2000 S70 2.4 Erratic Injector Pulse Topic is solved

fastcars1173 · Post by **fastcars1173** » 28 Sep 2016, 12:43

Has anyone ever had an issue with erratic injector pulse? When I start the vehicle it runs smooth and within 5 seconds it starts running like it has a misfire. The MAF signal was only changing between 1.50 and 2.50 with engine revving and running rich fouling the plugs. I changed the MAF. Now the values correlate with RPM. It seems to run a little better but it still starts smooth then goes rough. It has new plugs and all 5 coil packs are firing (I checked the actual spark not just the signal). I checked the injector pulse with a noid light and am getting erratic pulses to the injectors. Also some were getting a weak erratic signal and some were not even getting a signal. Then after checking through again the same ones that were not getting a signal started to have a good signal and the others that were low and erratic stopped getting one. I have come to the conclusion it may be the computer. I am a seasoned tech but do not have much experience with volvos. Thanks for any input!

Post by **kcodyjr** » 28 Sep 2016, 13:22

Does the 2000 have the same gray master fuel injector relay up on the cooling fan shroud, whose connector gets all crappy?

fastcars1173 · Post by **fastcars1173** » 28 Sep 2016, 13:45

I only see the MAP sensor and the fan relays there. There is a relay in the kidney shaped main fuse panel that has a relay for the injectors.

Post by **kcodyjr** » 28 Sep 2016, 14:06

Hm. They may have fixed that in the S70. (I have an 850). That relay, with its poor placement, is responsible for many a no-start.

Someone correct me if I'm wrong, but I believe the S70 injectors also get a constant 12V and then get grounded by the ECU to open them. Check how steady the 12V is (green wire?) - if it's rock solid, then the poor signal is the ECU isn't properly grounding the injector. If it's flaky, trace the wires looking for a bad connection, the ECU could be fine.

ECU failures in these cars are fairly rare, unless you do something stupid like cross wires and send 12V down the wrong path.

fastcars1173 · Post by **fastcars1173** » 28 Sep 2016, 14:54

It has solid voltage to the injectors. All of the injectors ohm out perfect, 15.4-15.6. As I unplug the injectors it seems as though the signal jumps around. Number 1 seems to fire consistently but the others don't. For example, if I check number 4 it won't be firing, then if I unplug 5 and 3 then number 4 starts to. I'm leaning more and more towards a bad injector driver in the ECU. All grounds are good. I pulled the cover off of the ECU and nothing is visibly burnt inside and no traces of moisture.

Post by **shaker_chi** » 28 Sep 2016, 15:03

Have you swapped injectors to see if the problem persists with the injector itself or with the electronics?

fastcars1173 · Post by **fastcars1173** » 28 Sep 2016, 15:48

I'm not thinking it's the injectors. They all ohm'd great. It seems to be the signal that's the issue. A high impedance injector usually ohm's out at 12 to 16 ohms. Pretty much all regular injectors are high impedance (Saturated). Low impedance injectors are usually used in racing apps with aftermarket ECU's(Peak and hold).

Post by **kcodyjr** » 28 Sep 2016, 17:09

OK, yeah, if you're sure there isn't a wiring fault that explains it, try swapping an ECU from the boneyard.

Someone chime in, did they start with the reprogramming to the car bullcrap in 2000? I think you can simply swap it.

Post by **abscate** » 28 Sep 2016, 18:27

1999-on require ECU to be married to car in software.

It's not your ECU.

Post by **kcodyjr** » 28 Sep 2016, 19:09

Thanks, abscate, I wasn't sure how much of it started with the late P80's and how much started with the P2's.

Does it take a legit VIDA setup to do the remarriage or will one of the chinese hack jobs off eBay do it?

Anyway, I agree that an ECU failure is really unlikely. I've never heard of one just crapping out. With all that hassle, it isn't worth swapping one from a junkyard just to check and see.

How closely have you inspected the wiring? The way it comes and goes really sounds like something wiggling loose, or a wire cracked and rotted to the point it's a marginal conductor.