383 Backfiers
Thread Starter
4th Gear
Joined: May 2003
Posts: 4
Likes: 0
From: Kungsbacka Halland
383 Backfiers
Hi guys
Does any one know about backfiering when shifting between 1 and 2 gear on a 92(only at full TPS) 383 Aut with hotcam and LT4 heads and 30 lbs inj and 58 mm TB?
Secondly is there any hardware to limit rpm to 6375 rpm i do not have any MSD box or anything else from stock but still i cant get over this limit with Tuner Cat as a tunering tool.But i do have every thing else changed to new stuff concerning ignition parts and injectors :confused: i´ve tried almost everything with TC more ign less ign more Fuel and less fuel but nothing makes any differens.?? do anyone have any ides on this?
It do run great except for this 2 thing´s.
Does any one know about backfiering when shifting between 1 and 2 gear on a 92(only at full TPS) 383 Aut with hotcam and LT4 heads and 30 lbs inj and 58 mm TB?
Secondly is there any hardware to limit rpm to 6375 rpm i do not have any MSD box or anything else from stock but still i cant get over this limit with Tuner Cat as a tunering tool.But i do have every thing else changed to new stuff concerning ignition parts and injectors :confused: i´ve tried almost everything with TC more ign less ign more Fuel and less fuel but nothing makes any differens.?? do anyone have any ides on this?
It do run great except for this 2 thing´s.
Team Owner
Joined: Apr 2001
Posts: 22,267
Likes: 3
From: Dallas TX
Re: 383 Backfiers (JB_Racing)
I'm not sure about the backfire ... I get a pop sometimes when letting off the gas at high and medium rpm's with my car. If you have open exhaust, it will do this - it's because of going lean when you let off the gas. Nothing wrong with it.
There is a limit of 7182rpm on OBDI (not sure about OBDII). This is a computer limit. If you go over 7182rpm, your engine will shut off and your PCM resets itself.
There is a limit of 7182rpm on OBDI (not sure about OBDII). This is a computer limit. If you go over 7182rpm, your engine will shut off and your PCM resets itself.
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Re: 383 Backfiers (JB_Racing)
When you say its backfiring is it backfiring through the exhaust or through the intake? Does it actually cutoff at high RPM? Do you have a scan tool to connect to it and do some datalogging, because it sounds like thats what you are going to need to get to the bottom of this.
Typically the ECM cuts off fuel to the engine when it hits the RPM limiter and not the ignition. You could have an opti-sprak problem if its ignition related.
Typically the ECM cuts off fuel to the engine when it hits the RPM limiter and not the ignition. You could have an opti-sprak problem if its ignition related.
Le Mans Master
Joined: Oct 2000
Posts: 6,362
Likes: 30
From: Oak Harbor WA
Re: 383 Backfiers (tjwong)
My car is doing the backfire issue out the exhaust when I put it to the floor when either accelerating from a stop or dropping down to 1st or 2nd for a passing situation. My cars an Auto, but that doesn't really matter.
I hooked up a fuel pressure gauge to see what that was doing. Nothing wrong there so I am now convinced it is the Opti going bad.
I hooked up a fuel pressure gauge to see what that was doing. Nothing wrong there so I am now convinced it is the Opti going bad.
Burning Brakes
Joined: May 1999
Posts: 760
Likes: 1
From: Greenwich, CT
Re: 383 Backfiers (JB_Racing)
Re: RPM limit
Check the TC tdf under the 'ECM Constants' table. Did you adjust the fuel cut-off limits there? Those can be raised, if you are confident the crank/rods in your engine are safe to spin at higher speeds.
ALSO - You may want to check the LT4 cam specs with something like DesktopDyno. I don't recall that cam having much power above 6K - but haven't looked at it closely.
Re: Backfire
Just a suggestion - you might try burning a chip with less part-throttle spark advance. The stock spark tables are usually pretty aggressive there, and don't always work well with a larger cam.
Thread Starter
4th Gear
Joined: May 2003
Posts: 4
Likes: 0
From: Kungsbacka Halland
Re: 383 Backfiers (DOCTOR J)
Hi Guys ,and thank´s for the reply´s.
Yes i do have a scan tool Diacom and TTS,I also use 2 WB O2.
First ign is set to 10° BTDC as the book say´s and dont give me any funny values from my logfiles. I`ll run with TC fuel cutoff constants over 7K I´ve even tried it at 10K but still every time i get 6375 rpm as a limit.I do have 9.2 Inj time Ign 30° (Ron98) and no knock when it hits the limit and it´s the same every time
:banghead:
I have measuerd the voltage at the Ign modul and it reads 11.8 V and i have tried with an oscilloscop and no problem.And as i saied befor i do not have any hardware other then stock but they are new.
So the 2 issu remance rpm limit and backfiering in the exhaust not mutch but it´s still bugs me.
(sorry about the bad English but engines sounds the same all over right?)
Thank´s
Yes i do have a scan tool Diacom and TTS,I also use 2 WB O2.
First ign is set to 10° BTDC as the book say´s and dont give me any funny values from my logfiles. I`ll run with TC fuel cutoff constants over 7K I´ve even tried it at 10K but still every time i get 6375 rpm as a limit.I do have 9.2 Inj time Ign 30° (Ron98) and no knock when it hits the limit and it´s the same every time
:banghead:
I have measuerd the voltage at the Ign modul and it reads 11.8 V and i have tried with an oscilloscop and no problem.And as i saied befor i do not have any hardware other then stock but they are new.
So the 2 issu remance rpm limit and backfiering in the exhaust not mutch but it´s still bugs me.
(sorry about the bad English but engines sounds the same all over right?)
Thank´s
Burning Brakes
Joined: May 1999
Posts: 760
Likes: 1
From: Greenwich, CT
Re: 383 Backfiers (JB_Racing)
I'm not sure I understand how you are seeing the RPM cut-off at 6400 rpm. Is this something you log from the ALDL data? Is it fuel or ignition cutoff?
If it's a case of the data not reading any higher in Diacom, it may just be the limitation of the ALDL software. On the P4 ECMs, I am under the impression that rpm recording is limited to a one byte word (?), so that even when the engine is above 6400 the ECM can't report any higher number. I thought that ignition & fuel control could extend past that point - just not within the range of the s/w record. Have you looked at your ALDL code to see if that is a limitation?
Or are you recording this limit on the WB? FWIW, I built a separate RPM signal into my WB data logger just to keep it away from the ECM processing - it was described in this thread: http://forums.corvetteforum.com/zero...postid=3960101
With that logger it is easy to see whether a problem is spark or fuel related.
Drifting
Joined: Mar 2001
Posts: 1,636
Likes: 3
From: Lafayette IN
Re: 383 Backfiers (DOCTOR J)
FWIW, I built a separate RPM signal into my WB data logger just to keep it away from the ECM processing - it was described in this thread: http://forums.corvetteforum.com/zero...postid=3960101
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