ECMlink 1G MAP sensor reads positive

[Nii]

I'm having issues getting my 1g to idle. I have a lot I need to dial in like fuel trims, AFR, and what not but I want to figure out why my MAP reads positive with key on and at idle. I'm seeing around 5psi on the GM 3bar and ECU boost is very similar.

Have y'all had this issue before?

 

[pauleyman]

I'm Having issues getting my 1g to idle I have a lot I need to dial in like fuel trims AFR and and what not but I want to figure out why my map reads positive with key on and at idle. I'm seeing around 5psi on the gm 3bar and ecu boost is very similar. have y'all had this issue before?

MAP sensor on a 1g? What ECU are you using?

 

[Nii]

MAP sensor on a 1g? What ECU are you using?

91 ECU with ECMLink v3. The car is not stock, all the information is in my build thread. I have a MAF conversation to MAP, IAT, and flexfuel from ECMTuning.

 

[steve]

So I assume you got past the no injector pulse issue from https://www.dsmtuners.com/threads/1g-no-start-no-injector-pulse.550283/ and got the car to start?

The log you just posted still shows the ECU configured for a Omni 4 bar MAP sensor.

 

[Nii]

So I assume you got past the no injector pulse issue from https://www.dsmtuners.com/threads/1g-no-start-no-injector-pulse.550283/ and got the car to start?

The log you just posted still shows the ECU configured for a Omni 4 bar MAP sensor.

yes I was able to get past it thank you! I reprogrammed the information for the 3bar I just didn't have that log since my data cable crapped out on me. I'll upload a log tomorrow when I get the cable but it still reads 5 as opposed to the -8 that the Omni read prior

 

[We're on Boost]

Look at the raw voltage from your MAP sensor when the car is just sitting there not running.

If your MAP sensor is a GM or Omni 3-bar, the raw voltage should be about 1.53 volts.
If your MAP sensor is a GM or Omni 4-bar, the raw voltage should be about 1.15 volts.

The log you posted in post #1 is showing a raw voltage of 0.82 volts. So that's a wrong voltage no matter which sensor you have.

 

[Nii]

Look at the raw voltage from your MAP sensor when the car is just sitting there not running.

If your MAP sensor is a GM or Omni 3-bar, the raw voltage should be about 1.53 volts.
If your MAP sensor is a GM or Omni 4-bar, the raw voltage should be about 1.15 volts.

The log you posted in post #1 is showing a raw voltage of 0.82 volts. So that's a wrong voltage no matter which sensor you have.

do you know what would cause low voltage like that?

 

[We're on Boost]

Hard to say but I would probably start by checking your power wire that goes to it to make sure it has 5 volts right near where it connects to the sensor.
Your ground wire might go to a bad place or have a bad connection at one end or the other.

If the power and ground both are good, then I would cut the signal wire someplace close to the sensor, someplace where you can get at it with a multimeter. Put a multimeter probe on the signal wire that comes out of the sensor. See what voltage the multimeter reads. If the multimeter is reading a wrong voltage when the power and ground are good, then it's just a bad sensor.

The reason for having the signal wire cut when you make this measurement is to prevent the signal from being corrupted by any load on it, like from a problem in the ecu or in the wire going to the ecu. Then of course you have to be really careful to not touch the bare end of the signal wire to any ground metal while it's powered up.

Always be sure that the black lead from the multimeter is going to a good ground, not painted stuff.

Maybe the multimeter will read a correct voltage. If the multimeter is reading the voltage that you'd expect but the ecu is reading it different, then there's a problem with the wire that goes to the ecu, or with the ecu itself. It's even possible you might measure (with the multimeter) a different voltage in the signal wire depending on whether it is cut or whether it is connected to the ecu. That would be a problem.

Whichever sensor you are using, you should make it clear what it is and who you bought it from. A good way to be real clear about this is to give us a link to the exact web page you bought it from.

It could even be that just the electrical plug is put together bad. That 3-conductor plug that plugs into the sensor. But usually that would either work ok or not work at all.

 

[Nii]

Hard to say but I would probably start by checking your power wire that goes to it to make sure it has 5 volts right near where it connects to the sensor.
Your ground wire might go to a bad place or have a bad connection at one end or the other.

If the power and ground both are good, then I would cut the signal wire someplace close to the sensor, someplace where you can get at it with a multimeter. Put a multimeter probe on the signal wire that comes out of the sensor. See what voltage the multimeter reads. If the multimeter is reading a wrong voltage when the power and ground are good, then it's just a bad sensor.

