Chevy TBI on a Jeep straight 6 questions.

[K5-newbie]

I have a buddy who is in the middle of a TBI swap on his Jeep and I have questions about the injector pulse. What voltage does it pulse? From what we can tell it is around 10.6v or so. Does anyone know where I could read up on this swap? Also I hear talk about a "tach filter". I am assuming this is using the tach signal and stepping it down. Is this assumption correct or am I off base? All help is greatly appreciated.

I have searched this forum and it brings up such broad topics I thought I should just ask.

[JohnnyJ]

Out of curiosity, why do you need to know the voltage to the injector?

For background, it'll cost a few bucks, but customefis.com has put together a good guide. There are other free sources, but I haven't seen anything as easy for the guy not wanting to buy a kit and install it.

[mbryson]

I just helped put a Howell kit on a 4.2L. Wasn't too bad, but I didn't have to break out the ohmeter or anything. It did help to read the destructions, though. So far, the best TBI info I've come across on the web is at www.thirdgen.org. Their search function yeilds up all kinds of good information :D

Are you using a TBI setup off a 4.3L or ????

[59cj5]

Voltage to the injectors is 12V...what are you going to use as the ECU or computer for this setup??

[yager]

yes definitly hit the thirdgen site. Those guys know thier stuff, and you can kill 4 weeks just on readig the FAQ/DOCs alone.. TBI swaps are old hat over there. (tip- read/search before you post) I'm mid way through a TBI swap onto my 307 but also working though all the setup, config AND understanding of the ECM etc.. Im also doing my own harness and redoing my fuse block etc..

Look up stuff on the data loging, via ALDL , with a simple RS232/serial cable you can see a TON of info on the data streem. Might be worth the $30 cable to see what your ECM is doing... I just got some basic logging going on my pickup truck to help my learning curve for the jeep project and seeing the data of all the sensors/status bits is cool, i have a better idea of how to troubleshoot it when i get to that point..

also, the injectors are12v but your pulse width changes, you not really going to be able to read that with out a scope. But the ALDL will show you the PW..

What ecm you using ?

[K5-newbie]

He has the complete injection system off of a Chevy 4.3 and has adapted the throttle body to the Jeep. Just need to figure out how to get the jeep electronics (I think its an '85) to talk to the chevy electronics...I believe he has talked to the guy at Affordable fuel injection. I will know more this afternoon.

[CSP]

There's nothing about the Jeep electronics that needs to talk to the Chevy stuff. All that's needed is power and a spark signal wire so the PCM knows when to fire the injectors.

You can make the PCM control spark timing, but that still has nothing to do with the Jeep's feedback carb garbage.

[Foxtrot]

Here are the answers. The original thread is here: http://monkeycage.island4x4.com/showthread.php?s=&threadid=11836


I've been driving the rig hard for a year, runs great on 87 octane, lots of power and very good fuel economy. I built the the TBI adapter plate my self also, it was simple. I can post the directions for that too, if anyone cares.

I cut and paste this from my original thread, so it doesn't flow perfectly, but all the info is here:

Goodbye Carb, Hello Fuel Injection

Everyone knows how crappy the Carter BBD carb on the Jeep 4.2L's is. Anyone who's wheel'd with me has watched and laughed as I've struggled to keep my engine running on just about every obstacle. Well enough is enough. I've had it with this crap, and I'm swapping on GM 4.3L TBI fuel injection.

I probably should just swap an MC2100 on, but life will be more interesting this way, and I should get even better fuel milage.

Here's a before shot:

http://members.shaw.ca/foreweb/efi_01.jpg

This is what's going on. Look at all those wires! It's actually a pretty simple system really, it just looks intimidating.

http://members.shaw.ca/foreweb/efi_02.jpg

I have all the engine sensors mounted and the TBI adapter plate fabbed up. What's left is wiring, mounting the ECM, and installing the high pressure fuel pump, filter and lines.
I spent a bit of time trying to decide exactly where to put everything. Most of the write ups I've seen place the ECM under the dash on the passenger side, above the heater box. That's the location of the 4.2's factory computer, and the GM ECM's fit there quite nicely from what I've seen.

The drawbacks of putting it there were many however. Firstly, I would have had to pull the dash to access that spot for installation, and if any future trouble arises. Secondly, I would have had to re-route a bunch accessories I've already wired in, in that area. Thirdly, just about every wire in the harness would have had to have been lengthened to reach their respective connections.

I looked around a bit, and decided that the drivers side under dash area was the perfect spot. There's lots of room and easy access there. The harness now has to be shortened here and there, instead of lengthened all round. I can mount the ECM nice a high, to keep it out of harms way.


