4.3 no start when damp

[imp68m22]

I have been reading posts on the forum for some time to help resolve some problems and for just general knowledge, but this is my first post.

 

I need some help with an odd problem. I did a search but could not find anything that quite covered my problem.

 

First the truck in question: '93 GMC Jimmy, 4.3 with CPI, automatic. It has around 255k miles, 50k of that on a rebuilt long block.

 

Problem is that when it is damp, usually in the morning when there is a moderate to heavy dew, it will not start. It will crank, but not start. Later in the day when things have dried out, it starts right away.

 

I installed a fuel pressure guage and found that (when it won't start) when I turn on the key, the fuel pressure comes up to 55 psi, when the pump shuts off, the pressure drops quickly to around 30 psi. Later in the day, I check it, and pressure comes up to 55 psi, and stays there when the pump shuts off. It will then start right up, and fuel pressure while running stays around 50-60 psi.

 

The injector spider has been replaced along with the 'nut kit' and the fuel pump was replaced about a year ago. The fuel filter has been replaced recently.

 

It seems to be an electrical or fuel pressure regulator type problem, but since it is tied to the morning moisture, and works fine later in the day, I am stumped!

 

Any help or advice would be appreciated.

[Wingnut]

Distributor cap and rotor would be my first guess.

[imp68m22]

Distributor cap and rotor would be my first guess.

 

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I checked the cap and rotor when I removed the distributor module, re-greased it, and re-installed it.

 

I am concentrating more on the fuel pressure problem as that seems to be where the root cause of the problem is.

[Stocklook]

I'm with Wingnut on the Dist/cap,

 

But also try this get a sealed drop lite or be VERY careful using a bulb type and hold it next to NOT touching the fuel reg to heat it up a bit and try to start it, REMOVE the lite before you do this. you may have a cracked O ring seal, when it warms up it will expan and seal properly

 

Hope this will help

[imp68m22]

I replaced the cap and rotor today. Before I did, I tried starting it, it started right off. It had been raining all day yesterday, and was still cold today. After I replaced the cap and rotor, it would not start again. After waiting about 45 minutes, I tried again, and it finally started. I let it run for a couple of minutes and tried to restart, no go.

 

For the regulator o-ring test, isn't that part of the fuel injector inside the intake? If it is, I am not sure how I would be able to start the engine with the intake apart. Let me know where the regulator is so I can test the o-ring seal. I have not had the intake apart for about a year, but plan to open it up next weekend or so.

[Stocklook]

I think it is behind the TB on top it will have the fuel lines going to it. it has been a wile, it should be the size of a c size battery

 

maybe someone can else can chime in and help with this

[imp68m22]

The engine is the "W" code 4.3 vortec. I think the fuel pressure regulator in inside the intake manifold, part of the CPI injector unit. Let me know if the regulator is located elsewhere.

[josephm]

I have a 2000 sierra with the exact same problem. It is also the 4.3 "w". After new cap, wires, fuel pump ans ignition module I am still having this problem. It has been over a year now and I am really getting fed up. Anyone ?