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Trouble shoot 4.3: swap into TJ, warm run problem.

bad zuki said:
My yj had a 350 tbi with that pump, It's currently really happy with the LS infront of it too.

Have you cleaned the fuel filter or tank? It might be sucking up dirt.
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I havent dropped the tank yet. It mostly ran good before this weekend.
 
It is running a return line.

MSD 125 psi pump.

Cap and rotor looks Okish. Some white crust on the terminals. I'll throw one on it as well.

I havent dropped the tank. Unsure what that will accomplish now having a return line.
 
First off what are the specs on this 4.3 engine?

I recently was chasing down a random stutter and occasional shut off on my TBI 5.7 I put in the S10. No codes at all.

Everything on that engine could potentially be 30 something years old. TPS I think had a bad spot or a loose pin. Replaced the whole sensor package under the air cleaner, new coil, new GM ignitor properly bonded to the dizzy, new GM pickup, etc.

Rebuilt the whole distributor because aftermarket is trash. The pickup also fell apart in my hand so I think that and the TPS were the culprits.

Long story short for the few dollars all this cheap crap costs is fire up the parts cannon and go through it. If you have no history on it and want it to be reliable you need to.

Last engine swap I did the engine had one bad injector and one clogged one. Bought a cheap pulsing tool off Amazon and cleaned them myself. You just don't know what shit you are getting so it's worth spending some money.

S10 has run flawless since. Fuck diagnosing 30 year old shit. I'm not going to sit on the side of the road over a $30 sensor. My time is worth more then that.
 
Is it a 4.3l Vortec? If it is it probably has that "spider" style fuel injector setup that's inside the plenum of the intake manifold.

If so that style of injectors needs a fairly high pressure, like 55-60psi otherwise they won't work at all. If this is the case, the stock TJ fuel pump module likely won't have enough pressure.

Like most have been saying, it sounds like your fuel tank isn't venting properly. Fix that and enjoy your well running Jeep.
 
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The Jeep already has a vented cap, I didn't notice. It must be blowing air out. So, the vacuum idea is bunk. I tested it, it is working. :homer:

Replaced cap/rotor no change.

Fuel pump could still be bad. Will order one.

Will try plugs/wires next.
 
That's a classic igniter issue. Let it sit to cool off and it starts right up like nothing ever happened.
 
20241028_172005.jpg

Whatever year has the plastic intake.

It was sputtering in 3rd coming out of a roundabout then, like a switch was flipped was back running well.

I can floor it, and accelerates fine after it sputters a bit.
 
Trashman said:
20241028_172005.jpg

Whatever year has the plastic intake.

It was sputtering in 3rd coming out of a roundabout then, like a switch was flipped was back running well.

I can floor it, and accelerates fine after it sputters a bit.
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Can you hook up a harbor freight fuel pressure tester on the engine and run it inside the cab. Monitor the pressure when it stumbles.
 
Gravy said:
Can you hook up a harbor freight fuel pressure tester on the engine and run it inside the cab. Monitor the pressure when it stumbles.
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Not sure how those attach. The truck has 2 AN fittings on the back of the manifold.

I didnt see a shrader fitting on any manifold rails.
 
I am using this to fuel my gen1 sbc with fast ez-efi
just take out tj fuel regulator and replace with this
100 psi of the factory XJ / TJ / LJ fuel pump


Kit FSK-9704RD, TJ fuel regulator delete & bypass kit

Doing a special project and just need the regulator delete bypass kit? This billet machined and ported assembly will permit the full native ~100 psi of the factory XJ / TJ / LJ fuel pump, which you can then regulate further down the line per the needs of your project.
$88

1730166466145.png
 
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Trashman said:
20241028_172005.jpg

Whatever year has the plastic intake.

It was sputtering in 3rd coming out of a roundabout then, like a switch was flipped was back running well.

I can floor it, and accelerates fine after it sputters a bit.
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That certainly looks like a Vortec motor. Somewhere on those 2 metal fuel lines that go into the top center of the manifold you should find a test port to hook up a fuel pressure gauge and do what Gravy recommended.
 
I have been reading about the MSD 2225 pump.

It seems that if the output flow was restricted it makes the pump work harder, which makes sense.

I will likely order another 2225 pump, but they prefer to be fed by constant flow (pull from the bottom of a tank) but can work if mounted within a foot of the tank and still pull. The rep told the source of the article it is a pusher, not puller pump.

Mine is mounted to the bottom of the Jeep tub, so I will remount it to the frame rail which should get me 1/2 way downish on the tank, and should thereretically create the suction needed due to physics.

The authors S10 was seemingly dealing with the same shudders mine seems to be afflicted with.

I am guessing, my pump was indeed working too hard, not at suction, but return pressure as the fuel cap only allows air in, and it was building pressure.

He also had to replace some fuel lines in his tank that were potentially collapsing.
 
They Y ed the return lines to route through each vent, and made a tube to go through the old fuel sending unit/pump
 
Local parts house had a factory punp/sending unit rated at 49psi

They also had a pump that seemingly replaces the 49psi for 60psi.

Grabbed those and will give it a whirl.
 
Pump is in, runs well. I don't have to listen to the loud MSD pump......



Didnt fix the issue.:homer:
 
Trashman said:
Pump is in, runs well. I don't have to listen to the loud MSD pump......



Didnt fix the issue.:homer:
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Which pump is a really important question to answer, the 49psi or the 60psi one? And have you found a way to actually verify fuel pressure yet? This is really bare bones info needed to even attempt making helpful suggestions for your problem.
 
It actually ran and sounded a little better. Still stumbles off idle for a second or two if you stab the throttle after warmed up. Cold seemed good.
 
The time/money spent today doesn't bother me as much as it should because I got rid of a fuel leak (the top of the tank fittings were leaking) got rid of the annoying MSD pump drone, got the pumo back into the tank (I preffered it that way) and will get the hoses/wiring cleaned up from the previous owners handiwork.

Still not the outcome I would prefer however.
 
TanTJJim said:
Which pump is a really important question to answer, the 49psi or the 60psi one? And have you found a way to actually verify fuel pressure yet? This is really bare bones info needed to even attempt making helpful suggestions for your problem.
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I agree, I should check the fuel psi. Likely need a trip to HF I guess.

I havent found an OBDII port yet, my scanner would tell me if the computer monitors that.
 
Trashman said:
I put in the 60psi pump into the stock TJ assembly
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Trashman said:
I agree, I should check the fuel psi. Likely need a trip to HF I guess.

I havent found an OBDII port yet, my scanner would tell me if the computer monitors that.
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Verifying the fuel pressure will help out immensely for troubleshooting.

edit, even if you find an OBD2 port the computer won't be able to tell you what fuel pressure is, but there's tons of other stuff that could help like fuel trim and MAF readings.

I assume there's still a return line going back to the tank from the 4.3l fuel system, is this correct? If so did you change it to where only 1 of the 2 vents are now being used for the return or how is it setup?

To confirm, the issue you have is that it loses power after an hour of driving or are there other symptoms?
 
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