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Discussion Starter · #1 ·
Hey Guys,

I was driving my jeep Saturday and it started hesitating between shifts, popping out exhaust when slowing down in gear and then idling really low when stopped. I took it home and now it wont start unless I constantly give it gas. If I let off the gas it dies.

Really confused what's going on and hoping for some guidance.

It's a 89, 4.2 5 speed. Has a motorcraft carb and the nutter bypass has been performed . In 2018 I did spark plug, wires, cap, rotor and fuel filter. Also replaced intake manifold gasket and ignition control module in 2018. No real issues until now. Only drive it a couple times a week in nice weather.

Any ideas what else to do?

Thanks in advance!
 

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1990 Jeep Wrangler 4.2L
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It could be a number if things but I'd start with looking for any vacuum leaks. It's possible you're having to give it gas to compensate for too much air.
 

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'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
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One small thing I do on a regular basis anytime I start to get a hint of poor performance, I drop in a new set of plugs. We use the least expensive copper core champion 82 or autolite 985 plugs in the 4.2's. With the carbs and only occasional use they tend to get slightly fouled and a new set usually cleans that crappy idle right up.
Next I'd inspect vacuum lines as warboomer suggested.
Then I'd look at distributor and timing.
Good luck.
 

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Discussion Starter · #4 ·
I was thinking vacuum as well but not quite sure how to check without the jeep running. I went and retorqued the manifold bolts. A couple were a little lose but did not make a difference after I tightened.

Ilwgen I get it running by constantly giving it throttle, It sounds rough and sputtering. I also noticed some smell of gas and the area my carb is a little wet with fuel.

Wondering if I need some new gaskets 9n Ky carb...

Thoughts?

Thanks!
 

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Have you torqued down the studs that hold your carb? You could absolutely be getting a huge vac leak there as well as depriving the engine of gas
 

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'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
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^^^ what he said...
 

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Discussion Starter · #7 ·
Si, I have gotten all new gaskets for the motorcraft carb, tightened down carb mounting nuts but that did not help. I replaced the pcv valve and fuel filter. That has allowed me to get the jeep to idle with my foot on accelerator but once I let off of it, the idle slowly falls and dies. Also, there is still popping out exhaust and running rough.

Any other ideas?

Thanks!
 

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If you can get an assistant to keep the Jeep running while you check the timing, that's where I would start. I'd also do a Seafoam gas treatment. If that doesn't help or only helps a little bit, I might rebuild the carb.
Have you replaced the plugs yet?

Good Luck, L.M.
 

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Discussion Starter · #9 ·
I have an update and hopefully it can help point me in the right direction.

I got some dry gas fuel treatment and after I put it in it the idle smoothed out quite a bit but eventually ended up dying again.

I pulled the hose off the fuel pump and put it in a cup with different fuel. Once the jeep started sucking up fuel from the cup, it idles nicely. So, I filled up.the tank with some of this fuel but it's still idling likes its cammed, blowing smoke and dies.

So. Is just the fuel seen bad? Should I fill it up with more fuel treatment? Sea foam? Anything else it might be?

Thanks!
 

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Could very possibly be your fuel pick up is clogged...or clogged lines from the tank.

To find out my fuel pick up was the issue, I took a fuel line and ran it to a gas tank mounted in the cab and drove down my street. It drove fine so I knew the issue was behind the pump.
 

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When I went to drop my gas tank to change out a rusted skid plate, I wanted to drain my tank. I couldn't get a siphon hose in the regular gas filler, behind the license plate. I disconnected the filler hoses at the tank and used a cheap Harbor Freight liquid pump to drain almost all the fuel from the tank.

What I would do is disconnect the fuel pump to gas tank hose, remove the gas cap and blow compressed air from the pump end toward the gas tank. Then, I'd drain the tank (see first paragraph) and put 5 gallons of fresh gas in the tank along with a couple cans of dry gas.
Test drive the Jeep and if it's cured, report back and let us know how it went. If the problem gets cured for a while but comes back, then, I'd drop the tank, pull the sending unit, clean the bottom of the tank real well. Check the pickup sock. If it's clogged, you may need to buy a new sending unit if you can't buy a sock only. While the tank is on the deck, check the top of the tank for any signs of leaking from the roll over valves. Replace any rubber vent lines that look the least bit iffy.

