2006 S40 2.4i (purchased in 2013 with 114k on the clock, now 162k)

One morning about two weeks ago I suddenly had a very rough start, followed soon after with a blinking CEL and a tough time getting down the on-ramp and merging onto the freeway. I read the codes - I had P0201 - Fuel Injector Circuit Malfunction Cyl 1 and P0301 - Misfire Cyl 1. Ok, I figured I had a bad fuel injector, which of course is causing the misfire - no fuel, no bang. I had to get my kids to school and had to get to work, decided I could limp along on 4 cylinders for the day. These 5-cylinder engines seem to run kinda ok on 4 cylinders, especially once you get up to speed on the freeway and just cruise along.

After being confused for a bit by some other codes that seemed to crop up randomly, and a P0103 - MAF Sensor Circuit High that was pretty consistent, I got under the hood. At first the combination of codes made me think of a wiring fault; I had recently had the ECU disconnected to remove the airbox (to replace the thermostat strategically located under the airbox), so I figured maybe I moved some wires around which had been pinched or damaged causing signals to find their way to the wrong wires. Finding nothing I pulled the intake manifold to get at the injectors, and checked the voltage at all the injectors with KOEO, all good. Then checked the resistance of all injectors, all 15 ohms except #1 - #1 was open. Finally just to be sure all was well I rigged an indicator light and verified I was getting injector pulses on plug #1. All checked out, injector #1 definitely bad (noticed only after doing it I could've gotten to injector #1 without removing the intake manifold... argh!).

I didn't understand the presence of the P0103 fault appearing along with the injector problem; there didn't seem to be any connection but I've never had any MAF sensor faults before. Having 100% confirmed a bad injector, I decided to replace that first and then see about the P0103 code after that.

So, I looked around at my options... if I could wait a few days I could've gotten a very cheap reman. injector for less than $50, but I wanted it quicker - I had some longer driving to do later in the week. So I found a local shop that could get me a real Bosch Volvo OE injector for $100 the next morning... seemed like the right thing to do.

When I got the fuel rail out, I realized the injectors had already been replaced with non-OE injectors (the brown ones, exactly like these ( ). They look quite different than the Bosch, they're shorter overall and even the nozzle pattern is different; however they match in the critical dimensions O-ring to O-ring. I proceeded with the replacement.

So initially the car ran great. However, soon I got new CE codes: P0172 - System Too Rich and P0304 - Cylinder 4 Misfire; both return very quickly after clearing them. Yet the P0103 - MAF fault has not returned. The misfires seem to only happen at cold startup; the startup fast idle is rough, I can feel the engine shake, and when I monitor the misfire counts I get around 80 almost immediately and then no more for the remainder of the drive. I don't feel any misfires while driving.

What's causing the P0172 - System too Rich? Is the fact that one of the injectors is different confusing the ECU somehow? That seems like the obvious answer, since I had no P0172 before swapping one injector, but do now. I know replacing all 5 injectors would've been the right thing to do, but that's mo' money, and I work on my own car in part because I don't have mo' money.

What's causing the P0304 - Misfire #4? Side effect of the fuel mix being too rich? Doesn't really make sense, at startup the mixture is supposed to be rich, doesn't seem like that'd cause a misfire at startup but not later. And why only #4? Why not #1, the one with the new, different fuel injector?

Any advice welcome.

 

 

I've been reading up on this some more... starting to think maybe I should replace the MAF sensor, or at least clean it (replacing it is the same amount of work, but I haven't looked up the part cost).

Most of the sites the discussing diagnosing rich conditions talk about the MAF being a possible source of a too rich condition, including this good explanation:

"An "over reporting" Mass Air Flow Sensor can be a common cause of a code P0172 and P0175. Essentially, this means that the Air Flow Sensor is telling the computer that much more air is entering the engine than actually is. Based on this large amount of air entering the engine, the engine computer or PCM sprays more fuel into the combustion chambers.
Since the oxygen sensors are telling the computer that less fuel is needed, this causes confusion in the computer because the Mass Air Flow Sensor is still saying there is too much air and the Oxygen Sensor is reporting that the mixture is still too rich. The computer tried to compensate, but since resolution is impossible, it sets the code."

Since I was getting a P0103 before, indicating a MAF fault that couldn't be explained by a dead fuel injector, that's two fingers pointing at the MAF sensor.

 

On further consideration, replacing the MAF Sensor feels like the right move. If the MAF sensor were merely dirty, it would "under report" and I'd have a different set of problems, like a system too lean code or something like that. Further, the P0103 code I had before was MAF Sensor Circuit HIGH, which seems like an "over report" condition... even though I'm not getting that code now, it must've meant something.

