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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: st3vomettler on August 01, 2018, 08:03:58 PM

Title: Carb to tbi conversation
Post by: st3vomettler on August 01, 2018, 08:03:58 PM
Iím converting my 77 c10 from carb to tbi. I took the wiring harness inside and out, intake, tbi and all sensors needed. I have a donor 90 c1500 that all the parts came off of. Iím getting spark but no fuel it will start with gas squirted in to tbi but pump and injectors wonít work. Need help please
Title: Re: Carb to tbi conversation
Post by: bd on August 01, 2018, 10:54:26 PM
Check the ECM-I (ignition power) and ECM-B (battery power) fuses in the fuse box using an incandescent test light.  Make sure all of the ECM grounds are properly connected and 100% functional.  Measure the fuel pressure using a proper gauge.  Will it start if you connect a fused jumper wire between battery positive and the 4" red pigtail with a single black connector at the fuel pump relay?
Title: Re: Carb to tbi conversation
Post by: st3vomettler on August 02, 2018, 06:08:48 AM
I donít have a test light but I did change the two fuses with new ones and there isnít a 4Ē red wire coming out of my fuel pump relay pig tail but there is a smaller red wire and I jumped it to battery and still nothing and all grounds are bolted down.
Title: Re: Carb to tbi conversation
Post by: bd on August 02, 2018, 08:44:40 AM
You need to determine whether there is power at the two ECM fuses - I recommend that you procure a test light.  Post a pic of the fuel pump relay
Title: Re: Carb to tbi conversation
Post by: Irish_Alley on August 02, 2018, 03:21:18 PM
this might help you
(http://forum.73-87chevytrucks.com/smforum/index.php?action=dlattach;topic=29825.0;attach=27609;image)
the red wire is the "C" plug
Title: Re: Carb to tbi conversation
Post by: Irish_Alley on August 02, 2018, 03:24:24 PM
(http://forum.73-87chevytrucks.com/smforum/index.php?action=dlattach;topic=29825.0;attach=27607;image)
(http://forum.73-87chevytrucks.com/smforum/index.php?action=dlattach;topic=29825.0;attach=27605;image)
Title: Re: Carb to tbi conversation
Post by: st3vomettler on August 02, 2018, 05:55:46 PM
Iím getting power to both fuses but no power to fuel pump
Title: Re: Carb to tbi conversation
Post by: Irish_Alley on August 02, 2018, 06:08:19 PM
are you getting power to the relay? what happens when you connect B+ to the red wire "C" on the relay.
Title: Re: Carb to tbi conversation
Post by: Irish_Alley on August 02, 2018, 06:08:53 PM
but x2 on this

You need to determine whether there is power at the two ECM fuses - I recommend that you procure a test light.  Post a pic of the fuel pump relay
Title: Re: Carb to tbi conversation
Post by: st3vomettler on August 02, 2018, 06:17:17 PM
The picture of the fuel relay wonít upload itís to big but the wires are org, grn/wht, rd/blk, rd/wht and blk/wht
Title: Re: Carb to tbi conversation
Post by: Irish_Alley on August 02, 2018, 06:49:39 PM
this one?
Title: Re: Carb to tbi conversation
Post by: st3vomettler on August 02, 2018, 07:11:09 PM
I checked fire at fuel relay pig tail only got fire at orange wire and when I jumped orange wire to other wires nothing happened but the black wire sparked
Title: Re: Carb to tbi conversation
Post by: bd on August 02, 2018, 07:39:52 PM
The black/white wire is relay ground.  Orange is B+ powered through the ECM-B fuse.  Green/white is relay control from the ECM.  Do you know how to read a wiring diagram?  Do you have a voltmeter?
Title: Re: Carb to tbi conversation
Post by: Irish_Alley on August 02, 2018, 07:51:20 PM
dont jump wires unless you understand how they work. if you jumped orange to black you prob blew a fuse.

