Another Compression Test Question

Another Compression Test Question
MDJEEPER said:
Could I disconnect the EGR, PCV, and cannister?

How would that change the engine performance?

Would it help with this diagnosis?
Click to expand...

The egr must be hooked up for it to run right. Have you checked it to be sure it's working right?
 
I have an idea thats out of the box, I had a chevy pu that had the same symptoms i had forgot about this until i asked my friend on what your problem could be and he reminded me of mine that he helped me fix. My prob. was a worn out cam shaft on two lobes. would run fine cold and at Idile. when you got on the gas it would spit and sputter and even backfire through the carb. - Replaced cam shaft and lifters, ran like new. He also told me that with a vacum gauge you can watch the needle and see if it bounces. cant remember but the vacum gauge should come with directions on that, at least mine did.

Tips on Reading Gauges: Vacuum Gauges

Here is a vacuum reading sheet that i found quick for ya...

How to Use and Interpret a Vacuum Gauge

This second one you can pick different ones and it will tell you about it....
 
Old Dog said:
The egr must be hooked up for it to run right. Have you checked it to be sure it's working right?
Click to expand...

As best I can tell, the EGR is working properly. I can manually work the diaphram which causes the engine RPM to change. However, I do not have a CTO valve, so the EGR should be working any time there is ported vacuum. Of course, since my problem occurs when it's hot, that shouldn't matter because the CTO is open when the engine is at operating temperature anyway.

How about the cannister and PCV valve? Should I try to do something with them to eliminate those systems as potential causes of the problem?
 
fire3096 said:
I have an idea thats out of the box, I had a chevy pu that had the same symptoms i had forgot about this until i asked my friend on what your problem could be and he reminded me of mine that he helped me fix. My prob. was a worn out cam shaft on two lobes. would run fine cold and at Idile. when you got on the gas it would spit and sputter and even backfire through the carb. - Replaced cam shaft and lifters, ran like new. He also told me that with a vacum gauge you can watch the needle and see if it bounces. cant remember but the vacum gauge should come with directions on that, at least mine did.

Tips on Reading Gauges: Vacuum Gauges

Here is a vacuum reading sheet that i found quick for ya...

How to Use and Interpret a Vacuum Gauge

This second one you can pick different ones and it will tell you about it....
Click to expand...

Thanks! I am not familar with a vacuum test specifically for a worn out cam shaft. However, my previous tries at reading the vacuum have all been within manual specs.
 
I really don't think the pcv would cause any problems as it only keeps any presure from building up in the crankcase. But it should be on full vac. to suck the fumes out all the time. I wonder though if the distrubter is getting enough vac with it being on the same vac. hose as the pcv.
 
Old Dog said:
I really don't think the pcv would cause any problems as it only keeps any pressure from building up in the crankcase. But it should be on full vac. to suck the fumes out all the time. I wonder though if the distrubter is getting enough vac with it being on the same vac. hose as the pcv.
Click to expand...

For the life of me, I cannot figure out why the BBD carb only has one ported vacuum port...except for the fact that at the time Jeep was try to control everything via that complicated valving system.

With only one ported vacuum connection, I don't know how I could also operate the EGR valve and give the dizzy an exclusive connection. Perhaps less important, I also could not run the purge signal on the cannister. Without the ported vac signal, would the cannister even operate?

The other thing I wonder about is the tee in the PCV line, with one leg going to the cannister and the other going to a large manifold vacuum port on the back of the carb. From the diagram in the FSM it appears to be correct, but seems somewhat strange.
 
MDJEEPER said:
From the diagram in the FSM it appears to be correct, but seems somewhat strange.
Click to expand...

As I said a few posts back, I'm not to in the "know" about the 6's and all the emission :dung:. So if it appears correct I would keep it that way.
I'll keep thinking about this maybe something will come to me.:D
 
Old Dog said:
As I said a few posts back, I'm not to in the "know" about the 6's and all the emission :dung:. So if it appears correct I would keep it that way.
I'll keep thinking about this maybe something will come to me.:D
Click to expand...

Right. I know you are a V8 guy, but I really appreciate your help just the same. Thanks!

..Gee if I could get it running I'd bring it to Ohio and get you to help me with a V8 upgrade! :notworthy:
 
I had another thought today (ouch!)...Could the problems I'm experiencing be caused by the metering rods/vacuum piston inside of the air horn?

...I already tried adjusting the floats and cleaning the bowl in the base of the carb, but did not think about those things (vacuum piston, accelerator pump) inside of the air horn...

On the other hand, you'd think if these were out of adjustment there would be a problem all the time and not just when the engine was hot??
 
