dimented24x7

iTrader: (2)

Wet flow systems suck. Ive just about had it with accel enrich. Originally my car always ran like crap so I never noticed it as being a problem, but now that its running properly, the AE has become a real annoyance.

Basically the problem is that the AE is based off of engine cool temp in the computers. All fine and good, but with an aftermarket manifold, the cool temp and manifold temp never match each other. During normal driving in this cold weather, the temperature of the manifold is anywhere from ~20 deg F on the highway all the way up to around 200 deg F after heat soaking for a bit. All the while, the coolant temp is around 195 deg F. Basically, when the manifold is real hot, the engine will stumble and blow smoke for a second or two when I hit the gas. When its real cold, it leans out real bad for several seconds before it finally catches up and goes. The rest of the time, it works the way it should. When the engine is first started cold, it runs great. No hesitation/stumbling at all. Its only when the engine has had a chance to begin warming up that I have problems.

Basically its the same problems I had with speed density. Due to the fact that theres gas in the manifold, the manifold and incoming air temp can basically be any temperature it wants to be due to fuel dynamics and theres no real way to compensate for it, other then drastic measures.

My latest drastic measure will be to use an edelbrock RPM air gap. Not only does it have a much smaller plenum then the performer, which is bigger then my appartment inside, but the plenum is seperated from the floor of the intake manifold. This means that I can finally actually know what the intake manifold plenum temperature is by sticking a thermister (thing inside a coolant temperature sensor) in the plenum wall. With the performer, the engine heat and heat lost from gasoline flashing to a vapor interact in a complex way that I cant really model.

Hopefully this is the last key ingredient to getting TBI to run like port fuel injecton. Right now it runs great under constant throttle, but its anyones guess when I move the gas pedal.

Oh... that, and the RPM ought to be a nice upgrade.

liquidh8

I'm with you on the AE issues. I've been playing with mine eversince I got the ability to tune. Grant it, with EBL it has improved, but i can't seem to get it right. I have vortec heads on a 350 too, with a GMPP 4 bbl vortec intake, similar to the RPM. I have the IAT hooked up, it's better with it than without, But I am having some issues getting the AE thing figured out.

dimented24x7

iTrader: (2)

This is one of the downsides to a wet flow system. The temperature of the manifold determines how much AE will be needed to compensate for fuel settling. With a hot manifold, you dont need much. With a cold manifold, youll need more as the fuel will settle out onto the walls of the intake. Problem is that in a vacuum, gasoline acts like refrigerant in an air conditioner. It really cools the manifold down alot. I take air in off my radiator, and with IATs around 80-120 degrees, Im seeing the manifold and TBI get down to near freezing during cruise from the gas sucking all the heat out of the manifold. Basically your trying to hit a moving target

GM handled this by using a fully heated manifold. This drives the fuel off the walls of the manifold, which lessens the need for AE. The blended IAT/CTS in EBL and the SD calibrations is great for WOT, but for AE, its of little use as the dynamics are quite complex. Thats why Im going to try a different manifold and measure the temperature of the plenum wall directly and use that to control the ammount of AE and decel enlean. Crossing my fingers and hoping it works.

kdrolt

IIRC a neighbor of mine dealt with this issue by relocating his IAT sensor from the air cleaner housing into a threaded bung provided in the factory TBI; the car was a 1991 Caprice LTZ with the same LO3 used in the 3rdgens. By doing the IAT relocation he had more of a direct measurement of what the true intake air temp was inside the intake manifold.

I haven't asked him about the details in a while (2 years?) but I'll ask him again and post it.

dimented24x7

iTrader: (2)

I think Fast did that as well, and it makes a lot of sense. At least the fueling will be closer to what it actually should be.

