I'm replacing my 85 computer and harness with a 165 ECM and a harness out of an 87. I've inspected my new and old harness at length, and I only found 2 significant differences. One is the distributer plug, but all 4 of the same wires are accounted for with each, so that's a no brainer. What's got me concerned is the plug for the oil pressure fuel shut-off switch. On my 85, it was a big 2-pronged plug with 12 AWG wire. On the 87 harness, it's a different plug with much smaller wire (16 AWG or thereabouts) and the wires are different colors. Here's a pic of each:

85 harness:


87 harness:


Can I just buy a shut off switch for an 87 and replace my 85 switch, or do I have more work to do? The big vs. small wire is making me think that the fuel pump circuit went through the switch on the 85, but on the 87 it's a sensing signal or it switches a relay somewhere. Anybody know about this?

 

Just do the repin/splice thing found here http://www.eecis.udel.edu/~davis/z28/ecm_swap/

That should solve that problem. If you do go that route, don't mount the new relays on the firewall, mount them to the metal bracket on the ECM that the MAS is mounted to, That way you won't have to run new wires through the firewall and won't need a long harness for them.


~M~

 

Thanks... but I'm not repinning my stock harness. I've got an 87 harness that's already 100% peachy except for this one plug that I've got to deal with. I'll go through that information on Mike's site to see if it answers my question... but this 87 harness is already set up for all of the relays in the stock location and I plan to keep it that way. Moving the relays would just create more work that I don't need.

 

Mike's site makes no mention of the different oil pressure switch. Maybe GM just decided to change the plug style, but I've got to find out for sure before I just put a new switch in and have starting problems.

If I was just converting my 85 harness, Mike's information would probably be more helpful, but unfortunately I've got to try and track down the functionality of this particular circuit on both the 87 and 85 system to determine if I can just simply replace the switch.

 

Jim,

I might not be a lot of help. My '86 (WITH the '165 ECM) has the same connector for the auxilliary oil pressure switch as your '85 did (the big one). Seems like us '85 and '86 TPI guys always have the bigger ones....

However, all the diagrams I have access to show the circuit wired the same for all cars through '92. The AUX pressure switch provides power to the pump. The smaller wire size is not AWG 16 on the '87. GM changed to metric wire sizes and high temp insulation. The wire should actually be 1.5mm and is rated at 14A continuous, higher for short durations. since the ECM/fuel pump fuse is only a 20A, that was probably deemed safe and adequate for the application.

My guess due to this information is that you should change to the newer style pressure switch and forget about it. But if anyone has a more definitive answer, I'm all ears - I'm up for learning something today - except about the size of us '86-'86 TPI guys.

 

n/m

 

Vader, thanks for the info. I bought a newer style switch earlier today, but in typical GM fashion, they've got 2 different possible part numbers. Apparently the thread pitch could be one of 2 sizes. Anyway... I'll know by tomorrow. Thanks!

One question though... why the huge gauge wire on the 85?

 

Good question. The power wires at the FP relay are huge on mine, too. I'm guessing that its typical GM overkill. The FP really shouldn't draw that much, but '85 was the first year for the higher pressure pumps for TPI and they likely wanted no issues with peak current. At least they didn't do the typical European thing, starting small then working up to the correct size after a few years (Porsche, VW, Audi used to have notoriously bad wiring/electrical engineering).

 

Not sure what the deal is on the wire sizes.

The later switch is mounted just above the oil filter and has a 2 wire connector. It serves as the oil pressure switch for the gauge on the dash and the ecm/pump deal as well. I dont know what or why there would be 2 different part numbers, bad parts listing I guess. Anyways it should be a 1/8" NPT on the end of the sender. If I had a digital cam I'd take a pic of mine for ya.

 

Well, it turned out that the one I bought was the wrong thread size. I exchanged it today for the right one. On my 85, as you both probably know, both the gauge sender and the fuel pump switch is on the back of the block behind the distributer. The 87 wiring harness I have has the connections at the same place, so it was a simple matter of swapping the switch for the new one. This appears to be the same generic dummy-light switch that GM has used for centuries. I asked for a "fuel pump switch" first but the book didn't show anything, so then I just asked for an oil pressure switch and got what I needed. Hopefully this thing won't blow up when I try to start the car.

 

alright, what is the PN for the older switch. I have a pre 86 engine and this is the only sensor i havnt been able to fenaigle on yet. I rethreaded my present one and like an idiot i over-torqued it and stripped the threads that i made.

Also, where can i get a new connector?

P.S. this is for a '88 tbi camaro

 

Uh... I don't know what the part number for the 86 piece is... maybe vader or madmax can chime in. I can get you the part number for the newer style if you can wait until tomorrow. I would guess that it would be easier for you to use the newer style instead of chopping up your harness... that's what I decided to do.

 

actually, its the other way around. im going from an 88 305 to a pre 86 crate 350 and i need to use a different unit. Its kida annoying because im sooo close to having it running after the weekend and now this... oh well, at least there is another unit that will fit.

 

nvm... read mine is just a backup switch for the fp in case of failure

 

you don't need the old one if you stay with your 88 wiring harness. Just take the piece off your 305 and put it on the 350. I doubt that crate motor will come with any of that crap anyway, so you'll have no choice but to swap it over.

But if you still decide that you need one, just go to whatever parts store you like and ask for an oil pressure switch for an 86. If they ask if you have a gauge or a light, tell them light. AFAIK, the switch used for the fuel pump is the same switch that they use for the idiot lights.

 

i tried using the one for my 305 but the older crate 350 uses different threads. Oh well... my swap is practlically complete so ill find out if i can get away with it shortly. I just plugged the hole with a bolt.