I was on a long trip over the weekend, lots of rain. I downshifted to 3rd to pass someone on the highway (about 60-65 mph) and when I hit the gas the car sputtered and didn't really go anywhere. I immediately let off the throttle and went back to 5th, but the car was running a little rough, vacuum was around 0 and the engine light was flashing. I thought oh no I need to get off the next exit, and about 10 seconds later, the car smoothed out and engine light stopped flashing and shut off. I was careful the rest of the trip and didn't have any issues, even tried a little 5 psi getting back on the highway and it seemed OK. The only difference was the idle has been just a bit more rough than usual (I've never been impressed with the idle, as it's always seemed rough to me, with maybe a very slight surge).

Anyway, today while driving home from work it started stuttering at 3000 rpm under normal (slow, no boost) acceleration. I checked my Aeroforce and saw it's knocking off and on now, small amounts of 1.7 or 2.4*. Any ideas what I could check to fix this problem? It's my only car so if something goes wrong I'm stranded.

Also, if anyone has an HPTuners scanner config file I can just load that would be awesome. Unfortunately, I lost my scanner config file when my Windows 10 upgrade didn't go well.

Mods: K&N sri, downpipe, IC, 3 bar maps, HPTuned to 23psi (not by me)

Thanks all

 

flashing cel is the result of a misfire. even though the light stopped flashing it would have set a code, use the interceptor and see what code it is.

 

Almost sounds like u got ur maf or something wet or even sucked in somw of the rain. U sure u dont have a boost leak on the cp that would let in some water? If ur filter wet? Alot of rain, some could have gotten under the hood.

 

Flashing CEL indicates misfires which will kill boost in no time and cause odd running if the plugs are screwed. Although he does describe two different issues (flashing CEL and KR although it's hard to say if the KR is actual or just the ECU being fussy).

OP start with looking at the plugs or changing them if they have over 10k miles tuned on them.

 

i def try looking at the plugs first and changing those out. be sure to get the proper OEM spark plugs that come already pre gapped. if im not mistaken they are acdelco 41-108

 

Checked the code, it was P0304 Misfire on Cylinder 4. The plugs have about 10k on them but that didn't really cross my mind since I thought they'd last longer than that.

I got new plugs but only had time to change out #4 while at work. Driving home the car felt a bit better but not much. Still had some misfires and little KR. Since it's not the plugs but there was a possible small improvement I'm thinking it's the #4 coil? I'll stop at an auto store for a new coil tomorrow unless there's something else I should check first.

 

Fuel pressure issues?

 

swap the coils around, watch the misfire counters and see what hole have the misfire. if the misfire follows the coil, thats your problem. if the misfire stays in cylinder 4 you have another issue.

id also get all the plugs changed, not just the one.

 

I know but it just seems suspicious that it started on a trip with lots of rain

 

I had the slightest cut in my lower map sensor prong due to install. I noticed after washing my car a few times that effected boost but not so much misfires. How does your afr look on the interceptor? I get and have always had just a small amount of knock at part throttle, or off throttle shifting, and that's pretty normal for a lnf, as I've figured it was false. I have 0 at wot. Where are you seeing the knock?

 

Update:

Changed all the plugs, plenty of dielectric grease, and cleaned the MAF sensor. Car runs great (better than before), but I still have knock, mostly at highway cruising and light/normal acceleration. At higher throttle (boost up to wot) I haven't seen any knock.

AFR/Lambda looks good, as does the timing, the knock doesn't seem to affect anything else. My concern is, I watched knock quite a bit when I first got the car and never saw any at all. Now I see it all the time.

Random misfires are still there too, an occasional 2 or 4 misfires at random times. Last time I watched they were spread out over cylinders 2, 3, 4.

 

Miles on the car? The valves may be coked up.

 

78k as of today. I walnut blasted the valves at about 68k right after I bought it and I keep the RPMs over 2k pretty much all the time unless I'm in heavy traffic in 1st or 2nd gear.

 

Oil and coolant look normal? Mine started knocking hard after it was making milkshake.

 

Light cruising or light acceleration knock can be due to fuel trims being off or the injector angle being off.

The occasional misfires may be related to the fuel trims and injector angle being off.

 

Coolant looked normal when I was under the hood. I haven't checked the oil but I'll do that as well.

The fuel trims stay really close to zero.

How would the injector angle get thrown off? I've never had the injectors out.

 

Sounds like you've fixed the problem to me. Knock is bad when you are WOT, and you're not getting it at wot. And unless you're getting another hard CEL about misfiring I wouldn't worry about that.


My aeroforce shows anywhere from 1 misfire to 79 misfires... on cylinder 6 lmao

 

It's in the tune, angle of the combustion cycle when injection starts. So it's not actual KR, the ecu throws things it doesnt like into KR. I can look at a log and see KR on a cylinder that isn't currently firing or was the last to fire (also should note the timing is at the commanded for the given rpm and load).

Completely eliminating KR (when read from an interceptor) is very difficult. It's very likely that it's been registering KR the entire time you just started noticing it after the spark plug issue.

 

I agree. It took me forever to get all the "knock" out of my tune. Constant spark timing, cam timing and injector timing changes to make it smooth through the entire RPM and load ranges.