You've already determined the problem is prior to the fuel pump (we hope). So, blowing the lose and replacing any gas or gas & water is the next step.
Hopefully that will do the job.

Good luck, L.M.
 
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Discussion Starter · #12 ·
Hey guys,

Bringing this back...

I drained all my gas and put new gas in. Unfortunately, that did not help. So, I un hooked the mechanical fuel pump and hooked up the electronic fuel pump I have.

With the electronic fuel pump, i am able to get it to idle but it bucks and runs terrible if i try and drive it. While just idling, I hear a very loud hissing toward the rear of the motor. Because of this I found a diagram for the motorcraft 2100 carb vacuum routing, found a few lines I did not need, capped ports and made sure everything was accurate. I also replaced the pvc grommet because that was old and brittle.

After all this, it idles a little better, but still sputters through exhaust and is undrveable. And, i still hear a very loud hissing with motor running and then a suction sound when I turn the engine off.

This leads me to beleive there is still a massive vacuum leak somewhere but i cant determine where. I replaced the intake manifold gasket a couple years ago because of a vacuum leak, but do you think it could have failed that quickly? It did go through and tighten the manifold bolts per the specs in the haynes manual again and a few were just a little loose.

Any other ideas what could be causing this large vacuum leak?

I know this thread is old but hoping to bring it hack with some new info to get some needed guidance.

Thanks!
 

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Try using a 3' long section of heater hose or a paper towel tube. Put one end of the hose or tube to your best ear and point the open end at different places around the engine compartment. The first place I'd aim at is the brake booster.

You may be dealing with more than one issue. Fuel being one and vacuum being the other. Since you can now get the Jeep running, I'd concentrate on the vacuum leaks.

Keep us posted on what you find.

Good Luck, L.M.
 
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Discussion Starter · #14 ·
Hey Guys,

Still working on this and having no luck. It's still just starting then dying and only stays idling if I give it gad. Things I've done...

Replaced spark plugs
Replaced intake/exhaust manifold gasket to eliminate vacuum leak
Rebuilt carb and cleaned/soaked
Did compression test and engine is within spec per Haynes manual
Bypassed fuel tank and ran fuel pump to gas can to make sure gas is good
Alternated between electric and mechanical fuel pump to make sure pump is good

None of this has gotten the jeep to be able to run and I am running out of ideas.

Anything else I can try? Can the carb just be bad? It is squirting a good stream of fuel when I hit the accelerator but it seems like it is just running out of gas. Again, only stays running if I am depressing the accelerator.

Thanks!
 

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How old is your timing chain? Have you checked your timing?
Have you tried running it with the air cleaner off to eliminate a clogged air filter as a cause?

Good Luck, L.M.
 

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Well... this is what I would do.... First verify that there is proper flow of gas into the carb. Are there ANY fuel filters between the gas tank and the carb? if so, they would be a suspect! Second, try having someone crank the engine while (safely) verifying that the mechanical fuel pump is pumping gas ( carb end of the fuel hose disconnected, and in a container to catch the fuel). Third, try leaving the gas cap ( fuel filler) OFF .... if the car magically runs, then it is likely a clogged vent. It is also possible that you may need to rebuild your carb. If something got jammed into the jets, it could explain the behavior. Start with these things and let us know..
 

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Discussion Starter · #17 ·
I have been starting it with the air cleaner off.

Not sure if the chain was ever replaced so I would assume it is the original. 145,000 miles on motor. I'm confused how to check timing without the motor running. I did pull #1 plug and made sure the rotor was pointed at #1 in distributor at tdc. It was lining up when I did that.

Thanks!
 

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Just re-read the thread... looks like you eliminated bad vent, bad fuel pump, etc.... Carb is still a suspect, IMO. Timing is another suspect... I believe that car has a magnetic pickup thingy in the distributor - which could cause issues if it is intermitent / bad...
 

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One more thing... to help narrow down fuel vs. timing issue.... if you get it running, and carefully spray little bursts of carb cleaner into the throat of the carb, will it idle / run good without having to press the gas pedal? if so, it is likely a fuel / carb issue...
 

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Discussion Starter · #20 ·
So, I'm pretty clueless to carbs. Soaked the carb in Berryman carb cleaner, blew everything out with compressed air, got a rebuilt kit, replaced gaskets and everything else in that kit.

It just seems like it is not getting gas after it initially starts unless I depress the accelerator.

What else can I check on the carb to ensure it's working properly?
 
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