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Discussion Starter #1 (Edited)
hi everyone.

had a couple newb questions about some TBI wiring on a 4.3. I got a 1993 TBI 4.3 at the junk yard, but it didnt come with a harness (well it had a couple plugs still but was hacked up), so I found an 88 astro that I pulled the harness and ECM out of. The two are TBI and 4.3 so it should be plug and play right? Not quite... The TPS, oil pressure, and a few other plugs were different. The oil press sensor plug had 2 pins on the astro harness, but the 93 motor OPS had 3 pins. The astro harness also deosnt seem to have any plug for the EGR. The 93 EGR motor plug has a 5 pin connector. Im not gonna run EGR, so can I just leave everything as-is without a check-engine light? The TPS plug was different, so I spliced the 93 style TPS plug onto the astro harness. There is also this two pin connector that comes out of the astro harness right around the TPS and MAP sensor connectors...I have no idea what its for. The 93 engine didnt include the spark control module so I need to find one (the astro harness has a flat wide 4 pin connector for the spark module).

The astro harness was also wierd in that it had two bulkhead connectors. One passed thru the firewall that JUST had ECM wiring in it. The other bulkhead connector on the driver side had all the ign, data, guage cluster info, etc crap. Anyone have any idea where I can find a pin-out for that drive side bulkhead connector so I can find IGN, oil press info, etc wires?

also im running the 4.3 to a TH400. The astro ECM and harness was obviously setup for a 700r4. But reading the ECM schematics it appears in 4.3/TH400 apps, one of the output from the ECM triggers the electronic kickdown on the TH400. Any place I can get a custom PROM chip to have the ECM setup for a TH400, no EGR, and stuff??? I tried affordable fuel injection but they wont sell the PROM chip alone, only WITH their harness...:mad3: Its the '7747 ECM which I understand is the main ECM supported with aftermarket.

So basically....are there any other issues that would make my 88 astro harness not work with my newer 93 TBI engine? Why does the oil press sensor have two pins on the astro and three on the 93? Whats the deal with EGR and TPS? I have a couple other mystery wires and plugs Ill post pics of...

VSS is another issue. Its going to be a 4.3 to TH400 to quadra-trac xfer case....so I rebuilt the chevy TH400 with the wierd 10 spline q-trac output. But now I dont have the tone wheel for the electric VSS that was on the original chevy TH400 output. Is this going to cause a problem with the engine, like going into idle mode, spark offset, DFCO? I dont want a check engine light from it either...can that be turned off with a custom chip?

Ill try to think of any other questions...go easy on this newb fawker tho.:flipoff2:

thanks
ben
 

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get a harness from painless wireing it will save all the bullshit it's plug & go they have good service & you can't screw it up only one plug can go in one place
 

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Discussion Starter #3
its also extra money that I dont have (or want) to spend...

I already have the complete harness 90% done and it was FREE. IMO it would be stupid to ditch this when it can be made to work easilly...I just need a few simple questions answered

ben
 

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A TH400 w/electric kickdown???:confused:

You can run with no VSS, I haven't seen any stalling issues without it. The TBI VSS is a 4 pulse/rev unit that you can add into the speedo cable if you really want.

The only differences I've seen in TBI harnesses is for the EGR valve, everything else was the same. But, the third wire on the OPS is for the oil gauge so it's not vital whether you have it or not. The harness' for all TBI (except the BB) should work for you. You shouldn't need a custom chip if you can deal with a few codes.
 

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Discussion Starter #5
A TH400 w/electric kickdown???:confused:
TH400's dont have a TV cable....only the vacuum modulator...kickdown is controlled by an electric solenoid in the trans. On carb'd engines there is a little switch on the accellerator pedal that energized the kickdown on TH400's...on EFI engines the ECM had an output that would apply 12volts to the TH400 kickdown solenoid when it sensed 5 volts on the TPS (full throttle)

or am I missing something? :confused:
 

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not missing a thing, youre right as rain.

have you thought that you can swap one oil pressure switch for the other? they should be a direct replacement on the engine side... allowing you to plug it right in.
 

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Discussion Starter #7
yeah Im not really worried about that...I swapped connectors, as long as the TPS's are the same voltage, just different connectors....
 

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Discussion Starter #8
anyone know where I can get wiring schematics for the bulkhead/firewall connector on a first gen Astro?
 

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Liljohn has a thread on pinning out the TBI harness, also check Bill USN-1 signature for link to all you ever wanted to know about TBI fuel injection. Read up sucka :mr-t:
 

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Might try a run to the library :p

As for the "painless" harness, it is only painless if you use their idea of what TBI is. If you have any version other than what they use, you are replacing a lot of sensors and such(TPS for example) Easier/cheaper to use the existing engine's harness.

On the "driver" bulkhead fitting, if I recall right, it is simply the ignition related stuff(ie hot wire, crank wire,etc) Better off getting pinout for the ECM and back tracking wires.

I've got a "generic" writeup in this forum. Try a search for TBI posted by me.

For the TH400, can't help you with the 4.3L engine. But it was used with some of the 7.4L TBI engines. From the ECM, it goes to a relay first then to the TH400 electric plug. I'm using this on my TBI cady conversion ;)
 
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