1 (edited by Lemon_Newton-Metre 2022-05-18 11:14 PM)

Topic: Dual fuel Chevy Express weirdness

(Detail with answers here, edited question in post #6), more information in another post.

Original thesis:

GM Express, CNG: range, + question on fuel gauge for multiple tanks:

BLUF (Bottom Line Up Front):

1. what is the expected range if the vehicle has only two CNG tanks in the rear?,
I found the dual-fuel Supplement! Amazing what you can find when you open up things that shouldn't have anything in them. .
Answer: in this configuration, it's got a10.2 gge CNG capacity between the two rear tanks. In a dedicated CNG only configuration, it could have had another, large tank where the gasoline tank was (yes, was)
, and

2. Does the fuel gauge read sequentially with regard to available volume?
Answer: yes; kakarot is correct, with a dual-fuel configuration when it switches between fuels, as far as I can tell. Apparently the CNG is a single connected total volume for the two rear tanks. I still don't know why the gauge changed.

These questions are specific to the CNG fuel system. I've included more background information because: unusual characteristics.

And:
3. Should I leave the gasoline tank and use the vehicle as a camel for Lemons races?
Answer:  Definitely NO. I dropped the tank, and the area around the pump opening was soft and crunchy from rust. The fuel that drained from the lines looked like urine.

CNG fuel vehicle:
Running out of fuel = getting towed to the pump. Nobody is coming with a tank for you. Nobody.

Background:
2001 Express 3500 extended passenger van, originally configured as a dual fuel van (gasoline and CNG), but had the gasoline deleted on the build sheet, so it wound up as CNG only. It has two CNG tanks in the rear (which interfere with me putting on a commercially available hitch receiver, dammit; it'll have to be custom).

This is a new-to-me van; I just bought it from a Mass. agency. I drove it from near Boston to Philly area, stopping at every CNG station which I could access on the way. It was _not_ a direct route.

Using the fuel gauge as a guide (because no owner's manual), the range appeared to be about 120+ highway miles before empty; for the trip from Boston to Philly this wasn't a problem.

Around town, however, a 100 mile range is ... inconvenient.

Apparently the van _could_ have had another _large_ tank midship, and there was a possibility of a fourth, mounted inside and upright in a rear corner; but this has only the two CNG tanks.

With the original configuration, gasoline was an option as the second fuel; apparently there could have been a second fuel rail mounted on the engine, and presumably: a fuel pump and other associated equipment for the remainder of a gasoline fuel system.

The build sheet has a gasoline delete code. I don't have that in front of me right now; I'll update this post later tonight. But I don't think it controls the answer to the questions.

I haven't yet pulled the dog box to look at the top of the engine to see if the 'gasoline delete' resulted in the factory _not_ installing the second rail onto the engine for a gasoline system.

But the van _does_ have a normal midship gasoline tank. I don't know why. So the 'gasoline delete' code doesn't remove all gasoline components from the vehicle.

Also, a button in the dash(!?!), presumably for a van which actually had the gasoline system installed to do the fuel switch to/from CNG.

So here's the weird part:

I was trying to see what the gauge would read when driven around town. I normally track fuel mileage in every vehicle I drive- mine, or not.

I planned a trip to run some errands, and wind up at the closest CNG pump at around 105 miles. When on the highway trip, 120+ miles seemed a good, safe interval; and the gauge showed a reasonable amount of fuel remaining when I got to the pump.

But during the recent trip, at 105 miles I was getting nervous looking at the fuel gauge. It was reading WAY too near empty for comfort.

I'm driving, and keeping an eye on the gauge, and I'm at about 106.3 miles on the odometer, and the needle almost on the red mark, when the I noticed the gauge now reads around a half tank.

There was no sputtering or stumbling from the engine. The van ran fine to the pump, at about 107.4 miles. It took about 8.7 gge (gasoline gallon equivalent); it had taken only a little less than that on the ~120 mile segment of the trip from Boston.

Each fill is different; the fill is based on pressure, and the amount is affected by the temperature as well as the pressure of the pump. So I do not consider the fuel gauge an absolute guarantee of driving range - not even close.

