4.3 TBI fueling issues

YJJPWrangler

YJJPWrangler

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Joined
Jul 19, 2005
Location
Charlotte
Got the fuel pump installed today and it works correctly. Issue is the drivers side injector(new) is dumping fuel into the TBI. Passenger side injector(old) is not doing anything. Could it be a bad pressure regulator? Or a stuck injector? Is it possible for a new injector to be stuck open? I am running a Carter P5000 external fuel pump. This was the recommended pump off Pirate and other sites. Motor is a 91 4.3l out of an S10. Any thoughts?
 
Swap the wires from side to side and see if the problem moves to the old injector. Rule out the ecm.
 
I will try that. Jim’s Performace tested the ECM and said that everything was functioning properly. I went ahead and picked up another injector and a pressure regulator but will try that first. If I switch the wires and the problem persists, would that just be the injector being stuck open?
 
Unless the injectors are new and not "new" from the pull a part, they are 25+ years old and the solenoids do go bad. So the wire switch should tell you a lot. There are different injectors for the 4.3, 5.0, 5.7, and the 8.1 so make sure you got the right one
 
When I got the motor, one injector was missing completely. I bought a new injector from advance and that is the injector that is pouring gas into the TBI. It’s not a spray, it’s not a dribble, it’s a steady stream. The other injector does nothing. To my understanding, it should be a fine spray when the ignition is switched on. Could my fuel pump be over pressured and just blowing past the regulator? The way I understand the regulator works, any fuel pressure that exceeds the working pressure gets sent through the return line back to the tank. If the regulator is bad or stuck “open” could that allow the gas to just effectively free flow?
 
If swapping wires like said above didn't change anything then you either got a bad injector or an oring got damaged on install

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My money on the o ring or sealing surface on the leaking new injector. There's a particular way they get installed.. Lube them well on install and replace the other injector with a parts store new one.. they varnish up and won't spray like they should, or won't at all. Here's a picture of it disassembled.
IMG_20180722_002125852.jpg

<From FSM>
The bottom (smaller) is an o ring and the filter screen.
The top (larger) is a steel backup ring and then a o ring. Be sure to fully seat the larger o ring and back up washer prior to installing the injector. Lubricate seals with ATF. Align lug on injector with notch in cavity. Push down on injector until fully seated.
</FSM>
 
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NC-V said:
My bet is o-ring
Click to expand...

Your bet would be correct. The small O-ring was missing on the bottom portion of the injector. I now have two functioning injectors but now I'm chasing a no spark issue. Fix one issue and another one pops up. Thanks for the help guys!
 
FWIW, TBI in general can NOT have fuel without spark... at least "spark" seen by the ECM ;)

I ran into an issue where the coil was grounded (Bozo visited)... had fuel, but no spark at the plugs/dizzy
 
Thats the same issue I'm having now. After fixing the fuel issue, I had a nice cone of fuel spray during cranking. The jeep didn't start. I pulled a plug and tried to verify spark by grounding the plug to the frame. No spark. I ohmed out the ignition coil and it was bad. So I replaced the ignition coil, rotor, and cap(just to be sure). New spark plugs and wires. Now, I am getting no fuel spray at crank and no spark. The fuel pump does run but will not spray fuel into the TBI unit. All connections are tight. I'm wondering if the ignition control module is bad or if there is something else that I'm missing. I am a complete newb when it comes to wiring so I'm sure I have wired something up wrong.
 
When I get home I'll post up the diagnostic procedure for a tbi no start for you. I have it printed out with my tbi stuff and it'll be easier to find than me looking for it on the computer here at work

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That would be a great help @Tim C:beer:

The harness was cut down by Jim's Performance and everything was labeled and tested. One wire was labeled "Needs to know starter is being cranked". I have that wired to the switched side of my ignition. That should let the computer know that the starter is being "cranked". I'm still running different wiring scenarios in my head to try and troubleshoot it but I'm above my level of knowledge.
 
Ok first if you're reasonably sure the rest of the wiring is good, here are two quick tests to check out the distributor:

1: Unplug the 4 wire connector from the ignition module at the base of the distributor. Pin "C" (which is a purple/white wire on a 88-91 fullsize truck, your color may be different but the letters a,b,c and d should be moulded into the connector if you look close) is the reference wire to the ecm (it gives the computer the rpm signal). Key on, Clip the alligator clip of a test light to the battery POSITIVE terminal and touch Pin C with the finger stabbing end, lol. This puts 12 volts to the ecm each time you touch the test light to pin c the fuel pump should run for a second or two and an injector should spray. If you touch it quick enough the injectors should alternate.

This test confirms the wiring is good between the module and the computer and that the computer is capable of firing the injectors.

