Ignition wiring My '90 RS 305 TBI is throwing a code 42, and it's a bit hard to start and idles a little rough. Other than that it runs fine. I've been trying to determine the cause of the code, which states it's either an open or short in the EST circuit, a faulty ignition module, or faulty ECM. I've tested the ignition module three times and all three times it came up good. I'm thinking there's a problem with wiring from the ECM to the ignition module. Here's a reference I've been using http://www.gearhead-efi.com/gearhead...c/TBIcodes.pdf I'm not experienced at all with electrical circuits, though I have a multimeter. Assuming I do find a problem with one of the circuits from the ECM to the ignition module, I'll have to tear through the wiring harness to locate this one wire and replace it, or what? Any advice is appreciated, thanks. |
Re: Ignition wiring With the hard to start problem, the problem is most likely a grounded EST line, circuit 423. Check that first. Also a PROM not fully seated in the ECM can cause a Code 42 |
Re: Ignition wiring Oh, just realized you said your not very good at electrical stuff. To test if its grounded: 1. Turn ignition to OFF 2. Unplug ECM connectors 3. Turn ignition to ON 4. Set OHM Meter to 1000-2000 OHM Range 5, Probe ECM harness connector Circuit 423 with the RED lead on the OHM meter and the BLACK lead on a ground. It SHOULD read LESS than 500 OHMS If it does not read less than 500 OHMs the you have an open circuit (no connection) or a bad ignition module (which you said tested good). |
Re: Ignition wiring
Originally Posted by 85irocinjected
(Post 5130570)
Oh, just realized you said your not very good at electrical stuff. To test if its grounded: 1. Turn ignition to OFF 2. Unplug ECM connectors 3. Turn ignition to ON 4. Set OHM Meter to 1000-2000 OHM Range 5, Probe ECM harness connector Circuit 423 with the RED lead on the OHM meter and the BLACK lead on a ground. It SHOULD read LESS than 500 OHMS If it does not read less than 500 OHMs the you have an open circuit (no connection) or a bad ignition module (which you said tested good). Also, assuming I do find a problem in the circuit, because I know the module is good, then I know there's a short/open in the circuit then what should I do? Try and somehow track the short in the circuit down? That sounds very tedious. |
Re: Ignition wiring Disconnect it from the ECU. Your testing what the ECU would see. If you do find a short/open then yes you will have to follow that wire through the harness and find the break. Or you can cheat and cut the wire a few inches from each end and solder/splice your own. Then you wont have to open the harness and the crap wire is taken out of the circuit completely. |
Re: Ignition wiring
Originally Posted by 85irocinjected
(Post 5130679)
Disconnect it from the ECU. Your testing what the ECU would see. If you do find a short/open then yes you will have to follow that wire through the harness and find the break. Or you can cheat and cut the wire a few inches from each end and solder/splice your own. Then you wont have to open the harness and the crap wire is taken out of the circuit completely. |
Re: Ignition wiring I tested it this morning, circuit 423 read .503 K Ohms. That's just outside of the 500 ohms it should be less than, what do you think? |
Re: Ignition wiring Bump. Anyone?? Also, if I do replace the circuit 423 wire, what gauge wire should I replace it with? |
Resistance Is Futile
Originally Posted by kkingsrulee circuit 423 read .503 K Ohms
Originally Posted by kkingsrulee what gauge wire should I replace it with? ◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙ Happy Racing! ◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙ He Must Have Been Be Cheating - Because I Was And He Almost Beat Me. . |
Re: Resistance Is Futile
Originally Posted by NINÅ
(Post 5135044)
That circuit should read less than one ohm. 18. ◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙ Happy Racing! ◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙ He Must Have Been Be Cheating - Because I Was And He Almost Beat Me. . The circuit should read less than one ohm? So right now it's reading 503 ohms, thus it's reading 503 times as high as the normal resistance reading? So there's most definitely a problem there, right? |
Resistance Is Futile
Originally Posted by kkingsrulee So there's most definitely a problem there, right? ◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙ Happy Racing! ◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙ He Must Have Been Be Cheating - Because I Was And He Almost Beat Me. . |
Re: Resistance Is Futile
Originally Posted by NINÅ
(Post 5135093)
That’s right. ◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙ Happy Racing! ◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙ He Must Have Been Be Cheating - Because I Was And He Almost Beat Me. . SES light still comes on about five seconds after starting the engine. |
Resistance Is Futile
Originally Posted by kkingsrulee it's a bit hard to start and idles a little rough. Other than that it runs fine. Make sure the sensor output isn’t more than 1.2 volts when your foot is off the loud pedal. ◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙ Happy Racing! ◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙ My Brakes Don’t Work AT ALL When The Car Is In The Air . |
Re: Ignition wiring Just figured I'd update you guys and anyone that has a code 42 problem. I replaced circuit 424 (tan/black wire) and that fixed the problem. So, if anyone experiences a code 42, check circuits 423 and 424, even though there might not be any visible damage at the ECM and ICM sides, there is likely a short somewhere. |
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