Check me, please:

What I'm thinking is the system is set up to run off one tank, and to open a valve when that tank runs down to a pressure low enough for the second tank to be needed; then the remaining CNG from both tanks is available; hence the change in fuel gauge.

But I don't know that.

Perhaps enough parts of the dual fuel system remain, that when the CNG tank ran low enough, the gauge from the gasoline tank showed the amount in the gasoline tank, so a driver could know when there were no more options before a needed fueling.

But I don't know that, either.

I've searched online for dual fuel tank questions, and there are many.

I've found threads related to Ford dual tanks, and the differences between some of those and GM systems.

My first thought is the CNG system would _not_ be integrated with the gasoline system, where the gauge would read first one fuel, and then the other, at least not without two complete systems installed, and a driver pushing the 'Gasoline' button on the dash to do a switch over.

I see the GM gasoline and diesel dual tank systems run off the front tank, and there's a low-pressure pump which is activated to move fuel from the rear tank to the front tank. And senders and associated modules to make the system function (and these do not always work).

But the postings seem to indicate the gauge reads the total fuel all the time, and not: first one tank and then the other, because a control module is supposed to balance the tanks on an ongoing basis.

I could easily conceive the tanks would have a safety system where if one tank ruptured the others would shut off; that makes perfect sense to me.

And that the normal operation of driving would _not_ trigger a shut off of sequential tanks, but a rapid decompression - like in a rupture - would.

I don't have a problem remembering whether the gauge changed reading (from almost empty to half remaining) - at least not yet ;-)

I'm curious if anyone has any experience or knowledge with such a system.

As an aside, the gasoline tank does have gasoline in it - of an indeterminate age, grade, and condition. I'm guessing someone either ran it out of CNG and panicked (hoping to avoid calling their manager to be towed to the pump), or perhaps wasn't convinced the 'gasoline deleted' was actually complete because, y'know, "gasoline tank"; regardless: the seller (Comm. of Mass.) was explicit - this was sold as a CNG ONLY vehicle.

Additional steps I'll take in the future include:
1. unplugging any electrical connectors to the gasoline tank, and
2. running it to almost empty again, but this time parking near the pump and just letting it run to see what the fuel gauge will do; but if a nominal range on the CNG system would be about twice what I expect from the one tank, that'd be burning a lot of CNG, and take about the equivalent of 100 miles of running time, but a lot longer because of idling.

I also have CNG Honda Civic, and I fill that with at most 7.? gge; that gets around a 200 mile range, but that's a small car and a 4-cylinder engine. The tanks look close to the same size, but I could be way off. I can't imagine if a Civic has a ~7 gge tank, that a GM van would be configured with _two_ which total out at around 9 gge.

I'd expect a full size V-8 van to still be configured to get about 200 miles on its primary fuel before needing to be filled.

   Thoughts?

Re: Dual fuel Chevy Express weirdness

I want to read and respond...but less than perfect build day left me drunk and jaded.  So the answer is 42.

Re: Dual fuel Chevy Express weirdness

wow, that is full size essay there.
depends on the config you got, you can read the stamping on the tank to see what gge its capacity. You got 12mpge on that trip, which is basically what you should get.
Honda range is also sounds good, 7gge*30mpg=210miles.
I would probably turn the van into dual fuel, just so I would not be towed to nearest CNG station. Even if its a basic 2br carb just to go places.
Gauge probably switches between CNG and Gas based on what is in use.

https://www.facebook.com/greatglobsofoil/
This car....Is said to have a will of it's Own. Twisting its own body in rage...It accelerates on.
1978 Opel/Buick Isuzu(B) - IOE, C class, Incredible Feats in Badge Engineering; 1996 Ford Probe GT(B)

Re: Dual fuel Chevy Express weirdness

OnkelUdo wrote:

I want to read and respond...but less than perfect build day left me drunk and jaded.  So the answer is 42.

Although the answer to the unknown is almost always 42, I look forward to your cogent and sober analysis - mañana.