Im thinking of using a small NPT pipe plug and embedding a thermister in it and then mounting it in the intake plenum wall. Currently my IAT is in use to help cover for the few millisecond response delay in my MAF. I need a split second pulse of TPS AE to prevent a lean cylinder firing or two. Hopefully using the manifold temp will at least get teh long term AE in the ballpark. Right now its not even close.

liquidh8

That's right, I forgot you had a MAF with your TBI. I have my IAT right in the air cleaner housing. I have a 4 inch cowl hood, so while driving I get the rush of abient air coming in. I should try mounting it in the manifold. But, I don't know if the IAT is designed to get fuel and all on it, since the TBI manifold is a wet flow design. In any case, keep us posted on how you make out with the manifold swap.

dimented24x7

iTrader: (2)

The IAT should be able to survive ok. IIRC, the plastic that the cage was made of made out ok in my air cleaner even though it was exposed to fuel. You could always use a cool temp sensor. Itll have a slower response and isnt as insolated thermally as the IAT sensing element, but its a sealed design, so it will be impervious to gas.

Fast355

iTrader: (2)

The CTS was used as the MAT sensor in alot of TPI applications.

liquidh8

O ok cool, I'll have to give it a try and see how it affects my AE.

kdrolt

IIRC the one my neighbor used was an IAT sensor from a GM fwd v6 car, a sensor that was designed to fit inside the intake manifold.

I haven't heard from him yet but I will confirm what he did when I talk to him.

dimented24x7

iTrader: (2)

Heres the one I made. I found some thermisters with the right characteristics on the net. Its a 1/8" pipe plug with the sensor inside and a GM weatherpack connector. The inside of the plug is filled with epoxy. Hopefully it survives. Ill have to soak some cured epoxy in gas and see if it survives.

Fast355

iTrader: (2)

Thats the same closed type sensor that is used in the TPI engines.

dimented24x7

iTrader: (2)

I finally got around to working on this. I ended up using a small piece of scrap aluminum for the sensor since gas likes to eat epoxy. I polished the side of the plenum and the face of the piece of aluminum and stuck some silver heatsink past between them. Seems to conduct heat quite well. The sensor has a thermister with a weatherpack pigtail embeded in the aluminum body.

I also had to radius the plenum to accomodate the larger TBI. The only airgap type plenums available for the vortecs are all square bores. The gasket surface gets pretty thin near the edges. Hopefully itll still seal properly.

liquidh8

That's rather ingenious. Nice work! So how does it work out for you??

dimented24x7

iTrader: (2)

Im installing it today. Going to have to wait a bit for all the ice and to finally go away before I can test it out, though. Cant afford to expose my rust-bucket to any more salt.

dimented24x7

iTrader: (2)

Finally shoehorned it in. Man these are high manifolds. I had to cut the bracing out from under the hood, cut the aircleaner stud off nearly flush with teh top of teh carb hat, and raise the stops on the rear hood linkages to bump the hood up, and it still just barely clears. Cars running, but I havnt wired up the sensor yet, though. Cant wait to try it later and see how it works.

dimented24x7

iTrader: (2)

The dedicated manifold temp sender is definatly the way to go. Much more consistant. I got it to where it seems to do fairly well under almost all operating conditions, from lugging it to slamming the gas down. Still has a slight momentary hesitation and goes to 9:1 on the WB every once in a while, but overall, it seems to be much better and more predictable. No more pig rich stumbles or vicious lean tip-ins.

Another thing is that edelbrock wasnt lying about that RPM part. The off idle sucks with this thing. The turbodiesel torque at 1200 RPM is gone. It pulls ok, but it doesnt wake up untill after 2500 RPM. Even with the crappy cam in it, it now pulls past 4000 RPM with the new manifold and has ok top end. Definatly not the choice for a stock TBI motor or anything with crappy heads. That and you wont be able to use an air cleaner with the stock hood. Too high...

dimented24x7

iTrader: (2)

The only other issue is that with the added functionality comes additional complexity (see all the damn tables in the pic). The transient stuff is a real nightmare. Might almost be easier to run a fully heated stock manifold. Power output would suck, but it would be alot easier to tune. The only thing I really cant help is if I slam the gas down and then lift suddenly. All the fuel vaporizes and the engine stumbles a little. Already using alot of decel enlean. Any more, and the engine would die under normal throttle lifts.

liquidh8

Dimented, I may have to put my IAT sensor in the manifold and try it out. I think I am running out of things to do to tune the AE in my setup. Though it is much better than it EVER was, my learning curve has gotten better. I think I may have to try it out in the spring. Keep us posted.

