96 PCM -- Adjustable Injection Start or End?
Thread Starter
Intermediate
Joined: Oct 2011
Posts: 28
Likes: 1
96 PCM -- Adjustable Injection Start or End?
Hi,
I have a modified LT4 (383, high lift cam with moderate overlap, headers, 39 lb/hr injectors, etc.) and am experiencing cam surge -- characterized by misfires at light cruise, low rpm, low load, low TPS %, but above idle conditions in all cases.
I'm working to test spark advance settings as well as AFR tweaks (wideband installed and linked to PCM) in this area of the MAP/RPM map, but haven't had much success yet.
We know that changing cams changes the timing of valve events, which means stock injection "timing" won't be optimal -- the end of injection won't coincide with the closing of the exhaust valve.
So, is there a way to change injection start or stop timing in C4 PCMs, 1996 version, in my case?
I've read the C5 and C6 have this ability, which can be used to nearly eliminate cam surge.
John
I have a modified LT4 (383, high lift cam with moderate overlap, headers, 39 lb/hr injectors, etc.) and am experiencing cam surge -- characterized by misfires at light cruise, low rpm, low load, low TPS %, but above idle conditions in all cases.
I'm working to test spark advance settings as well as AFR tweaks (wideband installed and linked to PCM) in this area of the MAP/RPM map, but haven't had much success yet.
We know that changing cams changes the timing of valve events, which means stock injection "timing" won't be optimal -- the end of injection won't coincide with the closing of the exhaust valve.
So, is there a way to change injection start or stop timing in C4 PCMs, 1996 version, in my case?
I've read the C5 and C6 have this ability, which can be used to nearly eliminate cam surge.
John
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The injector pulses are synchronized with the crankshaft rotation.
I don't know how the later PCM works, but in the earlier systems the injector pulses are done long before the intake valve opens. On my '86 there are two injector firings (once per engine rotation) before the intake valve opens. Given this, I've always wondered why injector spray patterns are so important to some people...
One of the things on my "to-do" list is to look into the timing of the spark, injector pulses and valves. My plan is to draw a diagram that shows the valve opening curves with the spark and injector pulses overlaid. At the rate I'm going it might never happen, as it's been on my list for well over a year...
I don't know how the later PCM works, but in the earlier systems the injector pulses are done long before the intake valve opens. On my '86 there are two injector firings (once per engine rotation) before the intake valve opens. Given this, I've always wondered why injector spray patterns are so important to some people...
One of the things on my "to-do" list is to look into the timing of the spark, injector pulses and valves. My plan is to draw a diagram that shows the valve opening curves with the spark and injector pulses overlaid. At the rate I'm going it might never happen, as it's been on my list for well over a year...
Burning Brakes
Joined: Apr 2001
Posts: 1,209
Likes: 0
From: Toronto Ontario
St. Jude Donor '13
I ran into the same problem, and my research has not uncovered any tuning option in the PCM.
I needed to adjust the injection timing due to the overlap of my cam, especially at lower RPMS however the ECU doesn't have a mechanism to compensate.
Most aftermarket ECU and newer systems have ways to sort this out, however if you find anything out let me m know.
Cheers.
I needed to adjust the injection timing due to the overlap of my cam, especially at lower RPMS however the ECU doesn't have a mechanism to compensate.
Most aftermarket ECU and newer systems have ways to sort this out, however if you find anything out let me m know.
Cheers.
Thread Starter
Intermediate
Joined: Oct 2011
Posts: 28
Likes: 1
No injection start/end timing adjustment in C4 PCM Tables
Thanks for the confirmation.
I came to the same conclusion after more research. Verified with TunerCat that the injection timing is in the PCM program -- not in a table we can adjust. So, you can change the timing -- You just have to write some code... Of course, I have absolutely no idea how to do that.
So, I'm trying my best to address with the rich/lean tables, individual cylinder balance and retarding timing. Not an ideal solution, but I've been able to improve driveability.
I came to the same conclusion after more research. Verified with TunerCat that the injection timing is in the PCM program -- not in a table we can adjust. So, you can change the timing -- You just have to write some code... Of course, I have absolutely no idea how to do that.
So, I'm trying my best to address with the rich/lean tables, individual cylinder balance and retarding timing. Not an ideal solution, but I've been able to improve driveability.
I ran into the same problem, and my research has not uncovered any tuning option in the PCM.
I needed to adjust the injection timing due to the overlap of my cam, especially at lower RPMS however the ECU doesn't have a mechanism to compensate.
Most aftermarket ECU and newer systems have ways to sort this out, however if you find anything out let me m know.
Cheers.
I needed to adjust the injection timing due to the overlap of my cam, especially at lower RPMS however the ECU doesn't have a mechanism to compensate.
Most aftermarket ECU and newer systems have ways to sort this out, however if you find anything out let me m know.
Cheers.
Safety Car
Joined: Sep 2001
Posts: 4,157
Likes: 554
From: Glenbeulah Wi
Are you using a WB to measure AFR when you are tuning. I would suppect your AFR is off and is causing the surge, at light throttle you should be running 14's for AFR. Make sure you tune the car in open loop (after tune is complete switch it back to closed loop) and dial in both the MAF table and VE table, this will really make the car run much better and eliminate the surge in most cases. If you still have a surge after VE and MAF is dialed in timing setting will eliminate the rest of the surge. If you have a really big cam you may need to force the car to run open loop at low RPM and closed loop at slightly higher RPM. This is a rare condition.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The brand of injector also affects all this, as different injectors open at different rates and the delay between the time the electric pulse hits the injector and the time it starts opening varies. It takes time for the magnetic field to build up and start moving the pintle.
Check out the technical articles here:
http://www.injectordynamics.com/tech.html
Check out the technical articles here:
http://www.injectordynamics.com/tech.html
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