5 (edited by Lemon_Newton-Metre 2022-05-18 11:33 PM)

Re: Dual fuel Chevy Express weirdness

kakarot1232001 wrote:

wow, that is full size essay there.

Yes; yes it is.

kakarot1232001 wrote:

depends on the config you got, you can read the stamping on the tank to see what gge its capacity. You got 12mpge on that trip, which is basically what you should get.

Right; I forgot to specify the drivetrain: appears to be either a 5.7 l Vortec engine, with a 3.7? rear, and the calculated mileage is within expectations.

kakarot1232001 wrote:

Honda range is also sounds good, 7gge*30mpg=210miles.

Yes, that seems to be a consistent mileage with the Civics; I have another (bent), but that's what it got, also.

kakarot1232001 wrote:

I would probably turn the van into dual fuel, just so I would not be towed to nearest CNG station. Even if its a basic 2br carb just to go places.

I do not currently have the skills to do that. The CNG has injector rails; the gasoline would have had rails also.

kakarot1232001 wrote:

Gauge probably switches between CNG and Gas based on what is in use.

You are correct!

My previous answer, with comments:
On a true dual fuel unit, I would agree, but I believe the switch requires
pushing the button to switch systems.

I'm wrong about this - it'll happen automatically when CNG is too low. Perhaps when the gauge changed, there was still a little bit of CNG left, enough to go the little more than a mile to the pump, yet, the gauge switched to what was in the gasoline tank. I don't know. Maybe I'll eventually test it using a plastic gas jug.
But this one had the gasoline delete, and so when the gauge suddenly changed from empty to about half full, it was still running on CNG, so I'm going to say that's not possible.


I'm still thinking the unit would have been built with a fuel tank capacity which would allow a range of around 200 miles.

If the gauge change indicated a valve opening, for example, that combined and equalized the CNG in both tanks, the change from empty to half full would be what was expected.

Since I was getting about 100 miles with a steady decrease in the indicated remaining fuel, by the time one tank was depleted to the point a valve would open, and a subsequent indication of about a half a tank displayed, the doubling of the volume at half the pressure would leave about an equivalent amout of fuel as the first tank, and another about 100 miles of range, but show as about half a tank left.

Which makes sense.

Re: Dual fuel Chevy Express weirdness

Still the CNG van:

Thoughts on keeping the extra gasoline tank to use for race fueling?

Or is the idea of setting up a pump or siphon system to fill 5-gallon jugs from the 30+ gallon tank too cumbersome?

I'm going to disconnect the electrical connectors to the tank today, to take it out of the equation for the fuel gauge, and work on running it empty to see what the gauge does.

Re: Dual fuel Chevy Express weirdness

Lemon_Newton-Metre wrote:

Still the CNG van:

Thoughts on keeping the extra gasoline tank to use for race fueling?

Or is the idea of setting up a pump or siphon system to fill 5-gallon jugs from the 30+ gallon tank too cumbersome?

I'm going to disconnect the electrical connectors to the tank today, to take it out of the equation for the fuel gauge, and work on running it empty to see what the gauge does.

could also see if could utilize the fuel pump in the tank to fill the 5 gallon jugs.
I am not sure about the valve between tanks, sounds like too much stuff. I would say, it was a glitch in the system.

https://www.facebook.com/greatglobsofoil/
This car....Is said to have a will of it's Own. Twisting its own body in rage...It accelerates on.
1978 Opel/Buick Isuzu(B) - IOE, C class, Incredible Feats in Badge Engineering; 1996 Ford Probe GT(B)

Re: Dual fuel Chevy Express weirdness

Still not time whentotally sober to answer...still honestly impressed by the detail of your question...maybe tomorrow.

9 (edited by Lemon_Newton-Metre 2022-05-11 06:51 PM)

Re: Dual fuel Chevy Express weirdness

kakarot1232001 wrote:
Lemon_Newton-Metre wrote:

Still the CNG van:

Thoughts on keeping the extra gasoline tank to use for race fueling?

Or is the idea of setting up a pump or siphon system to fill 5-gallon jugs from the 30+ gallon tank too cumbersome?

