So I have been having an issue for the last couple years with my s40 that only pops up during the heat of the summer. It usually only happens in the evening of very warm days. The car will misfire, typically in lower RPMs, and will occasionally stall when at a stop. Originally I was getting 2 codes, p0301 cylinder 1 misfire, and p0304 cylinder 4 misfire. 2-3 years ago I took it to a mechanic and they replaced the spark plugs and ignition coils and ended up determining that the electrical harness needed to be replaced for 1300$. They said they would jimmy rig it for me until I could get the part. That resulted in the first picture. This year I've decided to stop paying mechanics every year for them to not fix the issue.

I started troubleshooting the issue by checking the spark plugs which were pretty white which made me think the system was running lean but that wasn't the code i received. I hadn't seen the jimmy rig until this point and thought that this was probably the issue so I pulled the ignition coil harness from a junk yard and installed it on my car (pic 2 with old wire laying over it for comparison). The issue didn't happen for a couple days and the check engine light went away.

The issue came back a few days ago and I am now getting the original 2 codes, p0171 system too lean bank 1, and p0351 ignition coil "A" primary control circuit/open. The 2 new codes have the manifold absolute pressure (map) sensor in common so I checked that. I think the sensor looks good (pic 3) but the cable to the harness doesn't have its cover anymore and feels like the wires are really hard and could be the source of the problem (pic 4). What would this wire be called and do you think it could be the cause of the problem? I know I have the known issue of a small leak in the turbo oil return so that made me consider the boost sensor. Where would that be located and could that be the cause?

I know this is a huge wall of text but I wanted to be as descriptive as possible. I am new to working on cars so hopefully this all makes sense. Any education would be helpful and appreciated. Thanks for your time!

 

Look for an identical baro sensor under the fuel rail attached to the intake manifold between the two intake runners on the driver's side. Earlier models only had the one sensor but I believe yours has two.

For the coil misfire look at it's connector closely. On my 2001 when you pushed the connector onto the coil the wires would actually back out of the connector without making a solid connection to the coil. After a short bit of driving the vibration would cause an intermittant miss. I finally found I could ditch the faulty connector and push the female wire ends onto the male coil connectors for a secure connection. I have read of others buying new connectors and replacing the female ends. Your pictures suggest someone tried to use RTV or similar to hold the female ends securely to the plastic connector. I would bet your replacement harness has poor connectors also as this seems to be a design issue.

 

Thanks for the response. I checked the connectors and think you were right because it wasn't as tight. I covered the loose wires with tubing. Cleaned the map and maf sensor. I'm looking for the barrow sensor but didn't have time to get in there today. The check engine turned off so we will see if it comes back on the next hot day.

 

So I am still getting the misfires. I think they are happening because the system is too lean. I checked the connections again and they are good. I looked through my records and in the past two years I have replaced both map (barro) sensors. I double checked there connections and cleaned them with high sensitivity electrical components cleaner. I also replaced the spark plugs in the last two years and recently cleaned them up as well. At the same time as the spark plugs I replaced both ignition coils. Cylinder 1 and 4 run off the same coil so to test it I swapped them with no change. My air filter was changed 3k miles ago and I just cleaned the maf sensor. Thinking that the lean system might be the cause of all the problems I cleaned the throttle body. I can tell it's a bit more responsive but still sputters intermittently. Reading some other posts made me think it could be the fuel pressure regulator so I ran the car for a bit and checked the vacuum line for gas. It seemed clean so I let it run with the vacuum line off to watch for fuel coming through and it appears the fpr is ok. I'm at a loss for what else could be causing the problem. Could it be a problem with the ecu causing a lean system? I read on other forums that there is a thermostat in the "air box" under the filter that controls if it lets cold air or hot air in but I can't find anything specific to the 03 s40. The only thermostat I can find is on the left side of the engine. Am I missing anything or what would you guys do next?

 

Have you checked the fuel pressure? Changed the fuel filter?

 

I thought about checking fuel pressure but haven't. When I checked the fpr I accidentally removed the fuel line instead of the vacuum line it it was pretty forceful lol. I can rent one from orielly's this weekend. Fuel filters are pretty cheap and easy to change from my understanding so I might try that. Is there a way to test it before replacing it. I was also thinking about pulling a fuel injector harness off a junkyard car and using it to clean the fuel injectors (the technique using a syringe tube, cleaner, and a battery). What do you think?

 

Well that was quite an experience. I replaced the fuel filter (the plastic clips holding the protective plate over it are a fragile pain to remove) and cleaned the fuel injectors. While removing the injectors I didn't drop just one but 2 of the clips that hold them to the fuel rail down but not all the way to the floor. I had to get one of them off of the starter solenoid from under the car and felt around with a magnet for the other. In the end the car ran great. Well until the guy behind me ran up and said "your spilling gas all over the road." Then the car died and I luckily was able to see what had happened. The fuel filter wasn't clamped down tight enough and the exiting fuel line had become loose. In the end the car is running great and has more hp than when I bought it. I hope this idle issue is finally fixed.

 

good update. Curious what you did to clean the fuel injectors. I had looked into services that do ultrasonic injector cleaning (some DIYs suggested an ultrasonic jewelry cleaner) or did you simply use a solvent?

 

I basically followed this video. http://youtu.be/_NMM6Mk79rg

I went to a junkyard and pulled off a injector harnes for 3 bucks. I think you can buy new connectors individually for like 10-15. I bought a new set of rubber rings for 5$. Some things I wish I would have known that aren't brought up in the video are: before taking the fuel rail off make sure to relieve the fuel pressure or you will get gas everywhere, the clips that hold the injectors to the fuel rail are really important so don't drop them, you can use the battery that is in the car, you don't have to hook up a button but if u don't you need to only touch the positives for a half a second, you need to get a really good seal on the tube or syringe because it needs to hold pressure without blowing off and throwing cleaner in your eye like it did with me, 2-3 sprays from throttle body cleaner should have enough fluid and pressure for a couple sprays, once your putting everything back together I found that putting a little oil on the rings helped the injectors slide into the rail and once the are all in the rail putting them back on the engine was easier, and when you go to start the car back up its going to struggle for a few seconds while it gets fuel pressure back so don't be alarmed, just turn the key for a couple seconds then on your second try it will start right up. Hope that helps. Let me know how it goes or if you have any questions.