no injector pulse on #2,#3

lockwoodfe · Post by **lockwoodfe** » 24 Apr 2017, 19:45

I have a 2001 Volvo S60 (not turbo) that is only running on 3 cylinders. Compression 120PSI and spark on all cylinders. Used a pulse tester and found not getting an injector pulse for #2 and #3. Actually, the engine runs fine for the first few seconds after starting and then gets rough. Likewise, I get pulses for the first few seconds and then nothing. I downloaded a wiring diagram and did a continuity check from the injector plug back to the ECU socket (ECU pulled) for all of the injector wiring. All wiring rings out okay and also checked no shorts to each other or ground. Getting concerned this might be an ECU problem. Any suggestions?

Post by **abscate** » 24 Apr 2017, 23:49

Your injectors fire by grounding the injectors, not pulsing voltage. Almost always, a bad wiring fault will trip a P020x code , where x equals cylinder number.

Check for 12 VDC at the injector pins ( you might have to search Forum for Lin assignments) or swap injectors from cylinders 1 and 2 to fault confirm

lockwoodfe · Post by **lockwoodfe** » 25 Apr 2017, 19:07

So I like your sig "Its not your ECU" and I hope you are correct in my case. I am confused by your comment though. If I put the pulse testers on the injector plugs, I do not get pulses on #2 and #3 while I get them on the other 3. Isn't this indicative of a problem? I do successfully measure battery voltage at all the injector plugs. Also curious as to why it runs fine (and also shows pulses) for the first few seconds after starting up.

Post by **mrbrian200** » 27 Apr 2017, 02:34

Lower than spec injector coil resistance I would imagine could result in this behavior if it's bad enough. It would make sense that the ECU protection circuitry can't sense an overcurrent condition until after it pulses the injectors to complete the circuit. A PPTC (self resetting positive temperature coefficient "fuse") would act like this. It's not inconceivable 2 & 3 might share a ground path/circuit protection within the ECU not common to all injectors. They're also sort of pricey (protect more than one circuit per device instead of 5 separate PPTCs for each injector)
Unplug and measure resistance across those two injectors with an ohmmeter.
The green injectors Bosch 0280156336 (verify this is what is in your car) should measure 14.5 ohms. The tolerance is tight but I can't find the official spec (probably no more than +/- 0.3 ohms).

Post by **oragex** » 27 Apr 2017, 03:49

These are really cheap and plenty of them at the scrap yard, they almost never go bad unless a previous owner have tried to 'clean' them with some home made products

lockwoodfe · Post by **lockwoodfe** » 27 Apr 2017, 15:56

Resistance reads 14.5 on all injectors. For the heck of it, I plugged the ECU back in and started it up and surprisingly it ran smoothly for a few minutes. I proceeded to clear the car off so I could give it a test drive. While I was doing this, the idle speed started cycling up and down and continued to do so for the next several minutes until it suddenly stopped cycling and returned to missing cylinders. Checking the pulses again, #3 is working now but #2 and #5 aren't pulsing. What the heck? I did check the voltage on the injectors and they all have 14.4v on the green wire. The wiring diagram shows these green wires are all tied together and go to the same pin on the ECU. Since I did just try to drive it again, the one other thing I have not mentioned is that the engine will not rev up at all once you put the transmission in D. It just crawls along at a slow speed and pressing the gas pedal does not seem to change things. If you put it N or P then you can rev the engine. Initially thought this was just because I had no torque with only 3 cylinders firing but now thinking that is probably not the reason.

Post by **jimmy57** » 27 Apr 2017, 16:05

When it starts canceling the injector grounding for 2 and 3 is the idle speed high?
If it goes into throttle failure mode it stops throttle control and the preset opening gives high idle so the ECM drops some injectors to limit speed.
What are the codes stored, if any?

Post by **abscate** » 27 Apr 2017, 17:10

I think pinouts on the injectors are in a recent thread..is this really wired with individual constant12 VDC and common ground switched by ECU?

Were they handing out free EE design degrees that year in Sweden?

Post by **jimmy57** » 27 Apr 2017, 22:30

12V from relay and ground individually switched by ECM transistor is the way it is done as normal. But the individual grounds can be turned off for a few reasons. Repeated cylinder specific misfire can be another reason to stop injector grounding individually.

Post by **abscate** » 28 Apr 2017, 04:48

I misread above. Common B+ voltage to the injectors and individually grounded through ECM as makes sense