I have a 95 GMC Jimmy, 4.3L 4x4 with almost 200k on it. Have been having rough cold starts and have deduced from research that it is a leaky injector, a bad fuel pressure regulator, or a bad fuel pump check valve. Warm starts are always ok. I borrowed a pressure kit from the parts store and had 60PSI on key turn (no engine). Engine idles with 54PSI running. After engine is off, at 10 minutes it is down to 40PSI, 1 hour to 30PSI, and 2 hours to 20PSI. I replaced spark plugs because it needed it anyway and that did seam to help for awhile, but the problem is now back. I have had times where it will start right up, and others where it will not start until the second crank. Can anyone deduce the issue from this data or is another test needed? Thanks much...

 

It does also seam to run fine for the most part. I have noticed that at the first stop sign after the cold start, it does hesitate a little bit (lack of power). After that, it seams to run fine.

 

I sort of doubt that pressure is your problem but it cant hurt to make SURE. A leaky injector can usually be found by reading your spark plugs
Start with building the adapter needed to test deadhead pressure at the filter.

Since you borrow the one you use from the parts store, a better method might be to buy a 100lb gauge for ten bucks at Lowes plumbing dept and make an adapter to fuel line.

Of course once you have those pieces you can start gather other items for your own test gauge.

 

Morning update:
I primed the system once this morning and heard fuel pump come on for 2 seconds. I tried priming a second time and nothing. Third try, the pump was on for maybe 0.25 seconds and then turned off. Fourth prime was a full 2 seconds again. Started engine just fine after that. Should this be happening? WIll the pump not run if a pressure is met or is there a possible problem with the pump relay circuit?

Thanks for the response pettyfog. If I do the test you are talking about, what should I expect to see if the check valve in the pump is ok? Should it hold 55PSI for hours or would it leak at the rate that I described above?

 

on the deadend it will probably hold quite a while. The diy section has a writeup, here:
https://blazerforum.com/forum/tech-a...agnosis-23038/

I cant help you with the relay problem.. I only have 99 diagrams... way different

However you should have the oil pressure switch setup {block, next to dist} with three wires, Assuming same color conventions as other setup such as S15, then the gray wire {opposed to org and tan/white} should be connected to the FP relay output. That is you should see 12v on it whenever relay is on. Once the engine runs then the oil press switch closes and supplies the FP power from the orange wire.

The tan/white is the oil gauge from the gnd of engine block

 

The link is for 1996 & newer CSFI systems. Testing procedures are similar, but components and specs are different from your 1995 CMFI.

Key on, engine off, pump running, pressure must be 55psi to 61psi and must remain above 50psi for 10 minutes after the pump shuts off.

Maximum pump pressure, (dead end) should be ~100psi and remain above 50psi for 10 minutes after the pump shuts off. If it drops below 50psi like your previous test, there's a leak in the tank. If it remains above 50psi, the leak is in the plenum.

Your 1995 is equipped with the oil pressure sender circuit. As pettyfog mentioned, it is an additional circuit for current to flow through, (to the pump) only when oil pressure is above ~7psi. If oil pressure drops below ~7psi, the fuel pump will still be activated by the fuel pump relay, and the pump will continue to run. In other words, if oil pressure drops to zero, the oil pressure sending unit will not shut the fuel pump off.