Hi,
> the HPWM glitch doesnīt matter because its driving an electric fuel pump.
OK, no problem with that then.

> I read the UART section in the old PBP handbook and it says: "very complicated" which is a nogo for me .
If you say so.

> When i remember right I may use the HSERIN/HSEROUT command? Is that the USART thing?
Yes, HSERIN/HSEROUT is using the USART peripheral in the PIC instead of bitbanging.

> Can I let go of the "wait" statement when using HSERIN/HSEROUT?
Depends on how you go about doing the "whole thing". You can use the USART to receive characters in the background using interrupts but I suspect you don't want to go that route either.

> And using a timer to count....thanks for the advice that looks like a dive into assembler which causes freezing my neurons.
No need for any assembly language. Look at the Timer n section of the datasheet and you'll see how you can configure it as a counter.

Here's an idea:
Read up on how to use a timer as a counter and get that going.
Write your LCDOUT and housekeeping code in such a way that always takes the same amount of time, like 50ms
Use that time as the timebase for your counter.
Instead of sitting around waiting for the other PIC to send data use a handshaking or polling scheme so that you'll get the data when you're ready for it. This might obviously "push" the timing problem over to the other PIC but I don't know enough about your system to say. Even so I'm guessing it would be easier to it all in one PIC.

Cars are way to messy, greasy and complicated for me. I enjoy driving them but mostly it's just means of transportation for me and I absolutely hate fixing, servicing and messing around with them. It's a good thing we're not all alike :-)