I'm going to disconnect the electrical connectors to the tank today, to take it out of the equation for the fuel gauge, and work on running it empty to see what the gauge does.

could also see if could utilize the fuel pump in the tank to fill the 5 gallon jugs.

I hadn't thought about that; I'll look into that. Good suggestion - thanks.

kakarot1232001 wrote:

I am not sure about the valve between tanks, sounds like too much stuff. I would say, it was a glitch in the system.

Tomorrow I'll be running the van - right next to the pump - to see what happens.

Getting no answer from GM sources so far.

Other than what you'd expect when there's no _new_ money involved.

Or, perhaps I'm being too cynical

Re: Dual fuel Chevy Express weirdness

OnkelUdo wrote:

Still not time whentotally sober to answer...still honestly impressed by the detail of your question...maybe tomorrow.

Thanks! I look forward to your input.

Re: Dual fuel Chevy Express weirdness

TLDR: 30 gallons isn't enough.

I think 30-ish gallons isn't enough to bother supporting the racecar. No matter what it is. My 924 has a ~20-ish gallon tank and burns something that approximates 2 gph when it runs. It's a diesel and slow and I have diesel tow pig with 200 gallons of capacity. I have seen no reports that any gasoline car is less than 4 gph (Borgward on actual Borgward engine excluded, but it was slower than the Porsche for a variety of reasons).

4*9 is 36, and that's the long day. 24 gallon fuel cell is FIA cert (expensive) and you still have to go refuel half your support tank. 22 gallons means probably 4 jugs full at the start even if you start full and don't do practice, and you'll still have to hunt down a fuel station on Sunday or Saturday night. So I'd vote for a bigger support tank if that's how you want to roll.

That guy

Re: Dual fuel Chevy Express weirdness

Understood; good input - thanks.

But again: the van is CNG ONLY powered (originally configured as dual-fuel, but had the gasoline-delete code on the build sheet), and so the included (probably 33 gallon) OEM gasoline tank is completely useless to the van itself. But I _could_ leave it exactly where it is right now, instead of removing it.

I'd still have to bring several 5 gallon jugs to fuel the race car; the only question is how many would need to be full.

One good thing about the van tank is that I wouldn't have to carry fuel jugs inside the van. I could carry 6+ jugs worth underneath. And I could leave a trailer at the track instead of carrying jugs with it. (Yeah, I'm particular about that).

The only issue would be getting the gasoline from the OEM tank to the jugs; kakarot made a good suggestion (above). It is an extra step, though.

How many teams get to the track with enough fuel to last the whole race? As opposed to going for more fuel after the track goes cold on Saturday?

Re: Dual fuel Chevy Express weirdness

So, this isn't necessarily Lemons experience, but I have only run fuel sipping things in Lemons (minis, hyundais, Porsche diesel swaps, etc.).

E36 in Lucky Dog with a stock tank? 1 and 3/4 hours on a tank at race pace. 16 gallon tank. 30-ish gallons isn't going to help.

That guy

Re: Dual fuel Chevy Express weirdness

9+gph? WOT? ... I mean, WHAAAT??!!??

With my limited experience, I had not considered that scale of combustion. I mean rate of consumption.

That's more good information - thank you.

Re: Dual fuel Chevy Express weirdness

Lemon_Newton-Metre wrote:

9+gph? WOT? ... I mean, WHAAAT??!!??

With my limited experience, I had not considered that scale of combustion. I mean rate of consumption.

That's more good information - thank you.

What kind of car?  My 4 cylinder 2.3L turbo burns about 7 gallons an hour.  I bring the car with a full tank of fuel ~13-15 usable gallons and 8 five gallon jugs.  Some days I have to go back for more fuel.  I certainly have to refill everything after the first day.  Roughly about 100-120 gallons in a weekend.

What kind of car are you bringing?

Is the 30 gallon tank clean?  Can you get every drop out of it?  Seems like more hassle than its worth.  If you want to store a lot of fuel get a 55 gallon drum and pump.

