interesting find while logging startup on classic vs xfi

K

kidglok

Balls Deep
Joined
Oct 10, 2010
trying to figure out why i cant get my xfi 2.0 to start as well as pauls classic, we discovered his other car with xfi wont start as easy either. Mine has to crank and crank and crank before she will fire, his classic will make 2 revs then fire right up. Ive copied all the tables, iac cranking fuel, even scaled the injectors from his 72's to match the same pulswidth i would need with the 83's. I even have gone as far as to adjust the battery offset voltage to match. Still no dice.

we logged my car xfi 2.0 with caspers direct harness, his ttop with xfi (1.34) and caspers adapter, and finally his 87 gn(x) with classic fast and precision harness and noticed some weird things.

as you can see with the classic everything is fine, rpm readings and injector dutycyle are in line with what we would expect:
classic pte harness.png


ttop with xfi and caspers adapter- rpms read 12750 and dutycycle is maxed out for the moment
ttop xfi caspers adapter.png


my car- 2.0 with direct harness, notice the rpms jump to 1500 and the dutycycle is maxed at 100%. (as a side note mine would not record an a/f richer then the leanest (15.94) xfi can read untill 3 seconds after the initial crank.
xfi 2.0 caspers harness.png





Could this be why we cannot get any xfi to start as well as the classic?? something has to be going on in the background here...
 
"Could this be why we cannot get any xfi to start as well as the classic??"

My XFI starts fine - maybe better than any car I ever had? Are you saying anyone with XFI can't start their car?

Edit: I guess you are saying cars with XFI are harder to start.
 
I don't think it has to do with the kind of system but rather a bad connection or a short somewhere.

I have a fast classic car that acts up as well. Starts fine most of the time but once and a while it act's like the timing is off.

Electric gremlins. Got to love em..:confused:
 
TurboBuRick said:
I don't think it has to do with the kind of system but rather a bad connection or a short somewhere.

I have a fast classic car that acts up as well. Starts fine most of the time but once and a while it act's like the timing is off.

Electric gremlins. Got to love em..:confused:
Click to expand...


Could be. I initially thought the classic boxes were easier to start because they don't need a cam signal to start. Obviously there is something going on that shouldnt be, just trying to figure out where to start looking.
 
With key on engine off start wiggling some wires while logging. Check the pos cable. You know about that.
 
[quote="Your a smart one there longballs" :)[/quote]

Thank you. I'm not as dumb as I look, I hope! :eek:
 
Ok so it seems to be a noise issue. It was suggested to run 3 main grounds back to the battery (analog return, digital return, and main power return) back to the battery. There is multiple pins for these grounds at the ecm, which would be best to use?
 
My car starts great. Cal tuned on mine for 6 hours. You would never know it is capable of the HP it is just by cruising around. It acts same as stock...except it sounds way F'n better...
 
I'm sure it runs well, so does mine and everyone elses, but this is something that needs to be sorted out, you may not even notice it, depends on the injector size.
 
I have an xfi, car starts just as fast as a stock ecm car if not faster

Posted from the TurboBuick.Com mobile app
 
Boost231 said:
I have an xfi, car starts just as fast as a stock ecm car if not faster

Posted from the TurboBuick.Com mobile app
Click to expand...

Many cars start well, but this issue seems to be more of a problem with really big injectors. Please post a datalog if you have this spike also.......?
 
How Big We talking. I'm running 120s

Posted from the TurboBuick.Com mobile app
 
Boost231 said:
How Big We talking. I'm running 120s

Posted from the TurboBuick.Com mobile app
Click to expand...
It will happen on any injector, but the bigger just puts more fuel in the motor during the spike, I would say with 120s it would be still ok but anything bigger might cause flooding.
 
In the XFI, the Inj DC% sensor is a math based sensor where the ECU divides the gross injector pulse width by the available time to inject (derived from rpm). With the classic ECU, C-Com performed the math to display an Inj. DC% sensor from the same parameters. In any event, the Inj. DC% sensor does nothing internally and is only used for diagnostic, display and logging purposes. So, short of being some unknown and benign bug in the calculation, any spike in the DC should be accompanied by a spike in the rpm or the injector pulse width (which you may not always see due to the nature of logging asynchronously from rpm).
 
Last edited:
So is it possible to flood the engine with large injectors with the 1500 rpm spike?, or is this just a logging issue?
 
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