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'91 K5 Four Wheel Camper

This is the build for my 1991 V1500 Blazer, AKA the K5.3. It started out life being sold to the U.S. Government with a 350 TBI/700r4/241 combo. 4 years with a 5.3/700r4 Combo and now moving to an 8.1L Vortec and NV4500 5-speed.
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ZooMad75 said:
Thanks for the input guys.




I figured I was getting wonky readings for a reason, just wasn't sure why. That link explained a lot.



Makes sense.



Let me get a little more detailed on the lines. #1- It's stock TBI lines from the pump to the fuel filter. #2- The Workhorse lines are indeed for an 8.1, but directly match the feed and return points on the 5.3 fuel rail. Meaning, the lines aren't any different than if I lifted them from a 2002 Silverado.



Return seems to be doing its job. Since the rear lines are stock TBI stuff the return line comes right back to the sending unit and dumps into the tank from there.



That's an idea that I'll keep in mind.



I'm using an AC Delco EP341 pump as the ECM I'm running requires less fuel pressure than a stock 5.3. I ended up dialing up the pressure to 51 psi late in the trip in order to try and calm the problem down.



I'm sure with the lower pressure mine runs, its probably returning an average amount of fuel back. I know it's working as my problem gets more pronounced when the volume in the tank is less. With less fuel to dissipate the heat the pump runs hotter.

So let me throw this out there.. The idea in my head is to go ahead and wrap the rest of the pipe up to the muffler. Then add some insulation for both the fuel feed and return. I had a customer of mine suggest just splitting rubber fuel line and wrapping it around the hard lines. Cheap and simple. Thoughts?
Click to expand...
I do the hose split thing on mine, but a good old Moroso cool can would be the shiz
 
http://www.faqs.org/faqs/autos/gasoline-faq/part1/

So that seems that it doesn't really start boiling or vaporizing till at least 120 under carburetor pressures. Haven't found the boiling point under fuel injection pressures but it must be higher. Seems that maybe the fuel lines must be picking up some heat and bringing it back to the tank. And the fuel in the tank is boiling.

Found this excerpt:

4.10.1 Vapour Pressure and Distillation Classes.
6 different classes according to location and/or season.
As gasoline is distilled, the temperatures at which various fractions are
evaporated are calculated. Specifications define the temperatures at which
various percentages of the fuel are evaporated. Distillation limits
include maximum temperatures that 10% is evaporated (50-70C), 50% is
evaporated (110-121C), 90% is evaporated (185-190C), and the final boiling
point (225C). A minimum temperature for 50% evaporated (77C), and a maximum
amount of Residue (2%) after distillation. Vapour pressure limits for
each class ( 54, 62, 69, 79, 93, 103 kPa ) are also specified.


Then I found these interesting documents:
https://www.michigan.gov/documents/mda/Gasoline_Volatility_Information_-_endpoint_195239_7.pdf
http://www.militarytrader.com/milit...e-field-ethanol-vapor-lock-and-other-gas-woes

Are there a couple of places where you can place some sheet metal as a heat barrier around the fuel lines? Are modern cars using plastic lines to combat heat issues?
 
JoshHefnerX said:
http://www.faqs.org/faqs/autos/gasoline-faq/part1/

So that seems that it doesn't really start boiling or vaporizing till at least 120 under carburetor pressures. Haven't found the boiling point under fuel injection pressures but it must be higher. Seems that maybe the fuel lines must be picking up some heat and bringing it back to the tank. And the fuel in the tank is boiling.

Found this excerpt:

4.10.1 Vapour Pressure and Distillation Classes.
6 different classes according to location and/or season.
As gasoline is distilled, the temperatures at which various fractions are
evaporated are calculated. Specifications define the temperatures at which
various percentages of the fuel are evaporated. Distillation limits
include maximum temperatures that 10% is evaporated (50-70C), 50% is
evaporated (110-121C), 90% is evaporated (185-190C), and the final boiling
point (225C). A minimum temperature for 50% evaporated (77C), and a maximum
amount of Residue (2%) after distillation. Vapour pressure limits for
each class ( 54, 62, 69, 79, 93, 103 kPa ) are also specified.


Then I found these interesting documents:
https://www.michigan.gov/documents/mda/Gasoline_Volatility_Information_-_endpoint_195239_7.pdf
http://www.militarytrader.com/milit...e-field-ethanol-vapor-lock-and-other-gas-woes

Are there a couple of places where you can place some sheet metal as a heat barrier around the fuel lines? Are modern cars using plastic lines to combat heat issues?
Click to expand...

