MPi MEMS 2J Injection Help

Started by tmsmini, June 10, 2024, 02:27:09 PM

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I know not too many have fallen into the injection rabbit hole but...
We installed an SC injection kit almost ten years ago and while it has run well at times, it never ran as well as I thought it should. I was comparing it to the Rover MEMS 2J system, so perhaps not a fair comparison.

The engine had some oil leaks so i told myself, I will pull the engine to fix those and very carefully reassemble the SC components to make sure there are no issues. Even with careful checking, it was not running well. SC support was no help at all.

A MEMS 2J system was installed and seemed to be running well.  It has now developed a backfire at cruise or part throttle. It starts, idles and accelerates fine, but after lifting and going to cruise it starts to backfire. It is not a major miss backfire but a mild backfire through the exhaust. To me it is most like the backfire that one had on a late 60s or early 70s engine with air injection.

I have replaced many parts and o rings, gaskets etc to to try and fix a possible air leak that I cannot find or hear. I have a scan tool or the system and nothing pops out as unusual.

At about six minutes into this video, you can hear it. It is not a great recording as there is road noise and electrical interference of some kind.

It has to be something simple as it runs very well otherwise.
I would expect backfire when lifting, but not on cruise or light throttle.

Any suggestions would be appreciated.


How are the lines and connctors for any/all vacuum lines for the ECU?  I don't know what they are on the MPI, but have had experience with them on a SPI Mini.  The ECU's do not like leaks in the vacuum lines, especially the MAP sensor line into the ECU.  I had an SPI that would die on lift from the accelerator because the elbow at the ECU had cracked on the inside of the bend.


You should probably toss a temporary wideband on and see what the fuel is doing.


I have replaced the hoses that attach to the throttle body and inlet manifold. The MPi uses an external MAP sensor which I have also swapped out.

The transplanted engine does not have a servo so that is plugged and no purge valve so that is plugged as well.

The ECU uses a narrow band which does not provide much information. Some wide bands can provide an alternative narrowband signal in addition to driving a wideband gauge, but I have not explored that.


I'd start there to see if the fuel is doing wonky things intermittent or if your spark is going dead for a moment. It's possible the spark skips a beat. You'd just have to try and decipher the reading.    Anyway to watch the spark table while you're driving?


It looks like the AEM gauge I have does not have a narrowband output, but older AEM did.
I have a Spartan2 controller which does support narrow band, but the gauge to go with it is not available.
I also have an Innovative 2 with the tailpipe adapter, but I have never trusted it.

*Update* I found a 14point7 Spartan gauge to go with the controller, I just hope the website is legitimate.