1998 Jimmy "Hard Start"

Ok 98 Jimmy. When it has sat for a while (over night and such) it is very hard to start. Once it starts, it is fine. I'm in Michigan and it has been cold lately which doesn't help. The fuel pump is about 1 year old, the fuel filter about the same. The fuel pressure is right. I replaced the battery and that didn't help. When we changed the oil recently it was very hard to start even though it had been running 15 minutes before. My question is "is there an oil sensor that may not be sensing the oil and is not letting it crank over to save the engine. I'm thinking that when Im cranking it over in the morning the oil has decended back down into the engine, and with the repeated crankings in the morning it brings up enough oil to teh sensor to allow starting"
Is this possible?

Your fuel pump is energized by both a fuel pump relay and an oil pressure switch- so if the relay is bad, there can be an extended period of time, (few seconds) of cranking necessary to build enough oil pressure to make the oil pressure switch.....

So do you hear the fuel pump energize for 2 seconds when you turn ignition on to "run" without starting truck? If so, then the relay is okay. If not- better give it a look.

Of course, fuel pressure test would confirm this- as well as tell you when and hgow long it takes fuel pressure to build- also would be good to know if fuel pressure drops off after fuel pump shuts off- this would indicate a leak somewhere- and if inside plenum, could explain why it takes longer to start- due to the need to clear the flooding...

Well the fuel pressure is not good like I was told. Fuel pressure in the "on" position was about 60, after we started it it dropped down and is bouncing in the 50-55 range. Did not take it on the road. I cannot do a cold start as of right now

also, when you turn it off it goes to 60 and holds pressure

You need 60PSI+ when it is running for it to be running right. If it was an aftermarket pump and not an AC Delco pump it could very well be the issue.

Ignition in RUN position, engine cold and off, fuel pump running, pressure must be 60psi to 66psi. Must remain above 55psi for 3 to 5 minutes after the pump shuts off. GM does not publish ANY engine running fuel pressure specs for the 4.3L, (far too many variables involved).

Old master, does that mean that the fuel pump is ok?

If pressure and leakdown is within the specs as mentioned in post #6, the fuel delivery system is functioning properly.

As far as extended cranking to start.... In post #2 the question was asked, "So do you hear the fuel pump energize for 2 seconds when you turn ignition on to "run" without starting truck?" We can continue diagnosis after we know the answer to that question.

Yes, I do hear the fuel pump turn on and run for 2 seconds when turned to the on position

When the circuits are energized, the fuel pump relay supplies power to the fuel pump directly and immediately. The oil pressure sending unit is secondary in supplying power to the fuel pump. The current for both circuits comes from the same fuse. The oil pressure sending unit is not a safety device that shuts off the fuel pump if oil pressure is low. It is also not designed as a "backup" device in case the fuel pump relay fails, (although, the pump will remain activated if the relay fails). ** When current travels along a wire, it travels down the outside of the wire. The larger the wire diameter, or gauge, the more surface area is available for the current to travel along. A larger wire provides less resistance and more amperage available to the load, in this case, the fuel pump. The reason the oil pressure sending unit circuit is used is two fold: one, is to provide additional amperage to the fuel pump while it's running, and two, it keeps the fuel pump energized for a few seconds after the ignition is shut off. This helps to keep the fuel system pressurized for the next start up.

** If the relay fails, or the circuit to the fuel pump from the relay fails, you could expect extended crank time. The reason is because it takes a few seconds for the engine to build enough oil pressure to satisfy the switch in the oil pressure sending unit. If you're hearing the fuel pump when initially turning the ignition to the RUN position, and it's building proper fuel pressure, that's not the cause of your extended crank time.

Excessive fuel pressure leakdown can cause extended crank time, especially if it's leaking in the plenum. Make sure fuel pressure and leakdown rate is acceptable. When you're experiencing the extended crank time: make sure the pink wire at the ignition coil shows battery voltage when the ignition is in the START position and, that the white with black stripe wire shows a pulsing ground while cranking.

I have a 98 Jimmy that's getting hard starting too. First try of the day, it'll crank for ever (10-15 seconds) if I just keep cranking. But as soon as I turn the key off, and then back on, it'll start right up.

I do not hear the fuel pump run on "key on" position, but I do hear it run when I turn it off.

Is this the relay, and if yes, where is it located on a 98 with CSFI?

Start by checking fuel pressure when key is turned on only, look for about 65 psi. Prior posts have all the necessary info.

So I did that last night. Was about 62-63 on key on, then went to about 60. When after start, stayed about 60, and leak down was to about 56 after a couple minutes.

This morning, I did it again to asure it was a "cold start". This time I went right to cranking. The gauge fluctuated around 50ish, then started and stayed about 60. On key off, I can hear the pump run and pressure goes to 62. Relieved pressure. Again upon start, it fluctuated around 50ish and started.

50 is way too low, either a clogged filter, bad pump or bad regulator/spider assy.

Stricter, more systematic testing this morning

Test 1
Key on - pump ran, pressure went to 62, leak down to 58 after about a minute
On crank - started right up, pressure held around 54 while running
Relieved pressure
Test 2
Same as test 1
Relieve pressure
Test3
Key on - no pump running
On start, pressure was 52 while cranking
Motor started in about 3 seconds of cranking

I always hear the pump run when I turn the key off, but not always on "key on".

Ideas? Thanks for the help.

I replaced the $15 fuel pump relay, but the problem is still intermittant.

I had a problem with my 97 GMC v6 not wanting to start then after starting would run OK untill I wanted to pass someone and it just bogged down.
I changed the spider (fuel injector assy) and it runs great....
The problem just got worse over 6 months of putting up with it. It finally got to the point I have to use starting fluid. I installed the new MFI replacement and that was the ticket.