I suggest you look at the HScope Android app. I have it on an old, inexpensive Android tablet. I teamed it up with a Hantek 1008C scope that I bought used.
The 1008C gives you 4 channels with the HScope app. The specs of the scope are nothing to write home about but for most automotive tasks they're fine. This is actually an 8 channel scope but only 4 channels work with the app. If you want all 8 channels you need to use the Hantek factory software, which is nowhere near as usable as the app.
I recommend you look at a YouTube channel called Gadgets Playlist. Dennis (the host) showcases a lot of the capabilities of the app with a variety of different USB scopes, including some DIY ones built on the STM32 development board. He also covers a variety of different DIY probes and sensor implementations.
I already had the tablet and bought the scope used but if I had to replicate this setup, I could do it with all new stuff for under $300.
-The 1008C scope is on Amazon right now for about $110. Shop around, there may be better prices. I found a lightly used one on the infamous auction site for about $70 and snagged it.
-You can find a new Android tablet for about $100, give or take. My old tablet is practically a doorstop but runs the HScope app just fine so you don't need anything very high-end. I also have HScope running on a Kindle Fire (which takes some doing, as Kindles don't ship with the Google Play store) and also on my phone.
-There is a free version of the HScope app but to get all the channels and functionality you need to pay. Each license you buy (about $14 apiece) enables it for a particular oscilloscope type. I bought licenses for the Hantek 1008C and the Hantek 6022BL because those are the two USB scopes available to me. I may eventually build one of the ultra-compact scopes based on the STM32 board, at which time I'll have to buy another license. I wish I hadn't bought the 6022BL scope OR license, but too late now.
-You're also going to want to buy the HScope automotive module add-on, which is $12 or so. It adds data recording and analysis features (cylinder overlay, etc.). It's pretty useful and I recommend it for automotive work. There are audio and digital modules available but I've never used them so can't comment.
-You'll need a USB OTG adapter. I think mine was $12 on Amazon. Do a bit of research on Martin Loren's HScope website (
http://hscope.martinloren.com/) because some work better than others.
-Some scopes also require an external USB charger/battery bank but the 1008C does not. It gets its power from the tablet's USB port.
-The 1008C comes with BNC-to-alligator cables (but no scope probes) and I think a HV secondary ignition clamp. If you want actual scope probes, I've bought generic ones on Amazon for $14/pair. Search for P6100 oscilloscope probe. They are inexpensive but are fine for just about anything automotive. Then again, you may find that the alligator clip leads work fine for what you want to do.
-A pair of 20:1 attenuators (useful if you want to tame the inductive kick of a fuel injector or relay coil) are available for about $20. Look for Hantek HT-201 on Amazon.
-You'll probably want a tablet case of some kind and most likely a screen protector.
So $220ish for the scope and tablet, another $25 for the app, and maybe another $40 for a case and an OTG adapter gets you a decent automotive scope package for a little less than $300, or right around $300 if you need scope probes or attenuators. If you already have an Android tablet you might get this done for less than $200.
For that money you won't quite have a PicoScope, but you'll have a pretty capable automotive oscilloscope that's a little more portable than a laptop-based device. I find mine very useful for automotive work.