96 vs. 91 DOHC engine stuff

[qwikgta]

I have a 96 motor going into a 88 Fiero. I am using the 91 harness/ECM on the motor (i have a manual trans and need the manual trans ECM)..

Anyway... as i am putting the harness together with the 88 harness i have found that the EGR, Alt and fuel pump connectors are differant. I have not checked all, but i know these are.

So, can i install a 91 Atl in place of the one on the 96 motor.... will it bolt on no prob??, Can i remove the 96 EGR and replace it with a 91 also. In other words, will it bolt up and work correctly.

Thanks

Rob

[Lyle's GTP]

No, as far as I know you can't use a 91 ECM with a '96 motor they are way different. The alternators a different too, the mount is different I think. Also swapping EGR's is probably only going to screw things up. I recommend using the ECM from the 96 and getting it reprogramed for your standard trans, you may not even have to.

But this swap is pretty common some body must know everything about it.

Lyle

[4spdz34]

acctually u can use that harness but u will have to get the connector for a 96 alt cause the 91 alt will not bolt up at all. on the egr side the harness is different and how they bolt onto the car is different, i would suggest a block off plate and get your 91 pcm programmed so it does not need a egr. u don't need the manual trans ecm u just need the memcal from a manual 3.4 car.

[jmgtp]

No, as far as I know you can't use a 91 ECM with a '96 motor they are way different.

Incorrect. A 91 ecm/harness will run the 96 engine. You just wont be using some of the stuff that the 96 engine is equipped with (ie the intake cam position sensor is for the sfi and the mpfi 91 ecm wont use it, and I also believe the 96 engines have extra crank position sensors that wont be used, but they also have the one that the 91 engine will use)

The 96 manifold uses a different egr (not at all compatible with the obdI programming) so either you will have to have the egr disabled in the programming or build an adapter plate to use the OBDI egr.

[Lyle's GTP]

Hey you learn something new every day, shit I thought you needed all that stuff.....silly me. <-Me.

Lyle

[qwikgta]

Thanks for the fast reply....

Yea, i have been building he harness for about a week, on and off.... I have spliced all the Fiero wires onto the 91 harness... had to cut off the C100 bundle, and one by one, find the wire on the fiero (C203/C500) and splice together. I have been tracking down all the misc wires and finding out the my directions are way off. they never talked about all the "other" things that need to be swapped.....

I am using a 91 ECM and harness off a Manual Trans car. Found a 91 cutlass with 284 getrag in the junkyard, pulled the trans and got it for $70 bucks.

I see that the 96 EGR has a 5 wire plug and looks way diff than the 91 (4 wire plug) and i see they are wired diff too.

I also see that the 96 Alt only has one red wire coming out of the plug on the back, and the 91 has two. I was hoping i could just use a 91 Alt and the stock plug...

I have many more issues to work out, so i may return here often and ask for help, thanks

Rob

[jmgtp]

I dont know anything about the alts interchanging. I'd imagine the timing chain covers are the same or close enough to same that theyd interchange. Another thing that just popped into mind is the Map sensor, since you wont be using the MAF from the 96 engine. The 96 throttle arm that connects the TB to the plenum has a MAP sensor that plugs into it (I believe it was used for egr data) I think you can wire it into the 91 harness, but I think it would be much easier to knock the cap out of the rear of the plenum and put the 91 map in there especially since that way you dont have to deal with lengthening the wiring. The plastic block that retains the 91 map sensor will fit in the hole but only 1 of the bolt holes matches up. When I did this on my vehicle it leaked, I got a new o-ring for the plastic block and the leak ceased, worse case you could apply silicone to it. On my car I had to lengthen the TPS wire on the harness because it just wouldnt reach. If you have the harness entirely off the engine there may be enough wire to work it over and make it reach without hacking it, if not be careful when lengthening the TPS wires. I had a big problem, it was jittery on the signal and I ended up having to run new wiring for the TPS direct from the ecm.

[SappySE107]

Is that 91 cutlass still around? They are rare as hell and I would like to have the shifter out of it to play with.

You can make an adapter plate to bolt the older EGR in place of the new type. I know someone on beretta.net made one for the 3100s to use the older EGR with the newer style.

I have no idea on the alternator though.

[joey b]

John, what did you to for a throttle body or did the 96 match up to the sensors?

On the alternator the bracket is completely different. I had a self-exciting diode put in for the voltage regulator and all was well. The "check gages" light won't come on if the volts are low, but it is a gage I can see myself. The ECM does not cause the 91 alternator to work so mine has been left unplugged aside from the power wire.

[qwikgta]

Joey,

So there will be an issue with the fact that the 96 Alt has only one wire in the plug going off to the guage, and the 91 has two, one to the guage and the other was/is feeding what looks like 10A power to the ingnition...which leads to A/C relay, Fan relay and J on the mini harness...leading to the purge control valve and EGR.

your 92 harness is identical to my 91, and i have the 96 motor to your 97, so other than the fact that im putting it into a Fiero, overall we should have similar issues.

What did you do about the EGR... i think im going to get a chip made that ignores the EGR code, and leave a fake wire leading into the harness for the correct look.

Explain more about your Alt situation.... and is there any other issues you can think of.

Thanks

Rob

[Juglenaut]

I had a self-exciting diode put in for the voltage regulator

Hmm really now...explain...self exciting since almost all diodes are self excited. It is how the circuit is composed the AC voltage to allow Self-excited current, which means that the current remains at a constant opposed to voltage.

[brian89gp]

I have a 94 engine with a 91 harness, the 96 alternator is the same as mine I believe. Switching between the 2 is as simple as matching up the 2 wires on the alternator.

There are 2 wires on the alternator, one goes to the interior gauge and the other is tied to an ign positive. It DRAWS current from this wire, not provides; this wire is used for the voltage regulator on the alternator.

If you want to do a engine kill switch (if your drag strip requires it) you can put a relay on this wire, flip it and the alternator should cease generating.

[Cliff8928]

Not a DOHC, but i did convert from the CS130 to the CS130-D on my beretta, and i believe there were a couple wires which had gotten connected together (that did the same function)... i don't remember right now, but i DID have both wiring diagrams at the time.. The CS130-D works flawlessly!

Also, you can most likely run the SFI with a manual, because at least the pre-96 ECMs don't seem to care whether a transmission is there or not (at least in my friend's case with the 3100/5speed)

Cliff Scott
89 BerettaGT
89 Volvo740

[qwikgta]

Brian,
According to the wire diagram for the 96, it shows only one wire coming out of the Alt, which we know is true. The diagram does not show any other function for the Atl, now it may not show anymore "function", cause there are no more wires coming out... seams to make sence, why show wires leading away from the Alt if the car does not have them... i guess what im saying is that maybe the Alt for a 96, which has provisions for up to 4 wires, does have other functions but we dont use them on the 96.... does that make sence.

So.... if i understand what you are saying i need to cut the plug off the 91 harness, graft on the 96 plug, well not the 96 cause it only has the one wire... i picked up a plug that was the same as the 96 in size and shape, it has two wires, i can use that one, and keep the 96 Alt...

Is this correct.

Rob

[brian89gp]

I'm not sure. My 94 alternator had a wierd shape plug, oval but one end was wider then the other. There were 2 brown wires on the center pins (total of 4 pins, 2 unused).