Another Compression Test Question

[Old Dog]

Does anybody have any actual experience with 2.73 gears and larger than stock tires? Should it be able to run up a hill on the highway at 60 mph without losing speed??

My cj had 2;73 gears and 32's when I bought it, even with a v8 it had no balls going up hills on the highway.

 

[MDJEEPER]

NEW SYMPTOM! NEW SYMPTOM!!

So, I went out to test whether the clutch is slipping (doesn't seem to be but couldn't complete the testing) and found a new symptom...As soon as you step on the gas, it either massively sputters (with the exhaust sounding like a machine gun) or dies completely! It doesn't matter what gear you're in or speed. It sure made getting home fun!

It had a little sputter in the past, but it just happened every once in awhile.

Basically, it's like a switch...if you hit the throttle past halfway, you get the symptoms, but as soon as you let off the throttle past that point, all of the engine's power is back and is perfectly smooth again.

It also does the same thing at idle sitting still in the garage. If I ramp up the throttle slowly, I can get to about halfway and then the sputter begins. If I quickly open the throttle from idle, then the thing just completely dies.

The fuel pump was supposedly replaced by the PO about 6 years ago. I have no idea what may have been done to the carb in the past, other than I was told that it was rebuilt at some point.

What do you think??

 

[fire3096]

I had a co-worker that had the same prob. you are describing and his prob was the cat was cloged. he cut out the cat, put a piece of flex pipe and said it felt like a new engine. Replaced the cat with a new one and kept chugging along. (an engine is a big air pump, if it can not breathe. it makes it work very hard). hope this helps...

 

[MDJEEPER]

I had a co-worker that had the same prob. you are describing and his prob was the cat was cloged. he cut out the cat, put a piece of flex pipe and said it felt like a new engine. Replaced the cat with a new one and kept chugging along. (an engine is a big air pump, if it can not breathe. it makes it work very hard). hope this helps...

Thanks! I was thinking about the exhaust too. But, how do I tell the difference between an exhaust problem and a fuel system problem??

 

[priceg]

Thanks! I was thinking about the exhaust too. But, how do I tell the difference between an exhaust problem and a fuel system problem??

A fuel pressure gauge and a vacuum gauge are your friends.

 

[MDJEEPER]

A fuel pressure gauge and a vacuum gauge are your friends.

What?? You mean I can't just beat on it with a hammer!!?? :drool:

Obviously, more diagnosis is in order. However, I was just trying to short circuit the process a bit since there are several possibilities and I'm just a newbie Jeeper. The fact that by the end of yesterday it was sputtering and dying just sitting in the garage whenever I goosed the throttle seems very telling...of something...

 

[BrockGrimes]

When you ease into the throttle it'll go just fine, but getting on it it spits and sputters and doesn't want to go.

Clean out the float bowl and check the needle that the float pushes against.
Also the screen that filters the fuel, also check the orientation of you fuel filter.

 

[MDJEEPER]

When you ease into the throttle it'll go just fine, but getting on it it spits and sputters and doesn't want to go.

Clean out the float bowl and check the needle that the float pushes against.
Also the screen that filters the fuel, also check the orientation of you fuel filter.

Thanks! I am going to try taking the air horn off of the carb to check the bowl.

Today, instead of sputtering when you get on it, it sounds like a major backfire. Again, it was fine first thing when it's cold, but once the engine got hot the backfiring problems began.

Let the engine cool for about 20 minutes and the problem disappears...until it gets hot again.

Did check the fuel pump pressure...Held good at 6.5, so the pump is probably not the issue. But will also try a volume test.

Also, checked manifold vacuum, held steady around 20 at idle, then went up slightly then down slightly depending on how I reved the RPMs.

...Pulled the air horn off. There was a minor amount of sediment in the bowl (how much is too much??). Also, I adjusted the float just a fraction, but they were not off by much. Needle looked fine.

 

[MDJEEPER]

...Put the carb back together tonight and there was no change. Runs OK when cold, but the problems start as soon as she gets hot and I step on the gas.

I did notice at the tail pipe that there seems to be very little exhaust pressure. In fact, I could cup my hand over the end and could barely feel a breeze against the palm of my hand.

I could be wrong, but shouldn't I be able to feel the exhaust from a foot or two way from the tail pipe, let alone against my hand?

If the exhaust is plugged, why would the performance be worse when hot??

