G'day All,

After 8 months collecting dust in my garage while I've been busy with other ****, It's Spring Down Under, so the "fix the Corvette" juices are flowing once again.
After previous battles with 'starting issues', I have relented and asked for local knowledgeable workshops (in Melbourne, Australia).
https://www.corvetteforum.com/forums...post1607396366

After preliminary chat with one of the stores, it seems that I have now faced the financial reality that I can spend a few grand for someone to try to diagnose issues with the TPI setup, then tell me that we can't really "tune" anything with the obsolete ECU anyway, etc, etc.......with zero guarantees of acceptable outcomes, or....

I can go CARB, spend a limited amount, and get a guaranteed result.
Thanks to the plentiful info online, on forums, and on You tube, I am very confident in outcomes - mainly, being able to turn the key and GO!!!!!

Don't get me wrong - if I lived in downtown America, and I could get a referral to a local trusted specialist, I'd invest to get the TPI hunky-dory, but unfortunately, I'm about 8,000 miles away from any of those options, so the decision has been made.

Could I get some input about ONE TOPIC.

Once I have a Carb, a stand alone distributor, a TCC lockup kit (off pressure port indicating 4th gear),
What will be left that the original computer will still be doing??

I look forward to enlightened information from the eminently knowledgeable contributors of this forum!
Thanks in advance!

 

Current ammunition being loaded into the Parts Cannon;

• Edelbrock-knock off (made of pure Chineseium, but POLISHED) Performer manifold
• Genuine 1982 750 Holley Vac Sec
• Low height air plenum (which I will link to stock OTR air cleaner setup)
• TV Cable/throttle cable carb mounted bracket
• Zip Corvette TCC lockup kit
• 3 way EFI to Carb Fuel Pressure Reg with gauge
• Progression Ignition (provides significant real-time tuning, PLUS security lockout, all via blue tooth)
• Smog Pump delete
• Shorty headers (again.......polished Chineseium)

 

The only thing I can think of that the ECM will still be doing is primary cooling fan control for the radiator, but you'd be best moving that over to thermostatic control anyway. Same - control of the primary cooling fan when the A/C is on also, so setup for that. Fuel pump you'll be switching to mechanical right? Several temp / pressure gauges run from sensors and the tach feed for RPM, but obviously since the ECM isn't controlling the engine you'd lose your mileage calculations. Speed is from the VSS on the transmission.

That's about all that comes to mind, but I'm sure someone will correct me if I've missed something.

 

Thank you for your thoughts!!
Most things currently seem to still work, as far as original ECM is concerned.
I plan to avoid messing with the ECM wherever possible, but will be relieved that basic engine & trans will be isolated from the ECM......

The only thing I can think of that the ECM will still be doing is
primary cooling fan control for the radiator, but you'd be best moving that over to thermostatic control anyway.
control of the primary cooling fan when the A/C is on also, so setup for that.
Yes - I plan to install a temp switch. I guess I could run that to a relay, and have a pathway for A/C to also trigger that relay??

Fuel pump you'll be switching to mechanical right?
Current Plan is factory EFI Pump through a new EFI to Carb Fuel Pressure Regulator. Fingers crossed on longevity - if it doesn't last, I'll get a more suitable replacement in tank pump.

Several temp / pressure gauges run from sensors and the tach feed for RPM, but obviously since the ECM isn't controlling the engine you'd lose your mileage calculations.
Speed is from the VSS on the transmission.
I'm not sure which dash functions go through the ECM, or go direct from sensor to Dash, so I'll be careful to keep the ECM in place, and just bundle excess wires, not cut anything...

Thanks again for your input.

 

I suspect that the ecm is not seeing any reference pulses during cranking.

Here's a log showing what the ecm is doing during startup: https://datazap.me/u/tequilaboy/anti...4&mark=113-121

See drp, drp based rpm, inj bpw, IAC position, tps, battery voltage spark advance and coolant temperature signals. As you can see nothing much going on except for reference pulses (drp, drp based rpm) and injector bpw during cranking. I suspect your ecm doesn't know that the engine is cranking.

Try cranking it with the ALDL pins A & B shorted to see if it still blinks 12 even during cranking. This would be an indication of no reference pulses.

 

Thank You,

I'm a national specialist in chemical dosage systems.
I'm pretty good at troubleshooting my systems......

Your response is the kind of certainty that I expected I would get when it was diagnosed by somebody who confidently knows the specific C4 system!!
I thought the symptoms must point to certain steps in the information chain.
This is what I didn't 'feel' when I spoke to the very few local corvette specialists in Australia.....not to say that they don't do a very fine job for their many customers.

What is DRP ?
What is BPW?

Where is the ALDL you are referring to?

 

Sorry.

DRP = distributor reference period
BPW = injector base pulse width

ALDL is the diagnostic connector

Note: the DRP comes from the pickup coil and ignition module.

Some handy wiring diagrams: https://garage.grumpysperformance.co...iagrams.11835/

 

Thank You,

I believe I could probably sort the TPI with this quality of information, however....

I'm still committed to, and already have purchased, the bits to go Carb.......and it will still give me a guaranteed result for a relatively fixed price.

 

You may indeed have a double-failure including the cold start injector, both the ecm and csi work in tandem in 1985-1988 cars to provide start up fuel during cranking. I've eliminated the csi from my own car long ago, so I tend to forget about its contribution to starting. Good luck with your project.

 

Thank You.
Incredible information.

If I'm reading you right.......

In original form, car initially starts just on the CSI, then ECM sees the pulses from the distributor (coil &/or module), then starts firing main injectors to continue running?

And thus likely culprits may be;

• CSI itself
• Distributor ignition module

 

For clarification, the log that I attached is an example of starting with the ecm injector pulses only. The pickup coil generates the distributor reference pulses, and the time between pulses is the distributor reference period. The pickup coil signal is routed through the ignition module to the ecm. I'm not certain which module (ecm or ignition module) is actually calculating the distributor reference period, but the distributor reference period is the basis for the ecm's rpm signals. I can do some digging, but I've never really considered the source of the signal beyond the pickup coil.

The drp based rpm signal that I have shown is calculated by the (external) scan tool (in this case TunerPro) from the distributor reference period signal. The drp based rpm is not an ecm internal signal, but is useful for tuning purposes due to its greater resolution and signal range compared to the ecm's internal rpm or rpmx signals.

So for culprits: CSI, CSI fuse, wiring or thermal time switch. Pickup coil, ignition module, related wiring, ignition switch, cranking speed, battery voltage, tps, coolant temperature, fuel quality, fuel pump voltage, injectors, related tuning...It would be nice to see scan data like I have shown.

From what I have read in the preceding posts, once it is running by whatever external means necessary, it continues to run ok, so the basics (air, fuel, spark, compression) must should be ok.

For the ecm to provide injector pulse width during cranking, you must have ignition voltage, distributor reference pulses and the tps must not be 100% (WOT). If no distributor reference pulses or 100% tps -> no injector pulse width.