Hard start after engine is warm. Would appreaciate some help.

Hey all

Like many of the other posts, I am new to tuning and need some help.


I have a 76CJ5 with a mildly warm 304 and a transplanted a Chevy 305 TBI system.
The computer is a 7747 from DynamicEFI so I can flash on the fly and use TunerPro to make adjustments.
Ignition starts at the GM HEI module -> through a MSD 6A box -> big cap dizzy, thus the computer controls timing as well.
Sensors used are NBO2, knock, CTS and speed.

The motor runs pretty good, but the starter just doesn't want to roll the engine when it is warm, like it has a dead battery. Let things cool down and it starts right up again. One of the guys on a Jeep forum I visit suggests it is the initial timing.

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With GM style HEI distributors, it’s almost always too much initial timing.

GM style HEI modules don't have a 'Start' timing retard circuit in them,
So you get full initial advance timing thrown against the ring gear/starter motor.
The cylinders are warm, sealing up good, that raises compression and slows the starter down,
Then the high compression, fuel charged cylinders are simply firing too soon and trying to stop the piston/rod/crank on the 'Up' stroke.

The crank/rods/pistons simply don't have enough speed/momentum to continue over the top of the crank, and the starter motor gets blamed for 'Dragging'...
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Earlier this year I tuned my main SA table, I basically kept adding more advance until I saw the knock sensor kicking in and then I would back that area down 2-3 degrees and it really helped add what “feels” like a huge amount of torque. But the warm hard start has been ever present since I put the TBI system on.

My distrib is physically set at 0* and I am pretty sure that is what my “SA-Initial SA” value is set to as well (I’ll double check when I get home from work).

So what setting or table do I need to adjust to make starting the hot engine easier? What data can I post up that would help?

Thanks IA.

As a long time GM tech and a guy with some experience with ignition systems, I have to point out that the wording of the statement above makes the reality of the situation sound worse than it is. True, there is no "start retard" built into the distributor. But its not needed. When the ecm is not controlling timing the spark advance delivered, up to around 1600 RPM, is exactly the same as what the distributor is set at... 0 degrees in your case. That means the "full initial advance thrown against the ring gear/starter motor" is zero degrees. Literally, it's nothing. If you are getting a hard start due to spark advance then it may be necessary to adjust the parameters that control when the ecm begins to control spark and fuel delivery, or spark advance delivered during crank and / or additional advance related to temp.

The challenge is that I have no idea what tables or constants are available in the DynamicEFI calibration so I cannot provide guidance. If there are no restrictions on posting/sharing the definition file and a calibration then you might want to consider attaching those files. If DynamicEFI doesn't allow sharing then we might have to work a bit harder to get this solved.

I have to ask, have you confirmed the hot engine will crank easily with spark and fuel disconnected? Over the years I have seen plenty of issues related to heat that are due to a starter or wiring related problem. It would be a shame to miss the basic problem due to insufficient testing. If you haven't tried this already you might want to run the engine until warm then disable fuel and spark and try to crank. If the starter drags you have an issue elsewhere.

Thanks for the input. Checking the cranking while hot w/out spark has been the response from a couple different directions. I am learning the AMC starter can have a "heat soak" issue that can show the same symptoms, so that is the first check along with verifying that my dizzy is still set at 0*.

Bob over at DynamicEFI is good people and doesn't seem to have any problem with folks posting up definition or calibration files. Lots of folks on some of the hotrod forums do it all the time and he just jumps in and helps. I'll have those posted up in the next few day for review. Any help I can get tuning this engine to its reasonable potential is greatly appreciated.

just a couple of thoughts. I just completed a tbi swap on a buddies cj5 a few months ago. things I noted that could have caused us problems.
-rotor phasing (not sure what distributor you are using but if it was phased incorrectly that could cause problems)
-placement of the ignition control module if not in the distributor base (heat soak)
-worn distributor gear

Not sure if the TBI has IAC control or not.
If so, there should be a setting for "Warm Park" position and Cold position.
It makes it much easier to crank when the TB is open than with it closed.
Just a thought.

try opening the throttle blade adjustment 1/2 a turn.