4.3l Engine Idle troubleshooting

Spoke too soon. Put the new O2 sensor it, ran a bit rough for while but then it settled down to 650rpm and stayed there for 30 minutes. No issues. Would rev just fine and return right back to idle.

Made it 30ft up the driveway(slight incline), immediately bogs down, no pedal response, won't idle, dies immediately. Was able to limp it back to the garage. It runs for 10 secs, constantly hunting, idle swings from 1200 down to 400

I did multiple IAC resets/battery disconnects etc. Only thing I can think of right now is the fuel pump putting too much psi to the TBI. I can't remember what fuel pump I have currently in it, but I have 5 fuel pumps in boxes that are brand new, most of them are all different kinds.

I looked in the tank as it was running and fuel was spraying everywhere so maybe I have an over pressured pump that is overwhelming the TBI regulator? I don't have a fuel pressure tester and none of the stores around me rent them.
 
If you have a return line it should not matter. You should be running 9-13 PSI. I run a 75 PSI pump in my Trail Jeepster with 4.3. I bought a pressure guage kit to go behind the throttle body but have not installed yet.
 
I do have a return line that runs all the way back to the tank. I’m running a motobilt fuel cell that uses a TJ hanger. I put a cartridge style pump in it. @R Q, I remember talking to you years ago about the pump. I pulled the pump apart a few months back to re-mount the canister and everything looked good.

Injector spray pattern looks great at the TBI. Using Grok to fact check: when it died on the “test drive” it was very boggy/misfiring. I’m thinking it could be a combustion issue? All my spark plugs are black from running rich for years. Planning on cleaning them really well, checking gap and trying again in the morning.
 
I was having terrible combustion issues on Sweenz and was thinking the motor was done. I had plenty of spark with an inline tester. Finally Ohmed each plug and like yours, they had been run on too much fuel and many other issue and only one Ohmed out right. I replaced them and it made a world of difference.
 
New spark plugs are in. I’ve reset the IAC at least 5 times and it don’t make any difference. Cranks fine, idle swings between 900-400 for about 15 seconds and then dies. Throttle input doesn’t really help/hurt it
 
Got it.

Looked in the tank while it was trying to run and saw what looked like a sprinkler spraying everywhere. Cracked the fuel line and routed it back into the tank and it was very, very weak flow. Pulled the pump out and found this.

1776024595435.png


Put a new pump in and a new piece of fuel hose and she fired right up and held idle. Drove it around the neighborhood and it did perfect. Much more responsive, held idle easily. I'll drive it around a bit more to set ECM fuel trims etc but I think she's ready to go.
 
YJJPWrangler said:
Got it.

Looked in the tank while it was trying to run and saw what looked like a sprinkler spraying everywhere. Cracked the fuel line and routed it back into the tank and it was very, very weak flow. Pulled the pump out and found this.

View attachment 455278

Put a new pump in and a new piece of fuel hose and she fired right up and held idle. Drove it around the neighborhood and it did perfect. Much more responsive, held idle easily. I'll drive it around a bit more to set ECM fuel trims etc but I think she's ready to go.
Click to expand...
I had the same issue on my 4.0. I replaced my line with 5/16 fuel submersible from Summitt. I believe I may have been using 3/8 or it broke down from the gasoline and would not stay connected.
 
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