TBI for dummies

[Nazzcu]

I need some assistance troubleshooting my TBI setup. The truck is 87 silverado originally came with 305. Prior to my purchase the engine was swapped with a 92 350. The engine runs good just a little rich, when the ignition is turned the fuel pump runs nonstop and does not cycle back off. The fuel gauge sits at the 3:00 position while running and It is missing the oil switch beside the distributer.

I need some help getting this TBI back to stock condition, most of everything is missing or unhooked, and I don’t know enough about it do simply buy the parts and reconnect. In addition there has been some shadetree wiring done.



Can someone ID all these for me.



The brown wire above runs back trough the cab to the fuse box and is tied into the ECM fuse.

Thanks for any help. If someone can breakdown each part of this system for me I can get it working again.

[jared87350]

1. connector to map sensor ( manifold absolut pressure)
2. i couldnt tell you, sorry
3. looks like your spark control module
4. looks like your map sensor
5. dont know

[indyrenegade4x4]

i got the same problem. I have 1987 blazer with 89 motor. Mine isnt even wired up yet. They guy thought you could just swap wire block on firewall between years.

[leegrady]

If you go to your local library you will find component part location and identification manuals that will show a illustration of your engine compartment and most of the various sensors, outputs and related parts.
These computer controlled fuel delivery systems will default to what's known as 30 degrees dwell (no not breaker point dwell) injection pulse width, in open loop, and ignore O2 sensor input. The ECM will always "think" the engine is cold: on the rich side.

Some where there is a green tab (single) connector not connected to anything. Connect a six cylinder dwell meter (yes six cylinder mode on your dwell meter) to read rich and lean readings by the sweep of the analog meter. Low means the sensors are reading rich, and telling the computer to lean out, and vise versa. With all those components disconnected your reading will stay in the middle at about 30 degrees, open loop. When everything is within spec, and the computer goes into closed loop the needle will drift back and forth kinda randomly. This is just like O2 counts on a real scan tool.

[cableguy0]

Your other issue is going to be the 305 and 350 tbi is different. They use a different computer and injectors. the plug in your hand is for the map sensor and definately needs to be hooked up. Its responsible for most of the fuel metering in a tbi setup.There should also be a vacuum line hooked to it. You honestly might be better off starting with another harness. I have no idea why someone would do that to a harness everything should have plugged in regardless.

[gchemist]

This might help you: http://users.sfo.com/~eagle/howell.html

[SliverBlack86]

Originally Posted by Nazzcu

...The brown wire above runs back trough the cab to the fuse box and is tied into the ECM fuse.

Thanks for any help. If someone can breakdown each part of this system for me I can get it working again.

I assume you know that the Brown wire is providing 12v to both the red & white wires. But, it should not be connected to the ECM fuse. I believe the TBI injector resistance is in the 1.3 to 1.6 ohm range, the resistance would draw about 8 amps each so you need to provide a separate 10 amp fuse for each injector.
Find the common wire that the red & white wire connect to (I think it's Pink with a black strip) and use inline fuses, or aux. fuse locations in the fuse box connected to key on/start power, or a hot at all times source like the fuel pump power.

[Nazzcu]

So I need the ECM from a 350 and possibly a new harness? About the brown wire, it should not be there based on wiring diagrams. What purpose is it serving feeding power directly to that injector? To get this engine back to normal, what all components are needed in the tbi system?

This is what I know correct me where wrong: The oil switch, MAP sensor and vacuum line to rear of carb, Knock sensor, and O2 sensor.

The fuel pump runs non stop so like Leegrady said it is in the open loop, does this account for the 3:00 position on the fuel gauge?

[sandblaster]

will this thread help?

http://67-72chevytrucks.com/vboard/s...d.php?t=317519

[SliverBlack86]

Originally Posted by Nazzcu

So I need the ECM from a 350 and possibly a new harness? About the brown wire, it should not be there based on wiring diagrams. What purpose is it serving feeding power directly to that injector? To get this engine back to normal, what all components are needed in the tbi system?

This is what I know correct me where wrong: The oil switch, MAP sensor and vacuum line to rear of carb, Knock sensor, and O2 sensor.

The fuel pump runs non stop so like Leegrady said it is in the open loop, does this account for the 3:00 position on the fuel gauge?

If the SES light is working it would be lit if it's in open loop. The ECM doesn't provide 12v to the injectors it provides a calculated pulse to turn on the injector drivers which electronically connect the injectors to ground for the pulse duration without the 12v the injector won't work. The harnes wasn't properly connected to the existing wiring. Doing it correctly should be priority one.

[KazuyaIB]

i would say get the 91 Blazer/Suburban wiring for the easiest TBI wiring set up. its easy to take out from the junk yard and while your at it study all the parts that go into the wiring for the tbi. I'l post some pics later to show u all that hooks up.

[Nazzcu]

Thanks for the replys. No SES light showing and I assume it is because of a wiring issue. I have yet to find a good truck to reference for the connections, so pics of the hookups would be great.

[leegrady]

Upon cold start all computer controlled delivery systems that are functioning normally, without problems, operate in open loop for a few minutes, and the ses light remains off. Mostly, the coolant temp. sensor tells the ecm to go into close loop.

With all those components on your 87 non-operational your ses light should be on.

True tho', the ecm controls the ground to the injectors, and they run on 12v. Shoddy looking splice with the electrical tape.

Just because it is in open loop doesn't mean that's why the fuel pump runs all the time. That is controlled by the fuel pump regulator. High vacuum: low pressure. Low vacuum: high pressure is how that works. Vacuum is highest (manifold absolute pressure) when the throttle plate is closed, (idle), and lowest vacuum occurs at wide open throttle, when more fuel is needed, (high pressure&volume from the fuel pump).