I was finding similar stats. The one constant remains, when a liquid is pressurised it's boiling point is raised. Gasoline is no different. It also is good to point out at NO time on the trip or elsewhere for that matter did the system "vapor-lock" while driving. The boiling of fuel would lead to a stumble and die due to the resulting air formed within the line that the injectors can't deal with. The engine never stalled in that form. It did behave as if I reached up and shut the key off. Which is pretty indicative of the pump overheating and just shutting off.

As far as adding a sheet metal barrier, there is lots of places we could do that. We did add a chunk of 22ga sheet metal while parked in our campsite in Moab the first night out. Bent a 90* flange over the end of the picnic table and screwed it to the bottom of the rail from the h-H-pipe back to the muffler. The next day we were pretty confident we fixed the problem after a long hard pull from Green River to our jumping off point from the highway. Those were long hard steep pulls with a headwind. The engine was running at 220 and I was down in 2nd gear near the tops of a couple of the pulls. It never shut off. But I had just topped off with fuel in Green River too, so the capacity to absorb heat was at it's max in the tank. Off road the rest of the day and the next, ambient temps were 80 or lower. It never acted up. It wasn't until the 3rd day we were running up Beef Basin and it all caught up with us again. 95* degree temps and slow running uphill in silty deep sand and it shut down. We ended up removing the shield as it was showing to not make a difference at the time. Our thought was it just boxed in the rail to make it more oven-like and add to the problem.
 
ZooMad75 said:
And either type would go on the feed or return side? I'd say either would be a last ditch type of add. I start simple and work my way up.
Click to expand...

Return side would be the way to mount the cooler I'd think. That's how every engine I've ever seen has them plumbed anyways. Hopefully it doesn't come down to that though.
 
I don't think the fuel is vaporizing inside the pressurized lines I think it's boiling inside the tank and you're picking up bubbles from that, so putting a cooler on the return side should keep the tank cooler, would also remove heat picked up on it's journey. Have you double checked the pickup inside the tank. Maybe you're just sucking air because of a pickup problem. Filling up the tank would fix that also... Just a thought.
 
JoshHefnerX said:
I don't think the fuel is vaporizing inside the pressurized lines I think it's boiling inside the tank and you're picking up bubbles from that, so putting a cooler on the return side should keep the tank cooler, would also remove heat picked up on it's journey. Have you double checked the pickup inside the tank. Maybe you're just sucking air because of a pickup problem. Filling up the tank would fix that also... Just a thought.
Click to expand...

The pickup in the tank is ok. We just had it out the week before the trip. I've run the tank down to 1/4 this week and it's yet to stall out on me. If it was a problem with the pickup I would have it act up now that I'm low on fuel. I'll insulate the lines and give it some drive time.
 
Please correct me if I am wrong, but newer vehicles have plastic tanks,(maybe less heat soak), wider frames (more distance between the fuel lines and heat sources) and just the one exhaust pipe on the opposite side. Maybe that gives enough airflow , even past the t-case. ??

I wouldn't put a cooler on the feed line, I see that as too much chance for a leak from the thin walls of the cooler getting hit by a rock chip, then gasoline mist...

I agree that the cool can would be difficult to keep working. It should be an fluid to air style.
I believe that you are correct that keeping the fuel tank temps down will be the cure, but how many factors are going to get to that goal?
 
6872xtc said:
Please correct me if I am wrong, but newer vehicles have plastic tanks,(maybe less heat soak), wider frames (more distance between the fuel lines and heat sources) and just the one exhaust pipe on the opposite side. Maybe that gives enough airflow , even past the t-case. ??

I wouldn't put a cooler on the feed line, I see that as too much chance for a leak from the thin walls of the cooler getting hit by a rock chip, then gasoline mist...

I agree that the cool can would be difficult to keep working. It should be an fluid to air style.
I believe that you are correct that keeping the fuel tank temps down will be the cure, but how many factors are going to get to that goal?
Click to expand...

Based on my testing yesterday, the temps on the tailpipe near the tank was within the same reading I had on the fuel lines near it, on the corner of the tank itself and the ground. Given the fact that IR temp values can be flawed based on the surface, if we don't look at the temp number itself we can see if at least they are consistent. In this case they are. Post muffler temps on the tailpipe isn't any hotter than the ground it's sitting over.

Yes, the return line probably is picking up heat from the exhaust and taking it back to the tank. But I can't explain why the temps on the return line near the tank drop to a similar value of the surrounding area VS the temp of the line further forward of the muffler. Wouldn't the hot fuel inside the line be raising the temp of the line to be higher than the surrounding area?
 
I get what you are saying. However, with the uncertainty of the temperature readings, does it revert to physically touching It?
Back in the day, would the lines and fuel have been cooler than everything else?

But in the end, does the temperature value even matter, or just how to solve the problem?

