Today I finished reinstalling my completely rebuilt L71 and it simply will not start. I've basically replaced everything ignition wise other than the TI and distributor. The existing carbs were service replacements and since I was having trouble with the vacuum pods on the secondaries I bought 3 new ones. I'm out of ideas here and need advice. The new fuel pump is functioning and gas is getting to the carbs. The coil is hot and there is spark at the #1 plug. I've checked placement of the wires on the distributor cap and removed and reinserted the distributor by getting the #1 cylinder at top dead center at least 6 times. I've started out making sure the rotor is pointing to the #1 wire on the cap. By all accounts it acts as if the coil wire is missing or something. It simply will not fire or hit and I'm out of ideas.
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Re: L71 rebuilt engine won't start
Are you sure #1 is on the compression stroke, not just TDC? -
Re: L71 rebuilt engine won't start
Did it run before you rebuilt it?
The coil must be a known TI coil.
The amp may have failed & one of those soild block modules has been installed. They give very weak cranking spark.
Try a shot of ether. If it only starts with ether, then
use the shop manual to diagnose the TI system.Comment
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Re: L71 rebuilt engine won't start
Yes, the engine ran somewhat fine before rebuild. Although it was tired and had varying compression, coolant in the oil, etc. Thus, the rebuild. The coil is new from Corvette Central and seeming proper boxed in a Corvette Restoration Parts box with the red/silver TI labeling and such. Odd, the TI would fail simply from sitting for 2 months but that's why I'm on here seeking advice. I was hesitant to try ether but at this point am open to anything.Comment
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Re: L71 rebuilt engine won't start
Tom-----
One thing I would definitely try. Obtain another distributor which is a conventional points type. It doesn't need to be a Corvette tach drive type (unless you think you might want to continue to use it) and see if you can get the engine started with it. If you don't have one around, you can purchase a rebuilt distributor in a parts store for a very modest price. If it runs with this distributor, then you know it's a TI problem.
Personally, you'd NEVER catch me using one of these 64-71 TI set-ups. The possible failure modes and lack of reliability are just not off-set by any performance advantages. I have several of these distributors, including NOS examples, plus multiple NOS examples of all the other components of the system. However, I would not even consider using this set-up on my "ZL-1". Not for a second!In Appreciation of John HinckleyComment
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Re: L71 rebuilt engine won't start
You said you are getting a spark at #1. How did you determine this?
Are the wires indexed properly on the cap IAW the CSM?
This may not be your problem, but when installing the distributor, you should not set the engine at TDC #1.
Set it at the proper initial timing mark or about 10 degrees BTDC!!! After the dist. seats with a point type system you rotate the housing until the points just begin to open. With TI you rotate the housing until the rotating poll pieces are just past (clockwise) the pickup coil pole pieces. Using this method the VAC should be about halfway between the limits of travel, and the initial timing should be within a degree or two of where the balancer notch is on the timing tab.
It's not uncommon to fuel foul plugs on a new engine, so remove them for inspection and dry them if necessary.
DukeComment
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Re: L71 rebuilt engine won't start
Four things needed for it to run. If you have these it will run.
1. Fuel mix
2. Compression
3. Spark...
4. ...at the right time.
Fuel...manually open the throttle and confirm you are getting a shot of fuel from the accelerator pump
Compression...is the cranking speed OK? Too fast = low compression. Remove a plug and hold a finger or thumb over the hole while a helper cranks the engine. It should be strong enough to easily blow finger/thumb from the hole.
Spark...Use a new plug plugged on to the existing wire. Ground the plug threads to the block by either holding it to the block or using a jumper wire. Do you get a bright crisp blue spark while cranking? With the TI units I don't recommend just holding a wire near the block. Like Joe says they are sensitive and an open wire circuit could damage the amp. One type of failure on the TI units is a weak spark while cranking which comes back good as you return the key to the run position.
at the right time...Pull the #1 plug and put a finger or thumb over the hole
while a helper bumps the starter. when compression is felt, align the timing mark while still on the compression stroke. The distributor rotor should be pointing towards the #1 spark plug hole. Remove and realign the distributor if necessary. Check the firing order. From the #1 location and counting clockwise 1-8-4-3-6-5-7-2.