The harness has been stripped to the bare necessities, and installed on the firewall. I was able to use the factory firewall mount by cutting a 1 7/8" by 2 1/8" rectangular hole in the firewall. It looks like it belongs there. I've also figured out how I'm going to mount the ECM.

http://members.shaw.ca/foreweb/efi_03.jpg



I've done a lot more work today, and there is still tonnes left to do. I haven't even started the fuel system upgrades yet. Lots of wiring and component mounting.

http://members.shaw.ca/foreweb/efi_04.jpg

http://members.shaw.ca/foreweb/efi_05.jpg

[Foxtrot]

http://members.shaw.ca/foreweb/efi_06.jpg

http://members.shaw.ca/foreweb/efi_07.jpg

http://members.shaw.ca/foreweb/efi_08.jpg

The harness is almost finished as far as routing and mods are concerned. Then I have to solder about 200 connections. Loom it up etc... I wasted a lot of time trying to hook up the throttle cable. I'm going to have to fab a completely new cable bracket to get that done.....
I just drove it........feels like WAYYYYYY more power. Engine breathes easy now.

I have a misfire under heavy load, and I still have the flooding during crank problem.

Idle is perfect near 700 rpm.

Fuel Pump: Carter External mount universal TBI pump, 22psi, LOUD.

http://members.shaw.ca/foreweb/efi_09.jpg


More EFI goodies. I reused the Chev bracket for the EST module and MAP Sensor. I made my own bracket for the ICM and Fuel Pump Relay.

http://members.shaw.ca/foreweb/efi_10.jpg


Jim Sprang was correct in that the pump was seeing 12V during cranking. Unfortunately, I don't have a clue why. I had the fuel pump and relay hooked up exactly as GM intended it to be.

I have addressed the flooding symptoms by simply hooking the fuel pump to a "hot in run only" power source, so the pump cannot run during cranking regardless of what the ECM signals.

Like I say, this is a band-aid more than a solution, but it works like a charm at this point. The engine fires right up now, no flooding. I still have yet to see how cold starting will be affected, but I think it's good to go.

My only dis-like at this point is how obnoxiously loud the external fuel pump is. I'm sure I'll get used to it, but it has a lame, ear piercing whine.

I'd like to thank all you guys for the help and advice along the way. Also, I'd like to thank Tom Hallberg, whom I emailed from the gmecm mailing list.

Here's a diagram Tom sent me........I fixed it up a bit, and removed the duraspark module wiring, since I think it's redundant.

http://members.shaw.ca/foreweb/tbi_ign_diagram.jpg



Notice that Orange goes to N and Violet/Purpule goes to P. I had these backwards before, and it runs WAY better now.

Ya, I may have traded one problem for another, but we'll see. Cold starting takes prolonged cranking now, but at least is starts and runs reliably at this point, so I can fine tune it form here at my leisure.

I'll give the pump another week or two, to see if I get used to the noise, otherwise I'll get drastic. It's already double rubber insulated from the frame, but I can get creative.

I wired up the old A/C wire on the ECM for a fast idle circuit while using OBA.......so, I'm having fun with the little details now. It's a wicked little system, and it only gets better from here.

Couple more pics:

Parts.
http://members.shaw.ca/foreweb/efi_11.jpg

Distributor centrifugal advance de-activation. Weights and springs removed. Epoxy to hold it in place.
http://members.shaw.ca/foreweb/efi_12.jpg

All rebuilt and ready for a new life.
http://members.shaw.ca/foreweb/efi_13.jpg

If anyone out there is considering a swap like this, I can answer all your questions, so fire away.

[jchio]

What distributor did you use? 4.3 V6?? what mods did you do to it??

Sounds like a great project!!

[jchio]

the TBI is the same as a 305 or 350, right??

Damn Im excited about this!! I have a TBI on my CJ7's 383 and will install it on my dads wagobeer following your steps dude!!

[Foxtrot]

Just use the stock Motorcraft distributor. The computer will control timing now, so you have to deactivate the vacuum advance. The mods are pictured. Remove the centrifugal advance weights and fasten the dist down so it doesn't have play with the weights/springs removed. I used epoxy. You could bolt or weld it.

I don't know why guys bother swappng HEI distributors in. I run the Ford TFI style cap/rotor and the GM HEI coil from the donor 4.3L.

The 4.3L and 305/350 TBI systems are basically indentical, yes.

[jchio]

It already has a HEI in it, so I guess I can use that one.

What service number is your ECM?? Will one from an auto Astrovan Work?? must be a 4.3 ECM or a 5.0 will work?? I have almost all of the parts as spares for my 383 so what the heck, Ill give it a try! :D

[Foxtrot]

I'm running a 1227747. Look here: http://winaldl.joby.se/aldldata.htm

Even if the ECM is the same, the PROM will be different for the bigger motors.