Note on your sensor, what parts did you use to fab that up, i.e., the thermistor? If you want to keep a secret I understand

dimented24x7

iTrader: (2)

The sensor is made from a piece of scrap aluminum, a generic thermister from Jameco (dont remember the specs exactly) and a weatherpack pigtail from Pep-Boys. I drilled a hole in the center and epoxied the thermister with pigtail attached inside. Lastly, I polished teh face of the intake and sensor for good heat transfer. The caveat is that you have to use an intake with a seperated plenum to more accurately estimate the AE.

dimented24x7

iTrader: (2)

The only thing to be careful with with the IAT is that some of them have very looooonggg transient responses. I know the coolant temperature sender used on the TPI car intakes takes eons to reach steady state. The open cage type would probably be better, but still takes time to transition from one temperatue to another.

The best thing to do is to make sure the engine intakes warmed air. This will help the manifold maintain a more uniform temperature and make AE and fueling easier to tune.

liquidh8

I could do that, but it runs much better WOT with the open element and cowl air (4 inch hood). I am just trying to find a happy comprimise.

dimented24x7

iTrader: (2)

Heres some videos of it in action. The only real issue I have is it goes pig rich if you open and then quickly shut teh throttle. Even with decel enlean cranked up, its still pig rich. The manifold must hang onto alot of fuel during transitions.

Cold revving:
http://www.youtube.com/watch?v=Gv7c-F6qskA

Hot revving:
http://www.youtube.com/watch?v=ikMCOzuAQKc

WOT slam at low speed in second gear. 10-50 MPH This is the thing that would always cause it to really pop and stumble before.
http://www.youtube.com/watch?v=ye9XOBvGFWE

Lasty, driving the car around:
http://www.youtube.com/watch?v=idqt8B8y3iw

Fast355

iTrader: (2)

Sounds good, except your Camaro is as clunky as my Van, lol.

YouTube sucks for audio synchronization with the video, but here are mine.

Startup in 25* temps
http://www.youtube.com/watch?v=GeyY5UZ0V6I

WOT run from a stop to approximately 55-60 mph
http://www.youtube.com/watch?v=koWaPeAu3hg

2/3 pedal from 20 mph
http://www.youtube.com/watch?v=c6qV9T7ZCOI

Just a little highway cruise at 70.
http://www.youtube.com/watch?v=ggzfrxAt6FQ

Fast355

iTrader: (2)

I made a few more this morning.

Stomping it Wide Open on a cool engine. Hesitated slightly, but recovered quickly and went.

http://youtube.com/watch?v=p2kH39oC8O0

dimented24x7

iTrader: (2)

Thats how it used to be with the auto. Never really bothered me that much. Took the doctors advice: If it hurts, dont do it. Simply rolling into the gas would side skirt it. With the stick, though, it would do that in every gear on every shift.

Fast355

iTrader: (2)

When the engine and intake manifold is fully warmed up, doing that will blow the tires away. It still has a little too much AE to it. I am just leaving it be right now, because the 2" bore marine TBI unit is going on soon. That should help lean things out on throttle stomps.

dimented24x7

iTrader: (2)

You can play with the sync AE mult. vs. cool temp. As long as the engine isnt near operating temperature, you can play with the multiplier that cooresponds to the engine temp at the time of the issue to improve the stumble without effecting how it runs when fully warmed.

How big is the current TBI? If its the stock 305/350 one, then the 2" unit will really need more AE as well as more momentary TPS AE.

Fast355

iTrader: (2)

I know that I can, just really haven't had too much time to mess with it.

The current TBI unit is bored to 46mm from stock.

FWIW- This is how it runs when warmed up, just messing around.

http://youtube.com/watch?v=sNgHi85M6AY

slowolej

Yes, he did that. But IIRC it's not an option for guys using a stock 7747 ecm.

The L03 engine you're thinking of is still running, BTW, and takes a 1/2 ton pickup from Epping NH to Boston area daily. Still seems like a 350 from the driver's seat.

The 7427 pcm appears to use CTS only on B9 in the TBI trucks, but uses IAT on B9 and CTS on B8 when used in the 4.3 S and T vehicles. Interesting...

dimented24x7

iTrader: (2)

What years where those, out of curiosity?

