1990 Chevy Suburban 454 TBI

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nervala
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Location: St. Louis

1990 Chevy Suburban 454 TBI

Postby nervala » Sun Feb 13, 2011 3:18 pm

This is my first Megasquirt project and although the learning curve was steep I am very satisfied with the results. My goal was to have a stock appearing CPU, but one that is easily tunable to work with planned future mechanical upgrades. Right now the Suburban is completely stock except for removal of the cat and an aftermarket muffler. The planned upgrades include headers, dual exhaust, aluminum heads, cam, and port fuel injection. I also want to replace the stock Turbo 400 with a 4L80E transmission.
The stock CPU is a “747” so I purchased another one for the case and connector socket.from the salvage yard along with the wiring harness and plugs. While I was there I also picked up an IAT sensor which the 747 doesn't use. From DIYAutotune I purchased the MSII with 3.00 board and a 747 adapter board. I assembled the two boards and the MS passed the tests with the JimStim. After installing the boards into the 747 case I used the GM wiring harness and plugs that I got from the salvage yard to interface with the JimStim since the db37 is inaccessible.
I made several modifications to my setup, the only change in the engine compartment was the addition of an IAT sensor in the air filter housing and routing the wires to the appropriate pins. After I changed the base resistor from 560K to 1K I used the darlington transistor on the 747 adapter board to control the electric kick-down on the Turbo 400, it's set to engage when TPS exceeds 75%. I copied that circuit in the proto area to control the SES light, the light goes off above 400 RPM.. Several jumpers were routed directly to unused pins on the 747 connector. These include the two CAN jumpers which will be used down the road to interface with a GPIO to control the 4L80E. Also, since the db9 connector will not fit in the 747 case without cutting a hole (and I wanted this to look completely stock) I routed the three wires needed for serial communications to the three pins used for the ALDL connector. I then made up an ALDL to db9 cable to hook up my laptop to my ALDL which is connected to the MS thru the stock wiring.
After several days of tuning the Suburban is running great, the butt dyno says it's making a bunch more power and is running smoother too. One nice thing with this setup is that if I have trouble with the the MS I can plug the stock 747 back in and be on my way. This won't work after I make the engine mods of course, but by then I'll have any potential bugs worked out. I've included some pictures of my setup and my latest msq.

nervala
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denmah
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Re: 1990 Chevy Suburban 454 TBI

Postby denmah » Sat Mar 26, 2011 11:31 pm

that is some amazing work on the plug and play harness

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drholl
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Joined: Wed Jul 02, 2008 8:49 pm
Location: California, USA

Re: 1990 Chevy Suburban 454 TBI

Postby drholl » Mon May 09, 2011 10:32 pm

I really like some of the settings that you have. Many are very similar to mine in some places except I live in California and don't have to worry about 20 degree startup!!! You must have bigger injectors than I have as my RF is 7.2. I have a 502 CI (bored and stroked 454) in an old Cadillac with a tugboat cam (low RPM torque is what this car needs). Here's my MSQ but don't use my VE table as it's not dialed in yet. And my VE and Spark are setup for mileage.

What distributor are you using? an 8 pin? Let me know will you? Do you use a 5 volt reference on the "B" pin or a 12 Volt? I'm having an awful time with an 8 pin just freaking out, dropping the spark to zero for a time or two and backfireing through the TBI. Or it stops sparking through the module at the set time and drops back to the base setting (timing goes back to 10 degrees, engine falls on its face...). I'm trying to figure it out and then finish up the VE. If the engine is missing sometimes, it messes up the VE!!

Thanks
Holl

UPDATE: My MSQ is DONE. SEE See MS success stories I posted good stuff there. Search for "16 MPG".
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Last edited by drholl on Tue Oct 11, 2011 6:53 pm, edited 1 time in total.
Holl

MS-II, V 3, 2.886, LC-1. 1971 Chevrolet Monte Carlo 350, 270 HP. 1959 German Corvette, bought in Berlin. With a 160 "KPH" speedo. KPH??? - What were they thinking? 160 KPH is only 100 MPH. We can peg that in third gear!!! 1959 Cadillac, 502, huge Chrome Bumpers and really BIG FINS!!!

nervala
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Joined: Mon May 16, 2005 4:10 pm
Location: St. Louis

Re: 1990 Chevy Suburban 454 TBI

Postby nervala » Sun May 15, 2011 4:07 pm

I'm running 5 volts to the bypass. I did run into a problem with random cutouts and was able to resolve this by using the mod where you cut the trace and route the flyback straight to the injectors and I also put a Radio Shack filter in the 12v ignition in wire.
Today I picked up a 4L80E, so I'll be buying a GPIO board for Megashift soon

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drholl
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Joined: Wed Jul 02, 2008 8:49 pm
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Re: 1990 Chevy Suburban 454 TBI

Postby drholl » Thu Aug 04, 2011 8:03 pm

I found my "Issue". It was a bad fuel pump relay. The voltage to the fuel Pump would fall off, the pressure fell off, and the engine would go real lean. Runs great now.
Holl
Holl

MS-II, V 3, 2.886, LC-1. 1971 Chevrolet Monte Carlo 350, 270 HP. 1959 German Corvette, bought in Berlin. With a 160 "KPH" speedo. KPH??? - What were they thinking? 160 KPH is only 100 MPH. We can peg that in third gear!!! 1959 Cadillac, 502, huge Chrome Bumpers and really BIG FINS!!!


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