Misfire killing my soul

[Dnytro]

Ok so I put my 99 obs Tahoe up for sale after 3 years of flawless ownership for 2 years. Never had an issue, all maintenance done on time, took good care of it. Two days after posting it, it starts to misfire.

Never threw a code but, clearly misfiring.

Sprayed the plug wires in the dark, no sparking.

Changed pcv, hose, and grommet- no change
Changed plugs - no change
New cap and rotor - no change
Wires- no change
Fuel filter - no change

Fuel pressure 50-55 at start, increases when u rev it, holds 50psi when u shut it off for a long time, I stop timing after 30min.

I don’t have a smoke tester but all vacuum hoses look good.

I had never bought a new mpfi bcuz it ran so good, but I figured what else could it be? So I bought a new mpfi-, turns out it already had one! Changed it anyway. No change! Gonna keep the old one for my next obs.

Pulled off the passenger side valve cover, no broken valve springs.

Distributor isn’t loose.

Exhaust temps are all pretty close.

The cat temps are about the same as well.

Soooooooo what the hell?

I have a coil to try, and need to take off driver side valve cover, just ran outta time today.

Thoughts? The misfire doesn’t change no matter the load, rpm or throttle position.

 

[Schurkey]

Connect a scan tool, let the computer tell you which cylinder(s) are misfiring--and how badly.

I thought 50 psi fuel pressure was too low. Maybe that depends on which engine you have.

 

[Joe Dirte]

Connect a scan tool, let the computer tell you which cylinder(s) are misfiring--and how badly.

I thought 50 psi fuel pressure was too low. Maybe that depends on which engine you have.

I have similar issue but my scanner won't read misfires on my 98. Is there a special pid to add?

 

[Dnytro]

Thanks for the response, My mistake. It’s a 5.7 vortec motor. I thought Tahoe’s and Yukons only came with those.

50psi At idle and it increases as u open the throttle. That was parked. I could try and log it under a load of the hose is long enough I guess.

I haven’t found anyone with a good scanner willing to just scan it for me, still working on that.

I looked online and didn’t see anything under $300 for a capable scanner or tech 2 Or clone, any ideas? I Found a great truck to buy but I don’t wana sell mine like this

 

[1997]

did you check out the Actron CP9690? about $250 us.
seems a few of us on here have them.
i'm still figuring mine out but it seems to do pretty much what's needed. (i got it since it does OBD1 and OBD2)

there's the other option of cable, laptop and tuner pro.

 

[0xDEADBEEF]

Try a tank of supreme next time, see if it changes.

My guess is the dizzy gears are worn. Just a guess though.

 

[wirlybird]

Check out the MAF. I know when it starts to go bad on my 97 Tahoe all hell breaks loose.

 

[Schurkey]

I have similar issue but my scanner won't read misfires on my 98. Is there a special pid to add?

Depends on the tool you choose, I guess. The Snap-On MT/MTG 2500 and Solus Pro just "do it".

Dizzy gear, and MAF would also be easy to check with a proper scan tool.

 

[Dnytro]

I couldn’t find a solus pro or mtg 2500 so I bought the actron.

Different gas didn’t help, seafoam didn’t help, and I sprayed the maf too.

 

[Schurkey]

I couldn’t find a solus pro or mtg 2500 so I bought the actron.

So which cylinders are misfiring?

Did you verify the minimum spec for fuel pressure?