The reason for having the signal wire cut when you make this measurement is to prevent the signal from being corrupted by any load on it, like from a problem in the ecu or in the wire going to the ecu. Then of course you have to be really careful to not touch the bare end of the signal wire to any ground metal while it's powered up.

Always be sure that the black lead from the multimeter is going to a good ground, not painted stuff.

Maybe the multimeter will read a correct voltage. If the multimeter is reading the voltage that you'd expect but the ecu is reading it different, then there's a problem with the wire that goes to the ecu, or with the ecu itself. It's even possible you might measure (with the multimeter) a different voltage in the signal wire depending on whether it is cut or whether it is connected to the ecu. That would be a problem.

Whichever sensor you are using, you should make it clear what it is and who you bought it from. A good way to be real clear about this is to give us a link to the exact web page you bought it from.

It could even be that just the electrical plug is put together bad. That 3-conductor plug that plugs into the sensor. But usually that would either work ok or not work at all.

thank you I'll make sure to do this tomorrow here is the link of the sensor I bought it's a cheap one haha I bought it as a place holder till I could get a proper 3bar or 4bar

Amazon.com: KEJSTED 3Bar 3 Bar Manifold Absolute Pressure Map Sensor Turbo Boost & Connector Pigtail Plug Wire 12223861 Compatible with GM Chevy Buick GMC Pontiac Detroit Diesel Series 12219935 16040749 : Automotive

Buy KEJSTED 3Bar 3 Bar Manifold Absolute Pressure Map Sensor Turbo Boost & Connector Pigtail Plug Wire 12223861 Compatible with GM Chevy Buick GMC Pontiac Detroit Diesel Series 12219935 16040749: MAP - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

a.co

 

[danl]

Pet peeve of mine, but don’t cut wires. You are introducing a possible connection issue when splicing back together.

Remove the pin from the connector housing or remove the sensor completely to test back to the ECU.

First, I would bench test the sensor though….

 

[Nii]

Pet peeve of mine, but don’t cut wires. You are introducing a possible connection issue when splicing back together.

Remove the pin from the connector housing or remove the sensor completely to test back to the ecu.

First, I would bench test the sensor though….

I get that! I normally just probe the pin

 

[We're on Boost]

here is the link of the sensor I bought it's a cheap one haha I bought it as a place holder till I could get a proper 3bar or 4bar

Thanks for the link to it, that does nail it down what sensor you have.

That one might test ok but I'd be pretty un-confident in it even if it tests ok initially.

The sensor I would recommend for a 3-bar GM type is this one that Ballenger sells. You should read that page, especially the Description field. What they say there kind of fits with the complaints we see in here about the 4-bar GM type sensors like the Omni-Power 4-bar, which has seemed to become unreliable in recent years.

If you wanted a 4-bar instead of a 3-bar, I don't know what to recommend really. Ballenger does sell a US Made 4-bar. The cost of their 4-bar is higher and I don't have any experience with it. But their 3-bar, we put one on OhhShmit's 1990 Talon when he converted to speed density and it's been working fine.

On my own car I'm using an AEM 3.5 bar stainless sensor which is good, and with that the price is really getting up there.

 

[Nii]

I'm working on fixing my base tune. I'm still replacing and repairing some wiring. The car is really rich so I'll lean that out. What I'm seeking advise on is are there any parameters that are completely off? Or anything that indicates that I have a fundamental issue like a sensor that needs to be replaced or anything like that?

I have a new 3bar MAP sensor on the way. The idle is high, I need to adjust the s90 a bit more. I have no vacuum leaks from when I did a boost leak and vacuum leak test.

Sorry for the very fragmented paragraph I'm just throwing out all my thoughts haha. Thank y'all for any help!

 

[We're on Boost]

Well, if you really don't have any vacuum leaks, then your MAP sensor is way off while the engine is running. Because it says you have practically no vacuum while the engine is running at ~1000 rpm, and that's kind of impossible, unless you do have a huge vacuum leak. Are you still using that $16 MAP sensor from Amazon?

Also, I think the numbers from your LC1 wideband are very strange after 46 seconds where it all of a sudden goes dead lean. Doesn't look to me like it would actually be lean there at all. That's pretty important to have working because you are simulating narrow band.

If the wideband is still weird after you get the new MAP sensor going, you'd be better off to put a regular stock type narrow band O2 sensor in there for a while until the basic running is sorted out.

Your Speed Density map is kind of different, where did you get that?

Please go into your Captured Values and turn on CrankingFuelAdjust and ISCPosition so we can see those 2 things in the logs.

