I posted this on tech/gen eng and got no replies, so here goes. My efi chevy 383 takes 3-5 seconds to start, hot or cold. scanner info is iac counts 160, desired rpm 3187, key on eng off. the eng explodeds into life with some valve train clatter and then settles down within 2 seconds. i know this is hard on the engine, as well as my nerves. when it was a 350 i didnt have this problem. only things changed other than stroke,[ pistons] are 6 degree larger duration cam, 58mm t.b. chip from ed wright[fastchip]. tried 350 chip, same problem. Have checked iac motor, vacuum leaks, fuel press at 45 and holds, have not checked coil yet, same setup as before[msd]. This is otherwise a real good running engine. any ideas would be appreciated, starting to run out of patience.

 

You mentioned that the TB has been changed, so I'd look for the problem there first. It sounds to me like the blades are open too much. Make sure that the minimum air screw is not screwed in too far, thus keeping the TB blades too far open. This may be the reason that once the engine does start, it "roars" to life, only to settle down after a couple seconds. I'm thinking that those two seconds is when the ecm notices that the rpm is way too high, and closes the IAC motor. doesn't sound to me like a efi tuning problem at all...

 

you don't by chance have a superram manifold do you? happens to everyone w/ that manifold

 

hello 1320 Right Ln; Yes at first I had tha blades open to far. The iac counts were in the 20 range. I talked to ed wright[chip burner] and was told to close up the angle to get the iac counts around 45. also to keep the tps at .54 volts. no change in startup at all. I'm very busy right now and am planning to retard timing from what Warbird told me yesterday, about advanced timing causing this to happen. Its set at 8* btdc.
Hi Project, yes I do have a superram on it. But I dont recall the engine having this problem when it was a 350".

 

Trust me superrams are pita

Mine does the same thing, mine never did on my mild 350, when I went to wild it started being really touchy

 

Mine starts in just a couple of seconds. Using LS1 28# injectors. Adjust your cranking pulse width table in your prom. Another possibility it to low values in the bottm line of the VE table.

 

36lb here, takes me 5-10

 

Project - have you tried increasing the cranking pulse width?

 

yup

 

The issue with the slow starts may be due to the starter itself. It may not be cranking the engine over fast enough to get a good pump-down on the intake.

This past weekend I changed out the starter in a vehicle from a standard torque to a hi-torque starter. This particular vehicle is EFI'd and always did start. It just took a bit of cranking to do it.

The starter began to fail with the bendix spin so I rebuilt and installed a hi-torque starter in it's place. The difference is like night and day. The engine now starts so much quicker that the first time I was taken by surprise.

In the data logs the original standard torque starter would spin the engine at about 110 RPM. The hi-torque starter spins the engine at about 190 RPM.

With the std starter the MAP term would gently fall to about 95 KPa then the engine would start. With the hi-torque stater the MAP falls quickly to 75 Kpa and the engine is running.

It may be worth while looking into a better starter. The vehicle I am posting about is older then a Thirdgen. However, over the years starters have gotten smaller and lighter. It just may be something to look into. If your datalogs show cranking RPM that will help in showing a problem. Could also be cables or a weak battery. A fresh engine will present more drag (friction) then an older engine.

RBob.

 

hello vernw, this redjet. I tried to get cranking pulsewidths for you. remember the 383 with hard start and hi rpm's ? well. seems my autoxray is kinda slow in being able to pick that up . also while looking at scanner noticed the inj pulse width varies from 1.7 to 2.0 ms while at a steady idle. also map sensor volts at 1.51v, this is a maf car, and fourth and first gear engaged, this is a manual trans car. I'm not sure if any of this matters. It will be interesting to find out if you've figured out if increasing cranking pulse widths helps with the extended starts. anyone recommend a scanner program that will run on a fast windows computer?

 

As far as a scanning/data logging software - go with TunerPro (essentailly free) or Datamaster. I actually use both at different times.

As for the pulse width, I upped my about 30% and my car starts in 2-3 seconds, hot or cold. Don't know if this is the whole reasaon or not, but it was never more than 4 or 5 seconds. I still think pulse width controls this - provided the starter's turning the motor over faster enough per RBob's post above.

Have a Great Day!!!

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- Vern

 

hello vernw, the starter sounds pretty healthy to me. I am going to place an order for the APU1 and GP1 tonight. This is going to be interesting! and frustrating. and eventually, beneficial, I hope.