Another Compression Test Question

Another Compression Test Question
...Maybe I'm overly fixated on the exhaust, but I am about out of ideas!
 
MDJEEPER said:
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:
Click to expand...

The only doing it when hot thing has me confused.
 
New exhaust system...same problem....

I did not find any vacuum leaks.

I am really running out of ideas!!

Could it be a dizzy or timing chain issue? How would I know? Base timing has been...and continues to be dead on at 8 degrees.

Ignition module?

Is there a Doctor in the house??? :bang:
 
Ok the original problem was having no <-BAD WORD-> in the jeep at higher speeds right?
Any other symptoms?

List all that you've done so far.
 
...The key to this puzzle is the heat. I just let the Jeep cool off for an hour and then immediately went out and did the same test drive. As long as the engine has NOT reached full operating temperature (though is warm enough to not be running at normal idle), then there is no problem...

But as soon as it does get hot...it bucks, stumbles, and just plain wants to die if you step on the gas. I don't know if I'm using the right words, but is just horrible the moment you hit the throttle. Getting home was fun basically having to run at idle!

Does anybody have any ideas...even out of the box ideas??
 
BrockGrimes said:
Ok the original problem was having no <-BAD WORD-> in the jeep at higher speeds right?
Any other symptoms?

List all that you've done so far.
Click to expand...


OK. I will try to list everything…This could be a long post!

When I first got this project last winter, the biggest symptom I noticed was that it had no get up and go at higher speeds. I could put my foot to the floor and have it lose speed going uphill. However, the engine sounded smooth...it was like it just ran out of power.

At the time, I did all the usual stuff…replaced the spark plugs, wires, cap, rotor, coil, and belts. Also, replaced the water pump, radiator, fuel lines, vacuum lines, fuel filter, and did the Nutter Bypass. And, I set the timing to 8 degrees. As best I could tell, the vacuum advance was also working and was shifted over to ported vacuum.

After all that, nothing changed about its get up and go at high speeds.

About two months ago, I noticed that an occasional sputter would occur under load. At first, it would happen accelerating up an on-ramp in 3rd gear around 40 mph. However, as soon as I shifted to 4th, it went away. And, it didn’t do it all the time.

In the past month, it has developed this horrible bucking/sputtering/backfiring/dying problem once it gets hot. As soon as I put my foot into the throttle this happens now, at any speed and any gear...as long as it's hot. However, if I feather the throttle and not get into it more than 1/4-1/2 throttle, then the engine runs smooth.

When the engine is cool, it still does the usual going uphill. It chugs along WOT losing speed all the way up the hill, but the engine runs smooth.

The most recent things I’ve done have been mainly diagnostic…Did a compression test, a manifold vacuum test, and fuel pressure test. They were all within specs. I also rechecked the timing (still set at 8 degrees), and sprayed around the base of the carb and elsewhere for vacuum leaks. Also, I replaced the exhaust system to fix a rusty muffler and rule-out a backpressure problem. I also took the air horn off the carburetor and checked the float level and the inlet needle (both OK), and cleaned the bowl. Oh, and I replaced the gas cap.

Like I said before, the key to the current major problem seems to be heat since it still runs OK when it’s cold…or at least doesn’t buck, sputter, and die.

Going back to the very first problem, I still don’t know whether the original issue with no guts going uphill is also a symptom, or due to those crummy 2.73 rear gears. But right now, it doesn’t make any difference if it doesn’t want to run right at all when hot.

So, that’s the story. What haven’t I checked??
 
If it runs fine cold, then it is leaning out when it gets hot. These are your only choices, 1-fuel pressure, 2-vacuum leak[internal or external] 3-internal carburetor restriction.
 
Mine did that when it got hot and it was one of these things I did to fix it.
I cleaned out the float bowl and needle the float rests on(the one that would shut the fuel off), adjusted float to spec's.
I replaced the fuel lines with the proper size from the pump to the carb (all rubber lines under the hood) Use fuel line not just some rubber line.
Made sure the fuel filter was properly orientated.

Did this and it ran like a champ no more sputtering, bucking, or dieing.
Also make sure the lines aren't near/resting on a heat source.
 
Thanks Guys!!

If you don't mind, I let me address both of you...

priceg said:
If it runs fine cold, then it is leaning out when it gets hot. These are your only choices, 1-fuel pressure, 2-vacuum leak[internal or external] 3-internal carburetor restriction.
Click to expand...

Priceg: From your description, we are ruling out some sort of ignition/dizzy problem? If so, that simplifies things, or at least eliminates one system...

(1) I confirmed again last night that I can go WOT (or anything over 1/2 throttle) without bucking/sputtering/dying when the motor is cool.

(2) Fuel pressure is good (6.5) and holds steady even after the motor is shut off.

(3) I have replaced all of the external vacuum lines and sprayed everywhere I could with carb cleaner to try and find a leak. I could find nothing immediately wrong.

(4) I am not sure what you mean by internal vacuum leaks...Do you mean internally within the engine (do I need to do a cylinder leak down test?), or do you mean within the carburetor? If the latter, how would I find that?

(5) How would I find an internal carb restriction?


