Fuel/Performance Issue... immediate help requested

[dasbrick]

Started today. Out of the blue.

 

Patient: 87 MJ, 4.0L 6 Cyl

 

Symptom: VERY throaty under load, first gear, second gear are both hard to accelerate, its bucking and coughing so bad, third and fourth better a little, but still very hard to speed up. Fifth is non existent because i can't GET THERE. Smells rich in the fuel. throttle cable moves and springs back with little trouble.

 

Signs: rough engine is not present, or very little when in neutral. Only appears in gear. Very light gas makes it drivable, but when given a little more, roughness begins.

 

Treatment done: Changed cap and rotor. No effect.

 

This is a daily driver MJ. Immediate help requested.

[STERLING STINGER]

i would start checking my vacume lines first if that happened to me... :dunno:

[Unglar]

Do the fuel injected systems have a vacuum advance? This sounds like an issue I had way back when, on my carburated Mustang when the vacuum advance went haywire.

[Squeegy410]

Yeah i would definately check all vaccum hoses. I was ready to replace all the plugs wires and distributor on a friends car when i discovered it had a break booster vaccum hose loose. sounds like a similar problem

[kro10000]

Sounds like a fuel filter/pump, not sure why itd smell rich though. Id pull the plugs and take a look at them

[dasbrick]

Went to a boneyard today that has a hefty amount of XJs, and pulled a throttle sensor off another RENIX engine. (And saw a VERY nice MJ and took the tailgate...)

 

Replaced the sensor... it did NOT fix the problem.

 

Do we have a picture or guide to all the vacuum hoses so i can know which to trace?

[Squeegy410]

get the tail lights and check for a d44 in that boneyard ;) but back to the point check this site for the vac hose diagram... it has alot of diagrams. http://www.greatlakesxj.com/tech.html

[Oizarod115]

I'm thinking fuel pump checking out, sounds like it's got enough pressure/volume to run at idle but once its under load it hasn't got enough to run properly.

[Eagle]

I don't know what "throaty" means to you ... to me a "throaty" exhaust would be something deep, mellow and powerful, like a Ford Mustang V8. But ... for your symptoms, it sounds like a clogged catalytic converter.

[dasbrick]

It's not the cat. Thats all I will say.

[DJM/78]

I had a distributor that was grounding that caused the same problem , took me forever to find it because it only did it under

heavy throttle in gear . 1-2-3 were terrible and yeah no 5th . Thing is once I tested the Dist. , It worked fine .

 

Under heavy throttle older motor mounts flex and torque out and caused a clearance issue with the block and the dist.

 

It could be a number of things but I'd start with spark since you can still smell fuel ... :dunno:

[dasbrick]

Not the fuel pump. Not the filter (anymore). The rail is getting fuel. But the guy I go to for Jeep stuff alot said it might be bad fuel. the gas station i got it from has had bad fuel for him before.

[STERLING STINGER]

add that lucas stuff

[Oizarod115]

if it was a fuel pump issue it wouldn't be THAT you were getting fuel it would be HOW MUCH fuel you were getting.

 

i replaced the fuel pump in an astro van over the summer to fix a no-start, and it came back 6 months later with an intermittent loss of power, stumbling, just generally running like crap. warrantied the (ac-delco) pump, and its good again.

 

do you have a pressure gauge to use on the fuel rail? if so you could also test the fuel pressure regulator

[dasbrick]

I could look into that, where could I get one that I can place in a line joint, like the fuel filter?

 

Also, whats the PSI on that? 40?

[Squeegy410]

if you think your fuel has water in it you can pour about half a bottle of rubbing alcohol in your tank. Gasoline (especially octane) is hydrophobic and won't mix with water, and of course water won't burn on its own, but if you put soem rubbing alcohol in your tank it is hydrophylic and will mix with the water and cause it to burn. Its a pretty simple solution to a big problem

[dasbrick]

well i had already drained the tank and put a gallon of 91 octane in it. It idles higher (i blame the octane), but the problem persists.

[DJM/78]

What does the top of the spark plugs look like ?

 

Yesterday I had the same problem , so last night I drained the tank , added 87 with some Techron fuel system cleaner and

some Lucas oil fuel system cleaner and lubricant . Drove it around for a while and got some of that crap out of the injectors .

Then this morning I let it idle for about 30 min .

 

It already runs better , starts up better and took some of the valve noise out of the eng.

 

It will probably take a full tank or two to fully do its job .

 

I also cleaned all of the spark plug prongs and put a new fuel filter in , checked all connections on the plug wires and vac. lines .

Some of those vac. lines were lined in oil .

 

I would still check the fuel pressure , if you don't notice any difference . Get that throttle body/ injectors cleaned as best you can

and go from there .

[DansGreyMj]

My Mj did the same thing, check where the rotor is at TDC on the number on piston. Mine was off and i had to shave the locating tab and rotate the distributor.

[dasbrick]

Will do that next time i go out and work on it. And this caused it to be like this intermittantly?