Cheap Alternative for LT1 Opti Issues

[Supercharged111]

So this guy 411 (late LS1 PCM) swapped his 93 TA and used a 4X 96-97 OBDII LT1 reluctor/timing cover. He used an operating system from an Express van which was the only platform to receive this PCM and still have the older 5.7 engine. I'm using this PCM in both my 1500 and 3500. I guess it runs without the 1X cam sensor thus making it easier to fit to an LT1. A supposed consequence is that the engine then fires the injectors in batch mode vs multiport. Only thing we'd need to do for CMC is guinea pig it. If it has merit, we could have a spec CMC tune. Just as easy to cheat here as it is on pretty much any other car so I don't think we'd be opening up Pandora's box. These computers also came in jillions of trucks, so they're super easy to find. Just a red and blue connector 512k LSX PCM.

[Trublu]

And there it is again, the beast of magic and foreboding....the wizardry of GM personified.....slayer of dreams.....confuser of the blue oval clan......dah dah daaaa, The Opti (so special even the T is capitalized)

[Fbody383]

You have a source for more details?

[Supercharged111]

No, was hoping to not be the only one who saw this. What I can do is experiment with running on no cam sensor on my truck to mimic this phenomenon. Same operating system this Camaro is using.

[y5e06]

I've looked into this in the past, and have seen the videos.
Edit: he used a vortec type distributor in back, instead of the front mounted cam sensor, because he had the parts on hand. I saw the same videos. Not terribly expensive, but it is some work.
Edit There is a different route for sequential fire & front mount cam sensor:
basically, the top two items in this table:
https://www.eficonnection.com/home/category/engine-hardware/crank-and-cam-signal-kits/efi-24x-product-line/efi-24x-lt1lt4
you could do it fairly cheaply; junk yard/craiglist 411 PCM & ignition coils, '96-'97 front cover (for crank sensor), Efi Connect components, and some time to re-pin the harness. the re-pinning doesn't look to bad, actually. the one catch is finding and agreeing to a standardized program.

guy with the videos used this instead of the front cover mounted parts:
[edit:deleted. I listed wrong part]. He used the vortec style distributor with plug wire terminals.

https://www.youtube.com/playlist?list=PLblRhzbDvp3m0VgvMjG_BiVMa4pEUpWoD

oh, 411 doesn't need to come from the van. lots of vehicles used it... including LS1 4th gens.
Edit: vortec/van setup is batch fire. the '93 was batch fire. '94+ lt1 is sequential. 411 swap can be sequential if using LS type of setup and not vortec SBC stuff.
edityou also, as shown from EFI connect, don't need to use the distributor in back (i.e. modify lt1 manifold) but the opti location for a cam sensor instead.
edit edited incorrect details above. more investigation is warranted if there is interest. I wouldn't sign up to modify the manifold and mount a distributor in back (what a PITA that would be) but instead prefer the front mount cam sensor with coil-on-plug ignition. Perhaps you can use an LS1 type tune but would have to adjust for firing order and make sure correct for stock LT1 MAF etc. *maybe* you could do a sync only type of *distributor* in back and only have to mount the *distributor* ala LT1Intakes small cap HEI conversion. a sync distributor is not really a distributor as it doesn't distribute the spark to the cylinders but instead is just a position sensor.

[y5e06]

