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Stock ECM + 4 pin HEI.. is it possible?

11K views 16 replies 6 participants last post by  Augusto 
#1 ·
I have all the EFI parts and harness from a junked 1994 C10 except the OEM distribuitor, I was wondering if it is possible to make the TBI system work with a regular old 4 pin HEI distribuitor?

it will save me the problem to find one (they are not easy to find here, also expensive if new) and also will give the freedom to adjust timing the good old and already mastered way.

please comment.
 
#3 ·
It could run and probably would, I think you have the expertise to hook it up.
BUT I seriously doubt you could get it to run correctly as you would not be able to achieve closed loop without the module linking to the computer to map computed timing for the ignition,as the 4 pin has no feedback for computed engine timing.
This would no doubt have a negative effect on fueling and would probably result in poor gas mileage and poor performance. Without the 7 or 8 pin module the ECM couldnt get beyond base operation/startup mode
 
#4 ·
It can actually work, tho I don't know the tuning end of it. has been done in TBI conversions on older engines.. lot of people lock the advance out and it'll run like it should, but the correct dist is available for about $50 on ebay. if they will ship to your country, it'll all work out fine
 
#6 ·
cobalt327 said:
Use the early distributor but wire up the "late" module.



Don't use a vacuum or mechanical advance.

Edit- This assumes the large cap HEI will physically fit.
I think you are correct, even if the module does not fit inside it can be run outside of the distribuitor, I have used HEI modules on all kinds of engines, from toyotas to suzuki bikes for years, I mount them on heat sinks from old PC computers with a little of dielectric grease, they work great, I don't see why a 7 pin can't be mounted the same way, maybe even will perform better since it will run cooler.
 
#7 · (Edited)
Augusto said:
...even if the module does not fit inside it can be run outside of the distribuitor, I have used HEI modules on all kinds of engines, from toyotas to suzuki bikes for years, I mount them on heat sinks from old PC computers with a little of dielectric grease, they work great, I don't see why a 7 pin can't be mounted the same way, maybe even will perform better since it will run cooler.
↑X2

The only thing I would like to suggest is to use a heat sink compound instead of dielectric grease to conduct the heat from the module into the heat sink. Computer supply/electronic parts stores will carry something like that. One brand I found to be good is Arctic Silver 5 Polysynthetic Thermal Paste (~$5.00 US for a small tube), but any heat sink compound will do.

The module for a 1994 Chevy 1500 truck w/TBI and 5.7L, etc. has a different look to it than the 'traditional' 4, 5 or 7 pin modules, but can still be remotely mounted like you said. Just be sure the module and heat sink is grounded through the screw sleeve shown arrowed below.

Example of module:

 
#9 ·
Augusto said:
I have always used dielectric grease as a heat sink compound, I tought they were both the same, well, I tought they did the same function of conducting heat, am I wrong?
My understanding is that the primary function of dielectric grease is as an electrical insulator. It might (or might not, IDK) be better than nothing, but I can assure you that heat sink compound (seen as a white colored paste when an original module is removed from the distributor body) is what the OEM uses, not dielectric grease. ;)
 
#10 ·
ok, it's easy to find in computer stores, I'm gonna get a tube rigth away because time to clean up my computers is coming and I will need it for when I remove the heat disipators of the CPU's thanks for making me realize I was using wrong stuff.
 
#12 ·
You sure can use a 4 pin HEI distributor with a little work and change to a 7 pin module used in early EFI large cap distributors.

Disable vacuum and mechanical advance and use 7 pin module and wiring diagram attached.

Here's a link from a guy in Amman Jordan doing the same to a inline Six Cylinder which came with 4 pin.
http://www.gearhead-efi.com/Fuel-Injection/showthread.php?403-TBI-on-inline-6
 

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#13 ·
cool thanks a lot :thumbup:

one more thing, what does the ESC does? retards the timing when the knock sensor detects pinging? if so, can I just leave it out?, will the ECM advance the timing without the ESC?

reason for asking this : parts that are not used, cost nothing and give no trouble. I want to follow the KISS philosophy.
 
#14 ·
ESC (Electronic Spark Control) works with knock sensor and takes out spark when knock is detected. The knock sensor is specific to ECM and or different engines. It must be mounted in a water jacket in block to work correctly. Even if it's the wrong engine like a conversion they are nice to have even if just for tuning purposes because it is frequency based for engine. I like to have them and get a feel for it while tuning and bump up against the knock then back out a few degrees. It can be set off by gear drive cam setup or solid lifters or even a header tapping the frame so it can cause issues as well on conversions.

EST (Electronic Spark Timing) is the module we have been discussing here and it is a must for ECM control of timing. It produces a modified square wave form for the ECM. Some aftermarket EFI companies used to sell a Tach Filter to replace this so you could run your old ignition system without ECM control but they got so expensive you can do many things to make the spark control work cheaper. If you just run power to ECM instead of this EST you will fry ECM. ECM will not fire injectors without this signal.
 
#15 ·
OK, understood.

I have seen engines act weird because tapping noises were picked up by the knock sensors, it's funny.

I have nothing against them just wanted to make it simpler but seems like it's not possible, on the other hand they are cool because with open or loud exhaust you can't listen to the engine pinging but the sensor can and adjust timing back preventing the pistons from becoming donuts.

thanks a lot, I think I'll go efi in my 350 SBC powered sand buggie, it will be cool not bogging the engine where the carbs would spill out all the fuel.

if I need more help I'll ask for more, thanks again. :thumbup:
 
#16 ·
It's really not funny per say, it's a fact. I do a lot of offroaders and use the knock senor to tune an engine, then disable it. But when they whack the frame on a rock while crawling get a knock count, reduce spark and interferes with ther low RPM crawling.

GM test procedure for testing knock sensor is to have scan tool hooked up and car running and hit side of block with hammer...

And yes open headers can cause enough noise to set knock sensor.
 
#17 ·
I test the knock sensors using a timing light while tapping the exhaust manifold with a light hammer, I love seeing how it retards the timing, seems unbelievable that the combustion pinging could make such loud and potent vibrations.

I have had customeres complaining of low engine power and the cause has been something loose, like a bracket or engine mount triggering the knock sensor.
 
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