The more I think about this only running bad when hot, the more I have to think either the fuel is boiling in the line or filter, or it has something to do with the choke.
I would first try wrapping the fuel lines and filter in tin foil to act as a heat shield where its close to a heat source and see if it makes a difference.
If that doesn't work and your choke is opening all the way when warm, try to tie it part way closed and see how it runs.
 
Like olddog posted wraping to shield heat, is why i suggested checking the filter. i actually ran a clear filter for troubleshooting purposes, checking for fuel, flow/condition. besides how the filter is hooked up, also the poition/placement is important.
Another thought drive it till it cuts off or damn near, when it does hop out quick and yank the gas cap off, listen for it sucking air when it`s removed, if the tank is building a vaccum due to a nonvented cap it could starve the motor of fuel. the other thing could be a line gets warm and is being sucked close. is the line to the fuel pump rubber? if so try the foil trick
 
Last edited:
Old Dog said:
The more I think about this only running bad when hot, the more I have to think either the fuel is boiling in the line or filter, or it has something to do with the choke.
I would first try wrapping the fuel lines and filter in tin foil to act as a heat shield where its close to a heat source and see if it makes a difference.
If that doesn't work and your choke is opening all the way when warm, try to tie it part way closed and see how it runs.
Click to expand...

BrockGrimes said:
Like olddog posted wraping to shield heat, is why i suggested checking the filter. i actually ran a clear filter for troubleshooting purposes, checking for fuel, flow/condition. besides how the filter is hooked up, also the poition/placement is important.
Another thought drive it till it cuts off or damn near, when it does hop out quick and yank the gas cap off, listen for it sucking air when it`s removed, if the tank is building a vaccum due to a nonvented cap it could starve the motor of fuel. the other thing could be a line gets warm and is being sucked close. is the line to the fuel pump rubber? if so try the foil trick
Click to expand...

Thanks guys! I will experiment with moving the fuel line around and/or shielding it. And yes, it is rubber. It's my understanding that Jeep did not use a metal line between the fuel pump and carburetor in '86.

The choke does fully open when warm, but I will also try tying it partially closed.

I don't suppose you've seen a picture of a good fuel line setup where there is no possibility of boiling?? I'd really like to know how others with the all rubber fuel line set up are avoiding this problem.

Brock: Where did you find the clear fuel filter?

I did put a brand new Stant fuel cap on it. The new cap did not make any difference. But, I don't have any idea whether its vented or nonvented. It's just the cap they specify in their parts catalog.

My only concern about the idea of fuel starvation is that the problem as gone from being sporadic to happening every time I step on the gas when the engine is hot.
 
I cut the line from the pump to the carb and installed a clear filter.
This was in addition to the metal type you have.

The sputtering and cutting out and dieing was driving me crazy.
 
Hello Guys,

Well, I hate to say it, but I am feeling totally dejected. Over the weekend, I followed all of your suggestions, but nothing has eliminated my bucking/stalling/dying problem once it gets hot.

1. I replaced all of the remaining fuel lines that I hadn't already touched with brand new stuff.

2. I actually took some solid metal fuel line and bent it from the fuel pump to over my the carb. Now the fuel line does not come close to touching the engine anywhere.

3. I did another fuel pump volume and pressure test. Both were within specs.

4. When it started acting up I jumped out and checked the gas cap, but there was no hissing or pressure when I opened it.

5. I rechecked the timing and made sure the vacuum advance was working.

6. I checked the vacuum piston and accelerator pump adjustments in the carb and both seemed to be within specs. (How on earth do you accurately measure that vacuum piston gap!!??)

7. I did find that the vacuum actuator on the EGR valve will not hold a vacuum and will not open the diaphragm. However, the diaphragm itself seems to be intact and will drop the engine's RPM when I push on it. I temporarily removed the vacuum hose, but it did not make a difference. That also had the effect of making the distributor the only thing attached to ported vacuum, and that didn't make a difference either.

8. I sprayed all around the carburetor and could find no signs of a vacuum leak.



So, I don't think it's the fuel system...unless there is an internal carburetor problem. But again, why only when it's hot??

What else? Something in the ignition that breaks down when it's hot? But, it idles fine...It's only when you step on the gas that the problems begin.

Maybe the timing chain is stretching and slipping? Though base timing stays dead steady on 8 degrees (at idle).

I have been thinking and working on this for weeks and I am totally at a loss....

Any other ideas would be hugely appreciated!!
 
What kinda aircleaner do you have?
Open air or the stock setup?
What kinda carb is it again?
 
BrockGrimes said:
What kinda aircleaner do you have?
Open air or the stock setup?
What kinda carb is it again?
Click to expand...

