Going to the darkside; 258 TBI

[FSJ Guy]

LOL! : D

No worries.

I set my base timing to 10 degrees since it was hard to get the motor to idle at zero. You have to have it idle without the timing control active (disconnecting the set timing wire) to set the base timing. I found that my motor didn't like zero, so I tried 10 degrees and it was much happier.

The big thing is to make sure your base timing (aka static timing) set in the bin file and your actually base timing are the SAME.

[Grand_Wag_85]

Sounds...fun

Now comes the interesting part, cleaning the harness up and making it look pretty.

[243]

Ten degrees base timing works well on the 258 in my CJ.

But it sounds like ya'll have a 2-way conversation going to I will move on.

[FSJ Guy]

I don't think anyone has a monopoly on any thread. Feel free to chime in!

[sgtpoliteness]

I tried setting mine to 10* and then to 0* and didn't notice a difference. Mine is at 0* and idles great. However, there are differences between Ethan's rig and mine. I left mine @ 0* based upon recommendation by Eagle Mark @ gearhead-efi.com. But, like Ethan wrote, whatever you set it at be sure to make that change in the file. To pile on, be sure you're setting timing with the wire disconnected near the PCM.

[Grand_Wag_85]

Ten degrees base timing works well on the 258 in my CJ.

But it sounds like ya'll have a 2-way conversation going to I will move on.

This is a totally open discussion, no worries.

[Grand_Wag_85]

You want the 2PRS, IIRC, from JTR. Send them your $75 and they will send it out to you ASAP.

http://www.Moates.net will have your data logging stuff. For the 7747 ECM, you will want the G2 Adapter or any of its variants (You can get a bin switcher for it, too.)

The AutoProm will work to allow live updating and data logging all in one if you like. A less expensive option is an ALDL cable and the Burn2 burner. You will need at least one 27SF512 chip to burn your files. I'd order at least three because if you're like me, you'll burn one of them up when you accidentally insert it backwards. :- p

I don't recommend mail order tuning. It takes too long. You have to log, send data, wait for a chip in the mail.... Lather, rinse, repeat. I've burned over 10 different bins in a single day playing around with things.

Don't forget TunerPro! It's freeware, but well worth the $40 "registration" to thank the author of this software.

Been reading your page on SP's TBI setup. The autoprom worked well for you I take it?

I think I'm going to pull the trigger on that.

Will still need to get the 27SF512 chips and g2x adapter separately.

[Grand_Wag_85]

One more thing, are you guys running knock sensors?

[AwesomeJ10]

I never bothered with a knock sensor on any AMC TBI. It's easy enough to hear it pinging if you have too much timing. In that case, just back it off a little bit.

I recently did a TBI swap on a carb'd 350 that came in my dually. Even though I already had the 8.1L engine all ready to swap in, there was no way I was gonna drive it around with a carb (even though it was only a month). Anyways - I did connect the knock sensor and that was pretty much just because the knock sensor was already installed into the block and it only takes one wire. Didn't notice a difference...

[FSJ Guy]

I disabled the knock sensor. Blake can tell you specifically what flags to uncheck.

IIRC, I also zero'd out the retard tables, too. So if it thought it detected knocking, it wouldn't change the timing.

When I talked to AFI, they recommended not using the knock sensor because of false knock sensing and the reasons that Blake already mentioned.

[Grand_Wag_85]

Random question.

When I get everything together (after the new chip soldered in) will it attempt to run at all or does some sort of tune need to be uploaded? Probably not, right?

Slowly starting to understand.....

[Grand_Wag_85]

Couple more questions...................

Which have you guys had the best luck with, the stock Duraspark dizzy or large cap HEI? I have both at my disposal, currently.

Is the timing harness (the caddy one) available in the aftermarket? Not having luck at the u-pull-it guy.

Popped open my ECM, what do you guys think?

[tgreese]

Not that familiar with the GM ECU, but the chip stores the fuel and spark table that the computer uses to look up the size of the fuel shot and the advance. If you solder in a blank chip, there won't be much to look up ...

If you are going to have spark control, it doesn't matter which one you use. They both detect the spark the same way, and you'll be disabling the mechanical and vacuum advance. For my 258, I have a HEI from a 250 Chevy. I'm using the short cap from a Blazer, putting the coil outside the distributor, and removing the vacuum advance. You will need the 7-pin or 8-pin module for spark control, which you should be able to put under the cap of a HEI... though I have not gotten that far yet.

[FSJ Guy]

Does the 258 use the same distributor as the 360? If so, go with the stock distributor. You can disconnect the vac advance and weld the centrifugal advance mechanism to lock it out.

[derf]

Does the 258 use the same distributor as the 360? If so, go with the stock distributor. You can disconnect the vac advance and weld the centrifugal advance mechanism to lock it out.

I may be wrong but I'm betting if you try to use an 8 cylinder distributor in a 6 cylinder engine you won't get satisfactory results so I really doubt they're interchangeable.

Though I do think AMC used a Motorcraft distributor similar to the Ford 300 straight 6 for the 258, just with a different base.

[Stuka]

Does the 258 use the same distributor as the 360? If so, go with the stock distributor. You can disconnect the vac advance and weld the centrifugal advance mechanism to lock it out.

No, V8 and i6 distributer are completely different.

They are of the same type year for year (ie: 78+ is all duraspark). But thats about it.

[tgreese]

Does the 258 use the same distributor as the 360? If so, go with the stock distributor. You can disconnect the vac advance and weld the centrifugal advance mechanism to lock it out.

The same as in same type, it's also a Motorcraft Duraspark, like the V8. Of course, the reluctor has 6 lobes not 8, and the cap is different, but it's the same type of distributor.

My 258 currently has the Prestolite distributor, and I got the Chevy 250 HEI distributor at the junkyard maybe a decade ago, so that's why I'm using it. But I would be using the factory Duraspark if I had it.

[Grand_Wag_85]

Both of my distributors are 6 cylinder models.

One more question, anybody have a photo break-down of what all the connectors are on the TBI harness? I'm trimming it down and trying to figure out what stays and what goes.

[FSJ Guy]

If they both trigger the same way, then you can use the stock distributor. The V8 pickup coil send the correct signal for the GM ECM and ignition module to read.

Head over to www.gearhead-efi.com and there is a TON of information there.

[tgreese]

Good chance to practice your Google-fu.

I made this search https://www.google.com/search?q=GM+TBI+ ... 8&oe=utf-8 and this is the #1 hit - http://www.pirate4x4.com/forum/chevy/43 ... nsive.html Looks like a start. There are lots of pages about this topic.

I would suggest that you simply unstring everything and lay it out. Tag all the plugs and wires with some masking tape and a Sharpy until you know what everything is, then make a plan to cut out what you don't need. Take good notes, on paper or with your camera or cell phone or whatever.

I'd also look for the relevant sections of FSM and wiring diagram for the donor vehicle online... it's probably online somewhere. Print or otherwise save them for later reference, since you never know when resources on the internet will disappear. I use a browser add-on called Scrapbook that will copy verbatim any page, including the embedded images and links, however many levels deep you want.

hth!