I hope you guys don't mind me posting here... I've had plenty of TransAms in my time, but working on my daughter's car which has an Iron Duke w/ a 300 TBI. I've got a scanner on the ALDL which is pulling back all the information.

I rebuilt the throttle body, had it bored out to 54mm, and went with a larger injector. It's definitely running rich, as I'm getting the O2 running rich error code (Which for this car is 45).

I'm not sure yet that I need to burn a new prom, as the engine itself, cam and displacement are all stock (though completely rebuilt, and slightly higher compression 9:1).

I ran the car initially, and it showed that I had a BLM of 128 with a long term modifier flag of -13 (whatever that means). Which I guess says it's trying to narrow the fuel adjustment.

For INT, it was jumping around anywhere from -27 to as high as -79 (or as low, I should say).

As I understand it, INT is the PID modifier that tells the ECM how much more fuel needs to be added for the next go-around... I think? It says it's running rich... which makes sense, I have a Corvette cross fire injection injector and a fuel pressure regulator from a Corvette on there (since it's bored to Corvette diameter). The intake was also bored out, and I have an exhaust header. I'm probably getting all of like 8 more horsepower on this Duke! Haha.

It ran pretty well, just definitely feels like it's running rich.

So I got the fancy tool that allows me to mechanically adjust the fuel pressure regulator while the car is running. I adjusted the fuel pressure regulator a couple of turns (closed it)... which I think reduces the amount of fuel going to the injector.

I then re-ran the ALDL capture and drove the car around a bit, and the BLM now says it's 115 with a modifier of -13. The INT generally seems a bit lower, but it's still giving me like anywhere from 0 to -50.

The car feels like it has more power, and is a bit more peppy... it's still saying it's running rich.

Can / should I reduce the fuel pressure a bit more? I'm trying to understand exactly what I'm doing.... if there's a primer on how these fuel maps work, and how the BLM and INT work... I'd really appreciate it.

 

You should put the stock injector back in. The bore'd TB isn't going to impact air flow in a meaningful way with a stock cam, stock head etc....you haven't really changed anything. Any additional fuel needs that the engine asks for with the larger TB can easily be handled by slightly increasing the fuel pressure with the FPR. Put the stock injector back in, set or ensure that fuel pressure is ~12-12.5 PSI as a starting point and the go drive the wee out of it.

You probably gained 0 hp with the bore'd TB. They stock TB is more than enough for the stock or stockish engine. It should have better low throttle angle response, tip-in "feel", however.

 

Thanks, that's actually a really good idea... I'd not really considered that, I just assumed I'd go with the injector that matched the TBI bore... but I'll do that (order a new stock injector, and replace it).

The engine does respond well to a larger bore. Just removing the air foil on the inside (that's used for atomizing the fuel better) actually increases horsepower by 3hp on a series of dyno tests. Individuals have gone with the Holley 3735 big bore TBI (which is 50mm), and when combined with the Holley intake (on an otherwise stock engine), they usually gain about ~12-15 horsepower. I mean... we're talking going from 92 horsepower to my goal of about 105hp. I had the intake bored out to 50mm, in case I want to put the 3735 on, but had XFire Performance do the boring for this 300 TBI and they re-used an original 400 TBI throttle plate.

It's my daughter's car though. She completely rebuilt the entire engine herself, and has basically completely restored the car herself, with me only doing a few fine details behind the scenes. She has a channel (hopes it'll help her get into a good college) if anyone is bored and wants to check it out: Gen Z Garage - YouTube


Anyway, that makes perfect sense. That's exactly what I'll do... I don't know why I didn't think of that.

And man... I really miss my 82 TransAm... I kinda want a 3rd gen. It's crazy... I "stepped away" from cars for over a decade when my daughter was born. I used to see rows of 3rd gens in the junkyard... I'd see GTAs in the junkyard, loaded 84 cars with the working cowl induction, to ones with the factory subwoofer... the weird Berlinettas with that strange console thing... all kinds of cars, all getting crushed. Now these cars are commanding $10k+ prices, it just blows me away. I used to see these almost given away at auctions. Makes me wish I could have saved some of those junkyard cars.


