Has anyone have this happen?

[90 Silverado]

Hot day driving normal then the truck starts running rough. Got to the station for gas and add some and push on the accelerator and the truck can barely make it home. It surges when idling so I changed out the fuel filter ( which had bits of rubber in it about 5k miles since the last change) If I plug up the map vacuum hose it idles better but still won't accelerate only very light throttle in third gear . Checked it for vacuum leaks, cleaned the throttle body, cleaned the plugs and cap and rotor and by passed the charcoal canister. Just before it happened, there was a alot of pressure in the fuel tank when I took off the cap. This truck is all original with 106k miles. Never had a a problem with it for 8 years. Not sure it is the fuel pump or the the distributor that's acting up. If I park on a slight incline, it's harder to start. It no longer starts right away anymore either. I would just start changing part by part but don't have the funds to do it here since I just got laid off. Only code I get sometimes is too lean.
( 90 Silverado 350 TBi 700r4)

Any suggestions would be appreciated, Doug in P.R.

 

[DerekTheGreat]

That hiss when you take the gas cap off is normal, the evap system is doing it's job.

Is this truck still sporting original intake & TBI gaskets? You could have some leakage, MAP sensor could be on the way out. A scanner would help you see if it's reading right.

 

[90 Silverado]

Tried another good map off my 92 Sunbird, had a little air come out all the time from the tank before but a ton of air when I stopped at the gas station when this all started.

Original gaskets are still on the motor.

Doug in P.R.

 

[DerekTheGreat]

Yeah, you'll notice more hiss after you've been driving but remove the cap within a few minutes. It is supposed to be that way.

If you've got a smoke machine you could try it out on the engine and see where your leak is coming from.

 

[90 Silverado]

Did have smoke come out of the exhaust when starting the truck , looked like oil for a long time . ( Blue)

Oil on the engine side of the EGR valve when I took it out to inspect. Oil sweat around the intake to the cylinder head center bolt area.

Common problem? I thought is was exhaust valve seals which it is on these motor.

Sprayed soapy water everywhere to check for vacuum leaks no change in idle. May try propane.

Doug in P.R.

 

[east302]

Tried another good map off my 92 Sunbird, had a little air come out all the time from the tank before but a ton of air when I stopped at the gas station when this all started.

Original gaskets are still on the motor.

Doug in P.R.

Since the EVAP system is bypassed, there is no place for gasoline vapors in the tank to go except out through the cap when you open it. They quit making vented gasoline tanks back in the 70s or 80s. Instead of venting gas vapor to the atmosphere with a vented tank or cap, it was vented to a charcoal canister and, from there, sent to the intake via a solenoid valve to be burned off.

Unless there is a vent for the vapors you’re going to keep getting that hiss as the vapors expand in the tank. It may also be difficult to fill the tank at times because the dispenser pump nozzle will see it as a tank full of gasoline and shut off.

I don’t know if it has any bearing on your issue, but the pump was likely designed assuming something close to atmospheric pressure in the tank...not a pressurized tank.

A vented gas cap may help, but there’s still the little flapper in the neck to deal with. I suppose it could be removed...careful you don’t create a spark, though.

Sent from my iPhone using Tapatalk

 

[biggbiker]

I would leave the cas cap on loose to vent to see if anything changes.

 

[90 Silverado]

I just eliminated the charcoal canister altogether and put a clear gas filter in between the 2 hoses. ( So it still vents in the TBi so that problem is solved)

Alot of people say they have to change alot of parts to get it run right again, don't have the money to do that, was hoping someone had the same problem so I can narrow it down because this is frustrating as this is our best vehicle. Plus parts are expensive down here.

Doug in P.R .

 

[Doughnuts]

I doubt that the issue has anything to do with your EVAP set up . Have you checked your fuel pressure? Pretty simple way is to hook one up right after the fuel filter, though you do have to climb under and check it . But it's the cheapest and quickest way of checking.

The only reason I mention it, is that it sounds like a pretty typical fuel pump death right there. Especially if you saw bits of rubber in your filter .

 

[90 Silverado]

I was suspicious of this as I read that the hose from the pump to the line in the tank likes to split. I forgot to mention I saw shinny bits in the fuel when I dumped out the filter. I do hear the pump running with the cap off with the engine running. Don't know if they put ethenol safe hoses on vehicles way back in the 90's?

Doug in P.R.