, but no power.... I would say that about 80% of the time, someone finds a couple of plug wires crossed....

Chris........
 

jbt1

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thanks for the replies! I do have the wing nut type connectors on the battery posts, so I will update and tighten using stainless nuts & lock washers as well as charge the battery to make sure it is at peak (battery is 3 weeks old by the way - Marine deep cycle 950 CCA). I did connect up the black wire from the sensor to the stud on the back of the engine ground point as shown in the pic as well as connect the black smaller wire in my harness to the stud on the bottom of the distributor. I did not have "bullet style" connectors as the old wires connected up directly to the old distributor with spade connectors on posts. I cut those off and striped wire ends and then used wire nuts to secure all connections together. ( white w/green trace & white w/red trace wiring). The pre-owned distributor is an OEM unit with a matching part/model number on it to my old one. I am under the understanding GM used this distributor on a lot of models over a lot of years.

How am I going to know if I am getting any advance at all? I do not think I am getting any because when I give the engine even a slight amount of throttle, I do not get any increase in RPM.....just a noticeable fuel increase that seems to begin to flood the engine like it is choking if you were adding with a manual choke so to speak. This is what is strange to me, every engine I have ever worked on has increased in RPM at least some when given more fuel....this engine doesn't....it just starts to labor as if being overwhelmed with the added fuel from idle. Is it possible this system is stuck in some type of "limp" mode and the brain box is purposely keeping any advance at all from happening? Thanks again.
 

jbt1

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I also don't understand your comment about not sending service questions in private messages. I posted this problem by clicking on "forums" and then "engine and maintenance issues" and then "new topic" per instructions to start a new thread.......is this not correct?? thanks.
 

achris

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There is no 'limp' mode with these engines. And the symptom of no increasing revs on throttle advance is very indicative of crossed plug leads. Have you checked them? How to check the advance is working? You need to point a timing light at the timing marks and watch them move as the engine speed increases. No engine speed increase? Go back to my original suggestion. GM never used a Mercrury Marine Thunderbolt distributor in any of their engines, ever. If you have a GM distributor in there, GET IT OUT!!!

"Comment about service questions in PMs" That line is part of my signature file, which includes all the boat/engine information etc. I added that MANY years ago because I was receiving a lot of service requests through the PM system. That signature file comes up on every post I make... It's not aimed at you personally, it's generic, and has cut down the number of PMs I receive...:D
 
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jbt1

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I understand about the message line....thanks! I should have been more clear on the distributor.....I will clarify......the old one is a SAE J1171 Marine unit with old style sensor that is no longer available......2 contact leads........the pre-owned working replacement is a SAE J1171 Marine unit as well with newer type 3 wire electronic sensor. I should have said that this Marine unit was used in a lot of boat models and years just like the units in GM's automobiles & trucks. I do understand about spark advance when PRM's start to rise......but I do not get any rise in RPM's by adding fuel...so hence, how do you check to see if you are even getting spark advance from the brain box if no RPM increase is present?? Timing light isn't much help with no increase in RPM's.....right?? Also still looking to find out if I could have a compatibility issue with newer electronic sensor vs my older 2 lead style?? thanks!
 

achris

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There is no compatibility issue, they're the same unit. The newer style has the third wire, for grounding directly, not relying on the case of the distributor. And, the advance is not done in the sensor, it's done in the amplifier (module mounted on the exhaust elbow). All the sensor does is give the amplifier a pulse as the rotor window passes. If the engine it's running, the sensor and amplifier are working. If you have no engine speed increase, it's not the ignition system. Have you checked the plug leads yet? If they look right, check then again.

Btw, SAE J1171 is the maine rating, not the distributor part number. You'll also find that number on the starter motor and the alternator, and the main engine circuit breaker. Anything electrical with a maine rating.



Chris.....
 
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JustJason

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You really need to post a picture of what you have if you want a right answer. Some ignition systems are point and shoot when it comes to checking/setting the timing. Other systems have a procedure in which you have to set the ignition module into a base timing mode in order to program the module. Without knowing whatcha got you might as well throw darts at it.
 

DeepBlue2010

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The possibility of having spark plugs wires crossed was mentioned in this thread twice at least with possibility of 80% that it might be the reason for what you having. It was also mentioned by an expert which adds more weight to it.

You did not even give an answer if you checked them or not! Why are you not looking into this?
 

jbt1

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Again, thanks for the replies! In answer to the spark plug wire issue.....the wires have been checked THREE times.....2 visually for correct location and connection.....third time with an multimeter for continuity & orientation.....all is in order with the wires. Here are some pics: Also, prior to my doing the tune up work, the boat idled well in the water and did have acceleration and could get up on plane with 6 of the 8 cylinders firing although it took a couple min's and occasionally would run on all 8 cylinders as you could here and feel the horsepower kick in. Hope this helps.
 

