back fires!

[shellboy]

please help. car is a 87 Z T-II. starts fine. idles fine. but starts to miss fire around 6 to 7 PSI of boost. drove car home and found code 15 and 22(just set base timing to 12 btdc) does the speed sensor effect timing under load? i also checked all my new silicone vacuum lines and everything looks good and going to the right places. I also reset the AIS because i added a stock roller cam and roller followers. car has a MP stage II LM for 14 PSI WOT. and a stock T-II turbo just rebuilt by TU. any ideas on whats going on?

[zin]

Try squeezing the plug gap down a bit, maybe to .028" or so. This will make the spark's "job" easier and allow it to fire the cylinder to a higher rpm/boost level.

This is just to help diagnose if it is related to the ignition... I'm suspecting the plug wires are cross firing, or an intake valve is hanging open.

The SDS won't have anything to do with timing, just AIS position based on speed.

Mike

[shellboy]

Got the plugs at 32 right now but I'll try it. Wires are new magna cores.

[22shelby]

i know in smec and sbec VSS signal is used to determine load... i found this as my vss/speedo didnt work... was always recording 10.5> on the wide band... would pop fart back fire and make all sorts of gurgling noises out the tail pipe under deceleration

swapped out transmissions that happened to have a good sensor and WOW what a difference in drive-ability, WOT and just idling...WB would sit at 14.7 cruicing and wot would fall to 11.7-11.4 and the drag strip showed it for sure!!

[shellboy]

Turns out I have a bad coil and coil wire! Arching from coil tower to the plus and neg wires. Coil wire looks like a Xmas tree in the shop when we turned off the lights! Off to the parts store in the AM! Then re-time it! Finally!

[zin]

Good to hear you got it figured out!

Mike

- - - Updated - - -

Good to hear you got it figured out!

Mike

[shellboy]

Also found a "loose" shutter wheel in the dizzy! What a PITA to figure out! Times like this make me miss my spirit RT! No dizzy no problem! Lol👍 new old block on the way from Cindy! Can't wait to get her back on the road!

[shellboy]

Found a "good" dizzy in the shed gonna install tomarrow for test flight! Can't wait!🚗 vroom vroom!

[zin]

Awesome!

Mike

- - - Updated - - -

Awesome!

Mike

[shellboy]

Dizzy I found "had" four solid tabs on shutter wheel. Drilled a hole in one to get her started! Worked fine! Going to order from rock auto to get it right! Car is a blast! Hope my son enjoys it!