LS1 Swap

[BonzoHansen]

Im still way up in the air over it. There are a lot of benifits, but also some sizeable drawbacks.
Ive gone over it before, but Ill bring it up again.
4th gen tank allows the tank to regulate the pressure and not an aftermarket unit.
I get a plastic tank thats a bit lighter, but I get the advantage of the bucket that keeps the pump surrounded in gas.
I also have to adapt either the sender or the gauge so that I know how much fuel is in the tank
4th gen tank also gives me an evap canister attached to the tank.
But...i cant use all that fancy stuff unless I go with a total 4th gen dash. The dash has something to do with controlling the evap canister.

I highlighted a very important pat for a street car. EFI does not like to be fuel starved.

The comment about the 4th gen dash required to use 4th gen evap can't be right. I'm going to read the book. I still don't understand why using the entire fuel system from a 4th gen doesn't work for you. My experiences still tell me GM engineers are better engineers than I am.

[BonzoHansen]

So I thumbed through my 99 Camaro service manual (ebay score $50) and it looks like the EVAP solenoids get ground from the PCM and power from a hot run/start circuit. I see nothing interesting in regards to needing a dash

[BonzoHansen]

Talk to John @ speartech, I bet there is a way to make your gas gauge work with this.

[BigAls87Z28]

99 might not have the plastic tank. I thought it was 00 and up. I didn't understand the dash thing either.

[BonzoHansen]

99 does. I still have the one I pulled from the one I stripped.

[Mike]

my 99 has plastic too...

[BigAls87Z28]

Hrm I thought 00 was the change over. Oh well whatever still needs something with the dash to activate the evap because the sending unit sends a signal to the gauge which then activates the whole process. Something like that.

[BonzoHansen]

Who told you that?

[Mike]

i have had my dash out and played with every wire behind it, i dont remember any emissions related wires

[sweetbmxrider]

S244, fuel level sensor and fuel pressure sensor are on the same circuit. there's your problem.

[BigAls87Z28]

IYeah its on TGO. when I get home ill post up the correct info as I forget the correct wording.

[PolarBear]

Originally Posted by BigAls87Z28

but I get the advantage of the bucket that keeps the pump surrounded in gas.

This, and the fact your tank would never rust.

Originally Posted by BigAls87Z28

I also have to adapt either the sender or the gauge so that I know how much fuel is in the

If you are not worried about the PCM getting the proper input then it is as easy as swapping the sender board, I did it and while I was in there I did the Racetronix pump. Took me about 30 minutes for both.

Originally Posted by BigAls87Z28

Now if I stay with the stock tank, I guess I will have to reuse my old evap canister? But how will that be connected? I gotta start digging around TGO and LS1tech more.

No one answered my queestion on TGO about how the dash controls anything. From my understanding the PCM does ALL the work regarding the EVAP. IMO I think changing the resistor on the back of the fuel level gauge is the way to go in the situation. I have another cluster I can mess with and another fuel bucket I am can try, but I hadnt planned on doing any of that right now. I will get it all out this week/weekend and see what I can do, for a few dollars at Radio Shack I think this is a no brainer.


Also FYI to all, the 98 had a steel tank and 99 and up got the plastic tank.

[BigAls87Z28]

James, yeah I didnt understand how the dash did anything. It sounded as if the gauge in the factory dash sent a signal to the pcm, which would then activate the evap...if thats whats im reading right on TGO.

The advantages of the 4th gen tank is a great deal, and I already have one so that really helps things.

[BonzoHansen]

I think TGO info may be wrong on that according to my book. Reading more now, be right back...

[sweetbmxrider]

The PCM uses the fuel level sensor input in order to determine the amount of fuel in the fuel tank. The PCM disables the engine misfire diagnostic when the fuel level is too low and the EVAP system diagnostic when the fuel level is either too high or too low. The PCM also controls the fuel gauge based on the fuel level input.

it really seems like if you want to use the 4th gen tank and have your fancy emissions crap connected and working, you need to use an ls1 cluster. i'm sure there's ways around everything if you don't wanna do that.

[BonzoHansen]

Originally Posted by sweetbmxrider

S244, fuel level sensor and fuel pressure sensor are on the same circuit. there's your problem.

My initial instinct is you are looking on the wrong side of the pcm for fuel gauge reading. that is the serial out of the PCM. I'm thinking you can tap the lead right off the sender. I'm not even sure why the pcm needs fuel level info for running the engine, but it does appear to impact emissions related items. I'd bet 99.9% of the conversions out there do not use fuel level in. You can't tell me that all the LS swaps in old cars use fuel level in.

