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Question on oil switch in GM FI system
https://www.slantsix.org/forum/viewtopic.php?t=22907		 Page 1 of 1
Author:  Carbide6 [ Thu Apr 26, 2007 8:25 pm ]
Post subject:  Question on oil switch in GM FI system
Hello, I'm sorta new to this site. I've done some research on FI systems here and based my build on you guy's data. I have a 67 Dart GT with a SL6 225. I have scavenged the FI system from my old 91 Pontiac. I used a standard fuel rail drilled for the injectors and an aluminum intake with drilled 3/4 by 14 mm reducers from the hardware store. I have pics of it on Moparstyle in the a body section. Anyway, my question is . I'm ready to finish the wiring. I did not use the oil switch wires. Will I need to ground it for the system to operate? I remember reading something about them needing to be grounded somewhere. Maybe for the fuel pump to be energized or something like that. ( thru the emc ) I only used the wiring required for a stand alone fuel system, nothing on the ignition part of it.
:?:
Author:  Sam Powell [ Fri Apr 27, 2007 7:34 pm ]
Post subject: 
If I am not mistaken, this is a safety divice to keep the engine from running without oil pressure. It is not a bad idea, but a faulty switch can kill your engine even when things are good. I suspect you will need to ground it to get your fuel pump to run. You can play with this and see if this is true. If you cannot get the pump to prime your fuel rail, then try grounding the output from the safety switch, and see if this makes the fuel pump work. Is there a way to just wire it as intended to make it function as a saftey? How does GM wire it?
Sam
Author:  Charrlie_S [ Sat Apr 28, 2007 4:04 am ]
Post subject: 
Actually the fuel pump gets it power from two sources. The oil pressure switch and the fuel pump relay, which is triggered by the ecm. The FP relay and the oil pressure switch are wired in parrallel. Either one can turn on the pump. In the stock GM system, the ECM will ground the FP relay, for approx two seconds, when the key is turned on. This primes the fuel system. If the ECM see's ignition pulses it keeps the ground on the relay. If it does not see pulses it opens the ground circuit to turn the pump off. If the fuel pump relay circuirt has a failure, the engine can still start. While cranking the engine, oil pressure will build and close the oil pressure switch, and power the fuel pump, and the engine will start. This is a common problem with older GM systems. With a long crank time before starting, it is usually a bad fuel pump relay.
Author:  Carbide6 [ Sun Apr 29, 2007 9:11 am ]
Post subject: 
Thanks guys. I remember reading something about that somewhere. It makes sense. I wonder if I need to wire the fuel pump seperate? I don't like a lot of extra things to do to crank a car up, just turn the key!!I took all the wires out of the connector that I did not need. I guess I can put the oil switch back in and ground it just to be safe? I should get the wiring finished this week and wiil know soon if it works or not!
Author:  dakight [ Sun Apr 29, 2007 9:46 am ]
Post subject: 
There's another active thread in this forum that addresses some of these issues.

http://www.slantsix.org/forum/viewtopic.php?t=21798
Author:  Carbide6 [ Mon May 21, 2007 6:39 pm ]
Post subject: 
Ok guy's, I give up! It will crank and run for about 30 seconds, then die. I guess the 91 Bonneville ecu is to complicated for me. On the plus side, the fuel ran and other delivery components held up great!!! I don't know if I want to look thru the junk yards for a 85 - 88 model GM car or not. I have a Holley TBI inj. system I just bought off e-bay with the o2 sensor. It's a 670 cfm unit. I know it's to big for the sl6 but will it work on 1 injector? Or, even better, will it batch fire my fuel rail with the pontiac injectors? I know all the calculations in the ecu are figuired on a V8 but would that really matter on a batch fire system? The system is very simple to install. Also would the 22 psi holley pump work with the GM injectors, or would I need the MSD 45 psi unit? :twisted:
Author:  Sam Powell [ Mon May 21, 2007 6:54 pm ]
Post subject: 
Dart270 ran the Holley projection system on his slant for awhile, and it ran real strong. He has a pretty big cam in the engine. He then went to firing the Holley TB and injectors,(I think there might be two injectors in the TB), with Mega Squirt. That gave him a problem because the Holley injector(s) were low impedence and he burned something out, but after he got that straightened out, he was still running his Holley with the Mega Squirt for some time. He might still be actually. But, to answer your question, it seems as if the projection ECu might work to batch fire your fuel rail injectors. I dont; see why it would not if the ECU is tunable. PM Dart270 and see what he has to say about this.
Sam
Author:  Matt Cramer [ Tue May 22, 2007 5:31 pm ]
Post subject: 
There's a couple of different Holley ECUs out there. The Commander 950 seems to be all right and should be capable of operating a batch fire system without trouble. The Pro-Jection is an alpha-N (throttle and RPM only) system with screwdriver adjustments. I think there may have been one or two other ones out there too. I would not try adapting one of their screwdriver adjustment systems to a slant six - these do not have very much room for tuning.
Author:  Carbide6 [ Tue May 22, 2007 7:30 pm ]
Post subject: 
Thanks for the advice. Are the gm injectors also low impedance? I read some other posts and wonder if my fuel regulator was bad. I did not put a guage on the rail as the fuel pump was new. The regulator is the stock unit. I could hear the pump load up and it sounded loaded during cranking. I incountered a similar problem with a 4.3 v-6 in my son's s-10 after we rebuilt the engine. A leaking o-ring and the thing would not crank! I guess I'll hook everything back up this weekend. The Holley system I have has 5 thumb screw adjustments and also has the o2 sensor kit. It uses tps,rpm, o2, voltage control to the fuel pump to run the system. I do not want to burn anything up as it will fit one of my Magnums. I bought a new cpu for the gm system thinking it was fried! None of the voltages checked right, that's why I finally give up on it. I'll keep you guy's posted on my progress or regress!!!!! 8)
Author:  Matt Cramer [ Wed May 23, 2007 6:29 am ]
Post subject: 
Quote:
Thanks for the advice. Are the gm injectors also low impedance?
Check them with an ohmmeter. Low impedance injectors are usually around 4 ohms or less.
Quote:
The Holley system I have has 5 thumb screw adjustments and also has the o2 sensor kit. It uses tps,rpm, o2, voltage control to the fuel pump to run the system. I do not want to burn anything up as it will fit one of my Magnums. I bought a new cpu for the gm system thinking it was fried! None of the voltages checked right, that's why I finally give up on it. I'll keep you guy's posted on my progress or regress!!!!! 8)
Sounds like the Pro-Jection instead of the Commander. It works on some engines, but it's not very tuneable.
Author:  Carbide6 [ Wed May 23, 2007 8:22 pm ]
Post subject: 
Thanks, I'm going to check the fuel psi on the rail to make sure the regulator is ok. I might then try to see is the pro-jector will fire the gm injectors if they are low impedence.
Author:  Sam Powell [ Fri May 25, 2007 5:05 am ]
Post subject: 
If there are just two injectors, they are probably low impedence. In general, the bigger the injector, the lower the impedence, and the more current they flow which can be hard on some circuits if they are not designed for high current draw. The Projection ECU would most likely be fine to fire the smaller ones.

Sam
Author:  Carbide6 [ Sun May 27, 2007 10:36 am ]
Post subject: 
Thanks again for the info. I worked so hard on making the fuel rail and running lines and wiring I want this to work. Both my Magnums have new carbs and $500.00(what I paid for the Pro-jection unit) would be worth the money to get it running!! I don't know if it will boost horsepower, but the driveability and wow factor would be cool!!
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