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Discussion Starter · #1 ·
Ok.. its going to be long.. but I thought I'd try you guys before spending big bucks to replace everything under my hood.

I have a problem when my engine is under load. Acceleration or up hills is where its more promenant.

The Jeep will run up to 2000 rpms.. then almost out of nowhere.. either 2-4 minuites after running it up under load .. it stops driving the wheels.. and the wheels start turning the engine.. sometimes it just dies like that and it takes smacking the gas a couple times before it kicks back in.. other times if I lay on the gas, it goes and stops.. and goes and stops.

Things I have observed: I tihnk I'm having pump problems.. but my fuel filter is absolutely FULL of fuel.

I've burned through 2 tanks in one week. (NOT COOL.)
And only driven a bit.

I have no-problem city driving...

A friend pointed out a new Vacume leak by the 6th cylinder... so I'll pull the manifolds and replace them suckers tomorrow. (any tips anyone? new gaskets and RTV? or do I just forget the RTV?)

Here's my thoughts.
-Fix vaccume leak.
-Replace plugs.. regap.
-Open carb and ensure there's no crap in it.


Anyone got any other ideas? I'm dumbfounded here.

It's a 4.2L from a 1989. MC2100 and TFI ignition.

checked the rotor and there was some magnezium dust.. but no scortch marks.

thanks everyone.. this is really anoyying me.

I don't think I'm doing anymore mods until I've sorted my jeep out. gonna get it reliable and simple. I really hate being the guy on the trail who's always like.. "hold on.. my carb crapped out.." "hold on the ignition is messed" "hold on the breaks aren't working."
 

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Discussion Starter · #3 ·
I suspected it too..

But a lack of fuel wouldn't make me burn through like 10X more then I should be.. should it?

Also, the fuel pump HAULS.. when I get out on the highway.. or about 2 grand.. the pump can fill a 2 liter bottle in about 15 seconds.

BUT.. when I went wheeling today (well spectating) the truck stalled twice.. both times i got out, and the lines from the pump to the carb were dry..

it took undoing it.. and cranking it over for 30-45 seconds till I got fuel squirting back out.

I want to replace the pump wiht an electric.. can I put it on the frame rail upfront next to the engine? I like the idea of not having to worry if the pump is pumping.. "click" "Whurrrr" "Fuel"

 
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Had a similar problem before.
Turned out to be a rusted out gas line.
Check out your lines, especially the steel one that runs from the tank to the pump.

CTjeepnut
 

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Something to try before doing anything.
Take off the gas cap as soon as it acts up. See if it goes "whoosh." It may be the vent's plugged. As you drive it you use gas, the tank gets a vacuum, enough that the pump can't overcome it. You stop, wait, crank, the tank has a tiny leak, air gets in, vacuum goes away, pump works again.
If no "whoosh", try leaving it off and driving it - see if it still stalls.

The vacuum leak on your #6 is not causing your problem. At worst it'll cause a slight misfire.

Just because there's fuel in a clear filter, it doesn't mean it's actually flowing. And the opposite's true - just because you see air in a filter (with some fuel) it doesn't mean it's not.

And - you said you have a TFI upgrade/downgrade - see if the module is terribly hot when you stall - and see if the coil's super hot. They get intermittant when they overheat - till they quit completely.


 

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Discussion Starter · #7 ·
Thanks Rich..

I've noticed a woosh when filling the tank..

pull the cap when the tanks empty.. and it sucks air..

I also have ONE fuel line.. I don't know what the stock YJ setup is because the previous owner decided to mod it before i bought it..

but I have ONE line that runs to the front and provides fuel.

There are no return lines or vents or anything.
 

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Discussion Starter · #8 ·
Also.

If It's not the gas-cap.. and not the manifold.. and not the carb.. I was planning on replacing the fuel lines from front to back.

Again, the previous owner in all his wisdom, has about 5 rubber hoses, and 5 steel hoses under the hood. 4X that many hose clamps keeping it all together.

It literally looks liek he broke on the trail and asked everyone for every little bit of hosse thy could sacrifice.

