Has anyone tried swapping the Direct Ignition System from later 2.8s and 3.1s onto the Fiero's 2.8?
I have looked over the electrical signals from the distributor to the ECM, and from the DIS to the ECM.
They appear identical.
I tried this once with my '84 GMC S-15 Jimmy. It turned out that there was a slight difference in the reference point of the timing signal. I had concluded that the swap would work with later distributors such as those used on the Fiero.
I have not had a chance to try it though.

The 60° V6 DIS systems use a crank sensor. The '88 block has the boss cast into it for the sensor but none of the machine work is done to mount the sensor and in any case the crank itself doesn't have the right shape to work with DIS. Once you swapped everything over to use the DIS you'd essentially have a DIS motor with Fiero heads and pistons, but then the fuel and timing tables in the DIS ECM are set up for the DIS heads and pistons, so you'll spend a lot of effort tuning things to get it to work right. It would be much, much easier to just do a full up swap with a DIS motor.

JazzMan

OK, Here is what I am really trying to do:
I live in California and I think it would be alot easier to pass a smog test (with a swapped motor) if I could run that engine with the fiero ECM. The block and crank would not be issues because they are already from a DIS engine. Given the engine mods I will be making, tuning will have to be done anyways.
I am really trying to confirm my earlier conclusion that the electrical interface between the DIS and the fiero's distributor is the same. There is no doubt that the actual signals are the same, but there is the matter of the relative timing between the reference signal and the signal that ECM sends to create the spark.
If anyone knows anything about this, I would sure appreciate hearing about it.

Uh, you do realize that DIS stands for Distributorless Ignition System, right? A DIS system integrates the cylinder firing sequence into the ECM and removes the distributor, instead going with individual coils for either individual cylinders or pairs of cylinders. There's no way a Fiero ECM can be made to work with any DIS system, and I can guarantee that what you think you're trying to do will fail any CA emissions test.

And no, there's nothing even remotely interchangeable between DIS and the Fiero motors. DIS motors are MAF and the Fiero is Speed-Density, for instance. Any "signals" are totally different between the two.

JazzMan

[This message has been edited by JazzMan (edited 06-18-2005).]

quote Originally posted by JazzMan: Uh, you do realize that DIS stands for Distributorless Ignition System, right? A DIS system integrates the cylinder firing sequence into the ECM and removes the distributor, instead going with individual coils for either individual cylinders or pairs of cylinders. There's no way a Fiero ECM can be made to work with any DIS system, and I can guarantee that what you think you're trying to do will fail any CA emissions test. And no, there's nothing even remotely interchangeable between DIS and the Fiero motors. DIS motors are MAF and the Fiero is Speed-Density, for instance. Any "signals" are totally different between the two. JazzMan

I must disagree with your last statement. The signals I am talking about are the signals that run between the ECM and distributor or DIS module. The fact is that these signals are identical. And the theory of operation is also identical.
Regardless of whether an engine is MAF, speed density, batch fire, SFI, or whatever, the distributor or DIS module performs the same function. The ECM provides a spark signal to the DIS or distributor with a given delay with respect to the reference signal. The only real variable is how that reference signal is derived.
I have actually hooked this up and tried it on my S-15. The engine will start, but dies after a very short time.
It was my best guess at the time that there is a fixed difference between the refernce signal generated by the DIS and the distributor.

[This message has been edited by sd_iconoclast (edited 06-18-2005).]

Good luck with that.

JazzMan

been there done that. It works, sorta.

It ran like crap though. It seems that there is a difference in the communication between the computer and the DIS or distributor. I wound up using a beretta's computer (1227730) and modifying the harness for it. It works much better now, though it could use a serious tuning session. I did this on a 3.4 witch is a DIS motor.

quote Originally posted by JazzMan: A DIS system integrates the cylinder firing sequence into the ECM and removes the distributor, instead going with individual coils for either individual cylinders or pairs of cylinders. There's no way a Fiero ECM can be made to work with any DIS system, and I can guarantee that what you think you're trying to do will fail any CA emissions test. And no, there's nothing even remotely interchangeable between DIS and the Fiero motors. DIS motors are MAF and the Fiero is Speed-Density, for instance. Any "signals" are totally different between the two. JazzMan

Thats not really true. The DIS system does NOT communicate with the computer to the level of witch cylenders are firing. That is handled strictly by the Ignition module. You can disconnect the computer and it will still fire the correct spark sequence. Oddly enough, the DIS pack has the same wires the distributor has, but its communication methods or timing vary from that of the distributor module. Making them ever so slightly incompatible, it will still run, fire the injectors and such, but will not run correctly. I don't know exactly what the difference is, but the fact that it doesn't run right tells you alot. As far as the speed density thing, I have never seen a 3.1 up to 93 that had a MAF sensor. They went to MAF with the SFI in the late 93 3100 series motors.