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funk6294

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I do not get any increase in RPM.....just a noticeable fuel increase that seems to begin to flood the engine like it is choking if you were adding with a manual choke so to speak.
How sure are you that you may not have a fuel issue? If it is dumping fuel in that maybe more your issue.
 
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funk6294

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#13 Sorry for the run on quote, seems it wouldn't space things out....
 
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jbt1

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100% sure it isn't a fuel issue. It isn't like it free flows when moving the remote handle forward....it is normal operation and adds fuel as it should just like stepping on the gas in your vehicle....the engine can't handle the increase, even though it is slight, because it isn't starting to increase RPM's. Like I said almost as if there is something causing it to purposely not advance and increase speed. Like it has more fuel but does not know what to do with it. In all my years I haven't seen anything quite like it. My best guess now that the experts here are at a loss might be that the brain box isn't acknowledging any increase in RPM. I am suspecting that there has to be some increase from the motor to start the advance and it all increases from that point. Any opinion on maybe disconnecting the battery and allowing the electronics to "reset" even though there isn't a limp mode??
 

Fun Times

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Disconnecting the battery on this ignition system unfortunately may not yield any results for you. But your more than welcome to try as it won't hurt anything and you may just find something like a loose or corroded battery cable or wire in the process of elimination. Check all wires including the wires going to the ignition control module to ensure they have not backed out of the wire connector plug as that is a common problem. You may want to ohms check the ignition control module "wires" as they could/known to be bad in the past. Also be sure the module is 100% grounded properly.

Have you verified your initial timing at idle is set to specifications using a timing light? At the very least you'll still want to "try" using a timing light to see if your timing is fluctuating "at all" even when you try to give it say 50 RPM for example.

What is the engine idle speed when running?

On the distributor cap, your using the big numbers and not the small numbers, correct?

And you are sure you were on number 1 top dead center on the compression stroke before pulling the old distributor? From your description in the first post you made it sound like you lined the timing marks up after pulling the old distributor out and before installing the new distributor. If so, you could be as much as 180 degrees out so you'll want to triple check this starting with knowing for sure your on cylinder number 1 compression stroke by pulling the #1 spark plug and feeling the air being pushed out then line your marks up on the timing tab.

Having too much fuel pressure from a bad fuel pump could also cause the engine to run like described. Pull a few spark plugs and see what they look like and check fuel pressure as it may just be a coincidence.

Any chance of posting a video of the engine running/acting up preferably with the flame arrestor removed if safety allows it? It's difficult not being there.;)





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jbt1

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Yeah I understand about the not being here issue to hear and see this engine run.....believe me, I would gladly welcome another experienced person here to add their two cents worth. I did not check engine position when I removed the old distributor....so upon installing the new distributor, I made a tool out of a plug fowler with 14mm threads like a spark plug, attached a 16" length hose to it and to the other end of the hose attached a balloon....put this tool in the #1 cylinder in place of the spark plug.......turned the engine over clockwise by hand.....found #1 compression stroke when the balloon just started to inflate......lined up the timing mark on harmonic balancer to 0 degrees.......put the new distributor in so that rotor is pointing to approx. #1 large numeral on cap.....finger tightened rotor hold down tab in position, secured cap & wires & grounds.....(distributor is flush with block).....rotated cap to approx. position of old cap which was maybe 10-12 degrees....very close to initial idle advance I'd say......and turned the key.....idles right away.....go to accelerate and she loads down right away.....moved cap 10-15 degrees either way a little at a time while engine running to see if anything changes with acceleration....nope.....but idle does cough out at either end point of clockwise or counterclockwise movement of distributor........

also....no plugs on ignition amplifier/brain box.....wires go directly inside unit. It is secured to water manifolds with 4 bolts...how much better grounding does it need?
I can take a few more pics.......& I'd be glad to send a video.
 

funk6294

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Maybe a crazy thought here, but from your first post where you purchased the new eistributor it sounded like it was a used one in good shape. If this is the case I am curious if the sensor maybe malfunctioning? Would the sensor from your old distributor fit to test that?
 

NHGuy

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Sure sounds like mis timed. I'd disconnect the cable and run the throttle at the carburetor while turning the distributor by hand.
Sounds like you know this but I'll say it as a way to cover all bases.
On the GM small blocks the forward port cylinder is #1, the port side goes 1,3,5,7, the starboard cylinders are numbered 2,4,6,8.
 

DeepBlue2010

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Most likely you did this but I will ask anyway just to be sure... Did you figure out the firing order and the direction of rotation of the distributor before connecting the wires?
 

jbt1

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firing order correct....clockwise rotation....cylinder number stamped right on top of block......1,3,5,7 & 2,4,6,8.....have the service & installation manual...so no guess work at these issues you bring up......old sensor kaput! I could not get engine to start with the old distributor as I did drill out the snapped off bolts and reinstalled it....not even a pop......that's why I got a different one.....the new one fired right up at idle speed......so I know old sensor is bad for sure.....no going back to it.

Starting to hear you guys scratching your heads too! :)

I came here before I rubbed the skin on mine raw.
 
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