SO... is there a reason for this? or can I just grab some rubber line and run clean from the fuel pump to the filter and filter to the carb? cause right now theres like 4 lines bettween the pump and the filter.. it also goes UNDER the block for some reason. I was going to rout it back up behind along the firewall..

Can I run soft lines from the fuel tank to the pump? or do they have to be hard lines?
 

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Since you are burning through a lot of gas, I suspect the carb is icing. My 304 with motorcraft 2100 acted like that once and I happened to pull the air filter to see the venturi's completely iced.
 

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Discussion Starter · #10 ·
I've got an open element.. but I setup a heater hose that ran from the heat sheild to the carb. Was sucking air ONLY out of there.. and it did the same thing..

Ok heres some more info.

When the engine isn't fully heated up, I can rev. the piss out of it.. right up on the highway at 3 grand..

On the way back though the engine was warm.. and it didn't do as good.. it sputtered and crap.

So I spent all afternoon in the rain :)() replacing the exhaust and intake gaskets.

Got it all back together, and except for a small leak by the collecter joint? its all good.

pulled the top off the carb and its all clean in there.

Took it out on the road.. got all excited because it ran like a champ..

But again on the way back it sputtered.. not as bad.. but it still did it.

Also, today, I pulled plugs, re-gapped them.. filed and cleaned them..

Anyone got anything else now? I'm just eliminating these problems bit by bit..

Thanks again for everyones help so far.
 

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Sounds like it's still lean. Or an ignition problem.

Try driving it with the vacuum to the distributor disconnected. You may have advance when you shouldn't have it.
Try setting the choke partially closed and drive it again. If it helps that proves it's lean.

Try hooking a vacuum gauge to intake manifold vacuum and watch how it acts when it's OK vs not OK. That will show an exhaust restriction - sometimes a baffle in the CAT or muffler bends when it gets hot, plugging it off. Ya can't run very well when constipated.


From my previous post:
"And - you said you have a TFI upgrade/downgrade - see if the module is terribly hot when you stall - and see if the coil's super hot. They get intermittant when they overheat - till they quit completely."

Do we assume they are not getting hot? You should be able to put your fingers on them without flinching.


 

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Discussion Starter · #12 ·
I haven't gotten around to putting my fingers on them yet.

I kind of have to get it warm.. and run it out on the highway for a stretch to get it to act up.

I'll do it tomorrow on my way home.

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That rules out an ignition problem.
After that were down to vaccume advance or fuel problem.

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Closing the choke doesn't help much. I'll try it again now that the vaccume leak is fixed.

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"Intake manifold vaccume." - Right now the advance runs off a ported vaccume on the side of the carb.. at the base. Is this good/alright?

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I don't have a vaccume gauge... but I'll get one and do a thurough tuning of the carb and check manifold vaccume while driving. (I should look funny hauling down the road
)

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Side note:
I've got a nasty tick in my head. Going to adjust the rockers sometime this week. (they are adjustable are they not?)

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Side note:
I advanced the timing to 15 deg? TDC when I did the TFI.. I've noticed that under acceleration shifting 3rd into 4th I get some gnarly pinging. It's been like that for a while and I haven't gotten around to fixing it yet. Will do it when I do the rockers.

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Question: When a carb "ices" how much does it ice? When this happens, I can pull over for 30 seconds or so and let it idle and it will run 2-3 min before doing the bumpy thing again.

If I pull the air cleaner, and get it to bump.. when I pop the hood.. and look down the intake.. will it be obvious? or not?

Getting it sorted.. one step at a time.
THanks again guys.

PS: I kept my stock coil... can I toss that in and wire it up and motor down the highway to see if it is the coil?
 

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The "baffle" in it is the filter. You should be able to blow through it.

For some reason you don't "want" it to be ignition?

When it dies, are the module or coil hot?
Is there spark when it won't start?

