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Broken Renix Injector Harness

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05LLYMaxx

NAXJA Forum User
Location
Roseville, CA
Ok, I'm sure most of you are tired of the Renix, as am I! But, this has to last me until the end of summer when racing season is over. Anyways, the number 4 injector harness isn't firing. Ground side is good, but instead of a on/off signal from the 12v side, it's just a dull light (test light). So, should I be looking at the harness as suspect or the ECU itself?

Also, could this have anything to do with a random drop in idle speed then rev up?
 
Year?

Could it be the connection itself?

"Ground is good" meaning what exactly?

I thought the Renix fired the injector by grounding it through the ECU. There have been a few reported Renix ECUs with that part gone bad.

Could the wires be damaged? is getting a solid 12 volts at the injector?
 
It's a '90. I used a DVOM from the positive terminal to one side of the injector plug, 12v there.

Then, I used a test light from the negative terminal to the other side of the injector plug, and got a small buzz of power, not flash like the others. So, that means I am getting some voltage to the injector, but not enough the fire it off. It's got to be in either the harness or ECU.

The reason I don't think it's the harness is because I am still getting some voltage to the injector, as well as it not being an on/off signal also makes me think its the ECU.

Anybody else see this? Also, this came up out of no where. I was making some laps on a short course track, finished up and went towards the trailer, then the miss started....
 
Run the injector harness from the injector back to the firewall and around to where the leads take off for the distributor--the harness tends to break right in that area.
 
joe_peters said:
Run the injector harness from the injector back to the firewall and around to where the leads take off for the distributor--the harness tends to break right in that area.
Click to expand...

Even though I am getting a constant ~4v to the injector? Could it be the harness? It is NOT giving me an on/off signal at all, just a low dull 4v. I will check that tonight anyways, I just wish I could quickly swap an ECM with someone to check it. Oh well, I will post up results.

Thanks
 
So, I hooked a DVOM from the ECM plug all the way to the injector plug, it read 1ohm! So, the wire is perfect.... Ground side is good. So, that only leaves the ECM, right?
 
So both wires, while disconnected from the injector and the ECU, read 1 ohm, end to end? Did you check to make sure that they are not shorted to each other? Or that the normally hot wire is not grounded in the harness somewhere. I would do that to make 100% sure it is the ECU, as a partially shorted wire could damage a good ECU!

One that is done, then yes the ECU is the bad guy. There is an old thread here where a guy from east Europe diagnosed his and his fixed the ECU with a $1 transistor if you want to to search for it. It was a bad transistor on one injector firing circuit.
 
If I check both sides to each other, it says incomplete circuit, meaning no short between the two sides.

Yes, 1ohm end to end. Checking from the hot side to 12v battery shows nothing, meaning the hot side is not grounding out anywhere either.

I have seen the fix you mentioned, but there are no visible issues, and I'm not sure what, or how to test each circuit in the ECM.
 
This makes no sense?

"Checking from the hot side to 12v battery shows nothing"
 
Ecomike said:
This makes no sense?

"Checking from the hot side to 12v battery shows nothing"
Click to expand...

Basically going from the switch side of the injector harness to 12v at the battery would show me if the wire is grounded out. If it read 12v then the wire is bare and touching either the block or firewall. But since there was zero continuity between 12v and the switch side, means there is no short in the wire.
 
No, you test from the negative post, or a bare metal area like the engine block (clean steel area, not rusted) to the injector side wires (test both, one at a time) with the meter set on ohms, with the ignition off, to see if either wire is grounded out at all, both should be over 1 meg ohm, or read an error (meaning infinite resistance).

If it reads about 200,000 ohms or less there is probably a shorted wire, but this is only if the wires are not connected the computer.
 
Ecomike said:
No, you test from the negative post, or a bare metal area like the engine block (clean steel area, not rusted) to the injector side wires (test both, one at a time) with the meter set on ohms, with the ignition off, to see if either wire is grounded out at all, both should be over 1 meg ohm, or read an error (meaning infinite resistance).

If it reads about 200,000 ohms or less there is probably a shorted wire, but this is only if the wires are not connected the computer.
Click to expand...


Ok, so, I double checked this morning. From ground to each side of the injector plug gave me 1ohm on one side and OL (NO Continuity) on the other. Then checking them to each other also said OL. I stripped the harness clean and all the wires look fantastic.

Any way to actually test each injector circuit at the ECM? There is probably not without some sort of computer testing equipment....

I am looking at a ReMan ECU for $100. Good, or?
 
The 1990 ECU is 99.9% bullet proof, they are usually cheaper at a junk yard or on EBAY. Yours is only the fourth Renix ECU in 7 years I have heard of going bad, if it is bad.

If you have a spare, known good injector you could install it on the suspect connection and see if it clicks with the engine running!!!

I usually pull the injectors and test them one at a time with alligator clip jumper wires and a 9 volt battery. No reason you could not test the installed injector and listen for a click. No clicky means it is a bad injector if a known good injector clicks on the same connector. Otherwise the ECU is bad if neither one clicks and the loose one clicks on a second injector connection, with the engine running.
 
my 89 did the same thing and come to find out the harness was bad and fried the ecu. I ran new wiring from the ecu to the injectors and got a used ecu from wrecking yard and all has been well for about 2 years now. the ecu was $30 at the jy.
 
Ecomike said:
The 1990 ECU is 99.9% bullet proof, they are usually cheaper at a junk yard or on EBAY. Yours is only the fourth Renix ECU in 7 years I have heard of going bad, if it is bad.

If you have a spare, known good injector you could install it on the suspect connection and see if it clicks with the engine running!!!

I usually pull the injectors and test them one at a time with alligator clip jumper wires and a 9 volt battery. No reason you could not test the installed injector and listen for a click. No clicky means it is a bad injector if a known good injector clicks on the same connector. Otherwise the ECU is bad if neither one clicks and the loose one clicks on a second injector connection, with the engine running.
Click to expand...


I did swap injectors around and the issue stayed in the same spot. I have a "test" ECM coming in tomorrow, so, I will know for sure then.
 
Ecomike said:
The 1990 ECU is 99.9% bullet proof, they are usually cheaper at a junk yard or on EBAY. Yours is only the fourth Renix ECU in 7 years I have heard of going bad, if it is bad.

If you have a spare, known good injector you could install it on the suspect connection and see if it clicks with the engine running!!!

I usually pull the injectors and test them one at a time with alligator clip jumper wires and a 9 volt battery. No reason you could not test the installed injector and listen for a click. No clicky means it is a bad injector if a known good injector clicks on the same connector. Otherwise the ECU is bad if neither one clicks and the loose one clicks on a second injector connection, with the engine running.
Click to expand...

Hey, so, I double checked the whole harness again, all looked good. So, I did swap the ECM out, and, DING DING, fixed the problem as soon as I plugged it in. Been driving for the past few days, all better.

Now, I just have to figure out the weird random change in idle speed.
 
05LLYMaxx said:
Hey, so, I double checked the whole harness again, all looked good. So, I did swap the ECM out, and, DING DING, fixed the problem as soon as I plugged it in. Been driving for the past few days, all better.

Now, I just have to figure out the weird random change in idle speed.
Click to expand...

If you don't have a use for the bad ECM might PM 5-90 and see if he can use it for testing.
 
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