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1966 427/425 when warmed up back fires, stahls,hard starting ect

 
dvestri
I love my Chevy Chevette!
Posts: 2
Joined: 08/10
Posted: 08/01/10 08:56 AM

HELP. i HAVE A 1966 BIG BLOCK STINGER CAR. TOP FLIGHT CAR WAS A TRAILER QUEEN. OVER THE LAST YEAR A HAVE DECIDED TO DRIVE HER. WHEN ITS COLD IT RUNS GREAT, ONCE HOT 180 ABOVE IT LOADS UP , STAHLS BACK FIRES ROUGH IDLE ECT....had MY LOCAL VINTAGE HOT ROD CHEVY GURU CHECK IT HE THOUGHT CARB PUT KITS IN 2X ... NO BETTER . PLUGS NO BETTER..SENT ti box to ti specialties (dave fielder)says it was okay.SENT DISTRIBUTOR TO HIM HE SAID THAT WAS THE PROBLEM BAD PICK UP COIL ECT 900.00 LATER PUT IN NO BETTER....WHEN IT WAS ACTING UP I PULLED IN TO MY LOCAL GURU(ACTUALLY COASTED IN OM THE STAHL )PUT OSCILLOSCOPE ON IT SPARK ISSUES HE SAID HE HAPPENED TO HAVE A TI COIL FROM ANOTHER TI VETTE PUT IT IN WAMO SPARK ON SCOPE PERFECT RAN GREAT I DID NOT DRIVE IT FOR 2 WEEKS TOOK IT OUT RAN GREAT UNTIL 30 MIN GETS REALLY WARMED UP  BOOM LOADS UP ,RUNS LIKE ITS DRAGGING ASS ROUGH IDLE , A LITTLE SMOKE POOR LOW RPM PERFORMANCE STAHLS  REAL DOG. HARD TO START AFTER THAT THEN FORGET IT TOTALLY LOADED UP AND DONE . MUST LET IT SIT UNTIL COLD THEN SAME DEAL Frown  ALL OVER AGAIN. WHAT GIVES ANY BODY HAVE A CLUE ITS BEEN A YEAR WITH THIS >>>>> DW Frown  

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waynep7122
I mow my lawn and find Chevys
Posts: 1114
Joined: 08/09
Posted: 08/01/10 10:17 PM

you have thermal issues with some part of the ignition system...

i would take it that your warrantee on the repairs done have expired...

i would really like to know if you have a digital volt meter..??????

and if you know how to use it..

i would like you to do some voltage drop tests..  on the ground side of the system..
takes about 2 minutes to ***

engine running.. headlights on..  digital volt meter set to 20 volt DC scale..

battery negative POST.. to the engine block...  0.04 volts is good..
battery negative post to a body ground..        0.02 volts is good
engine block to the body ground..                 0.02 volts is good..

positive battery POST.. to the alternator output terminal..  post what you find..  should be less than 0.1 volts..  post what you find..  closer to 0.02 is better but since there is a lot of current.. i expect more drop..

i am worried that you have a resistance problem between those parts..

the bulkhead connector.. the ignition switch... there are a lot of things that can fail...

including new or used ignition coils..


 I am going to say... swap in a conventional electronic ignition system..  even if you have to run separate wiring harness to control it..  so you don't have to tap into your existing harness..  this is ONLY a test.. or for a short time till you get the various parts tested and proven to work in a hot situation..



wow .. thats a LOT of money for TI stuff.. i wish i had bought some years ago when somebody offered it.. as they were closing their parts store..  


thermal failures are hard to find.. require duplicating the failure with the engine running and a tech standing there..

do you have a timing light????  hook it over the coil wire..  fire the engine up..  tape the trigger on..  watch the flashing light..  see if it starts flickering when the engine starts running bad...

this is a took box scope...

if you had access to an oid style automotive diagnostic scope.. or a new digital storage scope.. (NOT CHEEP)  you could watch the primary and secondary..

i have a pontiac TI distributer and module kicking around someplace.. i also have a bunch of old repair manuals.. i will have to look up the specs..  

i have on other models.. ohmed the pick up coil windings..   if they passed spec..  then i flipped the meter to AC volts..  spun the distributer shaft..  the pickup coil has to put out close to one volt..  or it will not put out enough wave form to turn on the power transistor so the primary windings get charged..   when the tips of the reluctor pass the tips of the pick up coil the voltage swings negative..  this drop below RMS 0 volts causes the power transistor to open the circuit and discharge the coil...


my older brother (rip ) worked in recording studios and had to check each power transistor that came in on a scope to make sure it had proper switching inside..  i never learned how he did it..  he was way deep into electonics... i was into automotive..  he chased a power problem in a big power supply for a week.. i mentioned that the power transistor must be failing.. he said that was one from a batch that another employee tested.. he pulled it.. and it failed..  when he pulled the drawer of power transistors and ran through.. 2 others of 20 also failed his inspection..  and they had the other techs dot on the bottom..  the other tech had a single incorrect setting on the scope..    the power transistors also have to be on transistor paste.. and probably on a mica isolator .. its been a while since i looked at the TI module i have..  these transistors went into $100,000 24 track tape recorders... so anything is possible....


do you have a friend with a distributer machine..   and an hand held scope..  so he can spin it up and examine the wave form from the pick up coil.. then heat it with a hair drier..


oh.. a bad solder joint in the TI module can also cause this problem...

you might want to print this response.. so you have it in your hand to read...  

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dvestri
I love my Chevy Chevette!
Posts: 2
Joined: 08/10
Posted: 10/22/10 06:23 PM

It was a bad ti harness, no mesh cover on the resistence wire  

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waynep7122
I mow my lawn and find Chevys
Posts: 1114
Joined: 08/09
Posted: 10/22/10 07:07 PM

wow... i had forgotten that the Ti wires from the distributer have a shield in the harness... and that one end of that has to be grounded...

if both ends are grounded...  its not a shield..

glad you got it fixed...  

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