Title: Re: Carb to tbi conversation
Post by: st3vomettler on August 02, 2018, 09:05:14 PM
All furs are good and the fuseable links are getting power past them and yes I have voltmeter and no I donít really now how to read them not my sting suit
Title: Re: Carb to tbi conversation
Post by: bd on August 02, 2018, 11:22:41 PM
Disconnect the wiring harness plug from the fuel pump relay.  Connect your voltmeter to a verified ground and probe the green/white wire at the F/P connector.  Have an assistant key the ignition ON w/o attempting to crank the engine.  Does the meter measure 12 volts on the grn/wht wire for a few seconds and then drop to zero?
Title: Re: Carb to tbi conversation
Post by: st3vomettler on August 03, 2018, 06:09:34 AM
Just tried that and no power coming from grn/wht wire when key is turn on
Title: Re: Carb to tbi conversation
Post by: bd on August 03, 2018, 09:47:39 AM
The green/white wire connecting to the fuel pump relay that you verified has zero power when the ignition is first keyed ON is CKT 465 (fuel pump relay driver) from the ECM.  Purchase or borrow a scan tool and connect it to the ALDL interface that should be accessible under the dash (assuming you acquired it with the rest of the TBI harness).  The ALDL is the interface port for the ECM and is a huge advantage during diagnosis.  Determine whether there is any communication available with the ECM.

Pick up some CRC brand QD or equivalent electrical contact cleaner.  With the ignition switched OFF, clean the two harness plug connections to the ECM.  It may be a steep gradient under the circumstances, but you need to learn the basics of reading a wiring diagram.  You can find factory wiring diagrams and the emissions and drivability manuals in the Technical Forum (http://forum.73-87chevytrucks.com/smforum/index.php?topic=30115.0).

Make absolutely certain that all ECM grounds to the engine and body are, in fact, connected and flawless, and that none were overlooked during installation.  Use your voltmeter or a test light to verify that 12-volt battery and ignition power is reaching the appropriate pins of the ECM while referencing the appropriate wiring diagram.  Power and ground are crucial to TBI function.  However, DO NOT randomly probe wires with an incandescent test light or you will run the risk of damaging the ECM.  Trace out the ECM/TBI harnesses to make sure that no wires were inadvertently chafed to ground or severed during installation.  If all of that fails to restore power to the fuel pump relay, see the attached image...
Title: Re: Carb to tbi conversation
Post by: st3vomettler on August 03, 2018, 11:19:04 AM
Ok I will try that when I get off work Iíll carefully look over all connections and grounds making sure everything thing is right and Iíll let yíall now what I come up with
Title: Re: Carb to tbi conversation
Post by: st3vomettler on August 04, 2018, 07:54:32 PM
Weíre my wiring harnesses that fasten to fuse box on fire wall has a bunch of black goo on it and I noticed that some of the male ends didnít go in fuse block so Iím going to widen fire wall a little to allow more clearance
Title: Re: Carb to tbi conversation
Post by: Irish_Alley on August 05, 2018, 02:37:25 AM
the black goo is a good thing
Title: Re: Carb to tbi conversation
Post by: st3vomettler on August 05, 2018, 06:25:02 AM
Ok just making sure Iíll update when I widen whole for fuse block
Title: Re: Carb to tbi conversation
Post by: st3vomettler on August 05, 2018, 09:12:56 AM
On the aldl how can I check to see if Iím getting power to it I donít have a scan tool but I have test light and voltmeter and notice the neutral/ park wire got caught under valve cover and it had a four prong pigtail were my trans only has two prong sensor
Title: Re: Carb to tbi conversation
Post by: st3vomettler on August 05, 2018, 05:15:35 PM
I got fuel pump to kick on now but injectors still wonít fire
Title: Re: Carb to tbi conversation
Post by: VileZambonie on August 05, 2018, 08:19:27 PM
well how did you get it to kick on? Are you bypassing things or is the system functioning correctly and we're onto another problem?
Title: Re: Carb to tbi conversation
Post by: st3vomettler on August 05, 2018, 08:31:37 PM
I watched a video on what wires need for tbi to work and he used prp/wht (c9) for tac on dizzy and the pink/blk (a6) for ecm power and once I did that fuel pump would kick on but injectors wouldnít
Title: Re: Carb to tbi conversation
Post by: st3vomettler on August 07, 2018, 07:10:28 PM
Is there something that Iím missing because I still can not get it to run with power going to computer and fuel pump coming on it still will not run I checked to see if the injectors were pulsing but there not can some one please help I check over all connections and fuses and there all hooked up and I canít find any more grounds and cleaned computer connections and fuse block still no power to injectors
Title: Re: Carb to tbi conversation
Post by: VileZambonie on August 07, 2018, 08:26:21 PM
I am not trying to sound harsh but this is not a job you should begin without the basic understanding of what the system needs to operate as well as having the tools and equipment to troubleshoot it. Thus far you have not been able to provide good answers to any of the questions that will lead you to the fix. So if you go back through this thread and read every post and clearly answer the questions, you will find your problem. It's difficult to assess what is going on and what exactly you are doing at this point. If the condition is crank no start:

