Looking for PCM P/N for L21 454 (99 P12 RV Chassis)

[N0DIH]

Anyone ever tune one and know what PCM this is?

It is a 454 that appears to be a L29 but has coil on plug and is called the L21.

[GMPX]

At a guess, if it is a coil on plug then it probably is an LS1 style PCM, in that case, the 1999 PCM was Service # 09354896.
Try looking the VIn up on CalID and let us know what the O.S number is.

Cheers,
Ross

[N0DIH]

I don't have the PCM, but I have a 99 K2500 Burb with the 454 and would like to go coil on plug.

Just found out about the 12200411 swap, is that a coil on plug setup? It is used on many LS v8's, or is it how it is configured/programmed?

[GMPX]

Yes, it's the replacement to the one I listed. That would work.

Cheers,
Ross

[Lextech]

The 12200411 PCM can run either a dist. Vortec or a coil on plug LS engine. To run coil on plug you would have to adapt a 24 tooth crank reluctor wheel to your engine, probably on the balancer. It can be done, but it would be a pretty big project. The 411 PCM is a much better PCM than the Black box PCM.

[N0DIH]

I thought the Vortec's already had the 24x res crankshaft position sensor. Is the output unique compared to the LSx V8's?

Is adaptable to the 454? Being the 99 454 RV had it?

[Lextech]

I am not familiar with the RV 454. On the 96-02 applications that used the small block Vortec with a distributor, the engine used a 4x reluctor wheel in front of the crank sprocket for the timing chain.

[N0DIH]

I'll check what the 454 has, but I think IIRC everything is same as the L31

[Steady Eddie]

I've got one. Let me know if I can help.

Steady Eddie
L21/Allison

[N0DIH]

I was digging in the P12 Chassis FSM and the L21 has a unique front cover that the L29 doesn't have, with a crankshaft sensor in it.

So, if was to convert to a 0411, running like the L31 was run on it, then later add the L21 front cover/crank sensor, would it be fairly easy to switch over to COP? I'll have to do some digging to get the proper L21 valve covers and the L21 front cover with sensor. Hopefully it isn't a unique crankshaft, but somehow a tone ring needs to be installed most likely.

I would think the COP ignition is much more accurate and potential for more power at higher rpms with the coils spending more time in saturation than with the old single coil/HEI setup.


The 12200411 PCM can run either a dist. Vortec or a coil on plug LS engine. To run coil on plug you would have to adapt a 24 tooth crank reluctor wheel to your engine, probably on the balancer. It can be done, but it would be a pretty big project. The 411 PCM is a much better PCM than the Black box PCM.

[Steady Eddie]

Our P12 is now 30 miles away, at a body shop.
When we get the Coach home, I can get
to the PCM easily. It is bolted to
the driver's side radiator frame, right on top.
I can get you the numbers. There was a calibration
re-flash from GM for this L21--#98060...

Most everything about the L21 is different except
for the 454 cu. inch displacement. Remember that
this is a 1998 vintage engine. It has many design
parameters that did not show up until the birth of
the 8.1 Liter in--I believe--2000 or so. It is not
cammed for anything like what you would consider
high (er) RPMs. It is built for torque and torque only.
Peak power (torque) is at 3200 RPMs and the engine
has many governors built into it, both mechanical and
in the PCM.

Steady Eddie
1998 P12 L21

[N0DIH]

Mine is the 99 K29. 290 hp @ 4000 rpm, and 410 @ 3200. Which I think is same as the L21. So why did they make so much difference in the L21 to the L29? And not rate it at any more hp/torque. Is it just for reliability??

I have always felt the L29 lacked the punch it should, probably in the torque management area.

[Steady Eddie]

I think we both need to look at the camshaft specs
and compare the L21 to the L29..I can't find the
numbers on lift and duration for the L21 camshaft
anywhere online..odd..my L21 has 405 ft.lbs. of
torque at 3200 RPMs and your L29 has 410 ft.lbs.
at 3200...they are within 5 rated ft. lbs. of each
other..my gut feelings are that the camshafts are the
same. It looks like GM picked the HP ratings off a HP
at "x" RPMs chart. The L21 is rated at 270 HP at (IIRC) 2600
RPMs. The Allison Guys call the transmission
a "2600 Trans", because that RPM is it's
shift point when mounted behind a L21. The
Cat Diesel that it normally is mated to, changes
the shift points to 1800 RPMs.
The Allison transmission it is has some restrictions. One is the "thru-torque" rating,
which is 445 ft. lbs, one is Maximum Horsepower, which is 175(diesel)HP, and one is Maximum Input RPMs,
which is (depending on the source),
either 3750 RPMs or 4000 RPMs and it has a mechanical
governor inside the Allison..and I've banged into it
more than once at, or near, 4K RPMs.