From reading the 99 service manual it appears EVAP and fuel pressure sensor work in unison to some degree. Some EVAP codes need 15%-85% fuel level as a testing condition. EVAP issues may throw off fuel pressure readings, which is based on tank pressure, not line pressure as you’d think of it. So based on 30 minutes of reading DTC codes and looking at diagrams, I think you can make both work but I’d stay as close to OE as possible and your EVAP connections need to be spot on. And I see zero evidence of feed back from the gauges. EVAP and FP readings both go to the pcm 1st, then a serieal out for fuel level to the gagues. Why would they get a reading back?


I think this is a decent primer document:
http://www.gmperformanceparts.com/_r...44807E-ROD.pdf

[BonzoHansen]

Originally Posted by sweetbmxrider

it really seems like if you want to use the 4th gen tank and have your fancy emissions crap connected and working, you need to use an ls1 cluster. i'm sure there's ways around everything if you don't wanna do that.

Why? That tells me the pcm feeds the gauge. I have not found anything on the opposite yet.



Al, good for you. EVAP is a zero HP loss, high gain emission control. Evaporating fuel is terrible for the air.

[BigAls87Z28]

Well, then I come to this question is that what do I do? I just let it vent out?
I guess GM needed a way to have the computer be in constant check of the pressure in the system for emissions control purposes where in older cars it was more or less kind of just hoped that everything was hooked up together.

Originally Posted by BonzoHansen

Al, good for you. EVAP is a zero HP loss, high gain emission control. Evaporating fuel is terrible for the air.

Im picking up sarcasim a bit?

[BonzoHansen]

Is speartech doing your harness? If so, call him for his $0.02.

I still think you can do the 4th gen fuel/evap swap part for part. Again, look at the e-rod instructions. pretty similar I think. with all your goofy gm nutwork at gmi can't you get a number of a gmpp tech to talk to?

[BigAls87Z28]

GM Performance Parts will know nothing
GM Performance Division was disbanded and the members were sent into each of the remaining divisions after Chap 11.

People I talk to are not engineers, they are PR/Communications people with very little contact with anyone from powertrain.

And no, Speartech is not doing my harness.

[sweetbmxrider]

listen, i'm having a little trouble thinking straight but from what i can gather you can't run the evap can without the instrument cluster. i'll try to read into it more but it just doesn't seem to be possible without all of the pieces.

evap **** is very finicky and i hate it

[BonzoHansen]

Originally Posted by sweetbmxrider

listen, i'm having a little trouble thinking straight but from what i can gather you can't run the evap can without the instrument cluster. i'll try to read into it more but it just doesn't seem to be possible without all of the pieces.

evap **** is very finicky and i hate it

I'd be curious to know as it makes no sense and the book mentions nothing in any of the related DTCs I read. I'm not saying you're wrong, I'm saying I do not see that in the book.


Al, how does evap work in your car now?

[Tru2Chevy]

The PCM uses the fuel level sensor input in order to determine the amount of fuel in the fuel tank. The PCM disables the engine misfire diagnostic when the fuel level is too low and the EVAP system diagnostic when the fuel level is either too high or too low. The PCM also controls the fuel gauge based on the fuel level input.

Is this what is throwing you off Adam?

I read this as the PCM uses the fuel level sensor input from the tank to determine the level in the tank. Then it does what it has to do with the codes based on the level in the tank, and then the PCM outputs a signal to the fuel gauge based on what it saw from the fuel level sensor in the tank.

I don't see any reason why this output from the PCM can't be used to run a stock fuel gauge in some way.

- Justin

[BonzoHansen]

Originally Posted by Tru2Chevy

Is this what is throwing you off Adam?

I read this as the PCM uses the fuel level sensor input from the tank to determine the level in the tank. Then it does what it has to do with the codes based on the level in the tank, and then the PCM outputs a signal to the fuel gauge based on what it saw from the fuel level sensor in the tank.

I don't see any reason why this output from the PCM can't be used to run a stock fuel gauge in some way.

- Justin

I don't see why the cluster is needed...but....that 'out' on the pcm is a serial out, so I assume it carries other info too. So I think that is no good.

[BigAls87Z28]

Originally Posted by BonzoHansen

I'd be curious to know as it makes no sense and the book mentions nothing in any of the related DTCs I read.


Al, how does evap work in your car now?

There is a canister on the driver side behind the headlights. There is a vent tube that comes up from the tank to the canister. There is a connector that I assume controls what goes on with the charcol canister, with vac tubes going into the engine.