MAP VOLTAGE ?

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MAP VOLTAGE ?

Postby Chas54 » Mon 01.11.2021, 16:21

I don't suppose anyone has any figures for the return voltage from their MAP sensor they could post.

Mine reaches 0.58 volts at 0.35 on the elanscan trace. This then stops my engine, possibly due to to little fuel. O2 voltage signal drops to 0 .02

With the MAP unplugged the engine runs fine and steady but the O2 signal hovers around 4 v which is to rich.

Every time the vacuum improves the fuel get pulled back to much i think.

The MAP works but i just wondered what voltage it is supposed to read .
The Chart in EMK3 only goes down to 60kpa at 0.7v. That would be 0.4 on elanscan.
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Re: MAP VOLTAGE ?

Postby Simon_P » Tue 02.11.2021, 10:48

Not sure what you're trying to prove here Charlie. The MAP reads the actual pressure in the Manifold. Your vac pump is making the MAP sensor tell the ECU something different. The ECU will change the fueling but the actual pressure hasn't changed so it will be too rich/lean (leaner as you increase the vacuum) the O2 sensor will try to correct. When it can't keep up with the error you have introduced it will give the wrong answer.

Unplugging certain sensors puts it into limp mode, so it is difficult to conclude anything from that.

The voltage should be in the closed loop manual.
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Re: MAP VOLTAGE ?

Postby Chas54 » Tue 02.11.2021, 14:15

Simon

I am trying to see if my problem is a faulty MAP sensor. Its only two year old and came from SJS after i snapped the pipe stub of the original unit.

I know if i have the MAP sensor unplugged , the engine runs smoothly and the actual vacuum is around 0.35 from my remote stand alone vacuum gauge. This must be the limp mode .

If its plugged in the engine is difficult to keep running and stops. I am suspecting that as the vacuum gets better, the voltage reported by the MAP sensor drops to low. I can also see the O2 sensor voltage drops to a very low figure which would indicate a lean mixture.
Ive jury rigged the MAP at the moment with 3 sort cables with minature croc clips so i can readily and easily read the voltages with the MAP plugged in and functioning.

With the MAP sensor plugged in , If the voltage from the MAP sensor was to low , i am wondering if the calculation done by the ECU would reduce the injection volume by width or injector duty as i see both decrease at normal vacuum .

Mainly though, i was hoping to get some figures for the voltage output of a known good MAP at a normal idle vacuum of 0.35.

The figures in the manual don't go down as low as my good vacuum.
I have looked on the internet and whilst it wasn't Lotus specific, i found some information on output voltages for simillar MAPS and i believe mine is to low at the 0.35 figure i find normal.

Ive checked the MAP cables through and they're good.

I have been looking for another source for a new MAP sensor..
Charlie
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Re: MAP VOLTAGE ?

Postby Saltire » Tue 02.11.2021, 17:13

Available from SJ Sportscars
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Re: MAP VOLTAGE ?

Postby Simon_P » Tue 02.11.2021, 18:22

Charlie, I think you are mixing things up a bit.
Forget the voltage, manual, mixture etc. Compare the reading from your gauge to what elanscan is reporting. If they are about the same it works.
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Re: MAP VOLTAGE ?

Postby Chas54 » Tue 02.11.2021, 20:00

Simon
I can see what you mean but iam having difficulty keeping the engine running with the map in service.
The only thing I have confirmed is that with the map powered at 5v , and with it forced into limp mode by disconnecting the reference wire, I can see the reference voltage bellow 0.5v . But I can't read elan scan at the same time as the ref wire is disconnected.
I did manage to keep the engine running for a sort time today after clearing the faults stored . When I eventually let the engine fail I got two faults on the service lamp record. Code 34 & code 44.
During the period the engine ran it would not idle and I did notice the voltage was all over the place. But I was operating the throttle.
I have ordered a GM MAP sensor from Rock auto . I decided against the SCS one.
code 34 low voltage high vacuum & Code44 lean exhaust.
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Re: MAP VOLTAGE ?

Postby Chas54 » Tue 02.11.2021, 21:12

Simon

I think i may be chasing another red herring.

Ive looked on the Code 34 error page and it states there the voltage at idle can be between 0.6v and 1v, I get around 0.65v. It also states the condition for the code 34 and i note it states a MAP pressure less than 14kpa (0.14pa) I get about 0.35pa at idle . If i manually pull 0.35pa on the sensor with a remote vacuum gauge in line I cant get it the reference voltage to change by agitating the wires or the sensor so maybe there's nothing wrong with it..

I am running out of ideas ..


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Re: MAP VOLTAGE ?

Postby Chas54 » Thu 04.11.2021, 20:31

New MAP sensor arrived and voltage on reference from MAP is very slightly higher But , much as stated by Simon P , it made no difference as the original was operating correctly anyway.

Ive checked the wiring through again to the ECM pins from the MAP and the O2 sensor. Nothing wrong.

I have attached a trace here as i can see something is wrong with the O2 sensor reference volts -- well the sensor is reporting a lean condition but ECM is doing nothing about it..
I had some difficulty getting the car started and so the first part of this trace is somewhat garbled. This was my second set of data so the engine was warming .

The O2 sensor reads a lean condition (or at least low volts from the reference) until 500secs when it starts fluctuations up and down and appears realistic. The vacuum sits around 0.35pa (normal) . TPS shows 0.4v . idling.

At 1005 secs i give the engine a short rev and hold for a few seconds then release the throttle at 1012 secs . The TPS goes to 0.42 vaults indicating it is slightly open , maybe an expansion problem with the body ?. But anyway the O2 sensor drops back to a lean condition and the fluctuating stops.
Now the vacuum is 0.32 pa..

I dont think the O2 sensor is faulty, i think it is actually reporting a lean condition that is true. Its just i cant see why the ECM doesn't increase the fueling by the injector width or duty.

The O2 sensor starts going lean as the throttle opens , this makes sense but surely the ECM should add more fuel ?

I tested the TPS and cant find wiring fault or anything wrong with its reference volts across its stroke.

Flag 42 bit 0 is indicating closed loop operation - thats the only flag i know the value for .

After stopping a fault code 44 was read from the ECU light sequence.


Any suggestions welcomed.

code 44 lean.zip
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