Fine Cold: Stumbles Warming: Dies when warmed and won't restart until cool

[Tahnka]

Another newb question: A search returns SO MANY suggestions that I've got nothin'. I wish people would respond with what the ultimate fix was.

When it's cold it runs great. I can fire it right up in the morning and immediately drive away nice and strong.

As it starts warming up it begins to stumble and choke. Occasionally it will clear something out and lurch back to full speed for a few minutes, then return to stumbling. Sometimes it backfires through the tailpipe when it begins to stumble. Sometimes (not all the time) the electrical will dim during the stumble.

Once it's fully warm it will start stumbling so bad that it will eventually cease to run under it's own power. It eventually dies and then it won't restart until I let it cool off for half an hour.

The temp gauge never reads any warmer than the far left bar; typical for this rig.

The big things that happened recently and which I suspect is the carb was rebuilt and the cat/muffler were replaced. Before rebuilding the car the cat was so restricted that it ran very poorly and had horrible gas mileage.

So brand new Power Valve, Accel Pump/Everything in the carb. Exhaust is finally flowing freely. Brand new cap and rotor, plugs and wires. The choke plates are operating as I would expect; closed 1/8" when cold, wide open when warm.

The flapper thing in the tailpipe works. The doors in the air filter housing open properly when warm.

There IS a chance that there was one backfire that could have ruined my brand new Power Valve. But there's no fuel in the PV's vacuum line and the line has vacuum.

Could the Power Valve run great when cold and horribly when warm? I seem to think that if the Power Valve was blown that it would always run horribly. Right now when it's cold it actually runs better than it ever has: TONS of power and as smooth as glass. I can actually make it to work before it warms up and stumbles if I don't hit too many red lights (3.7 miles hehe).

The choke plate is fully open when warm.

I don't have new aluminum headers that are boiling off the fuel in the bowl. (heh read that in a post, I'm trying everything )

Um; I'm still trying to figure out what the distributor pick up spring is (someone said to bend it).

The carb linkage is clean and lubricated and is functioning properly.

I haven't yet ruled out super heated fuel (still trying to figure out how).

Jay I have experienced a faulty ignition module, this doesn't feel like it. It won't just cut off; it instead seems to bog dog to the point that it just won't combust. When I had a bad ign module it would just suddenly go from running great to "bink", nothing.

I don't know how to check for slop in the timing chain; and I don't know how to check timing. I looked for timing marks on the dizzy/block and couldn't find anything. With a clean carb and freely flowing exhaust could the timing now be off?

[ January 29, 2006, 08:24 PM: Message edited by: Tahnka ]

[Jay Rayfield]

Ignition module? Kinda sounds like what I just went through, kinda. I started mine, drove down the road and it cut off, wouldnt start. Changed the ignition module and it ran. After that I had to go into the carb, that still a work in progress.

[Don S]

Originally posted by Tahnka:
Another newb question:

Could the Power Valve run great when cold and horribly when warm?

..
Tahnka:

... The back fire could have blown the Power Valve, Mabe. But I would look at the choke first. When the engine is good and warm Pop the hood and make sure the choke plate is fully open.

Have a good one and CUL.. Don S..

[Tahnka]

(Edit: Copied this response up to the initial post)

The choke plate is fully open when warm.

I don't have new aluminum headers that are boiling off the fuel in the bowl. (heh read that in a post, I'm trying everything )

Um; I'm still trying to figure out what the distributor pick up spring is (someone said to bend it).

The carb linkage is clean and lubricated and is functioning properly.

I haven't yet ruled out super heated fuel (still trying to figure out how).

Jay I have experienced a faulty ignition module, this doesn't feel like it. It won't just cut off; it instead seems to bog dog to the point that it just won't combust. When I had a bad ign module it would just suddenly go from running great to "bink", nothing.

I seem to think that if the Power Valve was blown that it would always run horribly. Right now when it's cold it actually runs better than it ever has. TONS of power and as smooth as glass. I can actually make it to work before it warms up and stumbles if I don't hit too many red lights (3.7 miles hehe).

I don't know how to check for slop in the timing chain; and I don't know how to check timing. I looked for timing marks on the dizzy/block and couldn't find anything. With a clean carb and freely flowing exhaust could it be timing? I haven't ruled out timing...

Many thanks for the suggestions.

[ January 29, 2006, 08:25 PM: Message edited by: Tahnka ]

[Don S]

..
Tahnka;

... OK, the next step is with the engine warm but turned off wire the choke plate in the open position so it can't move. If it doesn?t run any better at least you have ruled out the choke.

Have a good one and CUL.. Don S..