BrockGrimes said:
Mine did that when it got hot and it was one of these things I did to fix it.
I cleaned out the float bowl and needle the float rests on(the one that would shut the fuel off), adjusted float to spec's.
I replaced the fuel lines with the proper size from the pump to the carb (all rubber lines under the hood) Use fuel line not just some rubber line.
Made sure the fuel filter was properly orientated.

Did this and it ran like a champ no more sputtering, bucking, or dieing.
Also make sure the lines aren't near/resting on a heat source.
Click to expand...



BrockGrimes:

(1) Based on your previous suggestion, I did remove the air horn checked the floats and needle, and cleaned out the bowl. I have never rebuilt a carb before, so I cannot say that I would recognize if something was wrong. However, everything was within specs according to the manual.

(2) The fuel lines and fuel filter have been replaced with NAPA fuel line and filter, and (as I learned from this forum), the fuel filter is properly orientated with the return line directly on top.

(3) I am very curious about how you ran your fuel line since mine does run directly up from the pump and across the top of the valve cover. In fact, the fuel filter sits nearly on top of the cover. However, this is how with original lines were oriented...I just replicated what was there. I'll take a picture of it tonight...if that would help.


For both of you:

How about the problem of losing speed going uphill on the freeway even when the engine is running OK? Do you think this is another symptom, or the gutless rear end?


Finally, I just want to say again that I really appreciate everyone's input!! This is obviously some problem that's not easy to find...especially for a newbie like me!
 
BrockGrimes said:
Any vaccum :dung: on the carb, capped or otherwise?
Click to expand...

I believe all of the manifold vacuum ports on the carb are capped. The only thing that has lines going to it is the ported vacuum port. It has a tee with one leg going to the vacuum advance on the distributor and the other going down the left side of the engine to another tee that goes to the EGR valve and the canister.
 
As promised, here are a few pictures of the fuel line configuration and the vacuum lines.

I don't know if you can see it, but the dizzy, EGR, and cannister purge sig. are all tee-d together on the one (!) ported vaccum port on the BBD.

Also connected to the carb are the two vapor lines at the front.

And, there is a line (vapor?) that runs from the base of the carb in the rear to the EGR valve with a tee that goes down to the cannister.

Anything look wrong?
 
Well I'm not a 6 cly. guy but I think the dist. should be on the ported vac. by itself. It looks like it's hooked to the pcv valve which if it is it wouldn't be getting the correct vac. signal.
I also wonder if the fuel line is to close to the engine, and is getting hot and causing a vaper lock of sort. Try holding it up higher some how.
Two things I would try is putting a fuel pres. gauge on it that you can read while driving. find a hole in the firewall you can run the hose through temperally and see if the pres. holds when it gets hot running down the road.
Buy a new set of plugs, take it out and run it till it starts messing up on you, and than pull over and take a couple out and see what they have to say ie. lean or rich.
 
Old Dog said:
Well I'm not a 6 cly. guy but I think the dist. should be on the ported vac. by itself. It looks like it's hooked to the pcv valve which if it is it wouldn't be getting the correct vac. signal.
I also wonder if the fuel line is to close to the engine, and is getting hot and causing a vaper lock of sort. Try holding it up higher some how.
Two things I would try is putting a fuel pres. gauge on it that you can read while driving. find a hole in the firewall you can run the hose through temperally and see if the pres. holds when it gets hot running down the road.
Buy a new set of plugs, take it out and run it till it starts messing up on you, and than pull over and take a couple out and see what they have to say ie. lean or rich.
Click to expand...

Thanks!

As far as I know, the BBD carburetor only has one ported vacuum port, so I don't know how the EGR valve and cannister signal could be connected otherwise. Any ideas? But you're right that ideally the distributor should have its own port.

Do the other lines all look correct? Should that one be teeing from the back of the carb to the PCV valve and the cannister?

Any suggestions on how to run the fuel line differently? I know some Jeeps had a hard line that ran from the pump down around the front of the engine and back to the carb, but I don't think that was true for this model year.

I like your idea of testing the pressure when the engine is running down the road if I can find a way of not leaking gas all over the place!

The plugs are pretty new. However, I pulled them all but didn't see any immediate problems. Pictures attached...
 
not sure about the egr but the pcv should have full manifold vac.
The only way to truely read the plugs is to start with new ones and just pull one run on them, If you can find a place to pull off the road after it starts running bad and check them than.
Theres a few good links to reading plugs in this thread. What do you make of this? Photo inside - JeepsUnlimited.com Forums
 
Could I disconnect the EGR, PCV, and cannister?

How would that change the engine performance?

Would it help with this diagnosis?
 
Check your fuel filter postion:

Trapshooter said:
The first thing to check is your fuel filter position. Do you have this style of fuel filter, with one inlet and two outlets?

DSC01692.jpg DSC01691.jpg

On the end with the two outlets the top fitting needs to be above the lower or center fitting. The top fitting is the fuel return back to the tank. If the return fitting is lower than fuel outlet to the carb, fuel will be siphoned out of the carb bowl and back to the tank.

This situation will make for hard starts after your Jeep has sat for a day or two. This is a common problem and one I experienced myself with my AMC 304 when I first purchased my '79 CJ7 .

I repositioned the filter and now my AMC 304 starts within a few cranks even after sitting for weeks.

Hope this helps.........
Click to expand...
 
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