P0300 Misfire in all cylinders 2001 Tahoe

[OR VietVet]

Oil pressure sender.

 

[Fless]

^^^^ This. Connector & pigtail available at RockAuto:

 

[Nicolai8775]

Now I

You might do yourself well by replacing the can and crank sensors and make sure all wiring is intact. make sure when you plug wiring back in that the wire stays encased in the connector tab and does not push out of the connector.

Now why would I not get a code if these were malfunctioning?? I just don't like throwing parts and money at it at this point. Summit suggested o2 sensors but those aren't cheap.

Should I get thicker plug wires? I'm guessing I got the cheapest plug wire oreillys had, wasn't thinking about it.

Here is something else I've noticed, not sure if it's relevant. It only misfires at idle. Or at least torque is not logging any misfires under load. It also starts and idles great for maybe 30 seconds and THEN starts misfiring.

 

[OR VietVet]

I believe that it could be related to the injectors. What rpm does it idle at?

 

[BoxChevy216]

When I had that code, it was unfortunately a collapsed lifter.

 

[Nicolai8775]

I believe that it could be related to the injectors. What rpm does it idle at?

Well I fiddled with the set screw on the throttle body. I'm running stock TB with an adapter for now because the 92mm TB I had gave me TPS codes. So before it would jump around between 640 and 740. Now it's around 800-850.

 

[Nicolai8775]

When I had that code, it was unfortunately a collapsed lifter.

I hope not... I just replaced those too lol

 

[Mike Shockey]

On 01 the oil pressure and cam sensor are close to each other. Your truck will run with cam sensor not reading. It is just for reference that it and crank are reading tdc together. May run fine may not. With out getting that code I would think it's fine. You can run without a guide on your timing chain. I run them because heavy springs stretch a chain a little faster and the guide helps with chain deflection. If you put the gears on wrong you would know it would spin alot before it started or be hard to start. Next time just line them up together. Cam at 6 crank at 12. It makes it super easy. And because your not stabing a distributor it doesn't matter. 58 lbs is what you need to run the injector correctly.theres a 5 lb. + or - in there. Your pressure is fine. Your pump is fine you don't need a bigger one.
I like to play mechanic with a simple rule. You've heard of kiss( keep it simple stupid). If you have a miss fire look at your plugs not black look at wires if there no factory spec or better change them. Cheap autozone might work on hei not ls. They might even work on stock ls. Just not performance get the delco or 8.8 or 10mm. Non of them are that expensive and way easier then digging back in to motor.
Good luck

 

[Mike Shockey]

Oh and stop playing with screw on the side of the throttle body. It's not for idle. That is set in your tune.

 

[ks03]

Vacuum gauge?

How are your fuel trims at idle, and just above when it’s not missing? O2s showing anything unusual?

do you have a fuel pressure regulator that could be dumping through the vacuum line?

 

[Nicolai8775]

I got some AC Delco wires and they didn't help any. Tested everything on the intake, when I got to the IAC, I found that if I unplug it after I start the motor, there are no misfires on torque and it sounds great!

 

[Tonyrodz]

I got some AC Delco wires and they didn't help any. Tested everything on the intake, when I got to the IAC, I found that if I unplug it after I start the motor, there are no misfires on torque and it sounds great!

Might be bad. I have a bad iac on my van, which is dbc. Unfortunately they don't sell the correct iac by itself, and GM only sells the complete tb assembly, not just the iac.

 

[Nicolai8775]

Might be bad. I have a bad iac on my van, which is dbc. Unfortunately they don't sell the correct iac by itself, and GM only sells the complete tb assembly, not just the iac.

Might be braving a trip in the 10° weather to the salvage yard to grab an assortment of IAC sensors lol. Otherwise advance Auto has one in stock for like $150

 

[Tonyrodz]

Might be braving a trip in the 10° weather to the salvage yard to grab an assortment of IAC sensors lol. Otherwise advance Auto has one in stock for like $150

I tried there and they didn't show they even carried it in stock.

 

[Steve A]

Might be braving a trip in the 10° weather to the salvage yard to grab an assortment of IAC sensors lol. Otherwise advance Auto has one in stock for like $150

https://www.rockauto.com/en/catalog...,fuel+&+air,idle+air+control+(iac)+valve,6072

Will this one work?

 

[Nicolai8775]

Well here's the thing. It's still misfiring after I cleaned the TB and put a new IAC in. But I can still unplug the IAC right after a cold start and it will idle fine. What could be causing this?

 

[cam3439]

That I know of - if the tune was set with a vacuum leak, the tune will need to be redone. The same goes for throttle body sizes - if you adjusted the size then the tune will need to be updated to compensate.

Also, have you checked your MAF sensor? Clean the sensor with MAF sensor cleaner.

Are you able to check your fuel trims? They can be a useful tool. Like KS03 said, a leaking fuel pressure regulator can cause issues. Have you tested fuel pressure when the truck is off? Does it maintain pressure, or do you see the fuel pressure dropping?

If you unplugged the throttle body, you may need to do an idle relearn on the truck.

 

[Nicolai8775]

Well as Mike Shockey said, don't mess with the set screw. This was my first major project like this and I learned a lot lol. For some reason it wasn't clicking for me that opening the throttle by the set screw is giving it more air, but also telling the TPS it has moved and it needs more fuel etc... I thought the tiny little hole drilled into the throttle plate was good enough... Turns out I had to lower the set screw and make the hole bigger. I still need to make some adjustments because I have P0507 now, higher than expected RPM detected in IAC.

The tuner said he only saw a small leak, and the tune was "good to go" so he must not be worried about it.

I also did the scan cable tune with the stock TB on so hopefully I'm ok there. If not, I'm looking into picking up some electric fans from an 05-06 this week and I think I need a tune to make that work with the PCM anyways.

 

[Nicolai8775]

Well now I have a TPS P0122 code AND the P0507.

All I did was attempt to relearn the TPS by unplugging it after adjusting the screw down and drill a bigger hole in the blade.