Fuel Injection swap, engine sputtering/dying when warm

[maroon1872]

First post, sorry if it isn't in the right place.

I have a 1987 wagon with the 258 that I did a 4.0 head and camshaft swap as well as OBD1 fuel injection, also note I have the hesco crank position sensor kit on the harmonic balancer. I have it running and driving but when the engine gets warm after about 15 minutes, the engine goes from running smooth and strong to missing firing sporadically and it eventually stalls out. I thought it was the fuel boiling over in the new efi fuel line which was resting on the valve cover... unlikely I know, but I put a cooler thermostat in just to be sure, same misfires though... I am going to check the crank sensor spacing next, I think when it heats up the bracket expands from the heat and the spacing is just on the nose and it misses injection pulses. Going to try to re-set the spacing on the bracket next, just wondering if anyone has seen this before.

Also I am not pulling enough vacuum for the brake booster (13" Hg at 6000 ft above sea level) with the new setup.. no vac leaks I am positive, thing runs like a champ until it is warmed up. New booster and master cyl replaced last year, garaged, no harsh conditions. I put the equal length intake manifold on from a 00 cherokee, not sure if that matters. I am considering aux vacuum pump or going hydroboost, any inputs greatly appreciated.

[vangremlin]

It's my understanding that you won't be able to get as much vacuum at higher altitudes. 

This website has some info that may be useful.

https://anver.com/vacuum-lifters/atmospheric-pressure/

[atmafox]

I'm not sure re vacuum in these motors as yet but I can say I get pretty consistent 18-20 inHg here in Boulder County (~5500ft above sea level) on the rest of our motors.  It remains to be seen what I'll get when I eventually do a 258cu+4.0HO head swap.

[eaglefreek]

Could it be from when it goes from open loop to closed loop once it warms up and there is an issue with the oxygen sensor?

[maroon1872]

I'm not sure re vacuum in these motors as yet but I can say I get pretty consistent 18-20 inHg here in Boulder County (~5500ft above sea level) on the rest of our motors.  It remains to be seen what I'll get when I eventually do a 258cu+4.0HO head swap.

I'm actually in Boulder county also, ha! I can certainly answer questions about the head swap, just got her running a few weeks ago and trying to get things sorted for the dreaded advanced emissions test. It's crazy to see that thing on the 4x4 dyno.

I would assume my vac was good (18-20" Hg) before swapping intake mannys because the brakes were wayyyy stronger, too strong. Maybe I have a leaky manifold gasket or bolts too loose, but it doesnt display symptoms of a leak...

[maroon1872]

Could it be from when it goes from open loop to closed loop once it warms up and there is an issue with the oxygen sensor?

Aha. This is exactly what it is, yes thank you for this. O2 sensor is not connected at all. My mid pipe isnt even connected and no sensor port on my headers. Thing sounds mean revving right out of those headers.