Do you have spark, do you have injector pulse, do you have fuel pressure, is the distributor properly timed?
Title: Re: Carb to tbi conversation
Post by: st3vomettler on August 07, 2018, 09:15:51 PM
Yes I have spark and fuel pressure but no injector pulse it starts almost immediately when gas is poured in tbi and I understand I thought it would be easy to do but I was wrong. I have a 90 Silverado (that was my dads) with tbi and I thought that if I take Intake, wiring harness, computer, cab fuse block, fuel tank and all sensors and transfer it to my truck, hook all sensors and fuel pump it would run.
Title: Re: Carb to tbi conversation
Post by: VileZambonie on August 08, 2018, 02:58:24 AM
Did you get a test light yet?

Disconnect one of the injector harness connectors. Connect your test light to ground and probe the injector terminals with the key on. Do either of the terminals illuminate the test light?
Title: Re: Carb to tbi conversation
Post by: st3vomettler on August 08, 2018, 06:05:29 AM
No but I been doing some research and on 88-96 thereís a different style neutral safety switch for Manuel trans and this truck has it and I didnít now what it was till now Iíll try to post a pic of it
Title: Re: Carb to tbi conversation
Post by: st3vomettler on August 08, 2018, 06:08:03 AM
Neutral safety switch
Title: Re: Carb to tbi conversation
Post by: Irish_Alley on August 08, 2018, 07:27:04 AM
not 100% sure but would the engine crank at all in a manual without pressing in the clutch? thought it wouldnt do anything.

but did you hook the OBD system up? is there a way to get the check engine codes if there was any?
Title: Re: Carb to tbi conversation
Post by: Irish_Alley on August 08, 2018, 10:11:43 AM
try this
Title: Re: Carb to tbi conversation
Post by: Irish_Alley on August 08, 2018, 10:22:07 AM
Heres the A4 if you need them
Title: Re: Carb to tbi conversation
Post by: Irish_Alley on August 08, 2018, 10:28:05 AM
and A6 if you need it
Title: Re: Carb to tbi conversation
Post by: st3vomettler on August 08, 2018, 11:17:04 AM
Thank you Iíll get a scan tool from work to see if it can pull codes
Title: Re: Carb to tbi conversation
Post by: st3vomettler on August 13, 2018, 08:34:58 PM
Finally got my truck running. There were some more connectors by computer that wasnít hooked up that went from fuse block back to computer and hooked my distributor tach to computer and it fired up now on to new problem with clutch hydraulic system.
Title: Re: Carb to tbi conversation
Post by: haroldwca on August 28, 2018, 09:20:27 PM
Just a thought here:  On a vehicle that was built before computers controlled spark, fuel delivery, and practically everything else, most electrical circuits were designed to switch OFF when the key is in the START position, to send the maximum current to the starter.  Converting to an electric fuel pump requires the voltage to the fuel pump to be ON even when the key is in the START position.  If the voltage to the pump is inadvertently connected to a circuit that is OFF with the key in START position, the vehicle will not start due to no fuel pressure.  You probably already know that, but I throw it out here just in case.