Vortec 7.4 rough idle

[Supercharged111]

No, the truck will idle around 15-20 degrees BTDC.

 

[Seannn92]

Seems to be where it's idling then. I'll try to re-stab it one more time. It really has me scratching my head. I hope it didn't jump time or something chaotic like that. It only has 80k on it so hard to believe if that was the case.

 

[Seannn92]

I did a fuel pressure check at the rail. Clamped off return line and it read above 90 psi with key on. Bad regulator?

 

[454cid]

I did a fuel pressure check at the rail. Clamped off return line and it read above 90 psi with key on. Bad regulator?

Why would you think the regulator is bad? By clamping off the return line you unregulated it.... 90 is where mine went when I did that. Don't do that for long because it can break the regulator according to what I read at the time.

 

[Seannn92]

I followed the service manual procedure. Said to shut off return line and recheck pressure. If above specified amount (55-65 psi) regulator is bad. I got over 90 psi. I’ve replaced the regulator awhile back so I’m skeptical it’s bad.

 

[454cid]

I followed the service manual procedure. Said to shut off return line and recheck pressure. If above specified amount (55-65 psi) regulator is bad. I got over 90 psi. I’ve replaced the regulator awhile back so I’m skeptical it’s bad.

Interesting. I don't know then. Maybe I'm misunderstanding how the system works. I thought the extra fuel/pressure got shunted to the return line to maintain the proper pressure.

 

[Seannn92]

From what I gather the spring inside the regulator is controlled by vacuum. At idle you have vacuum which opens the flow to return line. Under load there’s no vacuum, return is closed and pressure should be slightly higher. After cycling the key without starting, I get 62ish psi then it drops back to zero almost immediately after the key is turned off. Regulator should be closed as no vacuum is present with key on. Am I crazy or on to something here? I realize my issue started with my distributor blowout but the truck wasn’t running too great leading up to it. Idled okay but strange things like almost stalling coming to a hard stop when cold, harder starts (never started great to begin with) and lacking power.

 

[454cid]

From what I gather the spring inside the regulator is controlled by vacuum. At idle you have vacuum which opens the flow to return line. Under load there’s no vacuum, return is closed and pressure should be slightly higher. After cycling the key without starting, I get 62ish psi then it drops back to zero almost immediately after the key is turned off. Regulator should be closed as no vacuum is present with key on. Am I crazy or on to something here? I realize my issue started with my distributor blowout but the truck wasn’t running too great leading up to it. Idled okay but strange things like almost stalling coming to a hard stop when cold, harder starts (never started great to begin with) and lacking power.

The fuel pressure should not be dropping right away. It could be the regulator, or the check valve in the pump.

 

[Seannn92]

The regulator responded to the vacuum line being disconnected so I’m gonna say it’s good. When I clamped off return line pressure stayed when I shut the key off so it has to be leaking down the return line. Either way I doubt that’s my misfire problem. I tried stabbing the distributor again still no luck on the idle. I guess it’s time to check the plugs and compression...

 

[Seannn92]

Checked compression, all cylinders 150 lbs. But spark plugs badly fouled. Gas residue on threads and about 6 plugs were only finger tight. (The previous owner changed the plugs, bright individual.) anyways, looks like I’m gonna need new plugs and wires. I’m guessing the timing is still off (pre-ignition looking plugs) but would the short amount of time it ran with the distributor in wrong foul the plugs that quickly??

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