Flex fuel or gas?

[Dutchman]

According to my VIN, my truck is flex fuel (Z). But I had to drop the tank to replace a line this weekend and the lines and pump match what online stores have for gas only trucks. Can the flex Tahoes be converted to gas only? I rarely even see E85 fuel anywhere, much less use it, so gas only is perfectly fine. I'm just wondering if mine has been converted some how.

Here's the top of the fuel pump. I looked it up and it's labelled gas only.

 

[Dutchman]

So, no responses so far. Is there an easy way to tell if my engine is gasoline only? My VIN says it’s flex, but I think it may have been swapped.

 

[OR VietVet]

No doubt that the one in the pic looks like this one from RA: https://www.rockauto.com/en/moreinfo.php?pk=496248&cc=1412244&jsn=932&jsn=932 which is listed as a gas pump assembly.

No idea why you would have a Z code instead of T code like mine does. That is strange. List at least the last 8 digits of the VIN and hopefully @915_Tahoe will chime in with some info.

 

[915_Tahoe]

So, no responses so far. Is there an easy way to tell if my engine is gasoline only? My VIN says it’s flex, but I think it may have been swapped.

What is the last 8 of the vin#

 

[Dutchman]

The VIN is 1GNEK13ZX3J283139. As you can see, the eight digit is Z. When I bought it, the engine looked very clean and runs like a champ. I think it has been replaced with. Gas only engine. Is there a way to tell?

 

[OR VietVet]

@915_Tahoe, would the vehicle come down the assembly line with all attachments and electrical for both options and so would all be there depending on which way the VIN 8th digit is?

 

[swathdiver]

Consider that the previous owner put the wrong pump for whatever reason, maybe GM put the wrong pump in by accident on the assembly line or a dealership. Should be date codes on that stuff.

The big difference between the two systems is that the Flex pump can flow more fuel and has plumbing for the flex fuel sensor and larger fuel injectors.

 

[OR VietVet]

If you look at the two choices for pumps, there is a world of difference. At least it looks like a lot of difference to me anyway.

Gas/Robust system fuel engine code T: https://www.rockauto.com/en/moreinfo.php?pk=496248&cc=1412244&jsn=1067

Flex engine code Z: https://www.rockauto.com/en/moreinfo.php?pk=7056044&cc=1412244&jsn=1068

Gas except robust system: https://www.rockauto.com/en/moreinfo.php?
pk=1300750&cc=1412244&jsn=1065

Looks to me like the first link is a match but maybe the 3rd link as well. Whatever a "Robust System" is?

 

[Dutchman]

Consider that the previous owner put the wrong pump for whatever reason, maybe GM put the wrong pump in by accident on the assembly line or a dealership. Should be date codes on that stuff.

The big difference between the two systems is that the Flex pump can flow more fuel and has plumbing for the flex fuel sensor and larger fuel injectors.

So, if that pump has worked previously, I should be okay with the same as a replacement, right?

That leaves me with my original question. Is there a way to tell, by looking at the engine, if it’s flex or gas? Because I think it has been changed. It’s in too good of shape to be original, I’m thinking.

 

[OR VietVet]

Curiouser and curiouser.

 

[Wylie_Tahoe]

Have you confirmed a VIN match on at least 2 other locations on the truck? Like dash and door match and dash and frame match, etc?

 

[Dutchman]

I had not thought of that. I’ll check that ASAP.

 

[iamdub]

So, if that pump has worked previously, I should be okay with the same as a replacement, right?

That leaves me with my original question. Is there a way to tell, by looking at the engine, if it’s flex or gas? Because I think it has been changed. It’s in too good of shape to be original, I’m thinking.

The engines themselves are all the same and I'm pretty sure the only difference between FF and non-FF are the injectors. I don't think the manifold nor the fuel rails are any different since using FF injectors on a non-FF engine for performance purposes (nitrous, boost, big cam, etc.) is a common swap. The injectors do look different. Their electrical connectors are different as well.

FF injector:

Gasoline-only injector:

 

[Dutchman]

Thanks @iamdub. That’s the kind of info I was looking for. I’ll check that when I look at the VIN numbers.

 

[mattbta]

What year? Does it have an inline fuel filter, underneath the driver door area? At some point in the vintage, only the Flex Fuel motors got serviceable fuel filters.

 

[Wylie_Tahoe]

Based on the VIN the OP posted, its an 03. My 03 F/F has an inline fuel filter canister

 

[Fless]

The OE fuel filter will most likely still be there even if the engine was replaced with a non-Flex engine. Doesn't really tell the story. The fuel injectors will.

 

[OR VietVet]

If it does have a filter, it needs changed for sure.

 

[Dutchman]

There is a filter on the frame rail. And I will be changing that as well.

 

[OR VietVet]

Some here will not agree but I always install a new fuel pump relay when I do an electric pump replacement. It all stems from a story from when I was running shops years ago.