GM TBI surfing

[Bart_3500]

Hello, I have a GM TBI system that I bought some years ago from a guy named John W who owned Custom EFI and I think he was outta the South somewhere around the Carolina's. I can't find the install manual and after installing a new Centec wiring harness I'm having trouble getting the TBI to power up. Anyone have a schematic I can use? Two or three wires is all I need to connect but somethings not right now. Any help would be appreciated.

[devind]

Welcome,

What kind of ECM?
Is it a 7747?

Look around this link I am sure you will find what your looking for.
http://www.gearhead-efi.com/Fuel-Inj...ams-Tuner-Info!

[1project2many]

He used 7747's for many years so that's likely what it is. I believe I have a copy of his tech manual around although you're probably better off just asking questions here. Wiring diagrams for the 7747 can be found in this thread: http://www.gearhead-efi.com/Fuel-Inj...Information-42

Good luck.

[EagleMark]

Since you own the system you should have the manual, but the one I have does not include any wiring? Just track them down one by one from diagrams linked to above and you'll be fine.

[Bart_3500]

Since you own the system you should have the manual, but the one I have does not include any wiring? Just track them down one by one from diagrams linked to above and you'll be fine.

I figured it out, with the aid of a shop manual I have for an '88 Pontiac we owned many years ago. Kinda screwy how the builder/modifier ran the wires, but it's clear now. Thanks for the inputs. I did find a good site here. Yes, I did have/had a manual but can't find it after 5 years. Also the builder ran everything in red and black wires within a couple inches of the computer so I don't believe the manual would have done any good, but with the aid of the s.m. and the bride watching for which wire moved as I pulled it, I got 'er traced out! On too finishing the Centec wiring harness and it's off to the Rubicon. Thanks for the wiring diagram too.
Yes, it is a 7747 computer and I'll print the attached manual and promise not to misplace it this time. One thing's for sure. Now that I have a copy of your manual, mine will show up. Thanks again. If anyone needs information from the '88 Firebird manual please let me know.

[Bart_3500]

Well, it's running, but very crappy! It's running very rich and surging from 500 to 1500 rpms. I'll be going back into it tomorrow but tonight I'm reading the shop manual. Any ideas would sure be appreciated.

[Bart_3500]

Well, it's running, but very crappy! It's running very rich and surging from 500 to 1500 rpms. I'll be going back into it tomorrow but tonight I'm reading the shop manual. Any ideas would sure be appreciated.

Update. It seems that the Ignition module was the problem. Why would an ignition module go out at the same time a wiring harness was install is beyond me. Another thing I learned was DON"T fuse the main feed wire between battery and ignition switch. The largest fuse I could get was 30 amps and when that blew it caused all kinds of problems. The fuel pump relay coil burnt out, two front parking lights burned out, one rear light (LED) gone, radio fuse blown, all the instrumentation gone (isn't that enough). Well, after leaving the camp ground up in Tahoe for the Rubicon trail is when all this happened. About 5 miles down the highway. I got the fuel pump going again with a jumper wire and made it back to Tahoe. I made an off/on switch to feed the fuel pump relay to turn the rig off and on. Ignition switch was only good for starting the engine. Made to the Rubicon trail head (3 rigs) and about 2 miles in one of the Jeeps broke a front leaf spring. I welded it back together, but welding spring steel isn't very good under premo conditions, much less a trail fix. We spent the night right there. Setting up camp after dark is fun. We were so tired that we didn't care if a bear came into camp after food. My 12 gauge with rifled slugs would deal with him. Next morning (no bears) we made it about 50 yards before the spring broke again. I decided it was time to throw in the towel. Two out of 3 rigs in poor shape. We drove back to pavement and wife then got stung by a wasp. When we got back to the camp ground where we left the RVs I found that a "widow maker" pine cone had fallen and put a large dent in the hood of my lovely F350 pickup.
Since then, I have repaired everything except the instrument cluster is back at the rebuilder to repair the gauges. He said it may be just a very fine wire burnt, I'll find out today. Hood was fixed by paintless dent repair outfit and looks like it never happened. Wife is okay, thanks to some spray one of the other guys had. Good Stuff, what ever it was. No more fuse on the main feed wire!
"Sometimes you're the windshield and sometimes you're the bug!" This trip we were THE BUG!!!!

[EagleMark]

I hate when that happens...

[Bart_3500]

I hate when that happens...

Well, it's a year later and we managed to finish the Rubicon trail without incident (to us). One thing I find curious is that the engine back fires when decelerating and going down hill. I was thinking the TSP isn't adjusted right. Any way to set that? Appreciate all the help.

[steveo]

glad you got it going

what's likely happening is you're dumping unburned fuel into the exhaust, then igniting it.

the engine requires way way less fuel when in decel. more timing advance in decel range will help burn that extra fuel, but it will weaken engine braking. this is also why decel enleanment exists, if you can tweak that a bit.

you should do a log and find the points where it's backfiring.

what does your timing look like in that low MAP range?

[Bart_3500]

I got a 7747 computer out of the local bone yard. Yesterday I picked up knock sensor. I was told that I'd need one to use the 7747 computer or I'd have a permanent error code and limp mod. Well, in reviewing the schematic for the 7747 I see I also need an ESC (electronic spark control?) module. I need this to wire the knock sensor into the ECM. Is this correct? If so, where would be the best place to get one. Local bone yard I know, but where is it located in the vehicles? As usual, thanks for all the information and help.

[Bart_3500]

glad you got it going

what's likely happening is you're dumping unburned fuel into the exhaust, then igniting it.

the engine requires way way less fuel when in decel. more timing advance in decel range will help burn that extra fuel, but it will weaken engine braking. this is also why decel enleanment exists, if you can tweak that a bit.

you should do a log and find the points where it's backfiring.

what does your timing look like in that low MAP range?

Timing in that low MAP range. I'm confused, how do I read the timing while decelerating down a hill with around 200 to 1 gearing ratio. I'm listening, please feel free to edumacate me.

I haven't addressed this yet. Working on '57 Fairlane 500 and then some guy re-ended my beautiful '02 F350. $2500 damage and all he did was hit the rear dually fender/mud flap. Expensive!!! Glad he had insurance.

[steveo]

as you decel, MAP decreases (vacuum increases) and it goes into a different part of the timing map. if you look at the far side of a MAP table where vacuum is really high, it usually kinda drops off or looks different than the rest of the map. if you play with timing in that range you can smooth out decel.

of course every engine and vehicle is a bit different, and goes into different ranges of vacuum during decel. cam plays a big factor in that. a giant cam is in decel for half the damn timing table 'cause it has so much trouble making vacuum.

that's why we datalog, to say...when im in hard engine braking and it pops, here's where on the timing map i am, and maybe i'll add a bit of fuel to VE in that range too. if you run a stock timing map with a big cam, you'll find where the stock cam was in cruise, you're in decel..