Pelican Parts Forums - ITB`s with EFI won`t start. Need ideas

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- - ITB`s with EFI won`t start. Need ideas (http://forums.pelicanparts.com/showthread.php?t=1106649)

I've been researching a future EFI project and ran across this article:

https://adaptronicecu.com/blogs/modular-instructional-videos/ecu-grounding-tips

A good read, especially keeping in mind the peculiarities of the 911 power distribution system. Depending on where you take your main power to things like the coils and injectors and ECU, you could get massive voltage drop on the main "battery" cable to the rear of the car. Probably better off taking power for all the EFI stuff by running a fresh new dedicated 12V supply direct from the battery (not from the alternator).

The article is about grounds, but keep in mind voltage drops on 12V power wires too while you're reading.

Quote:

Originally Posted by Cheshire Cat (Post 11531054)

Aaand another update. You know what?
Bloody ground strap from body to gearbox... The nut was tiny bit loose (not like loose-loose), tighten it up - almost started. Put some shielding grounds - here we go - she starts!
But... She dies after some time, for some reason I have many errors on trigger when she runs... Have to figure that one too...

Voltage drops.....a very good topic to bring up.
I was installing a 2.5SS/MFI engine in a friends 911 on Monday.........Dual Spark with 2 MSD Streetfire CDIs.......all tested on my test stand...so a good, working system and engine. Once installed in the car....the engine momentarily fired and died and then.....nothing. After 30 WTF minutes or so......I checked the voltage supply to the MSD....it was 12.4 and dropped to 6-7V when cranking (freshly charged battery)....I moved the un-switched power from the 3-fuse box in the engine compartment, to the starter +12V and ...the ground to a good engine case ground and.....success! Not an EFI application, but if your voltage drops too low, regardless of the system..it's a no-go!

regards,
al

PS: I've also fixed no-start conditions that were caused by corroded/loose ground straps.....

From 10,000 ft.:
The ECU wants a steady state voltage.
Reference voltage being steady with NO signal noise being induced during cranking for ALL sensors.
Being introduced is a large starter motor current draw with the corresponding voltage drop and some electrical noise.
Wire, ground, shield & source voltages accordingly like in any automated system that meets IEEE std'.s.

Quote:

Originally Posted by Jonny042 (Post 11543735)

Depending on where you take your main power to things like the coils and injectors and ECU, you could get massive voltage drop on the main "battery" cable to the rear of the car. Probably better off taking power for all the EFI stuff by running a fresh new dedicated 12V supply direct from the battery (not from the alternator).

I do have new 12V leads directly from battery to ecu, coils and injectors
p.s. and some part of that "mystery" was almost non existent signal wire to the cam sensor. My wiring skills could be better.

Quote:

Originally Posted by Cheshire Cat (Post 11544426)

I do have new 12V leads directly from battery to ecu, coils and injectors
p.s. and some part of that "mystery" was almost non existent signal wire to the cam sensor. My wiring skills could be better.

Well we're always learning!!! Sounds like you're on the right track then!

That cam synch is pretty important, not going to get far without that.... although there are settings in the EMU for startup that allow it to be ignored (coils fire batched instead) until it's fired up. Pretty cool feature, not sure how much difference it would actually make to have it enabled, I guess that's just to keep you from having to crank for two full rotations (or more if you're on a VR sensor that is weak at low speed).