Weak Spark?

[saxman9801]

I am trying to track down what seems to be a weak or no spark that caused me to stall out. My inital thought was that it was hydrolock but it is not. It cranks but just will not start. I tested for 12V at the coil and I am good, showing about 12.2. I checked for 12V on the lead going into the distributor and am showing about 11.4 with the key on. I followed the instructions to check for spark at the coli by tapping the lead from the module against ground, and I get no spark from the coil. But when I insert my spark tester and crank it I get spark at the coil. I checked for spark at the cylinders with both my timing light and my spark tester, with my spark tester I do not get a very strong spark if any, but with my timing light I can see spark. Thoughts? It is a 1995 with a thunderbolt V, carbed 4bbl 5.7 liter merc.

 

[searay3]

Re: Weak Spark?

Cap, rotor, plugs and wires are maintenance items. How long since the last tuneup. Also check the condition of all the connections at the module and distrib. Had a module go bad once, TBIV, barely ran, different animal but just as expensive. If the wires/plugs and such are old, I would start there...

 

[saxman9801]

Re: Weak Spark?

Cap, rotor, plugs, wires and coil are all new and got replaced when the motor went in. Checked the connections today and they all look good. Also verified that my tach was not grounding out on the coil. Still No luck.

 

[searay3]

Re: Weak Spark?

you could do a search on TBV flow chart. I believe I saw one once that DonS had posted, or it could have been TBIV. There are tests in the book regarding the pickup coil. It could be there. mine was rusted and busted. In my case there was an updated version of the coil. Check your manual for the ignition tests. If you haven't already, download your manual. They are available for free in the adults only sticky at the top of the forum.

 

[Don S]

Re: Weak Spark?

I have no idea what manual you are using, but here is the procedure for testing the TB5 ignition system per the OEM manual.

 

[saxman9801]

Re: Weak Spark?

Thanks Don and I have that flow chart already in front of me, it is the eigth box down where it gets goofy for me, when I strike the white with green rapidly against ground I get no spark at the coil. However if I hook everything back up and crank the engine over i get spark at the coil, does that make sense? As stated the coil is brand new this season, I am going to substitue a new coil but I still dont understand why I would see spark while cranking but not while performing the test.

 

[searay3]

Re: Weak Spark?

as I stated earlier, when the module went bad, it still ran.....barely. According to the flow chart you are at replacing the module.

 

[Don S]

Re: Weak Spark?

First off, put everything back together and hook up all wires as they should be.
Then follow exactly what the chart says. Don't unhook or take anything apart unless it says to. Then put it back when it tells you to.
Then, if you have no spark and it says substitute the coil, do so. It didn't say substitute the coil unless you bought it last year or last week. It said substitute the coil and repeat the test.

 

[saxman9801]

Re: Weak Spark?

Uhm I followed the flow chart exactly, and substituted a brand new performance coil I had in the garage, and no spark from the coil when tapping the white with green against ground, so according to the chart and the post be searay I am after a new ignition module, which I am cool with as long as it fixes my problem, I guess I still dont understand why the hell I get spark when cranking if this part is bad, but I guess I will replace the module and go from there. Any reccomendations on where I can find one with out auctioning a kidney?