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post #1 of (permalink) Old 06-19-2003, 11:19 AM Thread Starter
 
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Megasquirt: MPI or TBI on 258?

After reading up on the Megasquirt system I think I'm going to try it on my 258. I've built microcontrollers from scratch as a teenager so the electronics aspect doesn't concern me. The problem is, I know bupkis about fuel injection at this point. Doing the Megasquirt should solve that problem but in the meantime I could use a little help.

I'll start with a 4.0 head. No sense not to, right? After that, though, I'm not sure. The choice seems to be the 4.0 MPI or a GM TBI. With the current Megasquirt system, MPI would be batch fired not sequential so I'm not considering that except for future potential. Does anyone have arguments as to which to go with? I'm leaning MPI just because it's more stuff to play with and seems sexier than TBI, but informed rationale could easily outweigh that [img]images/graemlins/grin.gif[/img]

Also, any links to tech articles about FI in general would be appreciated.
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post #2 of (permalink) Old 06-19-2003, 11:33 AM
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Re: Megasquirt: MPI or TBI on 258?

1. IMHO you're plans are ambitious.
2. Start with ONE project at a time.
3. I'd start with the MegaSquirt first,
4. By doing this you can work out any bugs on a known system,
5. As for SMPI with the MegaSquirt...
6. That would be a fun project,
7. But more work and money compared to a TBI.
8. I'm not sure the payback would be warranted,
9. To install SMPI with batch firing.
10. Once the EFI was working like a finely tuned clock,
11. Then, and only then would I think about swapping heads.
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post #3 of (permalink) Old 06-19-2003, 11:47 AM
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Re: Megasquirt: MPI or TBI on 258?

If your going to go all-out on the EFI, go MPI. Throttle body is reliable but it forces you to use the crappy stock intake plenum which has horrible fuel flow characteristics.

As for the 4.0L head, you can have a experienced machine shop port and polish your 4.2L head for less money than you can buy and then refurbish a 4.0L

Sounds like you are a tech-nut. Hesco offers some pretty neat tuning options for their MPI computer. (www.hescosc.com) If you go with the Hesco kit either order the enhanced fuel delivery system (bigger fuel pump and external pressure regulator) or put in a gastank from a 91-95 Wrangler (internal fuel pump). Vapor lock is a problem.

I am not familiar with MegaSquirt. What is it?
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post #4 of (permalink) Old 06-19-2003, 11:56 AM Thread Starter
 
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Re: Megasquirt: MPI or TBI on 258?

MegaSquirt is a build-it-youself FI controller.
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post #5 of (permalink) Old 06-19-2003, 11:59 AM
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Re: Megasquirt: MPI or TBI on 258?

Holy Bleep!

You are brave! Good luck and let us know if it works! Better yet photograph it and create a tutorial.
post #6 of (permalink) Old 06-19-2003, 01:16 PM Thread Starter
 
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Re: Megasquirt: MPI or TBI on 258?

Ambitious is what I'm after. If it takes a year (or two) and costs almost as much as the Mopar MPI kit yet only batch fired, that's fine. My building-to-driving time ratio is like 100:1 and I like it that way [img]images/graemlins/grin.gif[/img] I have a Jeep because I enjoy building it and owning the build. That's why the MegaSquirt really appeals to me over a black-box kit or engine swap.

The HO head seems like the logical place to begin building the 258, and I'd prefer to get the whole shebang done at once. I'm perfectly comfortable exploring uncharted territory and can handle the surprises. I'm willing to accept all that.

What I need is knowledgeable input into the best direction to start off on. Right now MPI seems the way to go, but I'm only just getting my feet wet. I want to understand why to go that way. I don't want to be putting on 6 chrome shocks per wheel where one rancho will accomplish the same thing, you know?
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post #7 of (permalink) Old 06-19-2003, 02:04 PM
 
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Re: Megasquirt: MPI or TBI on 258?

Blaze new trails and use the 4.0L head, mpi and exhaust. The majority of megasquirt applications are mpi and the batch firing works just fine. At idle, sequential firing makes a difference in emissions, at speed, the difference is negligible. You will have less work than I did, making my owner adapter and modifying the intake manifold. You will have yourself a 185+ horsepower motor that is fully tunable and easy to diagnose.

I went with a GM TBI because I wanted to keep things simple and didn't have easy access to a 4.0L head and intake. Nor did I want to risk the cost of replacing 6 injectors that I got from the junkyard. Also, I admire the fuel economy that TBI setups were getting and wanted that too. Despite the original design of the engine being sequential injection, you will like many others before you on the megasquirt list find that batch firing works great. There are lots of inline 4's and 5's (audi's), and 6's (BMS's I believe) being megasquirted and they all report favorable results.

Go for it! I believe the end result will be superior to the factory 4.0L because it will be fully tunable for any future mod's. And having an independant ignition system, you won't have the pinging problems associated with the Mopar kit.
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post #8 of (permalink) Old 06-19-2003, 07:10 PM Thread Starter
 
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Re: Megasquirt: MPI or TBI on 258?

Thanks Tim, that's encouraging. I've read all your messages in the MS mail archive and would've thought you'd recommend the TBI since it went so successfully for you. Actually, your success is probably the reason I'm wondering if MPI is worth the extra bother. But glad to see you feel the MPI will be OK too.

There are plenty of 4.0 MPI Cherokees in the yards around my way so I'm thinking I could pull the entire top of an engine and go from there. As long as I get all the sensors and as much of the wiring as possible I could save a lot of time and keep everything "stock" (sort of). I do wonder if 6 injectors that essentially do the same thing as one is kind of a waste. That's the great part of the MS system, though, nothing stopping me from adding a CPS and modifying it for sequential operation myself if I really wanted to.
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post #9 of (permalink) Old 06-19-2003, 08:07 PM
 
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Re: Megasquirt: MPI or TBI on 258?

looks like you already got some good advice, especialy from SWB's 'MeagSquirt Man' TiminMb. I am also toying with idea of MegaSquirt but CA emission laws are not very friendly to it. Since you mentioned that you are not an expert on fuel injection systems, may I recommend the book "Bosch Fuel Injection & Engine Management"; ISBN0-8376-0300-5. Since Bosch developed FI you can apply principles in the book to any FI on the market. It's very informative read.
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