#1 Fuel Injector Harness Short Topic is solved

Shaokatan · Post by **Shaokatan** » 17 Nov 2016, 13:18

I recently bought a '98 V70 XC with some issues that I figured I could get sorted out. It has thick smoke from the exhaust and unburnt fuel dripping from the exhaust pipe if left idling. I did all of the tune up items on the ignition side, plugs, wires, distributor cap/points and rotor thinking that may be the culprit. All of which helped immensely and cleared my check engine light. However, I am still getting the same smoke and rough idle. So I moved on to the injectors. The previous owner said they replaced the injectors and they all seem to ohm-out just fine, until I got to the #1 injector harness connection. It appears to have a short on the + side. I visually inspected the harness and everything appears to be OK. And if I disconnect the ECM the short goes away...As I understand, that harness is grounded through the ECM? Does this mean I have a short in the ECM and it needs to be replaced??

I removed the cover from the ECM and did not see any obvious signs of trauma but I also only visually inspected the top of the circuit board. I found the wiring schematic for the fuel system on this site and it appears to be pin #10 for the #1 injector that I need to check and I will do so tonight. Am I chasing down the right path on this? Or, would a relay cause just one connector to show a short?

If it is deemed to be a short in the ECM is there any fix to it other than replacement? If I do need to replace the computer, I cannot just swap them out without getting it programmed correct? As I found after the fact, 1998 was a weird year for these cars so I have found all sorts of conflicting information.

Thank you in advance!!

Post by **jimmy57** » 17 Nov 2016, 14:05

The harness goes back is spliced behind the fuses to other parts of the circuit. The plus side is power supply and the other wire is from ECM to ground the injector to complete circuit so fuel is delivered. IF engine is running that + side wire (green wire on that car) should have the same voltage as the others. The other wire at the injector plug is the grounding wire and due to such a small percentage of time that it isgrounded it will check just a little lower than the green power side wire. With a meter capable of mS pulse display you will see an injector pulse of 2.3 +/- mS at idle warmed up. In gear and other engine loading will increase the pulse time to give the fuel needed for the higher loading.

Shaokatan · Post by **Shaokatan** » 17 Nov 2016, 16:03

Ahh hell...I misspoke. The + (green) side seems fine. It is the Gray wire going to the ECM that seems to be the problem. I believe it is getting grounded constantly and running that injector non-stop. I have not tested it with the car running yet so maybe I will check the pulse speed (if there is any pulse.) Thank you for that suggestion.

Do you know what component in the ECM is creating that pulse? Is it voltage based or signal based?

Post by **Ozark Lee** » 17 Nov 2016, 17:24

It is basically an open collector output that pulses to ground when triggered. The ECU doesn't supply a trigger voltage but rather goes from a high impedance when referenced to ground to a low impedance when referenced to ground in order to trigger the injector.

...Lee

Shaokatan · Post by **Shaokatan** » 09 Dec 2016, 08:18

Well, I went ahead and did what basically everyone says not to do and replaced the ECM. And guess what!? It didn't work...My only reprieve is that it only cost $66 and I figured I would have that in time spent trying to find a short.

I did do some more testing before deciding to replace that and now I am more confused than ever. I have a constant ground for the number 1 injector on the signal (grey) wire at the injector regardless of if the car is running or not and if I plug that connector into the injector it instantly floods the engine with gas and smokes like crazy. What has me confused is if I disconnect the ECM the ground continuity goes away and if I check continuity between the ECM connector at the #10 pin and the injector connector it is good with 0 ohms of resistance. I know that does not necessarily mean that wire does not have a short somewhere but I thought I would see it grounding somewhere or have higher resistance. Basically I am trying to avoid needing to tear that harness apart to try and find the short. Especially since today started off -4 below zero here in South Dakota and it's not supposed to warm up anytime soon...

Would a short-to-ground be the only culprit here? Would a bad fuse or relay cause just one of the injectors to stay grounded? Or, is it actually an issue within the ECM that it is not sending the signal to change the impedance on that injector?

Thanks again for your help

Post by **erikv11** » 09 Dec 2016, 09:46

I have not read the details of your post carefully so apologies if this is a dumb suggestion:

All of the injectors fire at the same time. Which probably rules out a relay or fuse problem. At any rate, given that fact, can you just grab another connector with lead wires from the junkyard (or I can clip one off my parts car and send it to you), and splice it in to the wiring for one of the other injectors? Sounds like you're going to end up messing with the harness no matter what, anyway. FWIW I have clipped off a full injector harness before, the wires are still all separated where it connects into the main harness.

Shaokatan · Post by **Shaokatan** » 09 Dec 2016, 10:35

Oh really!? I did not know they all fired at the same time! So in other words, I could just clip the grey wire from the #1 injector and splice it into the Grey-Orange wire from the #2 injector? That would make life way easier! I didn't think of that.

I have good power on the + Green wire across all of the injectors and I really don't care if I need to do some splicing. I will just leave the other end open for #1. The increased resistance shouldn't cause any problems will it? I guess it's just a signal to ground so I'm guessing it's fine?

Thank you for the suggestion!