L31 (Vortec 5700) swap

[benjaminearle]

Well, had a great weekend working on the truck and then...driving it.

I got the pushrod drilled out to install on the brake pedal and got that buttoned up. Then got the driver's side exhaust completely hung. I'm loving my $240 Jegs pipe and muffler kit - especially after Midas tried to rape me for $900 to put pipes under it. Went ahead and spent the money to have the wheels swapped out (had a slight problem when it turned out that the lugnuts which came with the wheels were M12x1.5 and would spin on and tighten down until you put an impact gun on them - then just spin. So I was able to quickly source 12 - 7/16x20 mag seat nuts down the street to get 3 on each wheel and drive away.) Found 12 more the next day.

Drilled my new TBI right side manifold and welded on a O2 sensor bung, painted the manifold and swapped out my old LM1 manifold (with a massively leaky heat riser valve) for the new with a doughnut to seal it up. Finished off that side of the exhaust and cleared the codes, cranked back up and got a nice oscillating signal from both pre-cat O2 sensors.

Still has a pending code for #6 misfire (probably needs a spider) but I can't put $400 towards that right now. All other codes are 4L60E-related which I guess I'll just have tuned out. Oddly is hasn't thrown a rear O2 code and those harnesses are cut off. Still having fuel gauge problems and i know it's not the ground because the fuel pump shares that ground and it works fine.

Brakes still have some life in them but I should do them when i save the scratch for shocks. Have half a mind to go ahead and put 4" into it with some used lift kits coming with good shocks for only $100 more than just shocks would cost.

I'm thankful autumn and winter are coming and i can use the good heat and wait for the AC expenditures.

Here' s the new pics

Oh, and I now have a set of aluminum 15x10 6-lug wheels for sale. I'll even spray them plastidip black for the right price. They're in Atlanta metro and probably not worth shipping.

 

[foamypirate]

Great work! Truck looks awesome man.

 

[benjaminearle]

Ok, with the help of all y'all i got her on the road and today solved my giant transmission leak (kick down cable was completely out of transmission). I still have a funny drivability problem - when i mat the gas and really load it up it tachs up and pulls but then shuts off at some point (no tach, so i can't say if it's always at the same RPM). I currently don't have vehicle speed going to the computer (driveshaft ate my pickup wires). Wonder if that could be causing it, as well as my apparently sub-10 mpg. Any ideas?

 

[benjaminearle]

Well, my mileage wasn't as bad as i thought. I have no speedo/odo right now so i filled up and then tracked my trips with google maps, filled up again (at ~1/3 tank) and did the math. Looks like 11.3mpg mixed city/highway. Not so bad for an NP203 running fulltime and a THM350, on 32" A/Ts.

Maybe once I get my speed sensor hooked up and can use the EGR system i can break 12.

To do much better I think I'd need to bit the bullet and fix up a 4L60/80E which would involve an adapter for the NP203 and potentially driveshafts. I can buy a lot of gas for that cost. On the other hand, I'm kinda tired of not being able to use my whole tank of fuel. Guess I'll break down and buy an 87TBI tank sometime soon.

 

[Driver4r]

4l60 is tha same as a 700, and a 700 will bolt right up, but with a 203, youll need a spacer that goes between the trans and the tcase.

And interesting swap, most people just takes the l-31 heads and put them on a gen I small block.

 

[kleedus]

makes me wonder what my crew cab will get for mileage with the vortec 383/4l80 4.10 gears and 35'' tires.

how do you like the vortec in your truck

 

[benjaminearle]

makes me wonder what my crew cab will get for mileage with the vortec 383/4l80 4.10 gears and 35'' tires.

how do you like the vortec in your truck

Mileage might not be as bad as you think if you keep EGR and run in 2wd for the most part.

For the most part I like it in the truck. I truly love that it cranks right up in freezing weather and after letting the trans build a little pressure and heat you're off to the races.

I wish it were more snappy, like a GMT400 with a L31 in it, but maybe that's just the NP203 taking all the snappiness out of it.

Latest challenge is that i got a Tractor Supply toolbox from craigslist and only paid $50 becuase once i got to the guy, we couldn't get it open. It's a pushbutton style and i think the pushrod is somehow out of whack. Anybody got any ideas?

 

[kleedus]

I have deleted the egr already I didn't like how messy it made the inside of the intake. and I think the egr in the l31 bakes the front intake gasket causing it to leak.

and plumbing exhaust back into the engine just does not seem right to me. I would think it would be cleaner with out it

 

[ScottyB]

Anytime I see discussions about EGR I go back to the same place: The idea of an EGR is like the idea that you eat your own **** to get the nutrients you missed the first time. It may look good on paper but it just doesn't make sense in the real world.

 

[kleedus]

my understanding of the egr system is the exhaust is an inert gas to take up combustion space. the computer should lean the fuel out when the egr kicks in so less fuel and less air to burn.

http://en.wikipedia.org/wiki/Exhaust_gas_recirculation

 

[benjaminearle]

Scotty, you're close but it's more like drinking your own urine (which, BTW, although gross, is sterile and won't do any harm - some folks do it while training for a fight and if stranded at sea it's much much better than attempting to drink seawater).

If the engine is running properly, the exhaust is just a hot, clean airstream full of water vapor and CO2. It works as a displacement reduction (the volume taken by exhaust gasses doesn't need fuel added to it - it just passes through). Not as efficient as cylinder deactivation because you still have the (sizable) pumping losses but it's better than nothing.

If it's coking the intake there's a different problem there - specifically unburnt hydrocarbons in the exhaust. As for the cooking of the gasket - yeah, i can see that as a weak point.

If anyone DOES do L31 EGR in a square body - find a 87+ TBI driver's side manifold (can go to 91 with a van, 'burb or K5) - you can use the O2 bung for, well, O2 and use the AIR pump fitting at Cyl #1 for EGR - just takes some plumbing (1/2" and 5/8" copper and brass plumbing fittings and tube make up a loop nicely).

 

[benjaminearle]

you beat me to it, Kleedus.

 

[kleedus]

every l31 I have torn apart has had a mess inside the intake from the egr and baked left side intake gasket.

I removed mine for those reasons and I think it would run better without it.

I live in WYO and we have no emission laws of any kind here

 

[Brennan88]

I have the complete L31 harness so I'm just tying in where i need to to the '79 harness and jumping out things that aren't present on the '79 like park safety switch, etc. I got a universal VSS unit from Dakota and everything else is factory sensors. I'm keeping it OBD2 for diagnostics so as much as possible needs to stay stock.

Where are you tying into the old harness at? im doing an l31 swap into an 88 camaro and im not to familiar with wireing. i cant find too much online about this swap normally all you find is on an ls series engine

 

[benjaminearle]

Where are you tying into the old harness at? im doing an l31 swap into an 88 camaro and im not to familiar with wireing. i cant find too much online about this swap normally all you find is on an ls series engine

I tied in, IIRC, at the distributor, alternator, and then at the big bulkhead connector for +12, +12sw, gauges, etc. I'll see if I can dig up the cutover diagrams I did for the project - truck has since been stolen.