interesting find while logging startup on classic vs xfi
- Thread starter kidglok
- Start date
I don't know... It depends on if it's just an issue with Inj DC% or it's from RPM. RPM is nothing more than the time between any two successive crank pulses. 1500 RPM is 10mS on a V8 and 13.3mS on a 6 cylinder. If it's a noise pulse (extra crank pulse) than there's going to be an extra shot of fuel from one injector while running. If cranking, the injectors fire bank to bank so there may be a bank that fires sooner than normal.
I don't experience this effect on my GN so I'm really not sure what the deal is.
Lance, my brother's and my GN both experience long cranking times before they start. Seventy five lb/hr injectors, 218-218 camshaft. Good grounds, battery and charging system up to specification. I was wondering if you might post your .gtc file so that I could use as a baseline/reference. I'm sure your tune is good as one could use as a reference. Thanks in advance. Bob
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C
coach
Guest
95# inj here. I'll log a start up and see if I get anything that looks like they posted log.
turbobitt
Well-Known Member
- Joined
- Feb 14, 2002
log an initial start (first from sitting overnight) than a second shortly after.
AG
If you switch to bigger injectors without making a corresponding change to the cranking fuel table, you'll increase the cranking fuel by virtue of the bigger injectors. The cranking fuel table like other pulse width based tables have to be calibrated independently.
Long cranking times on the C3I ignition should be limited to how long it takes for the C3I module to receive a cam pulse so it can sort the trigger pulses from the ECU or the crank trigger. Having the right fuel and the right air bypass is key to short cranking times. The XFI can also mimic an accelerator pump on a carb if you pump the gas pedal when cranking. Pumping the gas pedal will cause the ECU to pulse the injectors. If this helps, you can make corresponding adjustments in the cranking fuel table. You can also crack the throttle when cranking to see if you need more bypass air to shorten the cranking time.
I typically observe the injector pulse width on a properly calibrated, tuned, and warmed up engine during idle to establish a baseline cranking fuel at 2 to 3 times this amount.
The other thing is to wait a second or two after key on before cranking. This gives the fuel pump time to build pressure to a nominal level. This is a habit I picked up since I had a new 1985 GN which seemed to start better doing this. Before, with a carb, I used to just switch from off straight to cranking... This doesn't always work so well with EFI whether factory or aftermarket.
Long cranking times on the C3I ignition should be limited to how long it takes for the C3I module to receive a cam pulse so it can sort the trigger pulses from the ECU or the crank trigger. Having the right fuel and the right air bypass is key to short cranking times. The XFI can also mimic an accelerator pump on a carb if you pump the gas pedal when cranking. Pumping the gas pedal will cause the ECU to pulse the injectors. If this helps, you can make corresponding adjustments in the cranking fuel table. You can also crack the throttle when cranking to see if you need more bypass air to shorten the cranking time.
I typically observe the injector pulse width on a properly calibrated, tuned, and warmed up engine during idle to establish a baseline cranking fuel at 2 to 3 times this amount.
The other thing is to wait a second or two after key on before cranking. This gives the fuel pump time to build pressure to a nominal level. This is a habit I picked up since I had a new 1985 GN which seemed to start better doing this. Before, with a carb, I used to just switch from off straight to cranking... This doesn't always work so well with EFI whether factory or aftermarket.
Still trying to get my old man to start doing this with his TPI Camaro. He likes to just start cranking that thing right away from the off position.
Well, Cal spent Six hours or more on my car a couple weeks ago. (XFI 2.0)
IT STILL takes forever to start! ??
Crank, crank, crank.....stop....again crank crank...then fires up and runs smooth.
I find it very annoying. I have small injectors btw.
Small injectors will require a lot for cranking. It sounds like its just not enough cranking fuel. What is your pw at hot idle? The 1500 rpm spike is probably not hurting you in this situation.
turbobitt
Well-Known Member
- Joined
- Feb 14, 2002
I got to be honest, based in what I see in my car I think this is all a bunch if crap. My car has 160's and starts and runs fine. Yes I have logged the spike but doesn't appear to hurt anything. Those with issues should look elsewhere.
AG
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AG
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C
coach
Guest
Has anyone asked Cal about this? He is the Moderator for this section. I'm sure he would reply...or scan thru some logs.
That is a symptom of not enough afterstart fuel...needs a minor tweak...
That is not enough cranking fuel or IAC postion, increase cranking fuel...
