Hello, new i3 owner with broken Rex

Rusty911 · May 8, 2024

Hi fellow i3 folk. Thanks for having me!

I've not long bought a poorly i3 Rex that came up for sale local to me. Storm-Trooper on standard wheels, 66 plate / 94ah. Nice spec.

Love driving it and really appreciate the engineering that's gone into it.

I bought it with what seems a common Rex problem: misfires on 1 and 2, multiple misfires detected. Have done fuel pump relay and plugs (genuine), tested coils, new premium fuel and a compression test (fine) and that's as far as I've got to date!

Anyway will have a surf around here and if anyone has any tips I'll gratefully give things a try. Have ISTA btw.

All best,

Barry

3rigel · Oct 21, 2024

Hi Barry,

I'm new on here too, first thing that springs to mind if you've done the basics is timing. Any error codes from cam sensor?

Cheers, Rob

werdnam · Jan 12, 2025

Rusty911 said:
Hi fellow i3 folk. Thanks for having me!

I've not long bought a poorly i3 Rex that came up for sale local to me. Storm-Trooper on standard wheels, 66 plate / 94ah. Nice spec.

Love driving it and really appreciate the engineering that's gone into it.

I bought it with what seems a common Rex problem: misfires on 1 and 2, multiple misfires detected. Have done fuel pump relay and plugs (genuine), tested coils, new premium fuel and a compression test (fine) and that's as far as I've got to date!

Anyway will have a surf around here and if anyone has any tips I'll gratefully give things a try. Have ISTA btw.

All best,

Barry

Barry, how did you make out with this quest? I'm in a similar situation with a fairly unpredictable REX that is showing misfires among others. I'm always curious to know how others make out with these things. Thanks!

Stevick · Monday at 10:20 PM

I had misfires and REX shutdowns on the used i3 I bought. Scanner showed crankshaft position sensor implausibility fault. Dealers want $2k or more to replace the ~$50 sensor because the REX has to be dropped to reach it. My research showed a few instances where it was replaced by shops/DIY without dropping the REX - either through contortions or lowering the REX on loosened motor mounts, or some combination of both. Then I found a great YouTube video of a DIY where a hole was drilled in the CF bulkhead behind the rear seat to reach it. I went that route with great success! No issues since.

iain · 2025-01-21T08:01:04-0600

have a look here, i had the same issue

https://www.mybmwi3.com/threads/doe...ctor-ring-miss-fire-cam-position-error.19115/

christopher payne · 2025-01-21T10:59:33-0600

Stevick said:
I had misfires and REX shutdowns on the used i3 I bought. Scanner showed crankshaft position sensor implausibility fault. Dealers want $2k or more to replace the ~$50 sensor because the REX has to be dropped to reach it. My research showed a few instances where it was replaced by shops/DIY without dropping the REX - either through contortions or lowering the REX on loosened motor mounts, or some combination of both. Then I found a great YouTube video of a DIY where a hole was drilled in the CF bulkhead behind the rear seat to reach it. I went that route with great success! No issues since.

Does cutting a hole in the carbon fibre weaken it.and structural integrity of the passenger cell.i have the same problem but reluctant to cut a hole in carbon fibre .due to possible weakness in an accident.i would love to know how a crankshaft sensor is fitted buy DIY methods

.

mojo · 2025-01-21T11:46:57-0600

christopher payne said:
Does cutting a hole in the carbon fibre weaken it.and structural integrity of the passenger cell.i have the same problem but reluctant to cut a hole in carbon fibre .due to possible weakness in an accident.

I would go out on a limb here and say that nobody here knows the answer. I would expect that the only way to know would be either to put the modification into the computer models that BMW used when designing the shell, or to make the modification and crash test it.

I would expect the answer will be very heavily dependent of how the hole is "made good" after the work is done. If, for example, you covered the hole with two sheets of 5mm aluminium sheet, bolted and bonded inside and outside the shell with at least a 20mm overlap, it might be somewhere close to the original strength. A piece of cardboard over the hole probably won't be.

Stevick · 2025-01-21T15:49:36-0600

I can't argue with mojo, but I can give you my experience with it (which thankfully does not involve a crash). I used a 4" hole saw to cut it, which was just big enough to get a hand in there with the wrench. The area to be cut is the bulkhead portion of the wide and deep CF tub. The cut is best made just below a steel bar that is molded into the CF to reinforce the ISOFIT anchors. I know it was there because my cut was a little high and I had to cut through a bit of it. While I too was reluctant, I can now say that I do not believe the car's structure was weakened in any appreciable way. After the CPS R&R, I just covered the hole with a square piece of sheet aluminum, sealing and screwing down. I strongly recommend you look at the video. The guy who posted it had to keep expanding his hole to find the right spot, but I had the benefit of his video to make it less haphazard. And you can now have the benefit of learning from my small mistake.

Here's a link to the video, and I added comments below it to add my own tips:

Stevick · 2025-01-21T16:07:05-0600

Seems you'll have to click on the video title to access my comments there.

Hello, new i3 owner with broken Rex

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