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beren

crazy fuel pressure & engine speeds

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Since I updated to 2.7 my engine speed has been off. It changes, but it's about 15mph higher than actual. It's not the app as I tried downgrading it and it made no difference. Around the same time I saw my fuel pressure was 16-18 where it had been 12-14 before. I thought maybe there had been a bad connection and plugging the plug back in showed a more true pressure reading. Today I was taking my son to daycare and it showed 60psi as my fuel pressure. That scared me a little so while driving I shut the engine off for a sec then keyed it back on (manual trans) and it started running again. The fuel pressure didn't change but I noticed my vehicle speed was correct this time, and stayed correct the rest of the trip. After I got to work I shut off the truck and turned the key to run without starting, the fuel pressure showed as 30, then 44 when I turned it on. Just now an hour later I did the same thing it read 4 & 18psi. Any ideas why it would read like this?

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33 minutes ago, Mopar1973Man said:

Am I going to assume you installed the fuel pressure sensor at the VP44?

 

Yes, I have a tapped banjo bolt at the vp44 to measure the pressure after the filter, it also has a needle valve barely cracked open to protect the sensor

 

Although hmm maybe it opened itself up a little more… 

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Nope, the water hammer killed the fuel pressure sensor. You'll need a new fuel pressure sensor and relocate the sensor away from the VP44. This is one reason my fuel pressure sensor is mounted near the ABS module this gives over 6 feet of tube run away from the VP44 and pulses fade with distance. I'm sunning an ISSPro snubber and a needle valve which the needle valve has no purpose other to close the line if a leak occurs. 

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4 minutes ago, Mopar1973Man said:

Nope, the water hammer killed the fuel pressure sensor. You'll need a new fuel pressure sensor and relocate the sensor away from the VP44. This is one reason my fuel pressure sensor is mounted near the ABS module this gives over 6 feet of tube run away from the VP44 and pulses fade with distance. I'm sunning an ISSPro snubber and a needle valve which the needle valve has no purpose other to close the line if a leak occurs. 

Mother F…. I have whatever came with the sensor from quadzilla. I had hoped that would protect it.

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2 hours ago, beren said:

Since I updated to 2.7 my engine speed has been off

Are you talking about qwadzila screen, if so make sure you have everything selected under settings, drivetrain info. And for tire circumference if your is say 97 put 95" 

On fuel gauge you need a needle valve before sensor, that is only open enough to have enough pressure to move gauge up slowly to it operating psi

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Thats how I have the FP sensor setup Diesel, I just double checked. For the vehicle speed, It's something with the newer update, like I said if I restart the truck while driving it suddenly shows the correct speed in the app. My dash is correct, I took it to the dealer to get calibrated when I changed my tire size to 285/75/17.

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only if  i restart my truck while driving

 

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1 hour ago, Me78569 said:

whats your tire size set to? 

In the squad app? It's likely the default right not but I've changed it and it made no difference. It was set to my tire size before I updated to 2.7 i think 106.5"

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Strange. I tried the same thing today to fix the speedometer but it didn't work. The app still shows me going about 13 miles an hour fast

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Fun fact, if your ABS computer is programmed for aftermarket tire size, you need to leave the tire size as default or it won't be accurate.

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Yep, what kzimmer said. Also, your estimated gear will be off. There really isn't a good way to fix that other than a highly convoluted method requiring more settings that you would have to change. 

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On 3/14/2018 at 9:09 PM, kzimmer said:

Fun fact, if your ABS computer is programmed for aftermarket tire size, you need to leave the tire size as default or it won't be accurate.

 

It used to work though. If iQuad uses the rpm/trans/diff/tire size settings to calculate the speed it'll always be correct if you set it up correct. If you use the ABS to get the speed it will be correct if the ABS is correct. Right now iQuad is never correct. If i'm using defaults or I set everything to match my truck, it's always 10-15mph higher. Usually ~13mph. Maybe a setting to pick how you want speed displayed, calculated vs abs. Regardless, if you set your vehicle info it should work. 

On 3/14/2018 at 9:01 PM, Me78569 said:

Does your remember what Level you were on before you shutdown?

It might have been 0 when it worked, now that you mention it…

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No, I had unplugged it to check the connections but I can't recreate it getting the right speed. Real bummer now that there's a mpg estimator.

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The MPH correction only uses ABS speed and a tire size ratio to calculate the speed.

We do use the tire size, speed, RPM, rear end ratio and transmission selected to calculate the gear and transmission slip ratio. We would need to have better information about the gear and trans slip ratio to calculate the actual MPH given the other parameters. 

 

What this means is that if you have larger tires and a corrected speedo via programming, you will probably never have the right trans slip ratio or gear, but the MPG calcuations should still be close. 

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23 hours ago, Quadzilla Power said:

What this means is that if you have larger tires and a corrected speedo via programming, you will probably never have the right trans slip ratio or gear, but the MPG calcuations should still be close. 

 

235/85 R16 vs 265/75 R16 which is 1mm taller and 2 Rev/Mile less. But +3 MPH off at 65 MPH ??? Hua? Manual Transmission no slip...

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Every time you push in the clutch your transmission is "slipping". In a manual case, it would be closer to clutch slipping than trans slipping, but it is still just a calculation. 

 

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Posted (edited)

One thing I'm noticing is the speed sometimes jumps around. Like it'll  jump 3 to 10 miles an hour high and then come back down. This is with smooth study acceleration also

Edited by beren

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This is most often caused by malfunctioning speed sensors. Does it jump on your dash gauge as well? or only the iQuad app? 

I am assuming that these jumps in speed aren't real and only what is reported. 

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On 3/9/2018 at 9:04 AM, Mopar1973Man said:

Nope, the water hammer killed the fuel pressure sensor. You'll need a new fuel pressure sensor and relocate the sensor away from the VP44. This is one reason my fuel pressure sensor is mounted near the ABS module this gives over 6 feet of tube run away from the VP44 and pulses fade with distance. I'm sunning an ISSPro snubber and a needle valve which the needle valve has no purpose other to close the line if a leak occurs. 

 

So what did you do to move it, just get some ends and a length of fuel line? Do you think a small line would help to even out the pulses since it would stretch/absorb more? I just ordered a new sensor, gotta love eBay sales, I got 15% off :-)

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