OK, I have searched and read billions of lines of information, but am still perplexed by a few things.

1. Do I use the DOHC oil pressure sender or stick with the Fiero setup? Does the DOHC sender work the gauge correctly?

2. Do I use the DOHC temp sender to drive the Fiero gauge, or do I use the Fiero sender? Does the DOHC sender have an output for a warning light like the Fiero sender?

3. Does the ECM control the fan relay? Do I simply connect A9 (FAN #1 CONTROL) on the ECM to D1 at the C500? Is it that simple??

4. The A/C stuff has me stumped. Where is the A/C pressure sensor? Was I supposed to get it from the donor car? Where do I locate it? There is a switch on the back of the donor A/C compressor that appears to be broken. Is that it? I am completely lost on this.

5. Can I use the DOHC upshift light feed (connected to pin A on the C203 connector)?

6. The 91-93 Crank Sensor mini-harness has a twisted shielded pair, with the shield ground going through pin B on the 3-pin connector at the module, while the 94 harness uses a simple twisted pair with no shield. I have the 94 harness and module, but plan to use the 91-93 ECM. Is this OK? (I am probably worrying too much at this point...)

Sorry for all of the questions, but 6 weeks of searching has not yielded these answers.
Thanks in advance for your help.

P.S. I have printed out all of ltlfrari's diagrams and am going through them, but still have these questions.

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1986 SE 350 V8

Is there a link to said diagrams? I could use them right about now.


Rob

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Power is nothing without control.


Twin Engine Fiero Project

1987 Checkmate Starflite
1988 Fiero GT 3.4 DOHC
1990 Miata
1991 300ZX Twin Turbo
1997 F355 Berlinetta
1999 ex-CART FedEx Championship Series racecar
2000 Civic Si
2000 F-250 PSD 6-speed
2005 YZF-R1
2005 United 24ft enclosed hauler

www.ltlfrari.com

There is a link to his DOHC swap on there

1. I believe there are two types of oil pressure sender. a switch that just works an idiot light and an actual sensor. Mine had the sensor type on it and from what I can recall I just hoked it up to the gauge and it was fine. My 'sensor' also had a switch on it that goes to the fuel pump relay, same configuration as the Fiero. From what I can recall it was a three wire connector to the sender/switch.

2. I used the DOHC sender, seemed to work fine. Don't know about the light. Pretty sure I did not hook up a light tho which was great because that light is really annoying, plus I think I can figure out when to change gear LOL!

3. According to my diagrams, yes, it's that simple!

4. You will need to add your own pressure sensor to the a/c system. you can get them new but you'll need an adapter of some sort to mount it. It needs to go on the high pressure side.

5. So far as I can recall the DOHC ECM does not use/have an upshift light. At least I don't recall wiring mine up.

6. Should be fine. I created my own 'shield' by wrapping aluminum foil around the wires and earthed it but I really don't think it is needed. No harm in having it though.


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Dave

www.ltlfrari.com

[This message has been edited by ltlfrari (edited 01-02-2011).]

quote Originally posted by tesmith66: OK, I have searched and read billions of lines of information, but am still perplexed by a few things. 1. Do I use the DOHC oil pressure sender or stick with the Fiero setup? Does the DOHC sender work the gauge correctly?

Like lilfrari said, there are two types of sensors, one is analog, the other is just a switch. If you have one that has a body that is something like 2.5" long, it is the correct sensor for your gage. The other type looks the same, but is stubby, the body is very short. Both types have a pressure switch, but only the long one can run the gage. If you need a new one, get one for an 88 Fiero V6. They are better then the bulky old ones.

quote 2. Do I use the DOHC temp sender to drive the Fiero gauge, or do I use the Fiero sender? Does the DOHC sender have an output for a warning light like the Fiero sender?

The DOHC's sender runs the Fiero's temp gage just fine, but there is no provision for the dummy light. Unfortunately, the hole for the sensor is 1/4" NPT, and the Fiero's dual purpose sensor is 3/8" NPT. So the Fiero's sensor won't fit. Most of us are ok with just having the gage working. People with 3800's deal with this all the time.

quote 3. Does the ECM control the fan relay? Do I simply connect A9 (FAN #1 CONTROL) on the ECM to D1 at the C500? Is it that simple??

Yes, absolutely. If you ground that wire from the C500 while the ignition is on, the fan will run. All the ECM does, is ground A9 to run the fan. So it is that simple. Keep in mind that this ECM has a DUAL fan setup. If you happen to be installing into an 84 with A/C, you'll need to do two connections, as the dual fan controls are compatible.

quote 4. The A/C stuff has me stumped. Where is the A/C pressure sensor? Was I supposed to get it from the donor car? Where do I locate it? There is a switch on the back of the donor A/C compressor that appears to be broken. Is that it? I am completely lost on this.

Here's the thing about the 3.4 DOHC's A/C. It uses the same compressor as the 87-88 4 cyl. Fiero. So theoretically, you can do it up like a factory Fiero setup, where a high pressure cutoff switch is located on the back of the compressor, and the cycling switch is retained at the accumulator under the front hood, and these two sensors work in conjunction to turn on and off the A/C Compressor as needed. This is one way of doing it, and it's acceptable.

But on the 3.4 DOHC, the ECM controls the clutch cycling. You do need the 3 pin A/C Pressure sensor that wires straight to the ECM. It does need to be located in the high pressure line between the compressor and the condenser. I actually cut the sensor, and part of the pipe off the donor car, then drilled a hole in the high pressure line and welded the bung (with some of the pipe) over the top of the hole. I then wired the A/C relay to run off the ECM's (A12 on the 91-93 ECM) output to control. This way, the ECM has final say in weather or not the A/C Compressor is on. You also have to wire in the A/C Request wire (C203 "D" to ECM C17), so that the ECM knows when you want the A/C on, otherwise it will not turn it on. That should settle the A/C out. The sensor can be found near the condenser on the drivers side of the donor car (IIRC).

quote 5. Can I use the DOHC upshift light feed (connected to pin A on the C203 connector)?

Sure, don't see why not. Not totally sure if the programming is there to support it, but hey might as well pretend it is. Like the fan, if you ground it, the light should illuminate.

quote 6. The 91-93 Crank Sensor mini-harness has a twisted shielded pair, with the shield ground going through pin B on the 3-pin connector at the module, while the 94 harness uses a simple twisted pair with no shield. I have the 94 harness and module, but plan to use the 91-93 ECM. Is this OK? (I am probably worrying too much at this point...)

Yes, you are worrying too much. The ICM runs straight off the Crank sensor. That part of the circuit doesn't involve the computer at all. I personally am not running any shield on mine, the "B" pin has no connection at all, I have just the twisted pair and I'm trouble free. The computer only gets involved with the timing via the larger 6 pin connector.