What I am thinking , is I haven't heard of this problem with the factory TBI engine and pump. Maybe I don't have a clue.

But what has changed since this truck was new? The fuel pump pressure, which could maybe induce more heat into the fuel and pump, and the ethanol content of the fuel.
Have these 2 things stacked up against you? Can the ethanol change the vaporization temperature to help induce pump problems?

Maybe Larry doesn't have problems because the larger engine moves fuel through the pump faster?

I will quit rambling ....
Could a fuel cooler keep the gas tank temp down enough to fix it? Yeah, I still want to know what factor(s) cure this.... some data please.....
 
Good points. The major change from the TBI setup (besides the 5.3 sitting up front) would be the true dual exhaust. Normally the TBI exhaust would cross the right bank over to the left side, "Y" together before the cat and then run a single pipe down the left side and dump out under the left quarter behind the wheel. There wasn't any exhaust running down the side where the t-case gets close to the frame. So right there is a major difference from stock TBI.

As far as the higher pressure inducing more heat, probably not. Most LS swaps using stock PCMs end up running the EP381 pump running at the 55-65 psi range. This is what Larry's used on both 8.1 swaps and he's not had the issue I've had.

Ethanol content could be an issue, but probably not the defining issue. Most local fuel isn't running any more than 10% ethanol. Again, I hate to keep bringing Larry up, but on the trip we filled up at the same locations each time so if ethanol was a factor it should have effected him in the same way. It didn't.

As far as Larry running more fuel through, that's kind of a toss up. His overall trip mileage was only a couple mpg lower than mine. However, on the road while pulling I know for a fact he was doing so at a lower RPM than I was. The 8.1 wasn't working nearly as hard as the 5.3 was when pulling hills. I'm not sure moving a higher volume of fuel is going to fix the issue. I'll get some supplies this week and make some changes and drive it. I've got a 3 day run planned for the hills with the normal cast of characters plus a couple of 4wd noobs within the family that want to run with us. We'll hit a common spot for us to start out and then based on how they do crank it up a little. Temps will most likely be lower. But the elevations will peak out at 11,000 to 12,000 feet. Crawling will be similar to what I had on our validation run when the problem first cropped up. Biggest variable would be the ambient temps. I guess we will find out.

I appreciate all the input and am taking it all in.
 
Started to fix the broken photo links from the ransom of Photobucket. That's going to take some time.

In the meantime, I've got all the goodies to do the 6.2/big block radiator swap. Radiator upper neck has been redone by a local shop so there is no interference with the hose/clamp to the tank. The reproduction upper radiator brackets showed up and they look like the real deal. I'll get the other ones from Larry tomorrow and post up pics.

I've got a project this weekend to get my niece's Subaru safe to drive. Pads and rotors front and back, change the oil and top off the a/c. Might take my Dad for a banzai run around south Denver in it when we get done. 2.5 turbo Outback is a little screamer. It's got the millennial Anti-theft system too (AKA 5-speed manual trans).

Next week after work the radiator swap commences.
 
ZooMad75 said:
Started to fix the broken photo links from the ransom of Photobucket. That's going to take some time.

In the meantime, I've got all the goodies to do the 6.2/big block radiator swap. Radiator upper neck has been redone by a local shop so there is no interference with the hose/clamp to the tank. The reproduction upper radiator brackets showed up and they look like the real deal. I'll get the other ones from Larry tomorrow and post up pics.

I've got a project this weekend to get my niece's Subaru safe to drive. Pads and rotors front and back, change the oil and top off the a/c. Might take my Dad for a banzai run around south Denver in it when we get done. 2.5 turbo Outback is a little screamer. It's got the millennial Anti-theft system too (AKA 5-speed manual trans).

Next week after work the radiator swap commences.
Click to expand...


I'd like to see the work done to the radiator. Got any pics?
 
Tony Vickers said:
I'd like to see the work done to the radiator. Got any pics?
Click to expand...
Not right now I don't. I've got parts spread out between the garage and the back of the Blazer right now. When I get started on it after the weekend I'll get some detailed shots of it and the rest of the goodies.

My ordered upper radiator brackets turned out to be the smaller version. There is a slight possibility they sent the wrong ones as the part number on the package don't match the invoice or catalog. Arrgh!
 
So since the brackets were wrong, I've put off the swap. The shop I got the wrong ones from is taking them back. It pretty much proves that NOBODY is reproducing the larger 6.2L Diesel upper radiator brackets. The search got restarted locally, via craigslist and other leads. After dealing with Craigslist flakes that said they had them and then stopped responding I got a hold of a junkyard out in Hudson Colorado. Got the last set they had. My Dad went over picked them up for me. Now I need to get them from him. Then I can get the process started.
 
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