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post #1 of (permalink) Old 07-27-2009, 03:50 PM Thread Starter
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Chevy TBI Guru's...need a little help

My jeep with it's 5.7L TBI quit on me this morning....acted like it was out of fuel...happened once before when it was at my buddies shop when we were installing the bumper....we know it's a fuel problem.....a squirt of carb cleaner will get it to fire...so ign is ok....

Plenty of fuel in the tank....I can hear the pump running...

Prior to it quiting it was kind of chugging.....then running ok....then acted like it ran out of fuel....not a sudden cut off.

I popped the air cleaner....gave the wires on the injectors a wiggle....then she fired right up and ran fine.

Looking at the wiring...I have a fused hot going to both injectors and then each injector is fed from the comptuer....hence, the only thing common is the hot...but I'm inclined to think that if one injector was not making a good connection then other one would at least keep it kind of running....I think I need to do a voltage test.

Could the regulator in the TBI body be an issue? As a reminder, this engine sat up for about 3-4 years before it was ran again....and yes, I have ran sea foam through it.

I'm also wondering if there is any relationship between this problem and my poor fuel enconmy (12 mpg) and boderline HC readings on the smog sniffer.

AKA DDawg16
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post #2 of (permalink) Old 07-27-2009, 05:23 PM
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I have a Howell TBI on my Jeep 4.2L, other wise stock, motor. When I first installed the TBI the Jeep would run fine, for the most part. However, at times it would hesitate off of idle and then act like it just ran out of gas when I would come to a stop. When it would "run out of gas" I had to restart the Jeep with the pedal floored. It would blow black smoke and then I would have to feather the gas up until the motor started to run normally again. If I let off of the gas to quick after restarting it would die again.

Now, if your problem is similar, I spoke with Howell and they recommended adjusting the idle air mixture. In my application, this required grinding off a plug and then, essentially, turning the idle speed up a bit. I ended up bumping my idle up about 100 rpm during this process and have not had a problem since -- 7 years ago.

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post #3 of (permalink) Old 07-27-2009, 07:15 PM
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Wow, what a coincidence. A buddy of mine at work had the same thing happen. No ideas yet. Have you checked the fuel pressure/volume or the fuel filter yet?

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post #4 of (permalink) Old 07-27-2009, 11:03 PM
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It's been a long time so bear with me.

The injectors actually use a reduced voltage, something like 5-7 volts. You can probably check this with a volt meter however because of the pulse, the reading may fluctuate. You can also crank/run the engine and see the pulse with a regular test light, however it will be dim of course.

I never saw a TBI regulator unit go bad. I have seen the IAC motors gum up and the port within the TBI clog with carbon. Sometimes the entire bottom of the unit can clog up, but you would have definitely noticed this if you had it off for the motor swap.

If your injectors are pulsing but no fuel can be seen, it's a pump problem. As long as you can hear the pump run, the oil pressure switch is working, letting it have power.

I doubt it's injector(s). These are also tough as nails and the engine will run on one.

I still have my GMC electrical/driveability FSM. Are you setting any codes? I can run you through trouble shooting the code/problem or scan and e-mail you the pages if necessary. Let me know if you need anything else.

I would go through and re-check all of your connections, even at the PCM. I bet it's a bad connection or sensor going bad.

Is this the only hammer you've got?
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post #5 of (permalink) Old 07-28-2009, 06:15 AM
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Your significant clue here is:
"""""I popped the air cleaner....gave the wires on the injectors a wiggle....then she fired right up and ran fine."""""

That won't make a pump run, it won't fix an ECM, it won't unclog an IAC, it won't even make your taillights brighter or fix coffee.
All it will do is temporarily make connection to whatever connection was lost. OR - it wiggled the wire so it no longer touched the wrong thing.

Find that.
Splices?
The TBI connector itself?
Connections?
Extended wires?
Worn or melted insulation?
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post #6 of (permalink) Old 07-28-2009, 01:41 PM
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Quote:
Originally Posted by jdoggmoney View Post
The injectors actually use a reduced voltage, something like 5-7 volts.
^^I believe this is wrong^^... the injectors receive a full 12VDC (from usually from a fused/relayed source) and the ECM breaks/makes the ground (via D14 & D16) to fire them.

As I recently finished the TBI swap on the Moss, this stuff is fairly fresh in my mind. The first step to intelligently troubleshooting is double checking the obvious! Confirm the connections are good, that fuel pressure & flow are within spec, & that no codes are being thrown.

Do you own (or have access to) a code scanner or an ALDL cable/laptop?

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post #7 of (permalink) Old 07-28-2009, 02:50 PM
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Check and grease the connections. Sounds like dirty/oxidized contacts. Give ‘em the old in-out a few times.

Beyond that, buy a noid light, they’re pretty cheap. Is there a place to connect a pressure gauge? Don’t know about TBI, my TPI has a connector on the rail.

Doesn’t sound like the regulator is the problem but you should be able to pinch or block the return line to make sure.

A scanner is the best investment you can make. Not a code scanner but a full real time scanner.

Mine went to running rich. I checked everything I could but didn’t find anything. Even tried the parts swap method and failed. It was beyond me so I took it to Precision Tune. They charged me some money but weren’t successful either. I bought a scanner and hooked it up. I checked this and that but nothing seemed unusual so I scanned through everything again checking each reading. The water temp sensor was reading minus 39 degrees, it throws a code at minus 40. Unplugged the sensor and it ran fine then I replaced it.

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post #8 of (permalink) Old 07-29-2009, 01:43 AM
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When I used to work for Chevy, we saw some problems where the wiring harness went through the throttle body. Seems the wires like to break inside the insulation where it goes through that grommet. Might be worth a look.

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post #9 of (permalink) Old 07-29-2009, 01:46 AM Thread Starter
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I have a full scanner.....it was how I fixed my first problem back when I first put in the engine....same problem Taz had....the temp sensor was not making a good connection and it was causing it to run REAL rich....

Yea....checked all the readings....everything is in a 'reasonable' range...

I think tomorrow I'll crank it up and do the shake, rattle and yank test will all the wires.....

AKA DDawg16
84 CJ7, SOA, 5.7LTBI, 4L60E, 35"x12.5, 4.10 gears, F/Det, R/ARB, Full Roll Cage,
D44 Flat top in progress...
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post #10 of (permalink) Old 10-01-2009, 04:03 AM Thread Starter
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An update on my issue.....

I only have my problem when the jeep has been sitting for awhile.....in this case I was out of town for about 2 weeks. I go to start it...starts right up...I get about half way out of the driveway and it dies....no fuel....

I think the fuel pump is loosing prime and is having trouble pulling fuel up. My fuel level is down to about 1/8th of a tank....pump is running but not pulling up fuel.

My fuel pump is a Carter designed for TBI and is mounted on the frame rail in front of the tank. (see pic)

So...at this point it's either a bad fuel pump (less than 2K miles on it) or it's just too high to have enough suction.

I really don't want to go the in-tank route.....should I move it, replace it (with like unit) or replace with different unit?


AKA DDawg16
84 CJ7, SOA, 5.7LTBI, 4L60E, 35"x12.5, 4.10 gears, F/Det, R/ARB, Full Roll Cage,
D44 Flat top in progress...
Link to my Frame up Restore
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