Jump to content
BigBoiMR2

Sensor voltage rising over time

Recommended Posts

power runs.llgHello,

I recently installed an AEM Fuel Pressure sensor (30-2130-100)

I wired the Sensor to AN volt 3, 5V Power from the ECU to the sensor, and the ground to the sensor ground on the ECU. I used new lengths of wire and crimped on new pins and spliced into the power and sensor ground at the ecu side.

The sensor was reading properly and I had no issues, it would react to changes instantly. 

After driving for maybe 30 minutes the sensor voltage rises to a point where the sensor is reading above the actual fuel pressure. once it rises past, the reading will be stable at say 50psi until the actual fuel pressure surpasses 50 psi, then the sensor will read the correct pressure until pressure drops below this "floor". the floor seems to slowly rise up to about 54psi max.

setting the readout to 0-5V shows the same behaviour. the calibrations are correct it seems that the sensor wire is picking up voltage over time.

If i unplug the sensor the voltage drops to .20 but as soon as the pins make contact it will jump back up to the voltage it was at.

It seems to discharge once the car sits for a couple hours but short periods of time it holds the voltage.

The car is a 1988 toyota MR2 with a 3SGTE. the Ignitor is mounted to the transmission as I was getting too much interference to connect to the ECU when it was installed on the Firewall.

Other sensors do not seem to be affected by any rising voltage either, The MAP and IAT sensors continue to real correct values after long drives.

the ECU is grounded to the factory point on the Intake Manifold.

Edit: The 5V output is stable at 4.97V the whole time.

Hopefully it is something simple I am overlooking, I have attached a log with it working correctly. I will upload a log with the issue present also.

Thanks for the help

 

power runs.llg

Share this post


Link to post
Share on other sites

I dont see what you are talking about in your log, differential fuel pressure is far from the best I have seen but seems to control ok, in the power runs log it varies from about 330KPa to 360KPa.  In the other log differential is more like 380KPa.  

Share this post


Link to post
Share on other sites

I was looking through my saved logs and I dont seem to have any good examples saved, I will get a better log and upload it when I can. 

The issue mostly shows up at idle, the sensor will be reading say 54psi at idle and causing the car to idle really lean, if i change the fuel pressure setting to map based with 43.5 psi base it will correct the afr. 

Once it starts to read 54psi, it will run lean at light throttle also until the actual fuel pressure reaches 54psi, then it will track on target again.

Thanks for your response

Share this post


Link to post
Share on other sites

I've had the sensor off the car, and tested it with a air compressor, plus it does work for a while until it seems like a charge builds up and affects the minimum reading. 

Could the sensor have a bad ground that may not be properly discharging the voltage?

I'll hopefully get a clear log tonight so I can show what I'm talking about more clearly.

Share this post


Link to post
Share on other sites

Yes, I had a mechanical gauge mounted in the same spot for a few months and the fuel pressure would actually drop off a little after a long drive in the summer, I've heat wrapped a few fuel parts to take care of that issue, but wanted the pressure sensor to help keep fuelling on target even if the pressure drops a little.

Another thing that confirms the fuel pressure is not actually rising is that when the sensor reads high, the engine will idle lean as it thinks there is more fuel passing through the injectors than there actually is. When the sensor is reading high, around 54psi and idling lean,  If I manually set the fuel pressure to 43.5 psi it will idle on target again.

Share this post


Link to post
Share on other sites

Be careful as I've seen some liquid filled gauges read differently when the gauge gets hot. 

Do a log with differential fuel pressure not just fuel pressure. 

Share this post


Link to post
Share on other sites

It seemed to be reading accurately. with the mechanical gauge once the fuel pressure dropped the car would run lean at idle, since the ECU wasn't able to adjust for it. Now with the sensor it is thinking more fuel is going into the engine with the high sensor readings so again the engine is leaning out at idle LOL.

After first start and warm up it idles on target until the readings go too high.

In this photo I have the ecu fuel pressure calculation based off base pressure with MAP reference so the sensor reading is not affecting my AFR. The area I have circled you can see the Pressure reading is high and it isn't changing, even as the manifold pressure changes. when the sensor is working properly even the slightest map change will register a fuel pressure change as it should.

The Fuel pressure regulator, rail, lines and injectors have all been replaced and ruled out as issues.

high pressure no tracking.png

Share this post


Link to post
Share on other sites

This photo shows when the manifold pressure is high enough and the true fuel pressure rises above the sensor reading it does track the fuel pressure change. But the fuel pressure sensor wont read below the level it rose to.