I can get a new MAF Sensor for $40, seems like a small enough price to pay to know my MAF Sensor is good

 

well, nevermind about the MAF... I now have no reason to believe it's the MAF sensor causing the problem. I decided to clean it since it was easy enough to do, and then figured out how to monitor the MAF readings in realtime on my phone (Torque Pro). The MAF readings seem completely reasonable: about 3.6 g/s at low idle, ranging up as expected when accelerating. I cleared the codes immediately after cleaning the MAF sensor; both codes came back within 5 minutes of driving, and the CEL came on the next time I started it up.

I guess I'm back to the original theory about the ECU being confused by some difference in characteristics between the new Bosch injector and old whatever-they-are injectors (I see the same injectors sold under several different brands, I've no idea who actually makes them). I'm not sure that theory is even sensible: if there can be variances among injectors, then the ECU must already be able to adjust for such variances... well maybe the adjustments are overall adjustments and can't be done per injector? So there's no single adjustment that works with the mixed bag of injectors I've got? I dunno....

I guess I might try swapping injectors around as pierremcalpine suggested. Or maybe I just give in and replace the other 4 with Bosch injectors. FCPEuro has them for ~$40 ea last I checked.

Anyone's comments, advice, even crackpot theories welcome.

 

I think you're on the right track with the concept of getting all the injectors back to a matched (quality) set. 90% of the time when you fix something and end up with another problem, you look at what you fixed - often its just a case where something went wrong (like a connector not reconnected or a leak in a hose that cracked during the job, for example). In this case, it would be easy to imagine the ECU being confused by getting different results from only one of the injectors. And hey - given how expensive gas is, and how relatively cheap new, high-quality (Bosch) injectors are, it's hard to imagine that you wouldn't end up getting your money back in MPG improvements with better injectors, even if they don't fix the problem (though I bet they would).

 

JohnsonX42, I have a 2008 S40 and got two codes tonight (P0201 and P0301) along with the rough idle and poor acceleration. As I got the injector code with the misfire code, I suspect an injector issue. Your post is great, I am going to go down the same path of checking the #1 injector resistance for the noted 15 ohms. My question is regarding using an indicator light to verify you were getting injector pulses on plug #1. What sort of rig did you use for that? Would I be able to see the pulses on a digital multimeter? Thanks!

 

A noid light is the simple tool to check for injector pulses. There are more expensive testing tools available but not really practical for the home mechanic IMHO. If you ever watch the YouTube channel for South Main Auto you will see many videos on how to check for injector pulses and other diagnostic tools. The guy knows his stuff.

 

if there is easy access to the injector, you can always swap #1 and #2 to see if the codes change to xx02. there are also services which will clean injectors asssuming the circuit is still good.

 

To make my own noid light I went to my bin of electronics bits and found a LED and a 500 ohm resistor, twisted the resistor lead onto one leg of the LED, and then stuck the contraption into the injector plug and started the engine. It was rather dim, a 330ohm resistor would've been better (which I didn't have), but the pulses were definitely there. You could do the same with a small incandescent bulb rated for 6 to 12 volts, no resistor needed. (edit: you probably realize this, but a reminder that LED's only work one way... so if you get no light the first time, remove it and stick it in the other way around)

No, you wouldn't be able to see the pulses on a digital multi meter, they're much too short to register. On an analog meter you'd see the needle wiggle, but who has one of those any more?

To answer mt6127, the only thing you can get to without removing the intake manifold is the plug for injector #1. To actually swap injectors you have to remove the intake manifold, drain the fuel rail and then pull it out with all the injectors attached. I don't think it's worth doing without a replacement injector in hand (the CORRECT one!... or FIVE).

 

Thanks for the info. To update my issue, I took the intake manifold off and checked the resistance of the injectors as per your first step. The #1 injector was open, which explained my injector fault code. I was in a hurry this weekend to get it done, so rather than order one I went down to the Pick-N-Pull and took two injectors out of a 2007 they had there in the yard. They were only $5 each, so I grabbed two . Anyhow, dropped the injector in, cleared the fault codes, and my son is back on the road. Thanks!

 

Great "real world fix", and no doubt the cheapest option. And let's face it - these injectors don't die very often, so the odds of your junkyard injector going south are pretty slim (that's assuming it works when installed, of course).

 

The injector you have is for the turbo 2.5 I think you need a brown injecter for the 2.4i