Any thoughts on how to diagnose a slight miss/engine hesitation while under load? The car is a 2000 T/A WS6 w/ 6-speed transmission (headers and exhaust).

It is most pronounced between 900 - 1700 rpms in 1st and 2nd gear. In this case, the car seems to "sputter" and feels like the car is literally bouncing back in forth in a front to back motion. It is strange because it does not happen all the time.

Also, the car does not seem to pull as hard when cycling through the gears at 3/4 throttle or all out. You can feel and hear the car "flatten" for a brief second at higher rpms before picking back up.

Checked for codes, nothing. Any other suggestions on how to pin point the issue?

 

Check the fuel pressure.

 

I've had a similar problem a few times over the years. My headers burn my #6 plug wire regularly...even with the wires wrapped in heat shielding and with a protective heat shielding sleeve over it on top of the the wrapped heat shielding. I only get about 10K miles out of that wire...sometimes, not even that.

I've had other times when I just replace all plugs, wires, and clean the MAF and that solved the hesitation. I could always feel the miss, but it wasn't bad enough to set the SES and it was hard to catch when logging too, but was definitely there...

 

Thanks for the suggestion. I will add that to the list.

Is it safe to rule out anything related to the clutch or transmission?

 

Coil wire?

 

If it's a misfire, it would logically cause the SES light to flash, at least if it is severe enough to damage the catalytic converter. But the system should record the misfire count by individual cylinder, and that should be accessible by a scanner with "enhanced GM parameters". Knowing the misfire count by individual cylinder would either tell you it'a a truly random misfire, or possibly focussed on one (or two) cylinders.

Not really clear on what this is describing:

Do you mean it goes nose up under accel, and eases back down as power is intermittently lost?

Can't think of any typical ailments with the T56 that would cause that. A slipping clutch might. But why only at that RPM? You could check for slippage by pushing it hard in 3rd gear, at moderate RPM.

 

Thanks for the reply. The car has headers and exhaust, so the SES engine light has been disabled (otherwise it would constantly be on b/c the cats have been removed).

It seems the problem is not just isolated to low RPMs. Did a test in 3rd gear today...taking it from low to high RPM. When laying into it a bit (3/4 throttle), the car falls flat for a brief second at higher RPMs. In other words, it will pull hard but then "miss" briefly then continue pulling. When it misses you can feel it, and even hear it (the tone of the car gets quieter).

I just bought an INNOVA 3100 Diagnostic Scanner. Will look into the extended scan parameter...not sure if this machine can do it.

 

You do realize you can eliminate the SES light for the missing cats with O2 "sims", or having the PCM programmed?

 

The 3100 wil not read any enhanced GM data. Nor will it read any standard OBD2 data. It only reads the minimum stuff, like trouble codes, emission test status, etc. A much better solution is to use an Android phone with a $24 Bluetooth cable And a $5 Android scan app : https://play.google.com/store/apps/d...l.torque&hl=en

That combination, with the free Torquescan add-on, can read the enhanced GM data for a cost of under $30.

Need a cheap Android phone just to run the app, and you can use Wifi somewhere?