2: Plug the 4 pin terminal back up, leave key on. This test will bypass the pickup coil. Remove the cap and unplug the pickup from the ignition module. Cut two 6" or longer 16 gauge or thinner wire. Youll need a 1.5V battery (AA or AAA steal one from your tv remote if nothing else) Electrical tape one stripped end of each wire to the battery. Touch the other end of the (-) wire to the N terminal of the module and quickly touch the (+) wire to the P terminal (closest to the distributor shaft, see the picture i'll post next). Each time you touch the P terminal with 1.5v the coil should fire, injector should pulse and fuel pump should run. If all that happens you have a bad pickup. The module, ecm and wiring are all good. If none of that happens but the injectors pulsed in test 1 the module is bad.

Ive seen pickups ohm good but not fire so this test basically bypasses it with a battery.

Ill take some pictures of the full test in a few and post them up too.
 
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@Tim C that is very helpful. I appreciate you posting that up. I'll try and run those tests tomorrow and report back on what I've found.

Thanks again.
 
In my case, it was a total dumbass maneuver... the coils low side only gets positive VDC, grounds thru feet/mount and the other wire is the tach lead(?).
I had the tach lead grounded and got exactly what you have... fuel/no fire
 
Caver Dave said:
In my case, it was a total dumbass maneuver... the coils low side only gets positive VDC, grounds thru feet/mount and the other wire is the tach lead(?).
I had the tach lead grounded and got exactly what you have... fuel/no fire
Click to expand...
Actually the coil doesn't ground through its feet or the metal square frame. The tach wire is the ground side of the coil. A coil gets 12v constantly, when the points close, or the ignition module or computer applies the ground to the other primary (low side winding) the electromagnetic field builds up around the coil. When the points open or the module or ecm removes the ground, the magnetic field collapses inducing a voltage on the secondary winding which have many more wraps of wire, therefore a higher voltage.

A shorted tach or tach wire will cause a no start no fire because the mag field will never collapse. A tach is just counting the 12v pulse created when the ground makes or breaks.

Some coils ground the secondary winding through the feet or frame but most including GM TPI and tbi ground the secondary through the 12v positive in a round about way.

Long short short the coil doesn't have to be grounded or even bolted down and it'll fire, but the tach and it's signal wire definitely cannot be shorted to ground.

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So this is interesting. I have a tach wire coming from the computer that I have not hooked up yet. I was just planning on hooking it up to the tach(when I get it). From your post @Tim C , the tach needs to be hooked up, my question is where does it get hooked up to?
 
No it doesn't need to be hooked up, but if it is it can't be shorted to ground, such as where it passes through the firewall and chaffed for example.

The tbi and TPI coils have two, two wire connectors. One connection has the 12v hot from the ignition switch, and a white wire that can be used for a tach, but it is optional. The other connection is a short 1 foot long two wire harness that plugs into the module. It has a red wire that provides 12v to the module from the coil (the terminals are connected internally in the coil as a pass through if you will) to power it up. The white wire is the wire the module uses to fire (ground) the coil. The optional tach wire is piggybacked to it similar to the red wire.

Technically if the two wire harness is plugged up and the coil gets 12v power the coil will fire when the engine spins even with the 4 wire connection unplugged from the module, but without the 4 wire connection the injectors won't fire.

Sorry if that got you confused, but no you do not need a tach. Follow my above two diagnosis posts and report back what you find we can get to the bottom of this.

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YJJPWrangler said:
Clear as mud [emoji38]

Getting ready to perform both tests and will report back.
Click to expand...
Maybe this will help. Just remember tach is optional
58f444bf03975b64d82a750250102a30.jpg


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Ok. First test.

Everything passes. Both injectors spray and if I do it apply power fast enough, each injector sprays individually. So, according to @Tim C , this confirms that my wiring is good.

Second test.

Based on the diagrams, I'm assuming the ignition module lies underneath the rotor in the distributor. I hooked up alligator leads to the P and N. I held the other end of the clip to N and quickly touched the positive end of the P wire to the positive side of the battery. Nothing happened. I tried 4 different sets of batteries both AA and AAA. So with this knowledge I'm assuming the ignition module is bad.

Would this be a correct assumption?
 
YJJPWrangler said:
Ok. First test.

Everything passes. Both injectors spray and if I do it apply power fast enough, each injector sprays individually. So, according to @Tim C , this confirms that my wiring is good.

Second test.

Based on the diagrams, I'm assuming the ignition module lies underneath the rotor in the distributor. I hooked up alligator leads to the P and N. I held the other end of the clip to N and quickly touched the positive end of the P wire to the positive side of the battery. Nothing happened. I tried 4 different sets of batteries both AA and AAA. So with this knowledge I'm assuming the ignition module is bad.

Would this be a correct assumption?
Click to expand...
Sounds like a bad module for sure.

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