The air cleaner is the stock one that came with the Jeep. Because it doesn't have all the vacuum stuff, the heat flaps inside the horn of the air cleaner have be wired open so there is a free flow of air into cleaner at all times.

The carb is the BBD. It was supposedly rebuilt by a PO in the past, but who knows how good a job it was. Also, when I did the nutter bypass, I set the stepper pins according to TDHofstetter's procedure (see below). They are supposedly in that neutral position which improves fuel economy...Could it be I need to somehow pull them out to the fully rich position (aka the original nutter placement)??

As far as the other carb settings go, I intentionally set the vacuum piston a little rich and raised the accelerator pump up just a hair (which I believe think should it give a longer squirt). But neither of those things made any difference.

Also, as I mentioned before, I found that the vacuum mechanism on the EGR valve is not working, but the diaphram is closed. So, I wouldn't think that could be making the engine run lean when hot (as if it were stuck open).




*******************************************************
OK - first thing we need to do is find the plug (from the wiring harness) that connected to the original oxygen sensor.

Next... go to Radio Shack and buy the following two items:

47 ohm 1/2W 5% Carbon Film Resistor pk/5 - RadioShack.com (47-ohm resistor 5-pack... you only need ONE of these)
1.5K ohm 1/2W 5% Carbon Film Resistor pk/5 - RadioShack.com (1.5K resistor 5-pack... you only need ONE of these)

Select ONE resistor from each pack. Wrap a strip of masking tape around it and write the value of the resistor on the tape so you don't have to think about the color-code bands painted on the resistor (I hate peering).

For reference, the color bands on each of those resistors should be:

47 ohms = yellow - violet - black - gold
1.5K = brown - orange - red - gold

(or you can doublecheck 'em with a multimeter set to resistance)

Ok, now... connect the two resistors together - one lead each - and connect a short (12" -> 24") pigtail wire to that connection. That wire should be any color except red and black. Yellow is good, or blue, or orange, anything but red and black.

Connect a RED wire to the other lead of the 1.5K resistor (do NOT MAKE A MISTAKE HERE - connect it to the 47-ohm resistor and you risk blowing all the smoke out of your computer).

Connect a BLACK wire to the other lead of the 47-ohm resistor.

To recap... your wires should be

RED
|
1.5K ohms
|
|- YELLOW (or blue, or whatever)
|
47 ohms
|
BLACK

Cool? Cool.

Find a good ground someplace on the motor. Securely SECURELY connect the BLACK wire to that ground.

Connect the RED wire to the (+) terminal on the battery.

With your multimeter, verify that the voltage on the YELLOW wire is now between 0.35V and 0.5V. It'll vary a little, depending on the battery voltage, but it should be pretty close.

If that voltage is right, we're ready - connect the YELLOW wire to the oxygen sensor's harness plug. You've just simulated an oxygen sensor in a near-perfect neutral (ideal) fuel mix environment. Start the engine and let it warm up. When it's up to temperature, the computer will believe it's reading the most wondrous marvel of all - a perfect, unchanging fuel mix. :) It'll neutralize the carburetor, and you can unplug the carburetor at that point.

Read more: http://www.jeep-cj.com/forums/f2/shorten-throttle-cable-4836/index2.html#ixzz0wCzoVwMp
 
I took a couple pictures of the stepper motor pins...this is where they ended up after the nutter bypass.

Does this explain anything?
 
Your metering pins look like they're in the perfect position. I can't think they're responsible for... your Jeep sputters & won't run if you romp on it after it's warmed up? Na - I can't think that.

Quick check - get it to that point (hot, ready to romp on it) with the air cleaner off (do it in the driveway so you don't pick up a bunch of dust), and have someone else romp on it while you hold your hand partway over the carburetor throat to close it a little - your hand will be acting like a choke.

See if you can find a hand position (more air, less air) that makes the problem go away. If you CAN'T, then your motor is definitely not running lean at temperature. It could still be running rich, though - are you getting black smoke out the tailpipe? If you are, it's too rich. If not, you're not.

If you're not getting black smoke, and if you can't pretend to be a choke & improve the way it runs when it's hot, then the only thing I can think is that the problem is in the ignition... meaning possibly a poor ground or a bad connection someplace that gets worse when it's hot... or... dang. The distributor isn't slipping out of timing, is it? Is the vacuum line running to the distributor still going through the temperature-controlled switch on the intake manifold?

When it runs rough, can you improve the way it runs (somebody else romping on the pedal) by unplugging that vacuum line from the carburetor and sucking on it (I'm serious here)?

Did we check for a leaky power-brake booster?

The EGR doesn't hold vacuum, if I recall, but it does make the motor stumble when you manually move the diaphragm? What happens if you do that with the motor fully hot?

-- Tim --
 
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