 

[Nii]

Can do I'll add those parameters after work today.

I do still have that cheap map I have a propper 3 bar coming in the mail this week. it's the 3bar ECM link recommend in the speed density wiki. (Delphi / GM 3 Bar Style Map Sensor - 12223861 - 16040749 US Made)

As for my wideband it's an lc2 unfortunately that was not an option in the wideband section haha so I just had to select lc1. yesterday I did some rewiring for it because my numbers were way off. my gauge was reading one thing and my wideband in the ecu was reading another then my afr estimate was another. so I went to the wiki and my learned to ground it to the ecu so that's what I did. and then my numbers matched. I'm not completely sure why it went dead I'll need to look into that but you are correct that it shouldn't have been dead there. the car still was running at that point before it died.

The ve map that I have is just one I put together so it is a bit funky haha. I'm learning tuning from evens tuning academy so currently I'm just working on getting the car to idle properly.

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[diambo4life]

A MAP sensor is very important for engine operation. Why you would buy some unbranded cheap unit for something so critical befuddles me man. Get a good map sensor from a GM car with a reliable calibration curve. With ECMlink, I would stick to vetted combos. When you have a standalone, you can fix the curve and get the sensor to work. I ran the GM 3.3 bar in my 1G for years.

 

[Nii]

A MAP sensor is very important for engine operation. Why you would buy some unbranded cheap unit for something so critical befuddles me man. Get a good map sensor from a GM car with a reliable calibration curve. With ECMlink, I would stick to vetted combos. When you have a standalone, you can fix the curve and get the sensor to work. I ran the GM 3.3 bar in my 1G for years.

I had an Omni 4bar before this one but it came broken so I just bought a temporary one till I could get a proper MAP sensor. It was never a long term solution but just a temporary stand in till I get the correct one.

 

[diambo4life]

No worries. Omnis are hit and miss. I prefer genuine GM sensors or if you have the $$ get a SS AEM 3.5 bar. LoDoller Motorsports have affordable sensors as well with reliable calibration data.

 

[We're on Boost]

I have a propper 3 bar coming in the mail this week. it's the 3bar ECM link recommend in the speed density wiki. (Delphi / GM 3 Bar Style Map Sensor - 12223861 - 16040749 US Made)

Ok good, that sounds like it's the one from Ballenger which should be a good one.
If you are curious to see the calibration data for it, it's all laid out very nice right on the web page I gave you for it, on the "Specifications" tab and also on the "Images/Drawings" tab. But it matches the preset we have in ECMlink for GM 3bar which is the one you are already set to, so no fiddling needed there. Good.

As for my wideband it's an lc2 unfortunately that was not an option in the wideband section haha so I just had to select lc1. yesterday I did some rewiring for it because my numbers were way off. my gauge was reading one thing and my wideband in the ecu was reading another then my afr estimate was another. so I went to the wiki and my learned to ground it to the ecu so that's what I did. and then my numbers matched. I'm not completely sure why it went dead I'll need to look into that but you are correct that it shouldn't have been dead there. the car still was running at that point before it died.

Sounds like the LC2 is going to be OK then. Good. And it uses the same calibration as the LC1 so you are OK there too.

Looks like things are heading well then. Add CrankingFuelAdjust and ISCPosition to the logs, and put on the new MAP sensor when it comes, and then we should see it running much better.

We should know about your hose to the MAP sensor. It should not be Teed into the same hose that goes to the wastegate actuator. Could you describe your MAP hose for us, I mean, what all is it connected to besides the MAP sensor. Also of course it should not be some rotty old thing that is leaky or loose on the ends

Also, what do you have the MAP sensor physically mounted to? Body or engine, and where?

 

[Nii]

Ok good, that sounds like it's the one from Ballenger which should be a good one.
If you are curious to see the calibration data for it, it's all laid out very nice right on the web page I gave you for it, on the "Specifications" tab and also on the "Images/Drawings" tab. But it matches the preset we have in ECMlink for GM 3bar which is the one you are already set to, so no fiddling needed there. Good.


Sounds like the LC2 is going to be OK then. Good. And it uses the same calibration as the LC1 so you are OK there too.

Looks like things are heading well then. Add CrankingFuelAdjust and ISCPosition to the logs, and put on the new MAP sensor when it comes, and then we should see it running much better.