High pressure tracking only above.png

Here is my tune file

https://drive.google.com/open?id=11MN5eOtoGlmcGjYPoq5eDKvGpMTDPsmx

Here is the Log from the most recent screenshot

https://drive.google.com/open?id=1iB1gyl1of2LDCfKXT0W6wybrZRP3wEBa

Thanks

Share this post


Link to post
Share on other sites

The issue seemed to be getting worse, the sensor used to read normal after first start in the morning until about 30 minutes of driving, but today it didnt read correct at any point.

I've removed the sensor now while logging and it still shows 55 psi, if I unplug it the reading drops to 0 and plugging it back in it spikes to 55psi again, so it seems that the sensor is the issue.

Thanks for all of your help and suggestions, I'll be trying a new sensor when I can and I'll report back if I have any more issues!

Share this post


Link to post
Share on other sites

grab a Honeywell or other decent brand sensor, make sure it's remote mounted from the engine and you shouldn't have any issues

Share this post


Link to post
Share on other sites

Im not sure if I could trust that setup, why not just use a 1:1 rising rate fuel pressure regulator and simplify things? even if you wanted to simply log fuel pressure you could without using the output to alter the ecu's calculations.

Share this post


Link to post
Share on other sites
5 hours ago, motomattx said:

Im not sure if I could trust that setup, why not just use a 1:1 rising rate fuel pressure regulator and simplify things? even if you wanted to simply log fuel pressure you could without using the output to alter the ecu's calculations.

The ECU isnt altering anything. In fact the fuel pressure reading isn't being used by the ECU at all, its just there for logging purposes at present. The fuel config is set to MAP Referenced rather than FP sensor so the ecu assumes a diff fuel pressure of in this case 43.5psi at all times, and it looks like he has a 1:1 regulator that is working ok to make this actually happen.

@BigBoiMR2 now that you've got fuel pressure reporting correctly, it would be a good idea to change the fuel config to FP sensor so that any fuel pressure drops are automatically compensated for by the ECU. Depending on how close your current diff fuel pressure really is to the configured 43.5psi, you may need to make some corrections in your fuel table afterwards

Share this post


Link to post
Share on other sites
Just now, cj said:

The ECU isnt altering anything. In fact the fuel pressure reading isn't being used by the ECU at all, its just there for logging purposes at present. The fuel config is set to MAP Referenced rather than FP sensor so the ecu assumes a diff fuel pressure of in this case 43.5psi at all times, and it looks like he has a 1:1 regulator that is working ok to make this actually happen.

@BigBoiMR2 now that you've got fuel pressure reporting correctly, it would be a good idea to change the fuel config to FP sensor so that any fuel pressure drops are automatically compensated for by the ECU. Depending on how close your current diff fuel pressure really is to the configured 43.5psi, you may need to make some corrections in your fuel table afterwards

Yes that is correct, I did have it set to map references when I was having issues with the sensor.

@motomattx what is not to trust about the setup? I have verified the pressure with a manual gauge and now have the sensor installed and it is reading the correct pressure.

I am running the stock 1:1 rising rate regulator with a bored out fuel rail and 540cc injectors on a 3SGTE. I have a Walbro 250 for my fuel pump and wired the OEM fuel pump resistor to be switched by the ECU. I was having issues with fuel temp as well as fuel pressure being too high at idle and cruise. 

With the fuel pressure sensor installed now, I have been able to correctly set the resistor crossover point based off the injector pulse width. With the reduced flow at idle and cruise and additional heat shielding around the fuel delivery components I have greatly reduced the issues I was having that I attributed to fuel temp.

And yes once I confirmed the replacement sensor was working properly I switched the ecu to FP Sensor in the fuel config and re-tuned the fuel map.

Also, since iI do not currently have a fuel temp sensor, if the fuel temp increases enough to lower the pressure in the rail, the ecu will be able to at least partially compensate for that before closed loop lambda corrects the difference.

 

Thanks,

Cameron

Share this post


Link to post
Share on other sites
22 hours ago, motomattx said:

What Im getting at is that AEM sensors dont seem to have super high quality anymore, youve had one fail, it might not be the last.

Ah yes that is a good point.

I have run some braided ss fuel line from the rail and mounted the sensor to the chassis to isolate it from vibrations and hopefully that will reduce the chance of it failing again.

I will be keeping an eye on the readings and maybe figure out some kind of safeguard to implement.

Thanks,

Cameron 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

×
×
  • Create New...