Speed limiter on '91 454 SS ?

[L31MaxExpress]

Well,there you go man. Looks like she'll run balls to the wall.

The 1992 299 ECM with ALWD I ran my 83 G20 on would run balls to the wall too. No speed or rev limiter in it. The old 700r4 in that G20 would shift into overdrive at 5,000 rpm and keep on going.

 

[99xcss4]

what can you tell me about my pcm 454 tbi 4l80e service number 16196395

 

[Schurkey]

The secondary "rev-limit" is actually the ignition coil dwell being too long at high rpm. I have had the black box running 6,500.

Probably not a matter of the dwell being too long, but rather the saturation time being too short. The spark gets weaker as the RPM increases, until it becomes weak enough to misfire.

 

[L31MaxExpress]

Probably not a matter of the dwell being too long, but rather the saturation time being too short. The spark gets weaker as the RPM increases, until it becomes weak enough to misfire.

No the dwell is too long. The minimum dwell is too long for the time available at higher rpm, thus acting as a rev-limiter.

 

[Schurkey]

I don't understand.

Dwell is measured in degrees. There's 360 distributor degrees in two full rotations of the crankshaft, firing all cylinders. On a V8, there's 45 degrees of distributor rotation (90 degrees of crankshaft rotation) between cylinder firings. 45 x 8 = 360

Unlike points which were more-or-less fixed at 28--32 degrees of dwell no matter the RPM, dwell varies in the HEI systems, less at low rpm to conserve electrical power and reduce heat load, more at higher rpm. Adding more dwell degrees as the RPM goes up, partially-compensates for the reduced time between cylinder firings. At maximum dwell, there has to be a few degrees where the coil primary current flow is shut off. So even if there's ~40 degrees of dwell, there's ~5 degrees of no-primary-current-flow--which is when the spark is created and maintained. No matter what the RPM is, you still have that 45 degrees between firings in which to charge the coil and build magnetism, and then release that energy as "spark".

HOWEVER, if the TIME between firings is very short (high rpm) then even with 40 degrees of dwell, there isn't time for the coil to become saturated and build the magnetic field. As the magnetic field weakens, spark power drops off. When enough spark power is lost, misfire begins.

 

[L31MaxExpress]

I don't understand.

Dwell is measured in degrees. There's 360 distributor degrees in two full rotations of the crankshaft, firing all cylinders. On a V8, there's 45 degrees of distributor rotation (90 degrees of crankshaft rotation) between cylinder firings. 45 x 8 = 360

Unlike points which were more-or-less fixed at 28--32 degrees of dwell no matter the RPM, dwell varies in the HEI systems, less at low rpm to conserve electrical power and reduce heat load, more at higher rpm. Adding more dwell degrees as the RPM goes up, partially-compensates for the reduced time between cylinder firings. At maximum dwell, there has to be a few degrees where the coil primary current flow is shut off. So even if there's ~40 degrees of dwell, there's ~5 degrees of no-primary-current-flow--which is when the spark is created and maintained. No matter what the RPM is, you still have that 45 degrees between firings in which to charge the coil and build magnetism, and then release that energy as "spark".

HOWEVER, if the TIME between firings is very short (high rpm) then even with 40 degrees of dwell, there isn't time for the coil to become saturated and build the magnetic field. As the magnetic field weakens, spark power drops off. When enough spark power is lost, misfire begins.

Dwell is time based in a GM ECM and is in Msec. If the minimum dwell time is set too long, the ECM will basically prevent the coil from ever sparking.

 

[b454rat]

My old 89 with the TBI 406 would bury the speedo and then go back around to 45. Well over the 100pmh “limit”

 

[PlayingWithTBI]

Can I disable the speed limiter and go faster than 255?

You need a Dakota Digital dash - mine goes up to 255MPH but, only 17,500 RPM so, you're on your own after that

 

[Scooterwrench]

what can you tell me about my pcm 454 tbi 4l80e service number 16196395

Do you know the BCC? There are several .bins for '94 7.4L
Download TunerPro RT then go to gearheadefi.com and download the XDF($OE) and the .bin with your BCC then you can see what GM burned in there. If your .bin is not listed the only other way I know to retrieve the .bin is to buy a prom burner/reader and pop your prom out and read it using the $OE mask.
Be aware that all this could give you the tuner sickness.

 

[99xcss4]

Do you know the BCC? There are several .bins for '94 7.4L
Download TunerPro RT then go to gearheadefi.com and download the XDF($OE) and the .bin with your BCC then you can see what GM burned in there. If your .bin is not listed the only other way I know to retrieve the .bin is to buy a prom burner/reader and pop your prom out and read it using the $OE mask.
Be aware that all this could give you the tuner sickness.

thanks I do not know the bcc truck is some where else just curious abut it really do not want to change any thing on it did do some research on it and it seems that 350 tbi that was paired with 480e also used this pcm I do not know if this means any thing or not but it has one red and one blue connector I was told that I was also told that the engine transmission and t-case that are now in my truck came from a 94 K-2500 suburban