Or heck... the old '87/88 duke!

It's DIS, and is MAP/Speed density...

Consider swapping a 3.4, computer and all, from a pre-95 Camaro/Firebird. The intake manifold breathes better, but I'm told you'll have to use the 2.8's oil pan & timing cover so it'll fit a stock Fiero front mount.

The key to a swap like this is to treat it like any other swap. Use the Camaro computer, etc... and CARB will pass it.

To use DIS with an ECM that expects HEI, you have to change the advance, retard (not used in the Fiero) and the reference.

The key is that HEI uses the mechanical advance as a reference but DIS is 1/6 crank rotation forward.

So the reference in in HEI is 10 where as in DIS it would be 70 degrees.

Yes, you can run DIS in place of HEI if you make those changes in the code.

quote Originally posted by Fierobsessed: been there done that. It works, sorta. .. .

Nice work Fierobsessed! Strangely enough, this very same question went through my mind the other day as well. Nice to see that it can be done, if nothing more than for proof of concept!

quote Originally posted by TK: To use DIS with an ECM that expects HEI, you have to change the advance, retard (not used in the Fiero) and the reference. The key is that HEI uses the mechanical advance as a reference but DIS is 1/6 crank rotation forward. So the reference in in HEI is 10 where as in DIS it would be 70 degrees. Yes, you can run DIS in place of HEI if you make those changes in the code.

TK,
If you are correct, this is exactly the piece of info that I am looking for. How do you know that the DIS's reference is 1/6 of a crank rotation forward? and forward of what?

Also, I belive that the refernce used by the distributors is actually equal to the static timing of the engine. In other words, the reference is at 10 degrees btdc only if you set the engine's static timing to 10 deg BTDC. Is this correct? I raelize that for most cars this will end up being 10 deg btdc. I am only clarifying for thsoe out there (like me) who are trying to understand it.

Actually, I arrived at it sort of backward in that I've hacked a lot of GM ECM code and when I did my first DIS, I saw that the reference was 70 degrees. It was kinda of an epiphany. I flipped some 7730 V6 code and played with on my first Fiero but wound up working with the 7749 more for the Fiero.

But in your case, if you plan on getting it recertified you have to decide what you will tell them the engine is. Once you decide, you have to stick with everything for that selection. When they look it up, they will know very quickly if it should be DIS or HEI.

If you are swapping in a real-live 3.4L from the Camaro you have to either run it HEI with the Fiero intake and just don't bother telling them you changed something or swap in the Camaro intake and ECM and get it recertified.

[This message has been edited by TK (edited 06-19-2005).]

quote Originally posted by TK: Actually, I arrived at it sort of backward in that I've hacked a lot of GM ECM code and when I did my first DIS, I saw that the reference was 70 degrees. But in your case, if you plan on getting it recertified you have to decide what you will tell them the engine is.

When you say 70 degrees, you mean 70 degrees before top dead center on each cylinder. Is that correct?
I had been planning to make a box that would introduce the proper delay, but I guess it would be better to just reprogram the chip in the ecm. Can you recommend a good book or website or something that explains how to hack the fiero computer. I am an electrical engineer and I am very familiar with the electronics, I would just like to know how the data is organized.

Actually, the whole point of keeping the Fiero ECM is to avoid having to get the car recertified. California's process is so difficult, and so arbitrary, that I think recertification is a pipe dream. The guys at the regular smog stations do not know in detail what a fiero engine looks like. As long as the general description matches, they are happy. From what I can gather, they do not have any information as to whether an engine has DIS or not. They do have information as to whether the engine came with air injection or other smog systems.

I suggest you just get one of the many editors for the Fiero that are out there. TunerCat, WinBin, Carbytes, et al.

[This message has been edited by TK (edited 06-19-2005).]

quote Originally posted by Jim Gregory: Consider swapping a 3.4, computer and all, from a pre-95 Camaro/Firebird. The intake manifold breathes better, but I'm told you'll have to use the 2.8's oil pan & timing cover so it'll fit a stock Fiero front mount. The key to a swap like this is to treat it like any other swap. Use the Camaro computer, etc... and CARB will pass it.

You can just grind a small amount from the front motor mount bracket to clear the 3.4L oil pan. The 3.4L pan is deeper and I consider it beneficial. You can only use the 3.4L pan though with the 87-88 front timing cover. The earlier ones won't match up. As for DIS on the 3.4L in a Fiero , it's been done before, but there is more labor involved as a new wiring harness needs to be created. I've also seen several 3100 and 3400 DIS engines in Fieros and most always they use the ECM that came with the engine and a hybrid harness.

direct ignition system: (DIS) An ignition system which does not use a distributor but carries high voltage from the ignition coils to the spark plugs.

Dude, it's distributorless.