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383 TPI Idle

Old 07-13-2019, 02:36 PM
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Car: 1989 Camaro IROC-Z
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383 TPI Idle

Hello,

I started up my 383 today for the first time. After a few attempts messing with timing it started up. I have to keep my foot on the throttle to get it started and keep it running. Although when I give it more throttle, the RPM's do not change. When I come off the throttle, it sputters and dies. This is all with the EST connector DISCONNECTED. When i connect it and start it, it backfires. Hard to set timing with it not wanting to idle. I have a custom chip in it with all my aftermarket specs. I have checked IAC, MAF, TPS, vacuum leaks. Do I need to add timing to it? (Advance) Not sure about it not wanting to idle or why RPM's do not change with throttle change. Any help would be awesome!

Thanks!
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Old 07-13-2019, 02:58 PM
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Re: 383 TPI Idle

Distributor in right?

Also just because you had a chip burnt doesnt mean it is right. Mail order stuff can be hit or miss. You need a wideband to verify fuel
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Old 07-13-2019, 05:18 PM
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Car: Firebird Formula 1991 (Prod#201216)
Engine: SP383 Deluxe FIRST TPI Intake
Transmission: Tremec T56
Axle/Gears: Ford 9" Eaton Truetrac Motive 3.89
Re: 383 TPI Idle

The way I got mine going (GM SP383 Deluxe with FIRST Intake) was by opening the throttle screw a fair bit and readjusting TPS. My system is a speed density. I left the EST connected and set the idle at 1000 rpm in ECM (I do my own tuning). Timing will bounce because the ECM is constantly adjusting SA at idle. I set initial timing at 6 deg BTDC on the engine. Same was set in ECM. Once started, using a timing light, I grossly adjusted the distributor to be within range of commanded SA by ECM. That was around 25-26 Deg BTDC. I had eyeballed the distributor adjustment when I installed it and was off greatly!!!. Once the engine was warm, I disconnected the EST connector and adjusted the distributor to 6 Deg BTDC. It is a little low a must say. Engine had a hard time idling. I readjusted the throttle screw and TPS with EST connected to get the IAC operating within it's range (0 to 160 steps). The whole operation was possible because I was monitoring and data-logging with a scan tool (Datamaster). I also have an AFR gauge. I did the start-up using the old 305 open loop set-up in the ECM. AFR was a bit lean. So open loop had to be re-tuned later.

If you try to start with EST disconnected, it probably won't work. You'd have to set initial timing on the engine at probably 15 Deg BTDC for it to work (guesstimate). However, if your distributor is off, you might end-up being ATDC. It's tricky. That's why I started with EST connected. Distributor was off and ECM was trying to set SA at 26 Deg BTDC. I was only getting 6 or 7 on the timing light when the ECM was commanding 25-26!!!!!. Once distributor was adjusted to match ECM commanded SA, the engine was running way smoother.

I now have the idle set at 900 rpm. It's a bit choppy but insures good voltage. I have an under drive pulley on the alternator and going under 900 rpm affects voltage to the lower side. The choppiness comes from the GM Performance set-up (camshaft). It' normal. The ECM varies the AFR constantly at idle from rich to lean in a slow amplitude. That's for emission and cat converter operation. That's why the engine gets choppy. In open loop, the idle is way smother since AFR is constant.

IMHO, I don't know how they can custom tune a chip on line! I would suggest you get a scanning software and AFR gauge to see what's going on. Especially at WOT... You don't want to get lean. At WOT, there is no feed back to the ECM. Your AFR gauge would tell you what's happening.

Cheers

Last edited by SbFormula; 07-14-2019 at 10:23 AM. Reason: Forgot info!
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Old 07-13-2019, 06:04 PM
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Car: 1989 Camaro IROC-Z
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Re: 383 TPI Idle

If the distributor was off why would it fire and run at around 1500 RPM?
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Old 07-13-2019, 06:29 PM
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Axle/Gears: Ford 9" Eaton Truetrac Motive 3.89
Re: 383 TPI Idle

Originally Posted by IrocChuck View Post
If the distributor was off why would it fire and run at around 1500 RPM?
Thought you had to keep your foot on the pedal! It could still fire up even if the distributor was off. Mine did!
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Old 07-14-2019, 10:07 AM
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Car: 1989 Camaro IROC-Z
Engine: 383 TPI
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Re: 383 TPI Idle

Originally Posted by SbFormula View Post
Thought you had to keep your foot on the pedal! It could still fire up even if the distributor was off. Mine did!
Yes I do need to have my foot on the pedal to get it started and keep it running. Guess I did not know it would fire and run if the distributor was off.
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Old 07-14-2019, 10:12 AM
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Axle/Gears: Ford 9" Eaton Truetrac Motive 3.89
Re: 383 TPI Idle

It depends on how off it is I supposed...
Cheers
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Old 07-14-2019, 10:20 AM
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Re: 383 TPI Idle

Is your distributor 180 out? If its 180 it will run with backfire and be hard to start.
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