Does your L29 have an electronic-module throttle
pedal with no mechanical linkage to the throttle
body??

Steady Eddie

[N0DIH]

Regular throttle body, pretty similar to the LS1 actually, probably where the LS1 got it in the parts bin.

As much as I have been able to find for the L29:
Valve Lift (Inlet/Exhaust): 0.480"/0.483"
Duration at 0.050" cam lift (Inlet/Exhaust): 204/209 degrees

This is the same cam used in the HT502 crate engine which used the L29 cam.

Heads are:
Intake Port Flows
CFM @ Lift
63 .100
121 .200
165 .300
198 .400
226 .500
242 .600

Valve Size: 2.065"/1.725"
Chamber Volume CC: 99cc
Spark Plug Position: Angled
Spark Plug Size: 14mm
Spark Plug Reach: 0.708"
Spark Plug Number: RS12YC

If you can anything on the L21 I would appreciate it. It is interesting to compare these and see what goodies can be swapped to make each better.

I haven't figured out why the commercial engines often have less power than the civillian counterparts. Like the Duramax 7800, (http://sammemmolo.com/duramax_diesel.htm) nothing compared to the Duramax 6600. I guess it is purpose built and doesn't need the requirements of the 6600 and probably has better reliability....

[Steady Eddie]

Well, the two engines ARE different. If you go
to the Mr. Goodwrench Crate Engines Web-site
you will find the L21 listed on page 4 and GM
calls it there a "performance" engine, whatever
that means...there are different part numbers
listed there for each engine (?)...

Whenever I park it, and there are Chevy guys around
the campsite, and I mention the fact that it is a P12
Chassis, they actually dive under it, for a look.
Because they have never seen one. More than once
I have had to remove the engine doghouse cover
for them to view the coil-near-plug ignition system.

There exists a dual-fuel GM option for the L21, where
with the flip of a switch, you can run either Propane
OR gasoline. There is also another MD 6.0L/366cu. in. Vortec called the LP4, I think. The propane/gasoline
hardware is supplied to GM from an outside vendor,
and the kit carries GM part numbers.

COP = Coil On Plug ignition
CNP = Coil Near Plug as in the L21
(they have short plug wires.)

I believe (don't really know) that the L21 was the
very first GM Engine with the "3 modules-in-one"
electronic throttle module. That tells me that the
PCM is different.

It is interesting to hear that the steel, roller camshaft
carries the same specs as the monster 502 crate engine..

Steady Eddie

[N0DIH]

They say the L29 really wakes up with the ZZ502 cam.... It isn't too big, might be a decent choice in a truck. Not sure in a RV. I had a 455 Pontiac with a 228@0.050 cam, 0.480 lift, it was a very mild cam, drivability was nearly identical as my stock 067 cam was. I think it is a 228/234 duration.

How do you ID a P12? I would love to take a look and see the details on it. Can you send me your VIN? You can look up parts at acdelco.com with a VIN. I have dug up some punching in what I am guessing is a L21 truck (Like a C4500). They had L21's too IIRC...

Is yours engine code B or D? Mine is J.

[Steady Eddie]

Our VIN and Build Sheet is over on the Diesel
Place/Duramax Forum in the Vin Request Sub
Forum. Look for a request from Steady Eddie.

If you see a Motorcoach, of any Brand name,
that looks as big as a Diesel Pusher, but has
a grille in the front, it might be a P12 Chassis.
It can have either 19.5" wheels, or the bigger
22.5" "Bus/18-wheeler" wheels on it. I can now
spot one on sight. The wheels are rated at 5000#
load EACH, and all P12s have a double drop I-beam front axle..low riders.

Where is the engine code located?

