Vortec 7.4 rough idle

[Seannn92]

Hey guys, hoping to pick your brains on a rough idle issue I’m having with my 97 GMC 2500 pickup, 454, 80k miles. Long story short, I had a blow out towing my 30ft travel trailer a few weeks ago. Engine died pulling a hill, no restart. Upon diagnosing, I found the pin gear on the dizzy stripped out/broke. Replaced it and then I was getting no spark at plugs and only one spark from the coil. Finally traced the no spark/one spark issue back to the crank sensor. It strangely worked once when you cranked it over then nothing after that. Replaced it and it fired right up. Now it idles rough below 1000 rpms like a vacuum leak somewhere. Struggles to stay running at a stop light then kinda hesitates when I give it gas to get going. Also, kinda rich smelling when it idles. Runs like a champ driving on the road above 1000 rpm. Everything seems to check out fine, no codes, dizzy in correctly, just very poor idle. I haven’t started the shake down of the EGR, IAC, etc but plan to today. What really has me stumped is no cel or codes? Also, since the cam sensor and crank sensor have both been replaced (new cam sensor with the new dizzy) is the issue with the new crank sensor needing to be relearned? Then again, no codes or cel. Any thoughts??? New parts replaced within the last two years: fuel pump and filter, fuel regulator, Bosch injectors, egr pipe, plugs and wires.

 

[Supercharged111]

You need to do a crank relearn and how did you set the new distributor? What distributor did you end up buying? Chinese junk could be the cause here as well.

 

[Seannn92]

Spectra oem distributor. I could try putting a new gear on the old one and see if there’s a difference but I doubt it. Would a code be thrown if the crank sensor needed to be relearned?

 

[Seannn92]

Set the distributor with proper procedure. TDC on #1, fired right up no cmp code so must be within 2 degrees of spec.

 

[454cid]

Set the distributor with proper procedure. TDC on #1, fired right up no cmp code so must be within 2 degrees of spec.

NO.... the code doesn't set until it's 20-something out. My truck ran fine when it was 7 degrees.

 

[Supercharged111]

Mine ran fine 30 degrees out and yes, a crank relearn is required for a new crank sensor.

 

[Seannn92]

I’ve had the old distributor out before when I changed the fuel rail a few years ago. Installed it wrong and it gave me the code for cam correlation upon initial start up.

 

[Supercharged111]

Without a scanner there's no way in hell you're at +/-2 degrees. I've guessed as close as 11, but if all you did before this started was change out a distributor that's where my focus would be.

 

[Seannn92]

Without a scanner there's no way in hell you're at +/-2 degrees. I've guessed as close as 11, but if all you did before this started was change out a distributor that's where my focus would be.

I agree it needs to be set with a scanner to get perfect spec. Just seems odd it would idle rough and not throw the cam code if it was causing the issue.

 

[Supercharged111]

You can unplug the cam sensor and run without it. Truck will batch fire the injectors and run just fine. Good way to eliminate that.