Miss at 5 PSI

[granatl]

I've been reading other posts about people having a miss; so I followed the advice and put on a new Coil Pack + Ignition Module and then a new TPS.
The ignition module gave a slightly smoother idle.
The coil pack seemed to help with some mid-range knock I had.
The TPS took away the knock altogether???? Which of course really surprises me. (.42 at idle, 4.76 WOT)

I like what I've gained, but I still haven't solved the problem I set out to fix. At around 5 psi (part throttle) the car feels like it's missing. It pulsates.

Looking at Direct Scan, everything looks fantastic. All BLM's within 10% of 128 (no vacuum leaks, fuel pressure is good, etc.).
I do have the original MAF, but my numbers look clean from it.
Any ideas?

 

[Lee_Burough]

I fixed a problem similar to that with a set of plugs and wires....Do you have a MAF to switch out and try?

 

[Eric Stage I]

What do your O2's look like during the pulsating? You should be in PE at 5psi.


Regards,
Eric

 

[granatl]

Plug wires are 4 month old Accel 8.5MM cores. The problem pre-dates the wires + plugs.

I don't have a MAF immediately available, but I could probably borrow one from someone locally.

O2 sensor is roughly 4 months old Delco one-wire that has never seen leaded gas. O2 values are 835-890 range during 5 psi, and around 890 with MAF pegged in 1st gear.

Looking at where I got on it, the RPM has a nice clean climb. On the ~5 PSI one, I can see at the initial climbing edge where the RPM drops 200 RPM; this makes me think that I've got too much fuel in my chip entering PE mode.
MAF show 95 initially at this point and climbs to 208 at the peak all in 1.5s. (When I went above 5 psi earlier, it hit 255).

 

[Eric Stage I]

I agree, see if you can bump the PE trim down until the O2's are between 700-800 at that boost level. Maybe that will clean it up.

Also, could it be a little bit of compressor surge? Does the MAF reading surge or jump when the missing happens?


Eric

 

[granatl]

I drove to work again this morning and noticed the miss (or maybe better deemed quick drop-out) at low psi. At one point, I thought I heard backfire in the exhaust.

I'm pretty sure that it's not compressor surge. My wastegate is rusted shut. (Yeah, I know I should fix this ASAP).