Starting After Sitting

Yet another, "It won't start..." questions, but this one seems very strange.

1994 Roadmaster Wagon - Stock LT1 (of course)

A couple weeks ago I swapped in a new front brake caliper. Test drove fine. The next morning, it wouldn't start. Wait - what?? Nooooo.

It cranks just fine (new starter earlier this year). But on that first day, no matter how much I tried and fiddled, it wouldn't start. I pulled the ICM and had AZ check it -- they ran the test 6 times to allow it to heat up. Tested fine, so I put it back in. Finally, later that afternoon, it suddenly caught and ran - surprise!

Ever since then, whenever it sits overnight or all day at work, it takes three or four tries before it fires, then it starts right up and runs great. If I shut it down and restart a while later, like at the store or something, it fires right up. But after sitting for hours it needs three or four tries. Runs great other than this -- no misfiring, no hesitation, nothing.

Clearly, it's getting fuel and spark, except for those first few tries after sitting.

I sure would appreciate some educated ideas about where to look next. I'm afraid one time soon it's NOT going to start on the third or fourth try.

Thanks!

Measure key on priming fuel pressure and report back.

+1 on fuel pressure. Try cycling the key a few times before starting (gives it multiple prime cycles). The fuel system may be bleeding off pressure somewhere. Injector or check valve. There is a check valve in the pump for sure, and I believe there may be an anti siphon valve in the regulator. While testing fuel pressure for a similar issue, I noticed fuel pressure dropped to zero once key was off. I plugged off the regulator return and let the pressure spike to 60 lbs or so, and suddenly problem was fixed. Likely stuck check valve.

Hope that helps somewhat.

Thanks, guys. Turns out it was the fuel pump relay. I replaced it last week and that made no difference. But I spent some time studying the schematic and also tried using the test connection (that little empty plug with the red wire) and decided the relay didn't seem right. I took it back to Autozone and it turns out they sold me the wrong one. Plugged the right one in and problem solved.

I did learn something interesting in the process -- the car will run, just fine without the relay, once it's started. The fuel pump apparently gets power while running from the oil pressure switch -- the relay is only for priming. I was able to start the car with the bad relay, but it took four of five attempts. Apparently, during those attempts, the oil pressure would come up and allow enough power to the pump to eventually get it primed enough to start. I actually pulled the relay, got it started and drove to Autozone with the bad relay in my lap.