[brent]

You have a carb prob.
Maybe minor vapor lock.
Lack of choke has been the bane of a sh**load of my own problems. When I re-connected it, I was almost out of the woods. Rule that out per Don before proceeding.
Starting great when cold could easily be a testament to your battery. Starting crappy when warm sounds like the IMPOSSIBLE Holy Trinity of air/fuel/timing (carb). A lot of guys/girls on this forum know the Holy Secret of air/fuel/timing. Not me. A lot of guys/girls just go ahead an get fuel injection. That's down the road for me.
Your problem is the Holy Trinity.
My 2 cents, Brent

[Tahnka]

So a poorly tuned carb? That's entirely possible.

But it -runs- great while it's cold?

[ January 29, 2006, 09:43 PM: Message edited by: Tahnka ]

[Don S]

..

... A cold engine requires more fuel than when it is warm. The float may be set to high or in some cases we have seen the float clips were improperly installed. Also you might check the voltage to the ignition when cold and then when warm.

CARBURETOR FLOAT CLIPS ? MC-2150 ?
... There should be a horse-shoe clip that hooks over the float shaft and the needle seat housing. Its purpose is to insure that the shaft remains seated all the way down in the slot. There is also a coiled spring that looks like a clothespin spring and slides over the float-shaft. The ends of the coil stick out and one end is longer than the other. The short wire goes under the float lever and the long wire lays against the body. This coil spring serves as a dampener and is so named. Some times the tang on the float can get a dimple from wear at the point that it contacts the needle. On rare occasions the dimple can lock up with the needle causing a flow problem.
It would really pay to take photos or videos during tear-down procedures to bolster your memories. Don?t feel lonely if you discover that you goofed?
link> FSJ MC-2150 CARBURETOR
link> FSJ MC-2150 CARBURETOR
link>MC-2150 LINK

Have a good one and CUL.. Don S..

[Don S]

..
Tahnka;

... Also the vacuum lines may not be properly hooked up. Check the hose to the vacuum advance on the dizzy.

... I wish I knew more about the later model set ups like yours.

Have a good one and CUL.. Don S..

[GWChris]

There are a lot of vacuum devices that switch once a given temp is reached, by means of the various "CTO" devices. Not all of them are going to make a huge difference in how it runs, but if the device they turn on has a big vaccum leak in it, that could well make it run like crap.

If your PV holds vacuum and does not leak fuel, I would not worry about it. When they fail the mode is that they get a hole in the diaphram - and leak.

If it were mine, the first thing I would do would be to get a vacuum tester pump and go over all the vacuum devices - both hot and cold.

[BigRedChief]

I second checking (double-checking) all the vacuum devices and even double-checking your carburetor settings. I have another couple of ideas for you though.

Your EGR valve may be opening too quickly or too much. If you have a delay valve inline with the EGR valve, check it. If you don't have a delay valve, it might be a good idea to get one.

Check to make sure you don't have any leaks and that everything is hooked up properly for when your CTO switches the vacuum advance to port vacuum (when the engine is warmed up it should switch from manifold vacuum to port vacuum).

[wagonizzle]

I had a similar problem to yours that got worse over a period of a couple months. In that time, I rebuilt a 1405 (and bought an Edel intake so it would fit), installed a new fuel filter, fuel pump, eliminated vacuum leaks, but it just seemed like a fuel starvation issue. I never removed the dizzy cap; it looked new with new wires when I bought the truck. When I finally did (after it would run great for about 5-10 minutes, then with heavy throttle poorly, then lite throttle poorly, until dead, no more than 20 minutes), I found oil all over the inside of the cap. The dizzy shaft had some play, and once the engine temps got up, the oil thinned out and rode up the dizzy shaft and into the cap, causing crossfire, misses, whatever. New dizzy/cap/rotor, no more problems. Well, not that problem anyway. Good luck -

[JeepinPete]

Tahnka, do you have all of the emmisions goodies hooked up? If not, which ones are in place? As stated above, there are a lot of temperature operated vacuum devices on our Jeeps, and without knowing what is and isn't there, it is hard to say for certain what the problem may be...

Now for another idea, you may have a fuel line problem. Not likely being that you are from CA and all. But on my '87 Wag, I had a similar problem. Would run fine cold, and get worse warm. Turned out the fuel sender hard lines actually rusted away and created pinholes in the lines. When it was cold I had no problem, but once some heat got in there, the fuel pump started sucking air. It would starve the engine for fuel. But my truck was from PA, so rust was a given...

[andy d]

WAG : the coil is bad

[Tahnka]

The plot thickens.

I just fired up the Wag after it had sit all day. I drove about 300 feet and it died. When I attempted to restart it, it cranked fairly hard but then eventually started. After this second start, it stumbled really bad for a minute and then perked up. While it was stumbling all electrical dimmed. The Engine was still COLD and it stumbled hard. I've seen this behavior before (since the recent changes). It's running strong, it dies, then it runs horribly.

This Wag is originally from Georgia.

As far as I know, I'm running all emissions equipment that came on the 84.

Thanks for the suggestions; I'm working on checking things and will definitly post my findings.