96 xj MAP sensor issue

So a buddy of mine bought a 96 Cherokee he got a killer deal on it because it wasn't running. It had a bad fuel pump so we replaced that and also discovered a bad distributor and bad coil so we replaced them. And now we can't get it to start and stay running it will start and run and then die in 10-15 seconds it sounds like it floods out and backfires through the air box. It isn't throwing any codes but after inspecting the live data stream from my code reader when just setting there it's only reading 7.4hg so we replaced the senor but it's still reading the same also if you unplug the sensor it doesn't throw any codes but reads 9.4hg.
I'm completely puzzled any ideas?

If you're only getting 7.4 at the test port on the intake, you've got a huge leak. My 96 reads a steady 18-19hg at that port. Or do you mean the value at the MAP, not eh intake test port

Get a vacuum pump and test every single vacuum line manually until you find the one not connected or broken. Put old working OE map sensor back in until you've fixed all the vacuum leaks and then only replace if you find it really is the cause. You could be leaking from a break in the hard lines or at the connectors. The rubber for the connectors gets brittle after 20 years.

So could it be a vacuum issue if that's the reading with the motor off? Also I'm getting my reader from my bosh OBD code reader

It takes ten minutes to do. Using a vacuum pump is also the proper way to test the map sensor.

Do what I did. Tape up all the lines with electrical tape. see if issue is fixed.
While taping up lines. make a note of the broken ones. to replace and go from there.
or get fuel line. and press it over any breaks to connect the pieces as a temp fix.
Thats what I did.
And half my lines were cracked badly.

What kind of vacumm pump?

A cheap mityvac that you can get at any auto store and probably even walmart will do. You pump it to about 20 in hg and if it leaks down, you need to check the line and fittings. Replacement sets of vacuum lines are available as well if you want to just replace them all.