Low flow thru fuel filter

[81CJ7WY]

wow, seems like your having some long term trouble with this. I'd like to address the idle speed as it relates to idle mixture and perhaps that can shed some light here. Idle speed and mixture of the fuel air ratio is directly related. as an engine goes lean it will pick up in idle speed and start to miss erratically before it dies. It is easy to restart an engine if it quit due to being lean. However rich, an engine will lope, like a horse running. If an engine dies due to rich mixture it slowly gets slower in rpm and then dies. it isn't easy to start as it is in a flooded stage. Now if your engine lopes at idle, it is rich, but from what your saying i would guess it is lean, with no rhyme or reason as to its irratic misfire. Also if you end up with a .1 psi on the fuel pressure, (did I understand that right?) which is real close to 0, it is gone into a lean condition as the fuel bowl float level has dropped. Engine rpms goes up. If the fuel pressure didn't die I would look closely at the idle mixture jet being loose or dirty. But since your pressure died, I would suspect the pump. I had a fuel pump go out on me once and it actually blew the fuse as it siezed up, then I'd replace the fuse, it would run fine for 10 min till it got "hot", siezed, and blew the fuse again. I then put in some tin foil gum wrapper, ( not recommended at all!) to get me to the exit off the highway. I eventually replaced the pump and never had the problem again. I know pumps are pricey but at this point it seems like the next thing to do and if you haven't done that, it might be a good thing to do anyways. If it was spark related I would replace the coil next. Also if you want to monkey around with it you could always pressurize the gas tank a few psi and see if it keeps running in your driveway. And if you really want to do that, use a shop vacuum and almost empty toilet paper roll stuck in the filler port. Sure hope this helps in someway.

 

[3wheelingCJ]

Thank you for the reply.
Just to clarify, the fuel pressure drops by .1-.2psi, not down to that level.
Does that change your troubleshooting approach?

 

[007]

Well you have some possibilities.

Is a fuel pressure gauge acccurate enough to tell "accurately" .1-.2 lbs? Perhaps.

Can a fuel pump fluctuate .1-.2? Perhaps.

Can an ignition problem affect idle enough to affect mech fuel pump enough to fluctuate .1-.2? Yes.

Can an issue with gunk in tank affect fuel pressure .1-.2. Yes.

Idea 1. Try setting a gas can down in front of the Jeep and run a fuel line from it to your pump. This will rule in or out any issue between pump and your Jeeps tank.

Idea 2. Get/rent/borrow a handheld tach to see if psi fluctuation follows an rpm fluctuation.

I'm quitely thinking this is a carb issue anyway. But that's a mere hunch and is partly driven by my disdain for carbs and partly because I've seen them do this before.



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[Lumpy Grits]

Are BOTH idle mix screws set the same?
Take the cap off the tank and go for a drive.
LG

 

[81CJ7WY]

Well, it seems like trouble shooting this is like shooting at a moving target. Gotta loosen up my swing . . . . On a different eng in a different situation I had a flexible fuel line delaminate inside causing th rubber inside to pinch down and shut off flow. I also think of a stuck float and needle seat problem with a "sudden" flow of gas. I've also had a vacuum hose with a small crack and a gasket tear that affect idle mixture, replacing all th rubber parts was one of the first tasks I did after getting my Jeep. Another related issue was a shop rag in the gas tank, covering the inlet to the pump. Do you have any pollution equipment connected that could be changing the air ratio? Any open plug ports in the little plastic vacuum manifold? I was thinking maybe air is getting in someplace. Rule out the fuel pump as mentioned above, definitively. This may be over simplified, and I know I'm not there to hear and see it, but After the fine balance of gas spark and air, an engine should run unless it has something inside not right. The Air is the most touchy in its regulation at idle. Verify idle mixture is correct, clean. 007 had some good input.

 

[3wheelingCJ]

I like the idea of using a gas can to feed straight to the pump, will definitely that out.
The pump itself was replaced just last weekend, so it should be ok. Even though I already had a new pump in a few months ago and it didn't last.
The carb is new too and none of the idle mixture screws were adjusted. I never tried adjusting idle screws, but will look up a procedure and double check them.
no polution equipment, just a pvc valve in the back of the manifold. I'll definitely check again for vacuum leaks, especially around pvc connection, as it seems a little loose.
I took the gas cap off and listened for a suction vistle as someone suggested earlier, and didn't hear anything.

Just curious why the pressure would dip at such precise and repeatable intervals? I am, just thinking if something is stuck or blocked the fluctuations would be random.

 

[007]

Just curious why the pressure would dip at such precise and repeatable intervals? I am, just thinking if something is stuck or blocked the fluctuations would be random.

Agreed. I didn't know carb was new...now leaning more ignition if it's not fuel delivery.



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[Lumpy Grits]

I like the idea of using a gas can to feed straight to the pump, will definitely that out.
The pump itself was replaced just last weekend, so it should be ok. Even though I already had a new pump in a few months ago and it didn't last.
The carb is new too and none of the idle mixture screws were adjusted. I never tried adjusting idle screws, but will look up a procedure and double check them.
no polution equipment, just a pvc valve in the back of the manifold. I'll definitely check again for vacuum leaks, especially around pvc connection, as it seems a little loose.
I took the gas cap off and listened for a suction vistle as someone suggested earlier, and didn't hear anything.

Just curious why the pressure would dip at such precise and repeatable intervals? I am, just thinking if something is stuck or blocked the fluctuations would be random.

PLZ post some pictures so the forum can looky-see.
My SWAG is either your pull'n a vacuum in the gas tank or you have a slight manifold vacuum leak.
Take it for a drive without the gas tank cap on......
LG

 

[3wheelingCJ]

I'm all for posting pics, just not sure of what. Let me know what will help.

Did some more troubleshooting shooting this weekend. It was mostly consisted of just watching the engine react to different changes.
One of the things that I have noticed a while back and is still there, is that the engine really has to warm up and get running at lower rpm before any of the symptoms begin to show.

It was brought up earlier in this thread how the gas and air mixture can affect idle, and I noticed that as the rpms drop the idle becomes more unstable and eventually will get to the point of no return and die. With the new and pos timing light with built in tach started watching how much the idle will fluctuate as the screw is set to lower speed. As I approached 900 it started to swing by about 100+. I also started to notice consistent fuel pressure drop to 4psi and the every 2-3 momentary drops.
Also noticed bubbles in filter that were mostly caused by loose worm clamps and went away after tightening. However, there were still times when the pressure was still dropping to 4psi and the fuel would spray into the filter. Didn't see that in the past for some reason.
So, followed one of the advices here, got some gas in a canister and ran a line straight to the pump. All the spraying disappeared and I was able to settle down the idle at about 850 which is on the top limit of recommended idle and for timing. Turns out that the timing wasn't great and set just below 5deg advanced. With my cam it's much better closer to 10, so that adjustment was also made and idle set to 900. Not sure if the timing explains the momentary dips in pressure, but with the gas coming from can straight to the pump they were not present.
I also ran it without the gas cap (didn't drive) before using a gas can method and all the symptoms persisted.

At this point it seems that the fuel delivery was an issue from the beginning and possibly resulted in other side affects leading me on the goose chase.

How do you guys feel about that conclusion and should I check anything else before buying more parts and swapping them?
Also, any suggestions on which fuel line and tank to buy? All the line pics on line look odd with a big 180deg bend. And, did anyone attempt a tank size increase in a CJ5 ? Not sure how anything bigger than stock will fit.

One last thing. Autozone timing light is a total POS. Besides just having a very cheap feel to it, the display only worked for 1min at a time and shut off. Had to recycle power to get it back on.