Explorer EFI - sudden stumble/miss after high idle

[samamarshall]

So...wrapping up a 10 year resto...motor/EFI/trans from a 2000 explorer installed, EFI flashed EMC, etc. Fired up and ran great first time! Initial test drive, shifting and everything perfect, even with open headers and no exhaust/O2 sensors in yet. Months later, have like 40 miles on it so far and finishing interior...prepping for my first car show this SAT and suddenly it's missing/stumbling hard after the initial 10-15 seconds, possibly after the initial high idle loop (terminology might be wrong there). It's essentially a stock explorer motor - used EDIS, 4r70w, controlled by ECM, etc.

Pulled codes - I have EGR, EVAP, O2 sensors, what I would expect to see with it's current state and those things missing / not deleted from ECM.

Strangely the Alternator was VERY hot after that short stumbling ride...suspected cheap china alt was bad. It's at 14+ volts when running and during stumble. It's not draining battery (diode issue) overnight.

Fuel pressure is a steady 60psi

I'm thinking maybe the temps being hot here now? Most of my sensors are original, so possible something crapped out. Going to look for vacuum leaks tomorrow.

Hoping you all can point me in the right direction before Saturday! Was really looking forward to showing her off at the car show

 

[73azbronco]

I'd start with getting it o2 sensors. Do you smell gas in exhaust? Limp mode means seriously rich, fouling plugs

Worst case throw on a short section of pipes after headers with o2 sensors on.

 

[EFI Guy]

Hoping you all can point me in the right direction before Saturday! Was really looking forward to showing her off at the car show

See how fast Amazon can get a Vgate Vlinker FS, or an OBDlinkMX+ to your door. Or, borrow one from the other MO Bronco guys, then grab a laptop and give me a ring.

 

[samamarshall]

You’re the man EFI guy! Just ordered an OBDlinkMX+. Looks like it’ll be here by this afternoon. Let me know any programs/apps to grab.

Going to look for vacuum leaks as well, thinking maybe something with the higher summer temps or heat cycles causing a leak I didn’t have before.

Here are the codes I’m pulling with my Bosch code reader.

P0443 - Evap valve circuit
P0453 - evap pressure sensor high input
P1451 - evap vent control circuit malfunction
P0135 - O2 heater bank 1 sensor 1
P0141 - O2 heater bank 1 sensor 2
P0155 - O2 bank 2 sensor 1
P0161 - O2 bank 2 sensor 2
P0460 - fuel level sensor
P1000 - obd monitor drive cycle test not complete
P1460 - wide open throttle air conditioning cut off circuit

 

[EFI Guy]

The codes of concern are P0135 and P0155. Since it is throwing codes for both sensors, check your O2 sensor fuse, and check your harness by the O2 sensors to make sure it didn't melt on the exhaust or something. You'll use Forscan for software, but I will have to email you a link to remote in.

 

[73azbronco]

I think OP stated he has no o2 sensor on it yet? Which is my point, it will run bad until it has sensors.

 

[EFI Guy]

I think OP stated he has no o2 sensor on it yet? Which is my point, it will run bad until it has sensors.

Good catch. I had assumed it was finished in the "months later". But if it's still missing the front O2S, those are an absolute must.

 

[73azbronco]

Hope all is well Mr EFI, wish I went EFI a long time ago but it just wasn't in the cards.

I do have desire for a proflow 427... You work on those?

 

[EFI Guy]

I have dabbled in all brands at this point, but I don't consider myself an expert in anything other than OEM. I pretty much stick to OEM because I have little trust in aftermarket parts, especially electronics. I will say that I don't have a ton of people removing Proflows to go with something else. The same can't be said for the more common TBI variants. I think I do more harnesses for people coming from TBI than carburetors at this point.

 

[samamarshall]

Yeah - exhaust is my next step, had some issues with fitment and need to fab some down tubes with the o2 bungs. Drives thus far have been short (2-10 miles) while testing brakes, steering, transmission shifting, etc. O2 wiring is tucked away and intact, new sensors ready to go. Hopefully running without those didn't cause any damage. Guess my next step is to finally finish the exhaust and get o2 sensors hooked up.

It's just strange to be suddenly stumbling so much it can barely drive all of a sudden, after hours and ~40 miles of driving fine.

Received the OBDlinkMX+. Will play around with that as well and maybe download FORscan.

 

[DirtDonk]

Sorry, but it sounds pretty normal to me. Yes, it is surprising that it ran decent AT ALL with open headers and no sensors. But that also seems normal to me, after all the weirdness I've experienced over the years.
Stranger things have happened. And you could now be dealing with another failed sensor (coolant temp sensor comes to mind) and it's just not sure what's going on.
I'd just stop running it any further at this point. Get the exhaust, then worry about chasing down a rough-running situation.
If it's still there, that is.

Paul

 

[samamarshall]

Thanks all - will take the advice and get that exhaust done and O2 sensors hooked up so everything is setup as it should be. I did unhook the battery for a bit to reset the ECM, ran as “normal” or before this stumble.

Might still drive it the 1.2mi to the car show tomorrow