Team whatever_racecar #745 Volvo wagon

Re: Dual fuel Chevy Express weirdness

More good data - thanks!

Re: Dual fuel Chevy Express weirdness

Thank you all for your input.

Result so far: I have only verified I have a range of _about_ 100 miles for this vehicle without risking a tow.

I'm pulling the gasoline tank.

Maybe I'll check for the rest of the components needed to run on gasoline, maybe not. But the gasoline is old to begin with, and I'm sure the tank needs to be cleaned by 21 years later.

When I have it lifted, I'll also be able to check the CNG system - valves, connectors, whatever. Maybe a valve/solenoid is stuck, maybe something electrical corroded.

I didn't disconnect the electrical from the _gasoline_ tank; I just drove it around until near empty (for what's expected from one tank), with the needle touching the red mark.

I kept it running at idle for 2.5 hours after parking right next to the pump. It wasn't a busy location.  I don't know what the expected use would be at that rpm, but it's a 5.7 or 6.0 GM 8-cylinder, and probably uses the same CNG gge's as a gasoline engine uses gasoline.

There were no signs of stumbling, stopping, or running out of fuel.

The needle didn't jump to a half tank like last time. Maybe that's because it wasn't moving. Maybe I didn't run it long enough - idling isn't like driving on the highway.

The gauge shows CNG fuel remaining based on temperature and pressure.

I shut off the engine and connected the hose.

This is the pressure gauge on the side of the pump after the pressure is equalized - I'm surprised the engine didn't stop:

https://i.postimg.cc/Fshhp0jx/20220512-195815.jpg

This is how much I filled (~92 miles and 2.5hr. idling):

https://i.postimg.cc/tgnbJkj9/20220512-200527.jpg

This is the pressure at the end of filing, which is normal:

https://i.postimg.cc/y8bB752f/20220512-195840.jpg

Re: Dual fuel Chevy Express weirdness

There is a huge difference between a 5.7 and 6.0 power plant, being 2001 vintage it sounds like a 6.0, verifying what you have will go a long way to figuring out the rest.

More data: 4.5L infiniti A class consumes 10ish GPH

Homestead Chump 5th-Sebring 6th-PBIR Lemons 9th - Charlotte Chump  CrashnBurn 9th
Sebring 6th again -NOLA Chump 1st -PBIR Chump Trans Fail 16th
Daytona 11th - Sebring 6th - Atlanta Motor Speedway 2nd - Road Atlanta Trans Fail 61st-Road Atlanta 5th
Daytona 13th - Charlotte 9th - Sebring 2nd-Charlotte 25th broken brakes - Road Atlanta 14 10th-Daytona 14  58th- Humid TT 19th Judges' Choice!

Re: Dual fuel Chevy Express weirdness

Best I can find is it's a special version of the 5.7l Vortec, with hardened valves, etc.

My one experience was an arrive-and-drive in a Prelude; I don't remember fuel usage being much of a factor ;-) , so based on what I'm planning, I have to noodle that some more.

Cross off another dealer as an information source:

"I've got 40 years ...." "I've been here 35 years ..." (service advisors) "... and have never even seen one; I don't know anything about them, and I can't help you.".

Then there's the one quiet- no, silent - dirty-hands mechanic sitting in the neck of the front desk area, listening to the advisors bragging about their tenure, who glances at me when I clarify (repeat for the second time) what I said and ask a redirect question, can see my frustration, and he gets this almost imperceptible smile in the corner of his mouth; which disappears immediately when one desk guy (who clearly didn't want to spend any more time or effort) turns to leave.

HE is the guy I want to talk to; and of course I'd never be able to do so. The only one in the desk area who seemed to follow what I was saying during my initial explanation, and seemed to be actually thinking about what I said.

HIS opinion - speculation, sure - I would value; the other two - not so much.

Thank you all for your input and consideration.

