Trouble codes on 88 740 turbo
 

I'm so confused by the nomenclature of the different fuel systems, etc. I'm not sure if I can check codes at all?? I don't have that 6 pin connector, but there's somehing on my valve cover that looks like something?

That's to plug in a dwell meter. Your car being a 1988 740 Turbo is LH2.2 fuel injection with EZK117 ignition. It's identical to my car (unless it's a European spec car, which I would guess that it's not, since I'm guessing that you are in the US). In 1988 Volvo started putting in those diagnostic systems on LH2.4 cars. But the LH2.2 system continued in turbo cars until 1990. So 88 and 89 turbo Volvos had LH2.2 and unfortunately no on board diagnostic system. A good multimeter is your best friend. In a few cases you can make a test LED, for some other things. Also, a good manual will help you to test things. I have the Volvo Green Books on LH2.2 and EZK117 as do a few other members, so the info is out there when you need it. Your engine should also have a 'k' on the engine sticker on the timing belt cover. It means you have larger diameter main bearings, the thrust bearings are in the the back of the crank and the block has a l more internal webbing in the casting to make it a bit stronger than the original B230FT engine introduced in 1985. It also means that you have the larger Mitsubishi turbo: TD05-12B. That's a little more than you asked for, but you may find it interesting.

that is interesting, I appreciate it.

Engine and OBD Diagnostic Codes

I found this, scroll to the very bottom.

Have you tried this before??

I haven't tried it because I haven't really needed to yet, but I made up a test LED so I can. I've used it to set the CO content.