Hi all

I've swapped my oem map sensor for the apexi 3 bar one I used to use on the PFC before I swapped to the Simtek.
There's a problem related to the map sensor though and I need a little help if possible please.

In the Simtek software the map sensor is giving a constant reading of approx 500mbar whether the engine is running or not. It should be atmospheric (1000mbar) with the engine off I believe, but it's half that, as if it's a default value.

If I unplug the sensor the software states 1000mbar which I believe is the failed sensor setting.
Part of the problem is the apexi 3 bar sensor came with its own harness to plug straight into the PFC and it's always worked perfectly.
I found on the PFC faq site a page relating to the wiring which is as below:




The colour bars are the wire colours on the apexi map sensor to correspond with the pins shown.

So with this in mind I've wired it to the oem map sensor plug which has red, green, and white wires on the sensor. I assumed from this that the red & green wires would match to the red & green ones on the apexi one and am wondering if that's the case or not now since it doesn't seem to be working?

I have the wiring diagram for the sensors also:



But this does not give you any info on which signal/voltage is which wire so even though I have colour codes for the oem harness it doesn't really help.

If anyone can help clarify this or advise if there are other settings to check I'd be grateful. The multiplier and constant values in the ECU are set correctly for a 3 bar sensor.

Many thanks for any help!
Jim

 

Right, I found that on the wiring for the car's harness, the wire which was connected as the earth/-v did not have any continuity to the car body etc, whereas the pin connected as signal did have.

This does not seem logical so it seemed that the signal & earth pins must have been the wrong way round. I didn't worry too much about damage from this as 1) I've been told it's not that likely and 2) I think there's more chance if I'd connected the live/+v to the wrong pin.

Swapped these two pins over and it now reads approx 1300mbar at ignition with the engine off. Not sure why this is, but is it possible that the apexi sensor uses different values to the one supplied via simtek dealers? I believe the apexi one is a Denso item.

I've found I can get the reading at ignition down to 1bar by changing the multiplier, but should I do that? I've got 3.11 and 6 set as the values for the 3 bar but if I drop the multiplier quite a bit (I think to 2.75 which I believe is the setting for the OEM sensor?!) it gives the right value from the sensor.

The car has decided for the first time since I can remember that it's not going to start today and the battery is drained now. Bah. No idea why since it was fine last time I ran it, and that was with the sensor wired how it was at the start of today. Weird.

This means I still don't know for certain if the sensor is wired correctly but I think it's more likely as it wasn't right before and is at least closer now.

Any suggestions?

 

You need to resacle the values for the map sensor, as its probably looking for a 1.8 bar map sensor. I dont have these values to hand as i am away, but im sure if you get in touch with simtek they will help, or another mapper will be in touch im sure.

 

Thanks - as I said though the ECU is already setup for a 3 bar sensor as the map that I got recently was setup for that, using the settings I mentioned in my second post.

I thought the standard one was approx 1.3 bar anyway not 1.8 (unless you mean new age cars?).

Steve Simpson has already very kindly supplied me with this base map and I don't want to trouble him further unless I really can't avoid it.

I'm fairly sure it's wired correctly now mate, just not sure why it's giving 1300mbar at ignition instead of 1000. That's why I'm wondering if the apexi one uses different settings, meaning the usual 3 bar settings aren't suitable perhaps.

Any tuning gurus know the answer to this one?

 

Sorted it - the wiring is fine now and after applying both varying pressure and vaccum to it I get a signal that corresponds. Cools.

Have scaled it with the multiplier so it gives a better reading too.

Car still won't start though and this is out of the blue. Never before had startup issues but all of a sudden it's refusing to fire without anything being changed (as it has already run ok with this sensor). Mystified!

 

The multiplier and constant values I supplied were for a Delco 3 bar sensor.To correctly scale the sensor you have you need to do the following:

You will need some method of applying a known vacuum or pressure to the sensor such as a Mityvac or similar.

Apply pressure (say 1000 mbar) and read voltage on SimTek dashboard (say 3.3V)
Read voltage at atmospheric pressure with sensor open to atmosphere (say 1.6V)

Then value of multiplier (m) = Change in pressure (1000) x 5 / 1023/Change in volt (1.7) which would give 2.87 in this case.

Enter this value as m in the ECU .To obtain "c" just enter a value of C which gives the correct atmospheric pressure readingwith the sensor open to atmosphere.If you don't have a barometer handy then just assume a value of 1000 mBar; this will be near enough to get car running.

Just altering the m or c value in isolation will not give the correct readings across the pressure range.

You mentioned you had the car running with a reading of 500 mbar; I would suspect that the plugs have been fouled due to over-fuelling and this is the cause of the non starting...

Steve

 

Thanks very much for the reply and all the information Steve - it's very much appreciated.

Oddly enough after messing yesterday to try and isolate a cause of non starting I'd reached the conclusion of plugs since everything else seemed fine, ie it was getting fuel and spark from leads etc, and I knew it had run already with that base map (thankyou again!).

I pulled them out this morning and they were pretty nasty black which is obviously sooting from the previous maps I had I think since they were far too rich for my engine.
Cleaned them and having been out all day (dying to get back and try it) I refitted them and she fired up instantly. Result.

So now, the only thing really holding me back from getting on with mapping is the fact my good laptop is STILL away being repaired, and the one I have in the meantime cannot use the ecu software and the wideband at the same time since I need 2 usb ports for that and the key for the software uses up the single one that's there.

The map sensor was giving 500mbar because not being able to find wiring info for it I got the signal and the ground wires the wrong way round. Now I've tested and swapped them it's ok except it needs scaling I think, so your info above will be invaluable.
I've tested that the output changes by feeding pressure to it via my compressor and the signal varies just fine, but will need to be calibrated so my friend has a mightyvac he's going to lend me.

So at the moment, all's well again.

Thanks again for your kind assistance Steve - I really do appreciate it.

Jim

 

Once the SimTek software has booted up you can remove the USB dongle.....

 

Ahh, great! Never realised. Thanks for the tip. That will make it MUCH easier.

I can't wait to start getting on with this as I was just getting into mapping about 2-3 years ago when I decided the engine needed a rebuild and also then got married, bought a house, had a nipper etc. It's been a while and I'm keen to start off again, especially as the Simtek looks much nicer to use than PFC.

 

Just a little update to this thread to give credit where it's due.

Finally got this sorted out tonight and I'd like to thank Steve (and Stevieturbo) for his very kind and patient assistance in getting this sussed out.

So in case anyone else should somehow end up using one of these Apexi (Denso?) 3bar sensors with a Simtek, the calculated multiplier that has done the job for me is 3.26.

Car runs lovely now