There is a way to determine if it's a lack of fuel - propane.
Use a propane torch - take the tiny orfice out or drill it so you can get a greater volume of propane. Remove or cut off the torch head. Slip a long hose over the tube and run it to the carb's top - with the bottle and valve inside by the driver's seat so you can control it while driving.
Tie or secure the end so it stays in the airstream of the carb without a chance of it moving. Run it up through the hood crack in through the window.
No, you don't light it!

Drive it, make it stall, just as it stalls, open the propane valve a little. The engine should run on the propane. As the engine is still turning it should try to restart and run if it was a lack of fuel problem. Or if it's already stopped turning use the starter.
What you are doing is replacing one type of fuel - gas - with another - propane.
If the problem is not a lack of fuel but it is ignition, it won't even try to restart. You'll have to wait that cool-down period again.

That won't find the cure instantly, but at least you know the direction you have to take - fuel or ignition.

I have a feeling it's the ignition - you are describing the typical problem with mixing and matching components that were never designed to work together - the so-called TFI "downgrade."

Carb icing? I have no idea about icing. We don't get that sort of thing in Southern California.
 

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Discussion Starter · #16 ·
Thanks Rich, I'll double check the ignition components today.

IF.. they are all fine and dandy.. I plan on going ahead and replacing the fuel pump. (it's probably about due anyways.) if that doesn't work, then its a line somewhere? and i can lock that down by running fuel from a jerry can->pump..

if it doesn't happen it's tank/lines related.. if it does still happen, then it's between the pump and carb?

Anyone got a picture of an ignition module? Mines not in the stock location, and i don't know where the previous owner thought a GREAT place to put it owuld be.
 

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"I advanced the timing to 15 deg? TDC when I did the TFI.."
You did the TFI but don't even know where the module is or what it looks like?

Didn't I tell you the tiny vacuum leak on #6 didn't have anything to do with it? But you replaced the gaskets anyway, and you were surprised it didn't cure it.

Now: "I plan on going ahead and replacing the fuel pump"
Sounds like you'd rather arbitrarily throw parts at it rather than diagnose it. You must be a dealership "mechanic" - or maybe a doctor.

What are you going to say after you put in a new fuel pump, all new lines, new filters, a new tank, new filler, new cap, new carburetor and it still has the same problem?

Fuel vs ignition vs exhaust vs mechanical - there's an awful lot of parts you can still throw at it.

How 'bout just get a new Jeep and be done with it?

Do the propane trick.

 

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In reply to:

I haven't gotten around to putting my fingers on them yet.

I kind of have to get it warm.. and run it out on the highway for a stretch to get it to act up.

I'll do it tomorrow on my way home.

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That rules out an ignition problem.
After that were down to vaccume advance or fuel problem.

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I may be misunderstanding what you are saying, but what exactly rules out the ignition, the fact that you have to drive it a bit to get it to act up?
I used to have a motorcycle that would run great until it got warm, then would act like you are saying. Turns out it was a bad coil, it would get warm and malfunction then cool down and work great.
 

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Discussion Starter · #19 ·
Coil doesn't get warm.

It didn't fully do it on the way to shool this morning.. but it sorta did.. and the coil is cold.

Module? module doesn't get replaced with the TFI, only the coil.. right?

I'll get out on the highway this afternoon and get it to act up then check the coil again. My only hesitation is that I want to check a bunch of stuff at once. Every time it does it on the highway I risk my life with people racing up behind me, and pulling over, getting out..
So I'd rather check 1/2 dozen things at the same time.

A vaccume leak either way is something to worth fixing.
YOu don't go running around wiht 1/8" gaps between your head and your manifold do you?

I really appreciate all the help guys... but by eliminating the vaccume leak and the carb full of crap, and the plugs being fouled.. well cleaned up the sound of it running quite a bit.

So... on my way home.. check the coil.. and the module for heat when it acts up..
Is there anything else I should glance at, check when I'm pulled over?

And what I meant to say is.. "That WILL rule out an ignition problem if they are not hot.. right?"

Sorry I'm a little frazzled with midterms and my Jeep and heading 8 hours home this weekend.


Thanks again
 
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