We should know about your hose to the MAP sensor. It should not be Teed into the same hose that goes to the wastegate actuator. Could you describe your MAP hose for us, I mean, what all is it connected to besides the MAP sensor. Also of course it should not be some rotty old thing that is leaky or loose on the ends

my map sensor just plugs directly into my intake manifold with nothing else connected to it luckily

 

[We're on Boost]

my map sensor just plugs directly into my intake manifold with nothing else connected to it luckily

Good, yeah you have a nice manifold which probably has plenty of hose nipples for things like this. One of the nice things about the fancy manifolds.
So the hose connection should be good.
What about the mounting of the MAP sensor though? Is it attached to the body somewhere? Or is it attached to the engine, which would be worse because of all the vibration and higher temps?

Then there is one more detail about the mounting of the MAP sensor. Kind of a secondary point but good to know about. These sensors that have air going to them, the hose nipple should preferably not be pointed in any upward direction. The nipple should be pointed in some downward direction, or it could point out nearly sideways but slightly downward, and it should have a little bit of sag in the hose so that the low point of the hose is not immediately next to the sensor. As far as I know, this is just so that any water that condenses in the hose will not run into the sensor, or if it does get into the sensor, it will fall back out into the hose.
The "Images & Drawings" tab on the Ballenger web page shows a diagram for this. Their recommendation is a little more extreme than mine. They want you to point it within only 30 degrees of straight down. Not many vendors mention this.

The reason I think it's kind of a secondary point is because I had one of these flat rectangular sensors on my car for 6 years and it was pointing sideways but slightly upward instead of slightly downward. It was ok. But the hose was about 3 feet long and most of it was a few inches lower than the sensor. And my car was always kept in a garage.
Anyway, it's a "best practice" to have it pointing downward.

 

[Nii]

definitely! I can make a little bracket to mount it downwards. currently it's not really mounted on anything since I had to throw away the whole mounting bracket I had prior for the Omni 4 bar but the original plan was to just mount it on the firewall. but I have a little steel sitting aside. I can make a bracket to mount it facing downwards, the line itself has a lot of slack and is not putting any pressure on it!

 

[Nii]

I haven't replaced the map yet i just added the new parameters. i think my break booster line could be backwards possibly?

 

[We're on Boost]

i think my break booster line could be backwards possibly?

Well if your booster hose was backwards, it would allow boost pressure to pressurize the booster which you don't want, but when your engine is running with vacuum, it would not let air into the engine. So it would not be a vacuum leak as far as the engine is concerned, if that is what you are thinking about.

When the hose is on correctly, the check valve in it allows air to flow towards the engine. Sounds like a vacuum leak doesn't it? But it isn't a vacuum leak unless the Booster is leaking. If the booster itself is leaky, then the hose will pull air through the booster and it will go into the engine and that would be a vacuum leak.

That is something that could be happening on your car. Because you tested for leaks with a boost leak test. Pressure in other words.
A test using pressure at the throttle body flange won't find a leaky booster because the check valve in the booster hose will prevent your pressurized air from getting to the booster.

So I think what you need is a way to test the booster. The most direct way I think would be if you could take the hose off of the booster and put like a mighty vac pump with a gauge onto the booster and see if the booster will hold a vacuum.

I looked at the 1991 FSM (factory service manual) to see what they say about how to test the brake booster, and they have 3 tests that you can do without taking anything apart and no special tools, but you have to be able to run the engine for at least a minute or so. Here's a screen shot of what they say (it's on page 5-43):

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[Nii]

Well if your booster hose was backwards, it would allow boost pressure to pressurize the booster which you don't want, but when your engine is running with vacuum, it would not let air into the engine. So it would not be a vacuum leak as far as the engine is concerned, if that is what you are thinking about.

When the hose is on correctly, the check valve in it allows air to flow towards the engine. Sounds like a vacuum leak doesn't it? But it isn't a vacuum leak unless the Booster is leaking. If the booster itself is leaky, then the hose will pull air through the booster and it will go into the engine and that would be a vacuum leak.

That is something that could be happening on your car. Because you tested for leaks with a boost leak test. Pressure in other words.
A test using pressure at the throttle body flange won't find a leaky booster because the check valve in the booster hose will prevent your pressurized air from getting to the booster.

So I think what you need is a way to test the booster. The most direct way I think would be if you could take the hose off of the booster and put like a mighty vac pump with a gauge onto the booster and see if the booster will hold a vacuum.

I looked at the 1991 FSM (factory service manual) to see what they say about how to test the brake booster, and they have 3 tests that you can do without taking anything apart and no special tools, but you have to be able to run the engine for at least a minute or so. Here's a screen shot of what they say (it's on page 5-43):

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thank you!!