Park it and it wont restart sometimes

[jumpbluesdude]

This just happened to me this past weekend. This last time it was running and I got a few blocks down the road then it died. I couldnt get it restarted. It seems like it wants to start, and if it does, there is no power and it dies pretty soon after. It has done this to me twice and both times it was a hot day(104 last time, low 90s the first time), was running fine with no indication of a problem, and shut down running properly, then when started the next time had the issue. Given time, it corrects itself. I took the cover off the megasquirt hoping it would help. This last time I kept after it because I had freshly painted cycle parts in the truck and it ended up burning the ground trace, which didnt make any sense. My ground wire runs straight to the block along with the battery cable. I had to repair it with a wire and it started right up and made it home without any problems. Im afraid to drive it now for fear of getting stranded again. Anybody have any ideas. I believe the wiring is sound and the soldering - Im an electronic tech by profession and build/fix tube amplifiers as a hobby, so Im pretty proficient with wiring and soldering. Im thinking one of the components on the board might be overheating. Im sure I can track it down in time(and some cold spray), but was hoping someone had some idea which it might be(fingers crossed - not the daughter card).

[Bernard Fife]

jbd,

It's hard to comment until you tell us your board version, processor, code version, and you post your MSQ and a datalog so we can have a look.

In the meantime, if this is a v3 PCB you might want to look at D19, as described here: http://www.megamanual.com/ms2/V3trouble.htm

Lance.

[jumpbluesdude]

Thanks for the help, Lance. I replaced D19 with a 5.6v zener, but it didnt resolve the issue. I am running an MSII 3.0 with a 3.01 processor and updated to code version 2.905. It stops running randomly. It failed on friday night in the middle of running an errand and I went out the next day and reloaded the code and MSQ. I recalibrated the sensors and was able to get it to run again. I drove it around most of the day saturday with no issues then parked it in the garage. I had updated the code and adjusted the IAC setting because it would idle too low once warm. Im running an MPFI setup on a SBC. Yesterday I went to start it and it wouldnt start up or fire at all. Sometimes it will fire, but not idle. It wouldnt do anything and the last time I ran it it was fine. Any help is appreciated. Im about ready to go back to a carb.

[jumpbluesdude]

I also wanted to point out that my intake air temp never comes off 70 degrees no matter what temp it is. Saturday was in the 80s and it said 70. I replaced the sensor with another one I have a recalibrated with the same results. I didnt put them on a meter, but I doubt they are both bad.

[Matt Cramer]

If you put the Megasquirt on the Stim, does the IAT input respond? 70 degrees is a limp-home value it will default to if the sensor is not hooked up correctly.

[jumpbluesdude]

Thanks, Matt. I did mess with the relay board when it stuck me the first time and must have pulled the wire out without realizing. The stim worked exactly as it should on all inputs. The IAT works now that I re-inseerted the wire and secured it, but the truck still wont start. I did a pull check on all the other wires and cinched them down to make sure. I went through the other connections to make sure they were good - sensors, injectors, connectors, etc. The megasquirt appears to be working correctly, but the truck still wouldnt start. I reloaded the s.19, reloaded the project, rewrote all the the sensors, and reset the O2 sensor, then rewrote that again. I powercycled the megasquirt throughout these processes and it still doesnt start. It was running on saturday when I parked it in the garage. Now nothing.

[Matt Cramer]

In the no-start data log, the MS is not reading RPM. Is that still the case?

[jumpbluesdude]

I left the battery on the charger last night because it had gotten run down from trying to start. After some more trying today it started. Great, but its probably going to stick me again. I took another datalog when it started. Let me know if there is anything I can improve. It was reading RPMs in an occasional blip. It would jump to 44 and nothing for a second then 44 again. When it did start, it saw RPMs and the other guages looked good. The O2 bounces into the 16-17 area and goes red. When it stuck me the O2 was in the 20s and wouldnt stablize. Because I have had to re-calibrate the sensors I was wondering if those settings were getting dropped or may be just coincedence.

[trakkies]

The very first thing to do is get a consistent tach signal. MS won't inject without it.

[jumpbluesdude]

I read that again and it looks confusing. When the truck would not start, it would see RPM in blips. When it started, it read RPM fine. Im running an HEI and the RPM wire is attached to the RPM output spade on the distributor. It has not changed throughout this situation and I never saw RPMs drop out (I was tuning on tunerstudio once when it failed). Hope that clears up any ambguity. There was a point when idle was sitting down in the 400 rpm range and I attributed that to a low setting on the IAC. I readjusted it and that helped get it up into the 800 range out of gear and 600 in gear. I also reduced the advance a few degrees to make it easier to start. If you dont see anything obvious in the datalog, Ill just have to drive it and see if it fails again. Time to throw the bicycle in the back again!

[jumpbluesdude]

Thanks to all that tried to help. It turns out the issue was vapor lock, but it only occured when the temp rose above 90 degrees. My fuel filter is frame mounted and apparently too close to the exaust. Ill be moving it today and that shouldnt be an issue anymore.

I do have another issue that I could use some help on. When I start the engine and it is cold(below 160 degrees) it will hesitate unexpectedly at times and lose power while accelerating for just a moment. Sometimes it will backfire through the throttle body. Idle is fine. The closer it gets to operating temp, the less it occurs. It is completly eliminated over 180 degrees. I tweeked the IAC and that improved it a little. Im going to keep working the IAC, but does something else coming into play? Thanks.