Here's a challenge for ya!

[Twin Pinzies]

I'm perplexed...
BOTH of my trucks are starting to act as if they are running out of gas while going uphill in the heat of the day. Here are the details; Both have squeeky clean fuel systems (new filters, hoses, rebuilt pumps, no debris in the tank, etc), new air filters, plugs, and fresh fluids all around.
It ONLY happens when going uphill. After running perfectly all morning, They will start to bog down and intermittently lose power (as if running out of gas) then after increasingly poor running, the engine will just stop dead!
Sometimes letting if I let it sit for 5-10 minutes, it will start up run perfect again. Sometimes it won't restart at all until I get it facing downhill and jump start it. Once it's jumped and facing downhill, it will run fine again... until you start going back up! But sometimes it will run great even after facing back uphill!
I do travel at high elevations (9,000-13,000+ ft.) and in the heat (It's been HOT here this summer)!

Am I boiling off the fuel in the lines? Is my filling station adding weird stuff to the gas? Do I need high altitude jetting? (So far they have run perfectly at high elevations for 7+ summers) Do I need to check the timing?
I've tried everything that I can think of but it continues to plague both of my trucks in the exact same manner. WEIRD!!

Thanks in advance guys....

[Stekay]

While I suspect it's something technical and one of the "pro's" will know exactly what you need, I have seen people install fuel filters facing the wrong way. Since it was one of the things you changed, I'd just give it a check because it's so easy to do. Look forward to the solution.

[undysworld]

Yeah, I'll agree that's weird.

I'd have to assume that you're already running high-altitude jets, or you'd likely not be running at those elevations anyway. I can check later for the jet #s, if nobody else speaks up sooner.

A couple questions for you.

Sometimes it won't restart at all until I get it facing downhill and jump start it.

By "jump start" do you mean supplying an external charge to the batteries, like with jumper cables (either 24v or 2x12v)?
Do both trucks have the symptom of needing to be jump-started, if they fail to restart after 10 min.?

[Twin Pinzies]

Hey Undy,
Yes, if they don't fire up after sitting, they MUST be jumped! By jump start I mean "pop start." As you probably know Pinzies are really EASY to pop start on even a slight slope (in low range 4WD). It seems to "force" the fuel through the system and forces the engine to rev (like engine braking does) then it seems to "clear it's throat", sputter to life, and start running great again.
BOTH of my tour trucks now seem to do the SAME thing at almost THE SAME place on our most popular tour route.
Last summer, I removed and drained the gas tanks. This summer I looked into the tanks to make sure that they were still clean. They are. And NOTHING odd is showing up in the fuel filters or the screens on the fuel pumps.
WTF huh?

[Twin Pinzies]

I like the suggestions... There's no such thing as dumb advice. Keep the wild guesses coming!
I feel like the solution to this problem will be something....dumb and simple. Like a palm to the forehead dumb!

I'm just out of ideas at this point. DRY GAS!!?

[Twin Pinzies]

While I suspect it's something technical and one of the "pro's" will know exactly what you need, I have seen people install fuel filters facing the wrong way. Since it was one of the things you changed, I'd just give it a check because it's so easy to do. Look forward to the solution.

Good one! I'll check.

[M Wehrman]

Do you guys run ethenol? That stuff hates hot weather.Its real prone to old school vapor lock. OH! We are driving old school...

[Twin Pinzies]

Do you guys run ethenol? That stuff hates hot weather.Its real prone to old school vapor lock. OH! We are driving old school...

DUDE! I think that might be it!!
I noticing yesterday that the stickers on the pumps read "contains 10% ethenol" and I wondered if my old school trucks would get along with it. I guess that they don't! It HAS been hotter than ever this summer too. That makes sense.
THANK YOU!!!!

[undysworld]

Interesting idea, vapor lock. It would explain both trucks being effected similarly.

And does that explain the problems when facing uphill? Could vapor be accumulating in the front line when the front is higher, but able to be dissipated when the front is lower? ??

Try an A/B test. Run one truck on the ethanol gas and the other on non-ethanol gas and go for a ride.

[Twin Pinzies]

Thanks guys. You rule!

[edzz]

Is it possible that when you installed the new filters and hoses they became routed in such a way that they are now exposed to more heat than before?

[Twin Pinzies]

Is it possible that when you installed the new filters and hoses they became routed in such a way that they are now exposed to more heat than before?

Yep! They now follow a gentler bending/ kinking pattern which puts them right up against the engine! I was thinking "easier flow" but it looks like I got "hotter routing" instead!
The more I learn about ethanol, the more I'm convinced that we ALL should stay away from that stuff in our 70's vintage trucks!

[berger]

Checking the timing couldn't hurt. I had a similar issue recently where the truck would lose power under load, and I checked the timing again, warm, and I must not have tightened the dizzy enough, because I was down about 200RPM. Set it straight and it has run great since.

I don't know a lot about vapor lock, but all the 89 octane I run in the truck is listed at 10% ethanol. In fact, then only fuel I see without it is the 91-94. Could you have a vacuum leak? What about air getting into the fuel line somehow?

I was just doing some reading and found a few things....since it happens under load, could it be the coils? It is odd that it is happening to both.

You mentioned the hard starting when hot/warm, and in the Ural world, guys have had distributor rotor issues that cause this....

[totaljoint]

I have had problems in the carburetors of many engines worked on over the past couple of years. In every case, my mechanic tells me that they are seeing more
problems since the introduction of ethanol. I now use real gas in any carburated engine that I have, especially those that sit idle for any length of time.
There is a web site to find real gas geographicaly:
http://www.pure-gas.org/
Ed

[Jimm391730]

While this doesn't make sense for BOTH of your trucks to have this issue at the same time, check the voltage between the coil "+" term and the chassis. 15-19 volts would be the expected range (when running).

My reasoning is that if the spark gets weak (from a low coil input voltage) then it will run OK at idle, but as you add air and gas by stepping on the pedal, as to get power to go uphill, the richer mixture just quenches the spark and it will run very rough and/or die. Cranking the engine sucks the battery voltage down that it won't start, either. But a "bump" start will have full battery voltage.

The 4500 rpm modules eventually fail; I've seen several that started starving the coil for voltage, and I got the performance described above. A simple voltmeter test on the coil, while running, will check this possibility.

Vapor lock is worse when the tank is empty, and the head (the height that the gas must be sucked up) is larger. Does the problem go away with the tank full? Is it worse when the tank feels warm? Then vapor lock might be the issue. Usually, vapor lock means no more liquid fuel and it stops dead, quickly. Then if it sits for a while things get worse, since with no fuel flow the hot fuel just gets hotter, until things finally cool down (after a long time, like a half hour or longer). I just had this happen on a very hot day in the desert with my FI system (110 degree temps and sunshine heating the gas tank. The tank was hot to the touch). Topping off the tank reduced the head and it started right back up, but I could only run on the top 1/4 of the tank -- it would vapor lock below 3/4 full.

Best of luck.