Starting Problem after sitting

[sawmkw]

It seems that my 96 does not want to start after sitting a few days outside and humidity also seems to affect it. It cranks and cranks and occassionally has a little "bump" like it wants to start but doesn't. I have searched the posts and done everything I can think of. If I start it every day there doesn't seem to be a problem. Fuel pressure is good, measured at the port but I have also turned on the key and waited 20 seconds or so with no change in behavior.

Last time it wouldn't start I got out the tools, hooked up the fuel pressure gauge, took out a plug to check spark and had the wife turn it over. It started on 7 cylinders. Turned it off, put the plug back in and it's fine till I let it sit for a few days again. I have 280K miles on this vortec and it usually runs pretty decent. The oil looks good too, no head leaks at this time.

Any ideas?

 

[gpracer1]

I would try these two simple things that are both easy and free.

Wait three days and :

Turn key on, but not crank, turn off.
Do this 2 or three more times and make sure you hear the fuel pump.
Then try to start it and see what happens.

and,

Before crankning, floor the gas pedal and leave it there while cranking. If it starts, let off the pedal (obviously).


These two tests will tell if your truck is either starving for fuel or flooded, then you go from there.

If neither changes, it could be a spark issue.

 

[SunlitComet]

What is the pressure you are getting and under what engine conditions are are you checking? Off, after sitting, idle, etc.? also check you cap and rotor for build up of moisture, corrosion or pitting of terminal inside of them.

 

[sawmkw]

More Info

I once again took out a plug to check spark and had the wife turn it over. It sparked but also looked wet around the base of the plug. I sprayed starting fluid down the throat but it still would not start although it chugs once or twice when I let off the key. It feels like the timing is way off.

---------- Post added at 12:18 PM ---------- Previous post was at 12:15 PM ----------

I am getting 62 with the key and pump on. It drops to 59 when started at an idle. I had the fuel pump replace about 3 years ago buy a local shop. I'm guessing that they did not put the best replacement on...

What is the pressure you are getting and under what engine conditions are are you checking? Off, after sitting, idle, etc.? also check you cap and rotor for build up of moisture, corrosion or pitting of terminal inside of them.

 

[SunlitComet]

Your pump sound great actually. Can I use assume you mean wet with fuel? or wet from something else?

 

[gpracer1]

If it is wet around the base of the plug.....I assume with fuel, then the spider injection assembly may be leaking over time which is causing it to be flooded after it sits. Try the wide open throttle at start ( it cuts the fuel off).

 

[sawmkw]

Your pump sound great actually. Can I use assume you mean wet with fuel? or wet from something else?

yes, it was wet with fuel. I did a compression check as well and have a couple of cylinder that are a bit lower than the others, about 20%. I also changed the plugs and snugged up all the air hoses and it started right up. It has been a while on these plugs or maybe the ECM dried out. I'll let it sit a while and see if it has the same problem and then try the WOT.

Thanks all.

 

[SunlitComet]

If you can peek down the throttle body see if you see gas puddling.

 

[sawmkw]

Same problem, different day.

Try the wide open throttle at start ( it cuts the fuel off).

So I have been driving the Tahoe every day for a week now and it has always started right up. Last night I parked it at 8pm and this morning it was back to doing the old "turn over fine and chug a bit" trick but not starting. Today it is snowing and so it is very humid. I also am running on a tank of premimum fuel in the hopes that it might clean things up a bit. I did try the WOT and nothing, not even a chug. I'm wondering if the coil is weak as the fuel pressure is good and it has new plugs. I guess the injectors could be leaking as well but the WOT had no effect. I had thought it was related to humidity but two days ago it rained all day and it started right up and ran fine all day. Any idea what I can check now?

 

[gpracer1]

Hard one to diagnose over the internet, but if it is not the fuel pump or pressure issue, then I would start by checking all grounds for corrosion.....I mean all the ones there are in the book/schematic G102, G103 etc etc.

Also just do a visual of the harnesses to the coil, crank position sensor, distributor and anything you can think of or see.
May be a crank sensor going out.