Random misfire at idle 454 vortec

[elevatorman]

That's gotta get tracked-down and fixed. Valve stem seals? Wiped valve guides? Faulty rings? Sucking oil via PCV or intake gasket leak?


Does it still foul plugs, or is that problem FIXED?


Did you degree the cam, or just cram the parts together "dot-to-dot"?

Did you retest for slack by watching the rotor the same way you did before replacing the timing set?


Punctuation, capitalization, and sentence structure were taught in elementary school. This is more of a paragraph, not a sentence.


Yes.


Doesn't mean it's not leaking.


Seems low.

Also i did install a temporary egr block off before doing timing set with no change egr has been reinstalled

 

[elevatorman]

Small Blocks need the really high pressure. My 454 is a bit lower too. His still might be a bit low, but I would not expect that to be the cause at idle. I also have a misfire that I can hear/feel, but not the PCM. I am going to compare my plug wire routing to the manual, so as to be sure I'm not getting wires inducing spark to each other. I've also got an EVAP solenoid that I think is leaking, which would amount to a vacuum leak, If I understand it's operation correctly.

This should be an interesting thread to follow.

Pull the hose off the evap and plug the port unless its leaking around the base

 

[454cid]

Pull the hose off the evap and plug the port unless its leaking around the base

My preliminary plan was to attach a vacuum gauge. I suspect it's stuck at least partially open, at all times. I've already got a replacement sitting on my desk, waiting for time/weather.

 

[Scooterwrench]

You said it doesn't smoke so I'm thinking your plugs are fuel fouled,not oil fouled. You are going to need to start of with a new set of plugs or at least change out the ones that are fouled.
As shurkey said that's a pretty low IAC count. Either you have a vacuum leak or possibly someone has tampered with the curb idle screw and opened up the plate,may want to check those two possibilities.

 

[elevatorman]

You said it doesn't smoke so I'm thinking your plugs are fuel fouled,not oil fouled. You are going to need to start of with a new set of plugs or at least change out the ones that are fouled.
As shurkey said that's a pretty low IAC count. Either you have a vacuum leak or possibly someone has tampered with the curb idle screw and opened up the plate,may want to check those two possibilities.

It appears the fouling has stopped. Ive found the throttle plate stop screw but im not sure how too make sure its set too factory spec

 

[elevatorman]

Ok so i just got done changing a couple of questionable plugs on bank 1. Rerouted plug wires used 2 different sets of ac delco wires too get the correct lengths. Also adjusted the throttle stop screw down too where it is just touching.
My iac counts are staying at 50 when hot and misfire is more consistent on cylinder 1 8 and 5. When throttle is applied it jumps too all 8 momentarily before clearing out. Im wondering if i need a whole new distributor assembly .

 

[JOHNGAAA1]

New member here and ive got a 97 k3500 454 vortec that has got me stumped i bought the truck about 2 months ago had a very bad idle found the cap was missing a screw fixed that and truck ran hardly any better...
Since then ive found a bad fpr leaking injector replaced with bosch didnt help the idle
Fuel pressure was only getting too 46lb replaced the pump now up to 51 at prime and 47 at idle.
Replaced plugs and wires and after 2 days of running the truck a few were oil fould and fuel trims 25% after **** smoke test observed smoke out of dipstick tube so i replaced the intake gaskets fuel trims did come down some and idles slightly better.
Truck has true duals and ive reomved the cats due too being booger welded in and 2 different sizes.
I recently found 15 degrees of slack in timing chain by watching the rotor so i just replaced the timing chain and sprockets.
Still no change lt bank 1 trim 17% bank 2 10% it has a misfire on cylinder 1 in park at idle tmits not constant if i drop in gear foot on brake misfire moves too 6 of 8 cylinders and gets more frequent i know this has too be the cause of my high fuel trims but im stumped distributor has been inspected no play in bushing gear is good cam retard is 0degrees at 1200 rpm.
Im using a tech 2 tool all sensors are working. Truck has never thrown a code except for post 02 heaters. Also truck runs very well cruising fuel trims fall back too normal. Grounds have been cleaned and some replaced.
Compression 150ish all cylinders. Also does not smoke

In all this I do not see that you changed the fuel pressure regulator. This a notorious problem for the vortec 454. This will give you a black spark plug, poor idle, and hard start.

 

[elevatorman]

In all this I do not see that you changed the fuel pressure regulator. This a notorious problem for the vortec 454. This will give you a black spark plug, poor idle, and hard start.

First thing replaced

 

[elevatorman]

Im taking a step back and trying too go through the wiring. Having a hard time finding a descent wiring diagram.
A little more back story couple weeks ago i was cleaning the grounds at thermostat housing and noticed a large ball of electrical tape around the wiring too map sensor. There were 2 small resistors twisted inline to the map (terrible attempt at making connections) i did remove these unsure of the purpose.
Ive recently noticed the computer has been swapped with a blue streak which i believe too be oreillys brand. Hardly make out the label definitely been there a while.

 

[Blazerbiker]

We chased a random multiple misfire at one point and the culprit ended up being a new-ish cap. It was crossfiring in the cap itself. They're cheap enough that it might be worth trying that. This is where it would be nice to be able to check the plug wires to make sure they're actually firing at the right time and with the right energy. I'm sure that's possible but I don't know how.