3 ohm -vs-12 ohm injectors
08-18-01, 10:24 PM
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3 ohm -vs-12 ohm injectors
I asked this question once a while ago, but on the chance that some new Einstein type has come along recently...I'll try again.
I need to make some 12 ohm injectors work with my 3 ohm system, can I just change the ECU and the resistor block, or is it more complicated than that? I know the connectors are different, I have overcome that issue.
Thanks,
Bill
I need to make some 12 ohm injectors work with my 3 ohm system, can I just change the ECU and the resistor block, or is it more complicated than that? I know the connectors are different, I have overcome that issue.
Thanks,
Bill
08-19-01, 07:48 AM
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No real help here, but......it seems you could chunk the resistor assy. Now you would be left with a power wire and four wires going to the injectors. Light minded person like me figures you could splice the four wires to the power wire and it would work. Now that I have set myself up, somebody can come along and tell me why that would not work. Irv? Keith's father, or how about Keith? Six Rotors? I think I'll go out to the N/A and measure resistance to the ecu thru the resistors today. I've got a older 87with 3ohm injectors.
08-19-01, 08:54 AM
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I am not really sure how the car "knows" what resistance the injectors are . The ECU does not make the differance, as I have switched them between 2 cars w/ the different injectors. You mention something about a resistor block.I don't remember seeing that in the harness when I switched them out.Is that on the inside of the car?
08-19-01, 09:37 AM
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On the 86-87 and a half, the resistor block is under the air filter. Can't miss it. Bright shiney thing. The cars with 12ohm don't have one. Eat your hearts out. Humor. I think I read somewhere that if you put the 3ohm ones in a car meant for 12ohm, it will do harm to the ECU.
08-26-01, 10:43 AM
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So. you are telling me that the later cars have no resistor block at all? I figured it would be there but just a different resistance. It makes sense though so I think next weekend I will give this a try, thanks to all the practice....I've got it down to where I can switch the injectors in about an hour. Did I mention this setup is not really in an rx-7? Its an 89 pickup that I stuck the injected 13-B in about 3 years ago. But the harness I made has all the same stuff in it still and then some.
Bill
Bill
08-26-01, 02:22 PM
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I wish somebody on this site would tell us how to use the 12ohm injectors in a 3ohm system. I just made a wild *** guess and would hate for Dr. Switch to destroy his ECU or injectors. Maybe Irv, Keith's dad or Six Rotors. Or.....Dave Gibson from the fc3s.org site. Hey Switch, why don't you maybe pm Dave Gibson? I see a number of his answers to posts lately.
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08-26-01, 06:12 PM
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Dr.Switch, maybe you can be of assistance. There is a post called *newly installed motor won't start* by 88 nafc. He seems to have the same problem you had a while back where you has to put the right injectors in the car for it to work. Could you possibly write 88 nafc on his post and confirm that having the right ohm injectors in the car makes a difference whether the car starts or does not. Please. I have written some post to him and am not getting thru to him.
08-27-01, 12:40 AM
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HAILERS is correct. To put 12 ohm injectors in a 3-ohm system, just bypass the resistor pack. Each resistor in the pack is 5-7 ohms. Add that to the 3-ohm injector resistance, and you get 8-10 ohms. If the ECU is beefy enough to handle 8 ohms, it will definitely handle 12 ohms no problem (reducing current from 1.5 amps to 1 amp GREATLY reduces loading!). Also, this is the same as the later wiring diagrams. Nothing to worry about here, the only way to kill an ECU is to put 3-ohm injectors in a 12-ohm injector car without ADDING a resistor pack.
Irv, Keith's dad
Irv, Keith's dad
09-02-01, 11:38 AM
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"If the ECU is beefy enough to handle 8 ohms, it will definitely handle 12 ohms no problem (reducing current from 1.5 amps to 1 amp GREATLY reduces loading!)."
Ok, so here is another question. I just put the 12 ohm injectors in the engine and removed the resistor pack, it wont start. Is it possible that the extra 3.5 to 4 ohms is too muvh for the ecu and that the current isnt enough to open the injector?
In the meantime I'll just put it back the other way...
what a bummer
Ok, so here is another question. I just put the 12 ohm injectors in the engine and removed the resistor pack, it wont start. Is it possible that the extra 3.5 to 4 ohms is too muvh for the ecu and that the current isnt enough to open the injector?
In the meantime I'll just put it back the other way...
what a bummer
09-02-01, 07:03 PM
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Yes, I just cut the 5 wires and soldered them all together. I guess if you think about it, the combined resistance of the resistor and the injector is only about 9 ohms, thats quite a difference from the 12 ohm injectors. So, unless I'm a complete idiot......its back to the drawing board.
Bill
Bill
09-03-01, 10:18 AM
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Dr Swithch....this from Ted's site...http://www.k2rd.com/FC3S/MODS/FUEL/inj.htm....just more info. The k2rd is a worth while site.
09-03-01, 10:29 AM
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About the above url. I clicked on it and it did not respond so Try this one.....http://www.k2rd.com/FC3S/fc3s.html the thing you are looking for is under Mods and its Fuel Injectors. It seems there are two Fuel Injector headings. The lower one is the one to go to. Its the original information you were looking for. If the above url does not work try just the .com and then look for Mods and then fuel injectors. Did this help?
09-04-01, 12:36 AM
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Dr. Switch, I know of no reason why this should not work. If you have checked the K2RD web site as Hailers suggested, you will have noted that he, too, says it will work. Might just need to troubleshoot it to make sure you have 12V to the injectors, and if you do not, find out why. IMHO, if the ECU can sink (ground out effectively) a lower ohm level, a higher ohm level will always work, since the common open collector circuit used here is not affected by voltage on the collector. Sorry I can't give you a definitive reason for it not working.
Irv, Keith's dad
Irv, Keith's dad
09-19-01, 01:35 AM
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Effect of 3 ohm in 12 ohm system?
Does anyone know what the effect of using the wrong injectors would be? I have an 88 GTU that has been giving me problems for over a year. It started about 3 or 4 weeks after I had the injectors replaced. Everything was great immediately after the work was done but then it started cutting out under medium to hard acceleration. It feels like it could be fuel starvation but I've had it checked by several places & no one can find the cause. This is the only problem as everything else seems fine.
After stumbling across this thread earlier today I checked the resistance of my secondary injectors & got a very low reading (about 1 1/2 - 2 ohms). According to the factory manual, the 88's injectors should read 12 - 16 ohms.
I realize that I'll have to replace the injectors with the correct ones but has the ECU been totally screwed up as a result of this?
Thanks for any advice.
Don
After stumbling across this thread earlier today I checked the resistance of my secondary injectors & got a very low reading (about 1 1/2 - 2 ohms). According to the factory manual, the 88's injectors should read 12 - 16 ohms.
I realize that I'll have to replace the injectors with the correct ones but has the ECU been totally screwed up as a result of this?
Thanks for any advice.
Don
09-19-01, 11:59 AM
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You might read this url http://www.k2rd.com/FC3S/MODS/FUEL/inj.htm Its just some insite on them. I have read somewhere that the low impedence in a high impedence system would screw up the ECU. In you case I think I'd just replace them with the right product and see what happens. I know what you said about it being a 88 but just to be on the safe side I'd remove the air flow meter with the whole filter assy and look down below and see if there is a resistor pack. It would be about four inches long, mabe a inch and a half wide mounted with two 10mm bolts on the round part of the right hand wheel well. Your 88 should just have two threaded holes spaced approx 3 inches apart. Please write back when you have the new ones installed so we can see what happened.
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