EDIT: Wanted to add that I'm not recommending or suggesting someone should remove the air foil. I'm keeping it in, but there are a lot of individuals back in the day that would remove this, and they did a dyno test to see what the effect would be. Personally, the intake design of this motor in stock form is less than great. Fuel tends to pool at the bottom and without that foil, it doesn't really atomize like it should. Sorry... just wanted to make that clear. I had the intake bored to 50mm, but the throttle body only bored to 46mm so I'd get the full opening. The stock TBI is like 43mm, but with the foil installed, the actual opening of the stock intake is like 41.3mm, which is nuts.

 

The CFI has a little "propeller"/foil under the TB too. I took mine out and observed zero consequences. Cold start, idle, fuel economy all remained about the same.

 

I have an 84 Corvette that we're also restoring... I did the same thing, but figured I'd leave them in there as I'm restoring it to mostly stock... I just opened the propellers a bit more, haha...

I don't have pictures of the underside for some reason, but I'll share these just because... haha...

 

Those are cool cars, IMO. Diffinerent, interesting, and they respond very well to mods. Cool cars and projects!

 

So I took the car for a spin, just to add to this (while I'm waiting for the injector to arrive)... the car is spitting out black water when I start it. Which if memory serves... it's carbon buildup mixed with the water that the catalytic converter is creating... and usually is as a result of a lean condition. I don't know why I didn't think to just go with a stock injector in the first place.

Everything on the car is basically new and / or totally restored. So, I didn't think much about it... but the only thing I hadn't replaced, was a MAP sensor. I found an original DELCO MAP sensor that I installed, and so that error code went away. But I'm getting lean and rich conditions... the engine really is going nuts, even though it drives well... it's dumping so much fuel... I don't even drive but a few miles and the fuel gauge just goes down. It must be killing the catalytic converter.

 

BLMs in OBD1 is like the Long Term Fuel Trims of ODD2 ( long term fuel adjustment)
INT in OBD1 is like the Short Term Fuel Trims of OBD2 (in short term fuel command change)

A 128 reading is the same as a perfect 0% fuel trim
The higher the value from 128 BLM is leaner and below 128 is richer, so the ECM would be subtracting fuel flow

But to know through the engine load and RPM, have to analyze the OBD1 scanner data as to what each fuel trim cell fuel value is to
know where the AFR is too rich or too lean and tune than for each cell

 

I just realized that I never responded back to this, and wanted too give an update and say thank you (can't remember if I did above).

I think I mentioned it, but after your recommendation to go back to a stock injector, I ordered a brand new OEM replacement (from AC Delco) for stock flow, etc. My daughter and I installed it and did a few other things... including making sure all the sensors were 100%. We also focused on the TPS and out of like 5 TPS sensors, we picked the one that had the widest effective range (0.68v to 4.31v).

We put everything back together, reset the ECM and drove the car (with the new bored throttle body), and the car drives amazing. It's super-smooth, has no idle issues, no smoke of any kind anywhere, it's got perfect idle, no hesitation in any gear, at any speed, under any circumstance. Just perfect acceleration. Obviously, it's an Iron Duke, so it's not winning any races, but the car accelerates really, really well.

It has the adjustable fuel pressure regulator in it, but I adjusted it to match what the stock fuel pressure regulator looked like (e.g., making sure the tab sticking out the side of the regulator is in the same spot, with the same spring).

We're doing a few other things and will run some scans on the ECM with an ALDL logger, and then adjust the fuel pressure slightly depending on whether or not it shows lean or rich at different RPMs. At the time being though, it runs absolutely amazing... idle is great, and the gas gauge doesn't move. It used to be that taking it around for 20 minutes, and we'd used up like half the gas. Now, I can do the same drive and the gas gauge honestly barely moved, if at all.

The only thing... running rich definitely took a toll on the car. The exhaust is filled with soot, and when the car starts up, it gets a little bit of water coming out when it starts (which is a normal part of combustion from the catalytic converter) and it spits out a little bit of black water. We decided to run a bottle of catalytic converter cleaner, which is pretty similar to SeaFoam, but focusing on cleaning the cat.

Anyway, car runs amazing, just wanted to say thanks!


Hey, I forgot to respond to this too, but wanted to say thank you for this explanation... this makes perfect sense, and it's exactly the answer I was looking for. Thank you!!!

