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ECU Temp 302 F

Howard Coleman

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after running perfectly yesterday, my engine wouldn't start today. (G4X Extreme)

i logged four attempts and the primary feature is that the active cell while cranking is in the NE most corner of my tables... minus 14 MGP.

i did a compare between yesterday and today's maps and found no settings difference. 

during the compare i did notice one difference... my ECU temperature shows 302 F. a straight line on all 4 cranking logs from today. 

i am exactly two weeks from loading up for the Texas Mile effort. new engine, new trans and easily 6 months of prep work for 200 mph. 

when i discovered the readings i examined the ECU for any sign of 300 F and found none. i turned on the ignition waited a bit and the case remained cool to the touch.

yesterday's ECU temps were ambient... 70/80 F

any help greatly appreciated. 

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all the 5 volt readings checked out. by adding fuel i was able to get it started and it wanted to go lean. whereas it ran perfectly the day before, i am finding the fuel settings are too low. i am getting errors. a "connection" error 1019 "Link not responding correctly" the ecu today, as you will see in the log, is showing a normal temperature rather than the 302. my fuel pressure is normal yet my fuel settings are way higher just to make it run. it is currently not driveable. i do think there is something wrong with the ecu as the wiring checks out and a "compare" shows no differences between a map that worked well and the current map which does not. i am truly lost here. 

i attach;

October 11 map and log. both worked well

map https://drive.google.com/file/d/1kmF9dCEJZLfcwG2R49FYXuKfD0CMLFDA/view?usp=sharing

log https://drive.google.com/file/d/1eTbRuhxz9lzk3oAzpnHL1EZyWPs77SlT/view?usp=sharing

Oct 13 map and log. problems

map https://drive.google.com/file/d/1h0rRqCzdyWijc74Dbi8ICki0dxU0Pat8/view?usp=sharing

log https://drive.google.com/file/d/1hE_zn3NLPgW3i-0pQ0YMOoVZiAZKnt-R/view?usp=sharing

thanks for any help.


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As per my last message your files are restricted so are not accesable, you need to right click on them and change to anyone with link, something like below.

It is not a tune problem as the tune cannot effect ECU temp or the MAP reading.  I suspect you have an intermitant short or some other wiring issue which is why I want to see the log from when the problem was apparent.




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On 10/13/2021 at 1:22 PM, Howard Coleman said:

when i discovered the readings i examined the ECU for any sign of 300 F and found none. i turned on the ignition waited a bit and the case remained cool to the touch.

Side note on this, there was a bug fixed in 6.21 where the max ECU Temperature in Statistics was being reported wrong, would always revert to 150deg C (302F) on power cycle.

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I dont see any issue with MAP or ECU temp in either log.  

But one problem I see with fuel is the accel fuel deadband is too low so the accel fuel is dumping in extra fuel continuously - even at idle with no throttle movement.  You can see in the snip below, Inj PW is 1.1ms, but there is 0.5ms of accel fuel going in as well - which is nearly 50% extra.  

Some suggested changes below, but fuel table will need to be reworked after these changes since this would have messed up any mapping you have done.  



Suggested fuel changes in orange:



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thanks for the additional settings help Adam. 

after not starting i examined all the 5 volt systems/sensors etc and found they were O K. i swapped in an earlier Map added updated fuel settings and did a nice power run. all was well. i did some fuel table tuning and returned to the car for another run 3 hours later. no start. i pulled the plugs and they were pretty dry.

this morning i took a close look at the failed start log from yesterday. 

key on no crank MGP shows minus 13.5. cranking MGP oscillates between minus 13.4 and 4 or 5 positive psi???  i haven't spent a lot of time observing cranking MGP but did go back to an earlier log and it shows about zero MGP to minus half of a psi. way different.

of course fuel pressure reacts to these probably readings but here there is also something awry.

fuel pressure, during the 8 second no start crank topped out at 24-21 psi and had spikes down to 7-8 psi. i recently reset fuel pressure from 3 BAR to 4 BAR... around 57. 

differential fuel pressure followed loosely fuel pressure and showed a range of 34 to 12 psi. of course it should have been fairly flatline around 57.

i note that there seems to be a correlation to the bad logs with the ECU temp as it showed normal temps on my good run and 302 on my bad crank.

i have, since, downloaded the newer update which may change the ecu temp reading but perhaps the fact that on good runs the temp is normal and bad it is pegged may help towards a solution.

i have just posted on Google Drive an earlier normal crank log along with the no start bad crank from yesterday. 

good crank example:  https://drive.google.com/file/d/12KJUTcrrNHz6bvmNL0-TgytNpKNZf81U/view?usp=sharing

bad crank yesterday: https://drive.google.com/file/d/1vULqn2L7pWxJILvzz74eT8HnFH97D5Eb/view?usp=sharing



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i pressured up the map sensor to 15 psi and it did not respond other than cycling quickly within a range of around 10 or so psi in the negative range. i then swapped in two other Honeywell pressure sensors and they also were spinning through numbers like a slot machine. all negative. the ECU was showing 302 F. 

another item which i have neglected to mention is the ECT is similarly fast cycling between zero and around 150 F.

if my Extreme has an internal issue is there any possibility of getting another. i have to load up for the 1300 mile trip to the Texas Mile Oct 26. the next event is April 2022.


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Ok, you have caught it properly in this log.  As I suspected your 5V output is shorted out.  You can see below (yellow trace) it is bouncing between 0 & 2.2V, this means no 5V sensors are reading correctly.  It should normally be 4.98-5.02V if everything is good.



Most commonly in my experience this short is failing sensor - usually a pressure sensor.  To diagnose, put the 5V Out parameter on a large gauge similar to below on one of your screens, next time the fault occurs, set up the laptop somewhere you can see it from the engine bay and go around and unplug the 5V sensors one at a time.  If the 5V gauge suddenly pops back up to a stable 5V when you unplug a sensor you have found the culprit.  


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really, really, happy this morning. after pasteing up a big 5 V digital gauge i started removing my 6 digital pressure sensors as well as my TPS. the TPS had me holding my breath as they are almost impossible to source. it, of course, came down to the last sensor and bingo... a solid 4.97 V! 

when i bought my V88 in 2013 i wanted to instrument everything and bought Honeywell pressure sensors. correctly or not, i am convinced of the quality of HON products. eventually AEM entered the sensor market with "similar" looking sensors and i ended up over the years aquiring a few. 

it was an AEM sensor that failed. i had another AEM sensor lying around and swapped it in... it also was a fail. i swapped in a HON sensor and am now back to a solid 4.97 V reading.

 it is possible that the two AEM sensors were compromised from being exposed to the exhaust as they were reading exhaust manifold pressure. i do have an FFE module between the sensor and pressure line... but perhaps tough duty. 

i do have an AEM pressure sensor reading my fuel pressure.

Thank You Link and Thank You Adam for not only the fix but also for alerting me to the 5v Out which i can place in my toolbox.



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I've seen pretty much all brands of pressure sensor fail - Even the common Honeywell MLH.  As a general comment I have found the short ones like the AEM brass style (single board internal design) are the most unreliable, the longer ones like Honeywell PX2 and Link PS150 are a two board design and are more reliable.  

The most reliable in my experience so far in the Bosch combined pressure/temp.

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