Ugh. More misfires. (Drivetrain error)

[TheMK]

At first I thought the misfiring when starting the REx was a random event, but I've now decided that it seems to only happen on a cold start, and only when the ambient temperature is cold. Once the engine is warmed up, it can be stopped, and restarted without issue. Usually when this happens, the car gives you the dreaded drive train error, and says "electric only driving possible. Note remaining range". If you want to use the REx, you have to pull over, start emissions test mode, let the engine run for a few minutes to get it to warm up, and then go back and re-engage hold state of charge from inside the car. It seems to run okay at that point in time. In fact, I can even erase the check engine light, and it won't come back on, until you get a cold start misfire again. I was running 91 octane ethanol free (the highest octane I could find, short of 110 octane lead race fuel), but I'm going to try 88 octane ethanol free to see if that makes a difference. I know that at some point in this car's service history, the spark plugs and coils were replaced.

 

[jadnashuanh]

The REx is still an ICE, so misfires can be from ignition problems, fuel problems, or compression issues. WOrking once warm may be a sensor, moisture, a loose connection, fuel issues, and numerous other things. The first thing would be to see if there are any other error codes. You need a reader that can interpret the BMW specific messages, not a plain OBD II reader, but that may help lead to the problem. There are lots more sensors that a BMW specific reader can read.

I'd pull the cover and take a look to see if there's anything obvious like a loose connection somewhere.

 

[slac10]

I had this problem too. It was the fuel pump relay that was defective. $31 for the part. 15 minutes to change by removing the glove box.

Everything runs fine now.

 

[TheMK]

I finally got around to looking at it today. I checked the relay with a multimeter and a power supply, it was fine. slac10, when your relay went bad could you even start the REx at all?

I'll plug ISTA into my car tomorrow to read the fault codes stored. I poked around in the motor compartment and didn't notice anything unusual, though it was a bit dark out, so I'll look again tomorrow.

 

[slac10]

Yes I was able to start the REX but not every time.

 

[TheMK]

Okay, thank you much!

Unfortunately, I cleared the fault code before getting to read it with ISTA, so I'll have to wait until later for it to misfire again. A look under the engine cover seemed OK.

 

[i3Houston]

Same thing here. Rex failed to start, luckily I was only a mile away from home. Have to drop off the car at dealership next week.

I have rarely used rex and its nuts that it stopped working; hate going to the dealership.

 

[TheMK]

I'm wondering if fuel supply could have something to do with it- it seems to only happen below (or right around) freezing. This could mean a few things, fuel pump, relay, injectors.

 

[i3Houston]

Thanks.

It was 20F above freezing. What I do recall is that when Rex turned on I accelerated (was trying to reach home without burning any gas). Rex was on for couple or a few seconds and then appeared to have stopped on suddenly accelerating.

 

[TheMK]

For posterity's sake, I am using 88 octane ethanol-free now, and that cleared up the misfires. Previously, I was using 91 octane ethanol-free. I realize that there is much more to a gasoline than just the octane (additives are one thing), and that different additives, and "blends" of gasoline act a little bit differently. There's a very high likelihood that next spring/summer, I will return back to 91 octane ethanol-free, the REx engine has a high enough compression ratio that it's likely I'm loosing (some) power from 88 octane, though living at 5000ft, the amount of air that can enter a naturally aspirated engine is somewhat limited.

I used ISTA to diagnose the problem, the diagnosis was "If the temperature is below freezing, advise the customer about fuel supply", so I did some investigation and settled on 88 octane ethanol-free, 2.85/gallon too so that's nice!

 

[i3Houston]

Have not had a chance to take the car to shop yet...so I will check that out if Rex starts in emission mode, hopefully that will fix the problem for me too!

 

[i3Houston]

A few weeks ago the Rex failed to start and threw Drivetrain error, however, today i started emission mode and Rex fired up!! What does that mean now?

 

[slac10]

Mine does that all the time! It looks like all the first generation i3 with REX have this problem.

Doesn't seem to be a big problem since the check engine light will go off after a few starts.

 

[i3Houston]

Didn't know that... So what do I do when battery hits 6percent and Rex fails to start?

 

[PBNB]

Didn't know that... So what do I do when battery hits 6percent and Rex fails to start?

I had the same concern after reading about the troubles with running out of electrical power even with the REX starting but unable to keep up.

My concerns have all but gone now that I have the Hold SOC coded for 75%. I can run the REX more often now to make sure it start's. If it doesn't start, I will have more time to deal with the issues.

 

[i3Houston]

Well that's true but can't stomach the suspense this problem adds.

I really want to have dealership fix it since cars under factory warranty.... Did you happen to do that?

 

[PBNB]

Well that's true but can't stomach the suspense this problem adds.

I really want to have dealership fix it since cars under factory warranty.... Did you happen to do that?

I didn't take it in to the dealer for many reasons, there first being that I was working on getting the warranty transferred from BMW US to BMW Canada which just happened.

My Rex has never "not started" when it was supposed to. I just coded it so I could control the operation of the Rex and attempt to manage it on longer drives. It does a good job of keeping the SOC at one value and doesn't burn much fuel in the process. It is a bit noisy when running at full RPM's but that is expected.

I run the Rex at least weekly and for a longer period of time while commuting so I can let it warm up and run under full load. I have only had the maintenance cycle come on once and that was before coding it. We have had the car since July 2018.