Remember that system has a fuel return line. So fuel is just making the trip up to the tbi and back to the tank.

I would not suspect the reason for the non-op fuel gauge is because of your fuel pump running all the time. The fuel gauge is not controlled by the ecm. I would suspect the sending unit or an open circuit.

If I'm not mistaken the oil switch by the distributor you mentioned is a safety device that will shut off the engine if oil pressure drops too low. These are sometimes mounted down by the starter.

Keep plugging away at it, (no pun intended). Hay, if we can't fix it it an't broke.


'81 GMC K2500 longbed 350 Q-jet/sm465/corp 14bolt semi-floater/dana 60 up front
'95 T-bird 4.6L
Replica '65 Daytona Coupe stroked fordracing 351w w/gt-40 alum. heads, eight single Holley toilet bowls on Offy intake using a modified EEC-4/tremec tko 5sp/ford three link 9" w/detroit locker 3.55 gears 0-60 times around 3.4seconds/1/4mile 11.1/top speed 180mph. This beast will xlo8 harder at 130 than my t-bird with pi heads does in first gear.

[Nazzcu]

Thanks for the help so far. I have been tbi cramming for the last few days. Correct me where I go wrong here. Alot of this is assumption due to not knowing what the previous owner did.

1. I need a new ECM for the 350 because the calculations are different.
2. Idealy new injectors but worst case the 305(if thats what they are) will work.
3. MAP sensor to control amount of fuel routing to the injectors can be either 305 or 350.
4. Fuel pump delivering 9-13 psi.
5. Knock sensor, temperature sensor, VSS.

My main question is how can you tell when everything is functioning properly?

[leegrady]

The truck runs well, and the ses light stays off.

Do you know about jumping the A and B terminal of the ALDL connector with a paperclip, putting the ecm in self-diagnostic mode, and then counting the blinking ses light?

[rfmaster]

Originally Posted by Nazzcu

Thanks for the help so far. I have been tbi cramming for the last few days. Correct me where I go wrong here. Alot of this is assumption due to not knowing what the previous owner did.

1. I need a new ECM for the 350 because the calculations are different.
2. Idealy new injectors but worst case the 305(if thats what they are) will work.
3. MAP sensor to control amount of fuel routing to the injectors can be either 305 or 350.
4. Fuel pump delivering 9-13 psi.
5. Knock sensor, temperature sensor, VSS.

My main question is how can you tell when everything is functioning properly?

Yea, trying to fix hillbilly swap and wiring is always fun. Fuel pump runs constantly because (probably) PO blew up FP pump control circuit in ECM (a simple transistor) and just hard wired FP power circuit by forcing FP relay to close when ignition is on. Or worst - I can only imagine!

1) You do not need a new ECM. A simple EPROM swap will take care of the fuel calibrations (VE tables) when swapping between 305 and 350. If you are JY savvy look for 1227747 ECM with BCC code ASDU or ASDZ. These BCC codes were used with 350 TBI engines.

2) 305 TBI Engine was equipped with 2x 55 lb-hr injectors and 350 truck motors are equipped with 61 lb-hr injectors (5235206). TBI injectors are rated at 13 psi, bit will work up to 30 psi. The same 55 lb-hr injector can satisfy 350 appetite for fuel by simply increasing fuel pressure if you chose not to get larger, 350 injectors.

3) MAP sensors are the same. On OE GM MAP sensor look for 039 or 460 stamping (16137039). These are 1 BAR injectors and can be identified by either green or black connector insert.

4) Stock TBI fuel pressure is 9 to 13 psi (20 % range). Insomuch, fuel pump must be capable of delivering 30 psi dead headed. It is common upgrade to install TPI pumps (3rd gen, etc) for higher fuel pressure. Stock truck engine will do just fine with 13 psi. Anything lower - you may get lean during WOT, which is not good.

5) KS and ESC are different between 350 and 305. For 350 use 10456288 KS and 16128261 ESC modules. CTS and VSS are the same.

All part numbers mentioned above are original and probably have been superseded by updated Delco part numbers.

Get ALDL cable and WinALDL and you will see most critical parameters.

//RF

[Nazzcu]

Thanks rfmaster that was exactly what I needed. I still have one question that hopefully someone can clear up just for my understanding of the system.

Why straightwire the single injector? I plan to disconnect it and see what happens but I just dont get it unless it is another cut wire or bad circuit in the ECM.

[Nazzcu]

Update

I replaced the bulb in the SES light, that was why it was not working it had been removed to clear the light. I ran new vacuum line and connected the MAP sensor, and it works. Sensor off SES on, Sensor connected SES light clears. I disconnected the crazy wire to the injector and it did not effect anything.

[rfmaster]

Originally Posted by Nazzcu

Thanks rfmaster that was exactly what I needed. I still have one question that hopefully someone can clear up just for my understanding of the system.

Why straightwire the single injector? I plan to disconnect it and see what happens but I just dont get it unless it is another cut wire or bad circuit in the ECM.

It is hard to say what the hillbilly did but I venture to guess that one of the wires that provides +12 V IGN to the injector was damaged during swap. ECM acts as a grounding switch to complete injector circuit. When ECM grounds low side injector coil is energized and fuel is sprayed. So, one side of injector connector is tied to 12 IGN hot and the other side is pulled to ground by the switching circuit inside ECM.

Simple check - disconnect injector from injector, with ignition on (engine not running) one side should be +12 V and the other should read hardly any voltage on your trusty DVM.

Search guide to TBI swap on this board - there is a schematic of the injector circuit.

//RF