I am having a slight miss at idle and in the low rpms. I changed the opti, wires, coil, Icm and plugs; so I know it's not ignition related. Now for the fuel system I have a walbro 255lph pump, I checked the injectors, fuel pressure regulator and changed the fuel filter. I even had the car dyno tuned and the tuner could not fix it totally. When the tuner put propane gas down the intake the idle cleared up and ran as smooth as glass; he changed the fuel at Idle and it cleaned it up a lot, but not totally. I was thinking of buying a adjustable fuel pressure regulator, but I don't know if it will fix my problem or not. Can someone give me some imput on this? Thanks

 

Just because the ignition parts are new doesn't mean it can't be ignition related. Faulty connections or loose/exposed wiring can cause an intermittent miss.

An AFPR won't fix your problem.

 

The ignition parts have been changed more than twice and it did not make a difference. First I had msd wires, GM opti with autolite spark plugs. Second I had a autozone opti with MSD cap and rotor, msd wires and ngk plugs. Now I have a MSD opti with, autozone wires, and ngk plugs. All of these setups had the same miss. The coil was changed twice as well as the ICM. I am just about 100% sure that the ignition system is not my problem.

 

what are the results of your compression and leakdown tests

 

Maybe you didn't read my post.

Just because the ignition parts are new doesn't mean it can't be ignition related. Faulty connections or loose/exposed wiring can cause an intermittent miss.

And I should also point out that Autozone and MSD optisparks are utter crap.

 

did you gap the plugs?

 

I feel your pain and agree with Ramair it is most likely ignition. I would check on: the coil wire arcing to near metal; The harness that connects the opti to the ECM is often the culprit... Any wire that is not properly clicked in can cause intermitant misses. You can have all these tested by a pro and find out what the problem is.This GM harness is about 13 inches long and over priced by GM .... the end eletrode has been known to cause this kind of miss... the Opti itself, can have some odd part not working no matter what you do to the wires. Often when the problem persists like yours has in spite of the many changes, it is the opti. Yours is an off brand and they are known to fail. The GM unit is over priced but is trhe most reliable. After market optis are frought with problems and yet have the same guarantee as the OEM unit. The opti is a weak point on the LT1. This is a maddening problem for OB1 owners

 

How did you "check" the fuel injectors?

 

They were flow tested by the guy that did my dyno tune.

 

I ended up pulling my headers to get to a couple of the cylinders only to find that they are all fine. The car is not really running that bad; most people don't even notice it. But it has a little bit of a shake at idle and light throttle; it's aggravating.

 

If it is an ignition problem would putting gas down the intake filter clear it up? Because when I put gas down the ram air filter the car runs really well; it runs as smooth as glass.

 

not usually, adding fuel would indicate an issue with the fuel system, and i highly do not recommend "putting gas down the intake"

what is your fuel pressure reading at idle, and at idle with the vacuum line disconnected?

what plugs are you running and what are they gapped at?

 

Yes I know it was not a smart Idea; my dyno tuner did this and I tried it at home. I will not be doing this any more, but it makes the car run really good; almost makes me want to mount a gas tank under the hood. I have not checked the fuel pressure in some time, but I remember it was fine when it was tuned. I will check it tomorrow so I can get the exact numbers. This did start after my stock pump went out and I replaced it with a wabro 255lph pump. I put the pump into the stock plastic mounting box; don't know if that makes a difference. Plug gap is .040".

 

Check the fuel pressure to see if it drops off quickly when the pump shuts off. May indicate a leaking injector. Might not have been picked up with a flow test.

 

Aww dang... I have a very similar problem, but I don't want to go through hell and back trying to diagnose it like Henry is. Henry, do you also get shake at light gas and low RPMs, such as when accelerating at 50mph at about 1500 RPMs, etc?