BTW:

At the closest CNG station last night (KoP, PA, 05/14/22):

REG: $5.09
DSL: $6.59
CNG: $4.19

(the regular is just a little overpriced for the area)

Re: Dual fuel Chevy Express weirdness

So fuel usage is all over the place based on power and efficiency of both the engine and the driver.  Examples below:

Suzuki Esteem 1.6L auto on 7 year old all season tires raced 12 hours in a deluge...3.2 gph.  Track dries out, we put our hotshoe in AND we have enough laps to win IoE if offered so tell him to go nuts and see what it can do...5.8 gph and had to have a gallon added just to drive onto the dolly.

Dusbuster minivan, 3.8 NA with the awful 4T60E driven at 10:10's with a correctly functioning transmission...7 GPH.  Same Van driven at 10:10's with the manual swap...5.8 gph.  Driven at normal race pace with the manual trans 5.0 gph.

1947 Plymouth with the original flathead 6 and three-speed transmission driven as hard as such a combo can be driven...4 gph (1 1/4" carb might be the reason).  1947 Plymouth with a Buick 3800 SC, small pulley, headers, unknown tune, 5-speed, aggressive gearing and a driver not following race instructions chasing fast RX7...12 gph.  Same setup but driving 7-8/10s...8.5-9 gph.

I could go on but I think you get the idea.

Re: Dual fuel Chevy Express weirdness

Yes; thank you for this ^.

Still thinking an under carriage tank could be useful to transport fuel for race cars, but it's clear my impression of fuel consumption was _way_ low. And I'm not ready to cobble together a pump system, which would only wind up filling fuel jugs.

The closest track to me is NJMP, and there's a CNG fuel station where I previously filled my CNG Civic at $1.00/gge, when gasoline was at $2.25/g, and there are several CNG stations on the way.

So I could conceivably tow a car with this van and not run out of fuel on the way, as I'm expecting a nominal 12-16 mpg (gge - gasoline gallon equivalent) to drop to maybe 6-8 mpg when towing.

I'd be able to get to the track with a full tank, but I agree 33 gallons isn't ideal. And it's only the one pump with the cost so low; though the prevailing CNG cost is still a benefit.

Re: Dual fuel Chevy Express weirdness

Racing fuel economy when measured in gallons per hour can be all over the place depending upon track conditions, driver, and how big the fire under your ass is.

Measured in laps per gallon, however, one might see less variation.  That was certainly the case for one of our cars.  Regardless of who was in it, how wet it was, or how much the track was yellow, it would go N laps on a tank, plus or minus one.  (That car had a drivetrain with unique characteristics, though.)

That said, it is certainly possible to conserve fuel without massively impacting pace, particularly with fuel-injection.  Coasting at the top end of the straight will put the ECU into fuel cut.  Carbs not so much.  The biggest gain we saw there was not blipping the downshifts.  That requires a very late single downshift of however many gears you need, is hard on the clutch, and carries with it a certain level of risk vis a vis spinning on entry.

Anyway, thinking about economy in terms of how much distance instead of time can be covered has interesting strategy implications.

You mileage may vary.  Nyuk.

23 (edited by Lemon_Newton-Metre 2022-05-16 09:21 AM)

Re: Dual fuel Chevy Express weirdness

hoverducky wrote:

[snip]
Anyway, thinking about economy in terms of how much distance instead of time can be covered has interesting strategy implications.

You may have let loose the "secret sauce" here.

hoverducky wrote:

You mileage may vary.  Nyuk.

ROFLMAO!

This thread has way more interesting and useful information than my limited scope, individual situation topic would indicate to someone scanning the category.

You gotta love the drift.

Re: Dual fuel Chevy Express weirdness

Final situation:
10.2 gge CNG capacity; around 100 miles around town to be safe

The onboard gas tank is junk, and has been removed.

I think my maximum fill so far has been 7.6(?) gge's when the needle is on the red mark on the gauge. That gives me a nominal 40 mi. buffer after "empty".

Re: Dual fuel Chevy Express weirdness

Final situation:
10.2 gge CNG capacity; around 100 miles around town to be safe

The onboard gas tank is junk, and has been removed.

I think my maximum fill so far has been 7.6(?) gge's when the needle is on the red mark on the gauge. That gives me a nominal 40 mi. buffer after "empty".