partial list of 411 PCMs, from another web source. accuracy TBD
ADILLAC ESCALADE 2002
CADILLAC ESCALADE EXT 2002
CHEVROLET ASTRO (2001 - 2002)
CHEVROLET AVALANCHE 1500 2002
CHEVROLET AVALANCHE 2500 2002
CHEVROLET BLAZER (2001 - 2002)
CHEVROLET BLAZER TRAILBLAZER 2001
CHEVROLET C3500 PICKUP HD 2001
CHEVROLET C3500 PICKUP HD CHASSIS CAB 2002
CHEVROLET CAMARO SS (2001 - 2002)
CHEVROLET CAMARO Z28 (2001 - 2002)
CHEVROLET CORVETTE (2001 - 2003)
CHEVROLET CORVETTE Z06 (2001 - 2003)
CHEVROLET EXPRESS 1500 (2001 - 2002)
CHEVROLET EXPRESS 2500 (2001 - 2002)
CHEVROLET EXPRESS 3500 (2001 - 2002)
CHEVROLET S10 PICKUP (2001 - 2002)
CHEVROLET SILVERADO 1500 (2001 - 2002)
CHEVROLET SILVERADO 1500 HD (2001 - 2002)
CHEVROLET SILVERADO 2500 (2001 - 2002)
CHEVROLET SILVERADO 2500 HD (2001 - 2002)
CHEVROLET SILVERADO 3500 (2001 - 2002)
CHEVROLET SUBURBAN 1500 (2001 - 2002)
CHEVROLET SUBURBAN 2500 (2001 - 2002)
CHEVROLET TAHOE (2001 - 2002)
GMC C3500 PICKUP HD (2001 - 2002)
GMC JIMMY 2001
GMC JIMMY ENVOY 2001
GMC JIMMY SLS 2002
GMC SAFARI (2001 - 2002)
GMC SAVANA 1500 (2001 - 2002)
GMC SAVANA 2500 (2001 - 2002)
GMC SAVANA 3500 (2001 - 2002)
GMC SIERRA 1500 (2001 - 2002)
GMC SIERRA 1500 HD (2001 - 2002)
GMC SIERRA 2500 (2001 - 2002)
GMC SIERRA 2500 HD (2001 - 2002)
GMC SIERRA 3500 (2001 - 2002)
GMC SIERRA C3 2001
GMC SONOMA (2001 - 2002)
GMC YUKON (2001 - 2002)
GMC YUKON DENALI (2001 - 2002)
GMC YUKON DENALI XL (2001 - 2002)
GMC YUKON XL 1500 (2001 - 2002)
GMC YUKON XL 2500 (2001 - 2002)
OLDSMOBILE BRAVADA 2001
PONTIAC FIREBIRD FORMULA (2001 - 2002)
PONTIAC FIREBIRD TRANS AM (2001 - 2002)

[Pranav]

IPerhaps you can use an LS1 type tune but would have to adjust for firing order and make sure correct for stock LT1 MAF etc.

I will say that when I LS swapped my car, the LT1 MAF I was using for my 96+ OBD ECU carried right over to the 99-02 LS1 harness/ECU no problems.

Same MAF I believe was used 94-97 right?

That's one less thing possibly, although what the tune is looking for in regards to MAF reading vs RPM/Throttle is a different story...

[Supercharged111]

I've looked into this in the past, and have seen the videos.
Edit: he used a vortec type distributor in back, instead of the front mounted cam sensor, because he had the parts on hand. I saw the same videos. Not terribly expensive, but it is some work.
Edit There is a different route for sequential fire & front mount cam sensor:
basically, the top two items in this table:
https://www.eficonnection.com/home/category/engine-hardware/crank-and-cam-signal-kits/efi-24x-product-line/efi-24x-lt1lt4
you could do it fairly cheaply; junk yard/craiglist 411 PCM & ignition coils, '96-'97 front cover (for crank sensor), Efi Connect components, and some time to re-pin the harness. the re-pinning doesn't look to bad, actually. the one catch is finding and agreeing to a standardized program.

guy with the videos used this instead of the front cover mounted parts:
[edit:deleted. I listed wrong part]. He used the vortec style distributor with plug wire terminals.

https://www.youtube.com/playlist?list=PLblRhzbDvp3m0VgvMjG_BiVMa4pEUpWoD

oh, 411 doesn't need to come from the van. lots of vehicles used it... including LS1 4th gens.
Edit: vortec/van setup is batch fire. the '93 was batch fire. '94+ lt1 is sequential. 411 swap can be sequential if using LS type of setup and not vortec SBC stuff.
edityou also, as shown from EFI connect, don't need to use the distributor in back (i.e. modify lt1 manifold) but the opti location for a cam sensor instead.
edit edited incorrect details above. more investigation is warranted if there is interest. I wouldn't sign up to modify the manifold and mount a distributor in back (what a PITA that would be) but instead prefer the front mount cam sensor with coil-on-plug ignition. Perhaps you can use an LS1 type tune but would have to adjust for firing order and make sure correct for stock LT1 MAF etc. *maybe* you could do a sync only type of *distributor* in back and only have to mount the *distributor* ala LT1Intakes small cap HEI conversion. a sync distributor is not really a distributor as it doesn't distribute the spark to the cylinders but instead is just a position sensor.

The EFIConnection stuff is 24x, the LT1 was 4x and the Vortec was also 4x but used a 1x cam sensor. While the computer doesn't need to come from a van, its 4x operating system will. The problem with just yanking the cam sensor is the engine doesn't know when a cylinder is on its compression stroke or not. I'm not sure why his motor ran fine without and I haven't tried yanking the cam sensor on my truck, but the way it misfires is characteristic of a cam sensor on its way out.