Exact timing placement is not necessary for the engine to start. Anywhere between zero and 10-degrees advance should be OK. I like to set the timimng mark to 5-degrees advanced, pull the #1 plug, attach the wire and ground the plug threads to the block. With the key in the run position and the distributor just loose, swing the distributor cap slowly back and forth and watch for spark at the spark plug. Stop when you get a spark as you are swinging in the advance direction (counter-clockwise), and secure the distributor.
Some say theat the balance ring can slip and cause the timing mark to be off. While possible, I think it is rare. If you want to check, look to see that the crankshaft keyway is aligned with the timing mark on the outer ring.
Also check for flooding. Pull a few plugs and check that they are not wet with fuel. My tri-power tends to leak internally. I know if it sits more than a hour to press the accelerator to the floor and crank until it fires. If it sets more than 2-weeks I have to crank until the fuel bowl fills. Yours being new shouldn't have this problem...not yet.
Are you getting any hint of it wanting to start?Comment
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Re: L71 rebuilt engine won't start
1. Fuel, yes I can see the jets squirting
2. Compression, yes I can feel it strongly. I also have a gauge and
will check/measure it.
3. Spark, I thought so but didn't actually verify that myself. My helper said it was there but now I'm doubting. From what you describe, I can simply hold the plug while still in the plugwire to the block and it should spark while cranking, correct?
4. The distributor rotor: You say to point the rotor to the #1 hole and I may have had it towards the #1 wire on the distributor cap - I'll check that as well. I do have the wires indexed properly on the cap to match the firing order. Do you agree that the position of the #1 wire should be just to the right of center? I do know that the distributor itself is in the proper general position as the Vac advance unit is about halfway between the intake and ignition support.
Thanks for everyone's advice to this point.Comment
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Re: L71 rebuilt engine won't start
I had a problem with my TI a few years ago. I would crank and crank without a hint of firing. As I would let the key back to the run position it would fire. Sometimes just a kick, and sometimes it would start. The electronics are pretty sensitive and it turned out to be a weak magnetic pickup in the distributor. It checked out OK with an ohm check but it still caused a weak spark.
Also, are your distributor and coil leads correct? This system is so sensitive that even the polarity of the magnetic pickup leads needs to be correct or it can cause the system not to work right.
http://www.tispecialty.com/ or more specifically http://www.tispecialty.com/articles/66-71diagram.htm for the wiring diagram.Comment
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Re: L71 rebuilt engine won't start
Tom, if this is a new/fresh engine that has never run, I would highly recommend moving on past the TI ignition system, for now, and get this thing fired up. If necessary, just borrow a standatd point distributor, or HEI distributor if it will fit, and eliminate all the confusion until you get everything else sorted out.
Why? Because if this is a fresh engine, it should be fired as quickly as possible so oil has had a chance to circulate and lubricate everything, especially the cam and lifters. The prelube that was likely used on the cam is fast loosing it's ability to properly lubricate.
Also, it's recommended that a spark plug wire never be removed to check for spark if the engine is equipped with the Delco TI system. Supposedly, amplifier failure is the result. Use a timing light to check for spark instead.
When the engine is at #1 firing position, the rotor should point to/very near the #1 plug wire terminal in the distributor cap.Comment
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Re: L71 rebuilt engine won't start
I had the same thing with my 67 & 69. I beleave you are not getting 12 volts out of the TI to start the car. I beleave there are two wires & one is a resistor wire. Check this out with some one that knows TI ignition. I think you are trying to start the car on low voltage. It will crank but not start, GOOD LUCK.
KEN65 350 TI CONV 67 J56 435 CONV,67,390/AIR CONV,70 454/air CONV,
What A MAN WON'T SPEND TO GIVE HIS ASS A RIDEComment
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