Steady Eddie

[Steady Eddie]

When I type in our P12/L21's VIN at ACDelco.com
it tells me it has an engine code of "B"...
but some of the parts shown are not L21
specific..for some examples: It shows a
distributor rotor (L21s don't have a distributor)
It shows rear brake shoes (P12s have 4-wheel
disc brakes)It DOES show: the correct cover
plate for the Camshaft Positioner (sensor) and
(I think) the right Ignition Coil(s)....

Steady Eddie

[Steady Eddie]

I found a Web-site that claims the L21 has a
forged steel crankshaft. Same as a Marine 454
in a boat. The crank's GM Part # is 14096983..maybe
also forged rods..I am busting my buns on this
end trying to find out if this is true.
If it DOES have the forged parts, maybe that is
why Mr. Goodwrench, in the crate motor catalog,
calls it a "performance" engine (?).

Do you know if your L29 has a cast crank in it??

Steady Eddie

[N0DIH]

Good question. I would have to do some digging, I don't think there is anyway to know without opening up the oil pan, and I think my wife would take some issues with that....

I can see if the dealer can tell me what the crank P/N is and maybe there is some info there.

I would think Forged Rods would be. Let me check with my friend who is a pretty knowlegdeable gearhead. Even though he is playing with Pontiacs and Fords I'll cut him some slack.... But on the Fords, not so sure........ I play with Pontiacs too.... He got me hooked.

Teamchevelle.com might have info, there is a lot guys with L29s in the older Chevelles (retro) with carbs on them. The L29 is a fairly easy score at boneyards.

http://www.chevelles.com/forums/showthread.php?t=121059 Sounds like a possibility that they are cast in the L29.... Hmmm... starting to sound like it is worth using a L21 as a buildup motor....

[Steady Eddie]

Dammit--

There are no Part Numbers in my three-volume
P12 Chassis Service Manuals (?).

I thought I'd just "cut a fat hog" and simply look
up the crankshaft in the book..no such luck.
My Chevy Stealership, in the Parts Department,
does have some, if not all, of the P12 info on
their computer, I've seen the exhaust system
parts breakdown pictured and it is a P12 specific
set of parts. No other GM Chassis has it.

Part of "our" problem is due to the rarity of the
P12/L21 motor combo. I can't even find out
if there was a P12 made in 1999.
There exists a 1999 P12,
one volume (thick) Service Manual--
I've seen them for sale on eBay. But whether or
not GM ever actually produced any, I can't find
out. In the late fall of 1998, GM sold the rights
to the P30-series MH Chassis to Workhorse Custom
Chassis (WCC)--they did not sell the rights to the
P12, WCC had to copy GMs lead, and WCC finally
came out with their own version, around 2000,
they had the W22 about then..all 8.1 L Class A
motorhomes are on a Workhorse chassis.

Still coming up blank on the forged or not L21 Crank...
but it makes sense to have one in a Medium Duty
truck engine.

Steady Eddie

[N0DIH]

I have right next to me my 1999 P12 FSM, got it on eBay for $12 or so. Not exactly popular book.... Might be why they aren't so popular....

My mom and dad picked up a 38 foot 2003 Damon with the Workhorse with 8100/Allison slushbox. Ran great, that is a great power combo.

[Steady Eddie]

The Manuals aren't popular because of the rarity
of the P12/L-21 combo. I Moderate a Yahoo! Group:
The P12 Chassis Group, and I have but 8 Members,
it is a discussion group for Owners of the P12,
and I find that no one knows of the P12, they may
have walked right past one in a Campground, but
did not know what to look for. You all are invited
to come over and sign up...and look at the Photos
and Files Sections..it is free, and like the Plug Mod,
free is a very good price...

Steady Eddie

[Steady Eddie]

Just returned from a trip to Bend, Oregon, driving
our L-21 P12 Coach...Drove it 400 miles and used
40 gallons of gas..not bad mileage. But I had to
get it back to the Paint Shop right away and did
not have time to look for PCM Part Numbers...I did
find--out on the 'Net--a .pdf file from Delphi that
tells all about the Electronic Throttle Control.
It does a bunch of different things..

http://delphi.com/pdf/techpapers/2000-01-0556.pdf

Steady Eddie