I will say that when I LS swapped my car, the LT1 MAF I was using for my 96+ OBD ECU carried right over to the 99-02 LS1 harness/ECU no problems.

Same MAF I believe was used 94-97 right?

That's one less thing possibly, although what the tune is looking for in regards to MAF reading vs RPM/Throttle is a different story...

Same MAF. In order to get the MAF data right it needs to be pulled from an OBDII LT1, not sure if HPT supports this PCM or not. I know EFILive does not. No guarantee if you do snag the MAF data from an OBDII LT1 PCM that its reference points will be the same which means the data is then worthless. The only thing that should affect the MAF settings are MAF placement and intake plumbing. I know when I swapped my trucks from the black box to the 411 that the MAF data was different and used different data points. In the case of the 1500 it was on the same engine so it should have matched, but did not because of the different airbox setups between those 2 platforms.

[Al Fernandez]

How does the airbox impact MAF data? I mean...as long as everything going into the engine is going through the MAF the layout of the plumbing should have no impact.

[Supercharged111]

It does. Bends create turbulence and different diameters of tubing affect velocity.

[Al Fernandez]

I think that’s a lot more physics theory than practical impact. Have a look at the OE LS air inlet system upstream of the TB and tell me it conforms with any known guidance on things like diameters of straight pipe upstream of the maf, avoiding large cross sectional changes, or non smooth profiles.

[Cody Powell]

I think that’s a lot more physics theory than practical impact. Have a look at the OE LS air inlet system upstream of the TB and tell me it conforms with any known guidance on things like diameters of straight pipe upstream of the maf, avoiding large cross sectional changes, or non smooth profiles.

Check out the brain on Al! No wonder his head is so yuuuuugeee

[BryanL]

Disrupting/changing the airflow for the MAF can definitely have an impact. When Glenn and I were first working on a restrictor for the LS he made one that we put right in front of the MAF. Car wouldn't rev or pull about about 2,000-2,500.
I just have practical experience-no thermal velocity dynamics theory and it's impact on turbulence in a sphere of tubing. Where's my Bud Light Cody?

[Al Fernandez]

Putting a restrictor immediately in front of the maf is a bit extreme when talking about air inlet design not mattering. I was considering reasonable things like 3.5 vs 4” tubing, a 90 vs a 45 etc.

[Supercharged111]

I think that’s a lot more physics theory than practical impact. Have a look at the OE LS air inlet system upstream of the TB and tell me it conforms with any known guidance on things like diameters of straight pipe upstream of the maf, avoiding large cross sectional changes, or non smooth profiles.

Well it can and does, here are some stock MAF calibrations to prove it. The value is airflow in grams per second. First is a stock 5.7 Vortec truck.

1834

Next is a Chevy Express van. Same 5.7, same MAF, different intake tract.

1835

Now an LS1 Camaro. Same MAF, different intake tract..

1838

Now an LS1 Corvette with the same old style MAF as the Camaro and different intake tract.

1836

Now an LS1 Corvette with the later, 6.0 type larger MAF. Same intake tract as older style MAF, just larger tubing and MAF housing.

1837

And now a C5 Z06 with the same MAF, same intake tract, but the MAF came descreened from the factory. These cars in particular are sensitive to aftermarket cold air intakes and have a bit of a tendency to throw a check engine light and need a MAF recal to run properly. Fortunately mine has not done this with the Hurricane ram air intake.

1839

[Al Fernandez]

Cool
I stand corrected

[Supercharged111]

And as a proof of concept I unplugged my cam sensor this morning and, lo and behold, the truck ran the same as always. No difference that my butt cheeks could feel, so apparently he's correct when he says it throws the PCM into batch fire mode. Since this scheme retains a distributor spark is unaffected. For reference again my truck is the 5.7 Vortec that he constantly refers to in his video running the 411 PCM. If you have a 96-97 OBDII car this literally only requires the PCM with an appropriate tune to no longer rely on the optical sensor within the optispark unit. For everybody else, swap out your crank pulley hub, timing cover, and add that 4X reluctor. They can be found on OBDII F bodies or on the myriad of 96-02 5.7 Vortec engines piled up in junkyards. I may actually look into guinea pigging this if it's something you're willing to entertain Al.

[Supercharged111]

Still driving around with no cam sensor, gonna see what it does to my fuel economy.

[Pranav]

That's cool stuff!

[BryanL]

That's cool stuff!

What does it mean for our application? I need an intake tract from a Van?