Are GEMS maffless?
30 August 2009, 10:30 AM
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Are GEMS maffless?
I've a 96 V3 sti which has had a lot of engine work done by a previous owner and its running 390 bhp on a GEMS ECU. Does anyone know if this supposed to run without the MAF. It seems to have no effect whether the MAF is connected or not. 
However I still have the lumpy idle and sometimes poor cold starting which seems to be a trait of the GEMS. Thanks.
However I still have the lumpy idle and sometimes poor cold starting which seems to be a trait of the GEMS. Thanks.
30 August 2009, 11:45 AM
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hi I also run gems on my V5 RA and wood be interested in see if this is right, as the last owner sent a lot of money on the car why buy gems and not simtec? or can u update the software on a gems to a later version to run mafless thanks for the help guys 
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01 September 2009, 04:22 PM
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Benji and poo (
) - you both may as well remove the MAF tube and any other unrequired associated paraphernalia, and simply have the cone filter (assuming it has a cone?) fixed directly to the turbo intake pipe, for a shortened and less restrictive airflow path, etc.
) - you both may as well remove the MAF tube and any other unrequired associated paraphernalia, and simply have the cone filter (assuming it has a cone?) fixed directly to the turbo intake pipe, for a shortened and less restrictive airflow path, etc.
Last edited by joz8968; 01 September 2009 at 04:34 PM.
01 September 2009, 05:04 PM
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Might be worth checking whether the GEMS on the cars concerned are using an inlet air temperature sensor in the MAF unit before running with them disconnected as a matter of course.
Similarly if the cars have been mapped with elements of the OE intake in place, recommending that these bits be removed and replaced possibly isn't the safest advice, even with a speed density ECU.
Similarly if the cars have been mapped with elements of the OE intake in place, recommending that these bits be removed and replaced possibly isn't the safest advice, even with a speed density ECU.
Last edited by Splitpin; 01 September 2009 at 05:06 PM.
01 September 2009, 06:15 PM
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Thanks for your help guys. Am I right in thinking that you can also set up anti-lag on GEMs???
I still think i'm going to end up going down the Simtec route though eventually.
I still think i'm going to end up going down the Simtec route though eventually.
01 September 2009, 06:31 PM
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No, no switch unfortunately. I'm pretty sure I haven't got the anti-lag option. It can be a pig sometimes when starting from cold and just a bit lumpy when trying to crawl along in traffic. Once you are on an open road its great! I've heard that the poor cold start and lumpy idle are a GEMS trait and they are great for rally cars not so good for the road.
01 September 2009, 09:47 PM
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Gems does not use the MAF it uses a MAP sensor. This is connected to two of the wires cut from the MAF loom to connect to the ECU. I have had a GEMS on my bug for nearly 6 years and love it. Yes on a cold morning it is a pig to start, when I was up in Scotland anything below 8 centigrade was a sod but could be done, any lower and 15 mins work to re-fit oe ecu and get it warmed up. I know run a lovely 400 bhp which is lovely in town or on open road. Mine is looked after by Steve Simpson at TEG Sport but also Scoobyclinic do GEMS as well.
02 September 2009, 12:09 AM
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If the maf is plugged in I'd be tempted to leave it unless the wires have been cut further down and connected to a temp sensor or like someone else suggested it might be taking temp from maf sensor?. In the gems software there are options for maf or map so not sure how your car is set up (don't know a great lot about mapping). Its prop. best to get someone to plug it in find out if it needs that sensor. You can ugrade firmware on gems for later versions think its about £80.
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