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86 Jeep Comanche engine shuts off over 3000 RPM or so. Need help


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I have an 86 Jeep Comanche 2.5 l with a four speed stick shift recently added a tachometer and I went to drive it and realized maybe it's not as underpowered as I thought and I was shifting super early. I went to take it above 3,000 RPM and it just died and it'll do it every single time no matter what gear you're in. Spark plugs and wires are good. They are new fuel tank and pump is new. I'm really stumbled here. What could possibly be the problem. Maybe it needs an oxygen sensor or I have no idea if anybody has any ideas or have had this problem. I would really appreciate the help

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2 hours ago, gogmorgo said:

When you say it dies, like, does the engine stumble and quit or is it like you shut the key off?

If you're trying to take off say you give it half or full pedal it's like you turned the key off But if you push the clutch in, wait a second and let the clutch out. It'll start back up and then if you do it again it'll turn back off again

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2 minutes ago, eaglescout526 said:

Perhaps it’s dumping fuel. I only ask about the sock cause mine broke loose in the tank and stopped flow of fuel above 2k

I could try removing the tank and checking it. It's not shutting off at that low of RPM but never know. Also, the idle is a little inconsistent. Sometimes it runs smooth. Sometimes it runs rough. It literally varies. That's why I was wondering if the O2 sensor was bad

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5 minutes ago, eaglescout526 said:

Perhaps it’s dumping fuel. I only ask about the sock cause mine broke loose in the tank and stopped flow of fuel above 2k

When that happened to you, did the engine shut off completely? Because mine literally dies. Totally not running anymore at all. It'll start back up but if you hit that certain RPM again, it'll shut off again

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1 minute ago, eaglescout526 said:

O2 can be a cause of erratic idle. But we recommended cleaning your ground before we diagnose sensors and such first. Mine didn’t really turn off at 2k but it definitely struggled to get fuel to the engine when the sock got sucked up by the pump. 

What do you mean by cleaning the ground? Mine completely turns off like if you push the gas pedal it does not rev up because the motor is not running

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5 minutes ago, eaglescout526 said:

O2 can be a cause of erratic idle. But we recommended cleaning your ground before we diagnose sensors and such first. Mine didn’t really turn off at 2k but it definitely struggled to get fuel to the engine when the sock got sucked up by the pump. 

Is there a way I can send you a video of it? So you can see exactly what's going on? Because I could probably do that tomorrow morning

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1 minute ago, eaglescout526 said:

Like there’s Cruiser54’s tips we recommend every MJ owner do to eliminate any issues with their electronics. 

Well I know that the engine ground and all of that is good because when I had gotten the truck I put a new motor in it and replaced the engine ground

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22 minutes ago, eaglescout526 said:

There’s a ground behind the drivers tail lamp that is for the fuel pump. 

Also in your tag it says you have an 84 XJ hurricane carbed set up for four-wheel drive. Is it hard to swap these to carbureted and not deal with any of these issues? Because I've been wanting to switch mine to carbureted but everyone I've talked to said that there is no way because they don't make a HEI distributor for them

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4 minutes ago, Stephen staly said:

Also in your tag it says you have an 84 XJ hurricane carbed set up for four-wheel drive. Is it hard to swap these to carbureted and not deal with any of these issues? Because I've been wanting to switch mine to carbureted but everyone I've talked to said that there is no way because they don't make a HEI distributor for them

My XJ came from the factory with a carb. I’m going to swap it tot TBI in the future. 
 

 

And yes a film of what’s going on might help us see what it is exactly doing. 

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1 hour ago, eaglescout526 said:

My XJ came from the factory with a carb. I’m going to swap it tot TBI in the future. 
 

 

And yes a film of what’s going on might help us see what it is exactly doing. 

I would gladly trade you everything lol but I'll try and get a video in the morning 

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2 hours ago, Stephen staly said:

Because I've been wanting to switch mine to carbureted but everyone I've talked to said that there is no way because they don't make a HEI distributor for them

 

Check junk yards for '84 and '85 XJ Cherokee 2.5L. Or ...

 

https://www.summitracing.com/parts/aaz-84-4495/make/jeep

 

https://shop.advanceautoparts.com/c3/distributors/16062?filterValue=isFitted_uFilter%3AExact Fit&term=distributor&categoryGroupId=16062

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Go to www.cruiser54.com and complete Tips 1 through 5 as applicable. Also the fuel pump ground fix I will post in it's entirety.

Check the hose from the throttle body to MAP sensor. Attachment shows the 4.0 but you get the idea.

Check the vacuum hoses at the intake manifold.

Make sure the intake manifold bolts are tight. 

Make sure vacuum hoses are routed correctly.

IMPROVING THE FUEL PUMP GROUND

The fuel pump and fuel tank sending unit ground at a sheet metal screw up behind the spare tire on an XJ, XJ-Body-Ground.jpg?resize=300%2C162and behind the driver’s taillamp on an MJ.

Not only is a sheet metal screw a lousy way to ground things, this ground path is long and travels through some connectors that are prone to corrosion and moisture.

Locate the black wire on  the HARNESS side of the fuel pump/sender 3 wire connector. Remove a 6″ length of the split loom covering. Strip back about 1/2″ of insulation from the BLACK wire.1-fuel pump ground MJ

Take your new ground wire, preferably at least 14 gauge and 12 to 18 inches long as needed, strip it about 3/4″, and wrap it around the exposed part of the harness plug wire.1-fuel pump ground mj-002Solder the connection. Tape it up and reinstall the split loom covering.1-fuel pump ground mj-003

At the other end of your new ground wire, add a crimp on eyelet. Attach the eyelet under a bolt that goes directly into the chassis. Be sure to clean the attaching point til shiny and apply OxGard to the contact surfaces.1-fuel pump ground mj-004

 

Until all of this is COMPLETED, not just gandered at, you're peeing into the wind. 

 

TB to MAP tube 2.jpg

4 cyl TB hoses.jpg

vacuum diagram 4 cylinder TBI.jpg

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