Both inputs work the same, so theyre interchangeable. In the masks Ive seen, the TBI, CPI, MPFI code are all present, but the IAT compensation blending tables are zero'd out and the option bit to use the IAT is unchecked when TBI is in use. All modes have the CTS assigned to B9 and the optional IAT on B8, but I havnt seen all the masks yet.

91chevz71

I mght try relocating mine too. (from air cleaner to man.)
So is it OK to use the birdcage IAT in the manifold?

kdrolt

Nice to see Batman's work lives on.

How is the fuel economy over that run, and what exhaust is being used now that the 94-96 WX3-sourced N10 duals are gone? Do you still have your CFI pickup truck?

slowolej

My reference is aftermarket service software. I've got more time to sit and compare information and it looks like whoever manually entered the pinouts into this software got the columns misaligned on the 94 K truck w/ 5.7. The coolant temp sensor input on the K and S trucks in 94 are both on B9.
edited to specify which temp sensor

I saw this while roughing in a calibration for a 302 PFI engine. The 4.3 CFI S truck engine uses IAT and I copied some of these tables directly into the 5.7 TBI base cal I've chosen as part of the initial tune.



Yes, I have the Xfire pickup. The little 302 runs well with the 7747 but I'm really considering switching to 7427 and a Smoke Ram intake. I get limited time to tune it and the later / faster/ emulator friendly pcm would really be helpful.

I believe the fuel economy on the L03 is somewhere between 16 and 19 mpg now that the truck owner has finally replaced the faulty distributor. Exhaust was a conglomeration of short headers and truck single exhaust but has been recently replaced by full duals. I did have to make a couple of cuts at the prom to straighten some AE issues that showed up with V6 converter and 3.23 gears.

DENN_SHAH

iTrader: (1)

i thought i would mention that caddy used a caged type IAT sensor in one of the runners on the intake on some of their TBI engines.
i just replaced one a few days ago, i don't remember for certain, but i think it was a 88 4.5 sedan deville.

Street Lethal

iTrader: (16)

Dude, did you have the camera clenched under your neck, or were you holding it with your teeth LOL? Car sounds nice bro....

snflupigus

dimented... still having troubles with this? see my "saga" post - My stumble is pretty well gone but.. my air temp is almost always HOT here

dimented24x7

iTrader: (2)

I have a double-jointed jaw actually...

Held it with one hand and drove/shifted with the other.

Thanks, the budget blowmaster single exit exhaust actually doest sound half bad considering its the cheapest 3" exhasut they have... I like it better then the american thunder, which is too loud for my taste.
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It runs pretty good now. The only issue is that I run out of injector in the winter, so on a hard throtte drop, itll hesitate a little. With the moderate winters and summers here in dirty jerzy the car sees the full range of conditions.

RednGold86Z

iTrader: (1)

If you think about it, a water heated manifold might actually work well as a fuel-cooled coolant manifold, and may improve the cooling system AND get better economy WITHOUT sacrificing power due to heating the air (i.e. the fuel evaporating cools the air enough to bring its density back to ambient).

I love transients... It's my life's ambition to make the most perfect algorithm with the simplest code. Don't really want to go to a full model (that's no fun). May have to though...

snflupigus

i'm getting closer to my base maps being perfect... but you are SO right.. if my coolant temp doesnt stay constant, it all goes to hell by 2-3 percent off.

I wonder how low it took GM to get the maps and stock tables set. 1k man hours?

RednGold86Z

iTrader: (1)

Nope, just 1 AIR pump, and a few diverting switches. Throw in some EGR. Let the exhaust cross through the manifold. Retard the spark from MBT by several degrees. Keep the cam small. Use a restrictive air cleaner, with heat. Use as small a TB as possible. And probably a few other tricks that I'm not thinking about.

Then, throw in some man-hours. And verify the results in hot, cold, high and low.

dimented24x7

iTrader: (2)

Mmmm... Yeah. Perfect recipie for 170 HP, no matter whats parked underneath the TBI.

I remember when I replaced the 305 with the 350. Ran great, but didnt make any more power then the stock L03 it replaced. It seems that the tuning required increases exponentially to the number of performance parts added.
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The other trick was fudge factor. The stock code has LOTS of it. If you look at the code, even the inverse AFR table is based on fudge factor rather then reality.