I had to replace the injectors on a friends 91 lb9 the other day. The car has new life. But I noticed that when the car is nice and warm it doesn't want to start/catch very well. I can turn the key and the engine spins faster and faster until it fires. I guess you could say it's almost reluctant to start. Once it does start it doesn't display any of the characteristics of being even slightly flooded which ruled out leaky injectors on the new ones. I checked vacuum at idle and it came out to 18. I tried checking the fuel pressure but it looks like her schrader is trash. I can't get a reading at all on the fuel pressure tester.
I applied vacuum to the regulator to the tune of 15 and it ever so slightly dropped .25 after 5 minutes. That looks good to me.
Next I'm going to try checking electrical.
Do you guys have any ideas that can point me in the right direction?

One other interesting fact, I had her car in my garage for 3 days before I even started working on it. When I went to open her gas cap I found that the tank was still pressurized. Not sure if it was vacuum or positive pressure. Ideas?

 

Sounds like a head gasket may be involved. It may need replacing. Make sure the head isn't warped.

 

It would be nice to get a fuel pressure reading. The Schrader is replaceable, but I'm not sure what the lower thread is on the fuel rail.

Since the '91s don't have the cold start injector, they rely even more on an accurate CTS reading. You may want to check the CTS resistance at a know temperature.

 

Do you hear the fuel pump come on when the key is turned to "run" (without starting eng) ?
The fuel pump relay is supposed to run the pump when the key is turned to "run".


If your not hearing the pump, then you'll have to crank long enough to build up oil press. Once oil pressure is sufficient, the oil pressure switch will provide power to the pump.

 

I hope it's not a head gasket. I guess I can check into that if nothing else seems to be the problem.
Haven't checked the CTS yet. Thanks for the suggestion.
The fuel pump does prime when the key is turned to the on position.

I'm leaning towards something electrical being the problem. I guess it's time to get out the DMM.