Fuel Sender vs Fuel Sensor

It turned out to be vapor lock from using mogas.  We have been using mogas mixed with avgas and so far it has been fine and has not been a faulty fuel pressure sensor.

Interesting, it is often the simplest reason. Have you got a vapour return line to the fuel tank? It the pressure sensor mounted in a way that prevents vapour getting trapped?

Unfortunately, the fuel return line can only do so much to help prevent vapor lock and it is not the "ultimate" fix for this situation. Here is a write up regarding vapor lock - https://www.rotax-owner.com/en/flightsafety/476-ai476

If you are experiencing vapor lock with your Czech sport cruiser the best thing you can do is switch fuels. There is no official information regarding blended fuel (Av-Gas & MOGAS) however, we have seen positive results from doing this. The key is to keep the fuel vapor pressures low!!!

Unfortunately, the Czech SportCruiser aircraft have a very tight cowl design that doesn't allow for proper cooling of the fuel system. We have seen more vapor lock issues with Czech Sport cruisers over any other aircraft design and it's the unfortunate nature of the beast! 

Look into SWIFT fuel as it has a very low vapor pressure point and contains hardly any lead. The cost of SWIFT fuel is around the same as AV-GAS but the benefits of such fuel are high (higher than blended AV-Gas & MOGAS) 

Using the fuel Swift sells should solve your vapor lock problem. 

Just to avoid confusion though, the fuel from Swift is Avgas it is just UL94 Avgas which does not contain lead as opposed to 100LL which does.

Any Avgas you can find today will have a vapor pressure of about 7 RVP, where Auto Fuel will have as much as 15.  Unfortunately, due to the number of waivers issued lately you can find the high RVP "Winter Blend" auto fuel just about all year round in about any climate.

As far as mixing fuels go, the results are, well, mixed.  EASA found that due to the way some formulas of auto fuel mix with Avgas you might even make things worse while others have good results.  The PFA in the UK limits flight operation for any mixture that contains auto fuel to 6,000 feet as their testing showed a high vapor pressure with even a smaller amount of auto fuel in the mix. Some very dated tests by the FAA showed good results; however, the tests are so old that you are unlikely to find the auto fuel formula they tested.

Best bet is to ask the airframe manufacturer if they have any experience with winter blend (14 RVP) in their aircraft before using auto fuel.