 

You're Welcome

Just make sure if you're making fuel flow/AFR adjustments to take into account at time of your testrun with OBD1 scanner recording is what
the weather, elevation and type of gas used as how that effects colder or hotter weather to what AFR would be

 

RGR, thanks!
I don't know if I'm going to have a prom burned, since it may not make sense. In reality, the car is pretty stock. The engine is basically stock... just a .030 overbore, and even the cam is stock (though brand new). The only real difference is that it has a shorty header, and a bored throttle body with matching intake (43mm to 46mm, basically). It probably doesn't even need any reprogramming at all, I just figured since it's not a MAF system, it really has no way to make use of the extra air. So, my hope is that after we run some scans, all it needs is just a slight fuel pressure adjustment to compensate.

 

If the TB is actually doing something, then the air pressure inside the intake will be higher (than stock), which should translate to more fuel command from the ECM.

That should do it, but it sounds like it's running pretty great, right now.

 

Yeah, it is... I probably don't even need to do anything, but the whole point of all of this is really for my daughter to learn, both troubleshooting, completing projects, and engineering, and other life lessons, haha.

I need to learn more about how all of this works in the ECM, I've made prom changes in the past (many years ago when I'd have to pull the sticker back and wipe the PROM with UV light, etc.). But I didn't really know what i was doing, and usually trying to disable things per instructions I'd read online.

I know the TPS provides primary input for fuel calculation, and that's solid... and then the MAP sensor along with the O2 sensor provide the rest. The MAP sensor plugs into the TBI, in the same way it does on Cross-Fire Injection... it makes sense it's more of a vacuum than pressure, but I'm guessing it's the MAP then that would be determining this?

That's why I've always liked a MAF system better... it directly measures the air incoming, and then adjusts the fuel to compensate. This Iron Duke (and I think the Cross-Fire Injection system) do not even have Intake Air Temperature sensors... it seems they all rely on the ThermAC to properly adjust the temperature of the air to keep it consistent, rather than compensate for the temperature by adding more fuel when cold and less fuel when warm. It does still do this though, but it bases it entirely on the coolant temperature / CTS... just far less accurate since when the engine is at operating temperature, it has no idea what the temperature of the outside air is.

All the V6 / MPFI motors, and the 87+ Iron Dukes all came with IATs, but the 84-86 do not... and I didn't see anything similar on the Cross-Fire motor either.

But yeah, like you said... it runs pretty amazing. Probably the best running Iron Duke I've ever seen. I don't know what these were like when new. I've had several Iron Duke cars before that I bought at auction, and they all sounded like *** and / or just were totally, I mean totally gutless. This one scoots... it's no 3LT C8 Corvette, haha... but that lady in the walker doesn't stand a chance.

Here's a cheesy video we put together of us test driving it... the audio is a little ****-poor. We zip-tied a microphone to the license plate, so it picks up all the engine noise that you don't hear inside the car, or would hear if you were behind the car. But you do get an idea of how the exhaust sounds.


It's a video that will post in a week or so...

 

It gets along down the road pretty good.

I posted THIS THREAD a while back, MT had done an article on the effort that Pontiac put forth to support the Iron Duke in racing.

HERE is the original article that prompted my post.

 

Hahah... yeah. People made a lot of power with the Super Duty... but in line with the stuff you quoted, the Super Duty stuff... while it's all interchangeable, it's completely different. The SD4 block is twice the thickness of the normal block, and the SD4 crank has much better metallurgy. The weird thing is, any parts from either will interchange, because it's designed as such. On my daughter's car, we ended up having to swap out her 85 cyl head (it had a small crack by one of teh valves) with an older one that's still cross-through, but supposedly has unshrouded valves. This was just by happenstance, not intentional... but supposedly ads a bit more power.

The funny thing, I wouldn't let her get a V6 because I wanted her to be more responsible, and I felt like the Iron Duke was such a simple motor that she could rebuild it without too much complexity... but then she put so much effort into the Fiero, that I didn't want her to have to drive it to school every day, so we got her a Pontiac Solstice which she also worked on. It has a 2.0 liter LNF Turbo motor with like 260 horsepower, which is crazy in that car. And even more crazy, I just bought my wife a Bronco, and it came with a 2.3L Turbo that has 300hp in it. Just crazy.

