Random Limp Mode From Misfires

[arlisscm]

Back at the end of May at Pocono Raceway about halfway through session 3 on day one my car randomly went into limp mode (blinking CEL) and had cleared by the time I got back into the pits. Let it cool down and restarted and everything seemed fine. Didn't have any issues for session 4 or the next four sessions the next day. So, I thought it was a hiccup and moved on.

Now, Monday and Tuesday this week at Watkins Glen, no issues in session one, then about 7 laps into session two i got limp mode again and it cleared itself by the time I got back in. Again on session three, but after about 5 laps, this time limp mode cleared itself again but left on the CEL, misfires on cylinders 1+4. Cleared the codes before session 4, got limp mode again after only two laps, once again cleared itself and no hard CEL.

Swapped out the spark plugs for a new set, and swapped 1+2 coils and 3+4 coils. Session one day two, no limp mode (session was kind of a mess so I wasn't really getting after it). Session two finally got a bit of open track, then about 6 laps in limp mode, once again cleared itself.

Any thoughts? Evap purge valve/harness? Swapping the plugs and coils didn't change anything.

 

[Switchback]

Hey this is the exact same problem I'm currently having! Happens only on high-load, but I could also get the car to misfire when revving it to 3k RPM when the engine is hot but in neutral.

Since you're on a brand new built block I take it you have clean intake valves, which is the only thing I haven't checked on my car yet. Did you also get a P0316 code by chance? Diagnostics says that's a misfire within first 1000 Revs, but I get it after driving hard.

So far what I've done is swap plugs (brand new set of colder plugs), move coil packs around, and even moved the Fuel Injectors in Cyl 1 and 2 around to see if it was a fueling problem (It wasn't). Also, swapped tunes from the Dizzy stage 2 shelf tune to a Cobb stage 2 without any change.

 

[arlisscm]

Hey this is the exact same problem I'm currently having! Happens only on high-load, but I could also get the car to misfire when revving it to 3k RPM when the engine is hot but in neutral.

Since you're on a brand new built block I take it you have clean intake valves, which is the only thing I haven't checked on my car yet. Did you also get a P0316 code by chance? Diagnostics says that's a misfire within first 1000 Revs, but I get it after driving hard.

So far what I've done is swap plugs (brand new set of colder plugs), move coil packs around, and even moved the Fuel Injectors in Cyl 1 and 2 around to see if it was a fueling problem (It wasn't). Also, swapped tunes from the Dizzy stage 2 shelf tune to a Cobb stage 2 without any change.

Yeah, I for sure know the valves are clean (only about 1500 miles on them). And, the spark plug and coil swap/shuffle didn't change anything.

My codes are P0300, P0301, P0304 (random misfires, misfire cylinder 1, misfire cylinder 4 respectively).

 

[Switchback]

Yeah, those are the same codes I get, with P0316 coming up every once in a while. With an accessport set to misfires, if you rev your engine to 3k and hold it there does your misfire count start to go flying? I'm curious to see if you can replicate the issue without hammering on the car at track/canyon speeds.

I have a new purge valve on order, should be here tomorrow. Going to splice it in so I don't have to pay for the whole assembly.

 

[arlisscm]

Yeah, those are the same codes I get, with P0316 coming up every once in a while. With an accessport set to misfires, if you rev your engine to 3k and hold it there does your misfire count start to go flying? I'm curious to see if you can replicate the issue without hammering on the car at track/canyon speeds.

I have a new purge valve on order, should be here tomorrow. Going to splice it in so I don't have to pay for the whole assembly.

Went and checked, monitored knock on cylinders 1+4 and misfire count. None of which changed at all free revving at, and above 3000 rpm.

Seems like P0316 is detected within the first 1,000 rpm, i haven't popped that one. Mine pops up at least 10 minutes after starting, usually a few laps (sometimes many) in after sitting in the staging lanes for 5-10 minutes. Then clears itself after ~30 seconds and everything is good again. I still hop off track as being hamstringed that bad in traffic isn't fun (or safe).

 

[Switchback]

Hmm, maybe our problems are similar but not identical? When I was canyon driving it would pop off, and go into limp mode but quickly exit the limp mode as well. At one point I didn't even notice the CEL until I looked at my dash while I was navigating some corners driving up Palomar mountain chasing down a friend in a GT4, but I was still making power and didn't feel like limp mode was enabled.

Just thinking about the differences between your setup and mine there's not to much that we have in common in our fiestas. (We both have black, are all Black Fiestas cursed?) Purge valve maybe, but I feel like if our purge valves were bad it'd be more noticeable on a daily basis as opposed to only WOT/high load scenarios. I do stutter on fuel-up so I know mine is going bad though.

 

[arlisscm]

Talking with Jason, he thinks it's likely a ground and/or sensor issue.

I have a new EVAP harness on the way, figured might as well, but Jason said to check the harness ground near the starter, unseat and reseat the ECU connections (might hit them with some electronic cleaner), and to check/replace the crank position sensor (ordered a new one).

So, I'll get all that stuff sorted once the new parts come in.

Only issue is I haven't had it crop up on the street, only the track, so I might need to visit "Mexico" to see if I've fixed it before my next track day at the end of August.

 

[Switchback]

After work I'll check my ground as well. (If I can find it, I hate dealing with wiring harness stuff) I have the purge valve coming in today (Just the valve, I'm going to DIY this because I don't really want to spend $200 on the whole harness) so I'm likely going to try these two items first. I did previously replace a Camshaft position sensor on the intake side because while troubleshooting with Forscan it looked like data from that sensor was intermittent. Couldn't find the Crank position sensor value in Forscan or I would have checked that one too.

Where's the Crank Position sensor located on our cars?

 

[arlisscm]

After work I'll check my ground as well. (If I can find it, I hate dealing with wiring harness stuff) I have the purge valve coming in today (Just the valve, I'm going to DIY this because I don't really want to spend $200 on the whole harness) so I'm likely going to try these two items first. I did previously replace a Camshaft position sensor on the intake side because while troubleshooting with Forscan it looked like data from that sensor was intermittent. Couldn't find the Crank position sensor value in Forscan or I would have checked that one too.

Where's the Crank Position sensor located on our cars?

I think the ground we are after near the starter is the one that loops around and is tied into one of the transmission bolts. (But I'd check whichever ones you can find)

The crank position sensor is on the back side right by the crank pulley, just one bolt holding it in.