Cold start on W motor 1994 Jimmy
 

This truck has been in the family for 18 years and has off and on been driven daily. It has 90k miles now. Last week it suddenly became impossible to start cold, without using starting fluid. Here are the new parts that we installed the last week, some were bad and needed it: cap & rotor, fuel filter, ignition switch, fuel pump relay, oil pressure sensor ( it died when fuel pump relay was pulled, and book said oil pressure sensor).

Once started it runs great. Warm starts like always, but after sitting and cooling off, it stumbles and dies, will do that 2-4 times, then nothing until starting fluid is used.

I have a fuel pressure gauge and know where the connection is, but don't know where the pressure regulator is. I will do that test next. Any other ideas would be appreciated.

ECT - temp sensor for ecm

Changed it. Started once, then back stumble no start 2-4 times, then just cranked.

Latest, decided to check fuel pressure. It was low, but acted funny. So used the tester air bleed off till I got gas. Then, it started right up, multiple times. Now, if it sits all night and starts cold tomorrow, I can quit fighting this thing. So, it's unclear if the ECT was part of the problem since it tried harder to start after it was changed, or if it was all because of an air lock from changing the bad fuel filter. The fuel filter was almost plugged, but I didn't think a return style fuel system would trap air like that.
Tomorrow morning will tell.

Back to not starting, thought we had it figured out. Used starting fluid, starts and runs great. About to have a fire sale.

Found the timing was off by 9 degrees. Now runs smoother than it has in years. But, the cold start problem seems to still be there.

what is the fuel pressure when it cranking with those cold starts? Should be constant/steady 55-61 psi with either KOEO or KOER...

Not sure, the rental gauge I had wasn't reading right. Think I'm going to buy one so I can check it at home. I'm going to try it again this morning, it's 38 degrees outside. If it won't start without the starter fluid, I may just get a pump and install it. I can't imagine anything else stopping it from starting cold. Once it starts, it runs perfect, like it was new.

No, problem may be leaking injectors, regulator or something else internal....if it were fuel pump, it would never run perfect, like it was new.....do you understand now why testing is necessary? The whole reason why you posted here on the forum, right? For help figuring it out.

Well, apparently the rental gauge was reading right. It showed 35-40 psi with key on. If I cycled the key, I could get it up to 50-52 psi, but it took 12-15 times. Installed a new fuel pump. 35 degrees outside, started right up, runs even better.
I don't think anything accept the ignition switch was a waste of time. Everything else I replaced tested bad or was a high percentage of a possible solution. The completely clogged fuel filter probably weakened the fuel pump. Can't say it was fun, cause it wasn't. The new pump,is louder, but not audible inside. Couldn't hear the old one when you keyed on, even with the door open.