She's going to be building a 3.4 V6/60 from a 93-95 Camaro / Firebird in the next couple of months, it'll use all the stuff from the V6 in my Fiero, but will have an H272 Crane Cam, roller rockers, 9.7:1 compression pistons, and a few other little things to give it a bit more power. I'd like to see 200hp from it, which should get my 87 SE down the line in low 14s in the quarter, which is all I'm looking for.

When we're done with all these, and sell them off, I'm probably going to do another Third Gen. I hate to say it... LS motors are so cheap, I'll probably do an LS w/ 4L80e and be done with it. I want to get another 82 though, I just love that style...

 

Here's a video I stumble across and remembered this question was posted...

 

Right on, curious to see how the V6 turns out! Always love seeing people build a 60deg, they're great little motors! Since you're going to be changing the cam/ pistons already, and using a 3.4 (assumedly with the DIS ignition), have you considered doing the 3x00 gen 3 "hybrid" top end swap? The aluminum heads and the FWD intake flow much better than our Gen 1 iron head stuff, and you can get it all pretty cheap if you're willing to go pull 'em from a junkyard. I got a full top end off of a 3400 '01 Impala for about $220 at my local yard, with the heads/ manifold/ plenum/ fuel rail/ injectors/ exhaust manifolds and crossover and all. Worth looking into if you're already planning to change up the cam/ pistons there's a sticky in the V6 section that covers all the basics if you want to know more

 

Thanks man! I was actually just looking into this again.

I have a 3.4 V/60 block from a 93-95 Camaro / Firebird (don't know which)... it's just sitting in the garage, and that's ultimately what I plan to use. This is actually going to be for my V6 Fiero, so while I could go with the 3400 heads, it would prevent me from being able to use the Fiero's intake manifold and valve covers. Ultimately, my goal is to get as much power as possible, while keeping the car looking 100% stock. In that vein, I'll also still be using a distributor as well, even though I know switching to DIS would be a better option.

The heads I have are of course Gen-1 heads... but they've been professionally ported by ARI Racing Engines, and even have the SI Stainless Steel valves installed. They are hardened valves that narrow at the base, which allow for greater air flow into the combustion chamber (in lieu of actually grinding out and installing larger valves). My goal is 200hp, and I'm mating it to a Quad-4 SCX W41 5-Speed Getrag that's using a Fiero GM V6/60 Getrag bell-housing. 1st through 3rd are the same, but the final drive is 3.94:1, which will be totally wild. I'm going to keep the Fiero's 4th and 5th gear (which are a bit slower) so it doesn't kill me on the highway.

But again, if I go with the newer 3400 heads, then I can't make use of the stock intake and such (which I'll need to port anyway).

But I noticed a rash of 3400 rebuilt motors for sale on eBay... all around $1,000 bucks, with $500 shipping... the cost is insane. Have you considered using one of those in the Third Gen? They are super cheap, and they'll fit. The only thing I wonder though is that the starter will be on the other side. I can't imagine that would be a problem, but otherwise... everything else bolts up, AND... you get a roller cam. Apparently, even the Gen-1 heads will bolt onto the 3400 motor, which is wild, I didn't realize that. I was seriously considering it, but I already have a 3.4 Gen 1 V6/60, so it just didn't make much sense for me to go down that path... but at $1,500... I almost want to buy one... sort of a hammer looking or a nail if you know what I mean. Worst case, I drop it in a Porsche 944.

 

Good deal, sounds like a solid plan! Looking forward to see how far porting/ valve work on the iron heads will get you, haven't been able to find much data on that since so many people hybrid swap. Props for keeping the stock intake and all, I know I'm definitely going to miss my Fiero valve covers when I can get to the swap myself!

In my case, I'm going to be going the hybrid route because my dad won't let me pull a motor at the house, and I don't really have anywhere else to do work that involved, so I've been planning out what all I can do while keeping the block in the car. I'm still a ways off from getting the swap done, despite having the heads on hand already... still need the crank trigger/ pistons and all that jazz. Also going to be swapping in a TKX later this year hopefully, permission from dad for the driveway pending I've wanted to put a manual in it since I first got the car back in 2017, and I won't have to worry about hooking up the T.V. cable to the 3400 TB. My rambling aside, that 3.4 is going to be a great lil motor for your Fiero, I'm sure you're gonna love it!