Sorry for all of the questions, but I am running out of easy answers to this problem! I was really hoping it was just the fuel pump or filter!

 

[BrockGrimes]

If you can cover the exhaust while it's at idle with your hand it's gotta be a clogged cat, it should blow your hand off the pipe and maybe even burn you.

Bang real hard on the cat with you hand or foot and see if anything rattles or sounds loose if so, it's gota go.
Pick up a catco high flow cat from summit if you need a replacement, I used them on my YJ when I lived in CA and passed smog easy.

I used the universal one that fit my exhaust, a sawsall and 5 min and it was swapped an easy bolt in deal, but can be welded in by any shop for cheap.
http://www.jcwhitney.com/catalytic-converters/jeep-wrangler/c10821d1202j1s21.jcwx

 

[MDJEEPER]

If you can cover the exhaust while it's at idle with your hand it's gotta be a clogged cat, it should blow your hand off the pipe and maybe even burn you.

Bang real hard on the cat with you hand or foot and see if anything rattles or sounds loose if so, it's gota go.
Pick up a catco high flow cat from summit if you need a replacement, I used them on my YJ when I lived in CA and passed smog easy.

I used the universal one that fit my exhaust, a sawsall and 5 min and it was swapped an easy bolt in deal, but can be welded in by any shop for cheap.
Jeep Wrangler Catalytic Converters - JCWhitney

Thanks!! Got any suggestions for a new muffler as well? In fact, the whole thing is a rusted mess...I'd really like to start with a new front pipe and work all the way back, if it's not too $$$.

Meanwhile, are there any issues with loosening the pipe at the cat, or drilling a small hole at the junction between the pipe and cat to confirm?

 

[Thick]

Thanks!! Got any suggestions for a new muffler as well? In fact, the whole thing is a rusted mess...I'd really like to start with a new front pipe and work all the way back, if it's not too $$$.

Meanwhile, are there any issues with loosening the pipe at the cat, or drilling a small hole at the junction between the pipe and cat to confirm?

What diameter exhaust tubing?

I have a brand new JBA muffler sitting around. Bought it and never installed it or used it, its 2.5 in and out.

let me know if you are interested.

 

[BrockGrimes]

I ran the stock manifold, no cat and a cherry bomb with my AMC 258 i6 / 4.2l and it sounded nice, not loud or droning, just a nice jeep sound.
If it's a rust piece of junk just replace it from the manifold back, a local muffler shop can do the swap in a few min's and should be fairly cheap if you go with something
stock and not to crazy, cost comes when people start getting fancy. Do you really want that stainless tip in the end of the exhaust? LOL

 

[Old Dog]

For now just cut the cat out and put a piece of straight pipe in and see how it runs.

 

[MDJEEPER]

For now just cut the cat out and put a piece of straight pipe in and see how it runs.

Thanks!

I'm finally getting back to this project today and, unfortunately, have found another complication. Turns out that at least part of the reason why I had no exhaust pressure at the tail pipe is because the seam on the muffler has separated on the bottom...very difficult to see without a close inspection!

So, now I have to wonder again whether there is any problem with the cat at all. Or, could a muffler leak also cause the off idle sputter and dying problem? Maybe it's the muffler that's partially plugged??

And why is this a problem only when the engine is hot?

 

[Old Dog]

mufflers can come apart inside and get blocked up.
As to why it only does it when hot :dunno: might be more than one problem.

 

[MDJEEPER]

mufflers can come apart inside and get blocked up.
As to why it only does it when hot :dunno: might be more than one problem.

Would you still try doing something with the cat as well, or assume it's working? It actually looks like it could be a replacement, but who knows from when...

 

[Old Dog]

To be honest if you need a new muffler anyway I would cut them both out and just half *** a new muffler in with no cat to see how it ran. If it cures the problem than I would redo it right.

 

[Old Dog]

On second thought a cloged exaust will show up with a vacume gauge so thats where I would start.
I don't know why I didn't think of this sooner.

 

[MDJEEPER]

On second thought a cloged exaust will show up with a vacume gauge so thats where I would start.
I don't know why I didn't think of this sooner.

That's OK...I didn't think of that either...or rather I tried doing a vacuum test when this first started (seems like forever ago!). There was some drop but not completely out of specs. But I did not know at the time that the real problem is when it's HOT.

I haven't yet repeated the test when it has been really hot...didn't think of redoing it...

A mind is a terrible thing to lose!! :drool: