topfuelman

iTrader: (6)

A new issue has surfaced during tuning and testing of our new combination.
Under normal acceleration, no problems. Under WOT acceleration or full throttle acceleration under load, the engine stumbles or misses above 3000rpm-redline, limiting the rate of acceleration.
The car starts, idles and accelerates fine under part throttle conditions.
According to our data logging, the afr looks good, the timing adjusts as it should.
We are using ls-edit and have the VE tables well adjusted.
It used to pull full throttle with no issues, the problem just surfaced.
There are no codes or misfires being recorded by the pcm

383 stroker, Stage 2+ 5.3 Heads with 2.02 intakes, 12:1 compression, Custom Cam by EDC (242/250) Long tube headers, x pipe, dual 3" exhaust, LS6 intake, ported TB, 42lb injectors, MSD Wires, stock descreen MAF, custom 4" freeflow intake filter, ducting.

Here is what I've checked so far.
Reloaded earlier LS-edit tunes to see if issue would go away - nope!
Fuel pump (custom dual set-up) -both operating
Fuel filter clean, Corvette regulator - new
Fuel - Tried 2 different fills of different Premium gas
Injector harness - all connected
Injectors - no leaks ( 600 miles on these from new)
Plug wires (1000 miles from new) pulled and cleaned no evidence of tracking
All wires clicking into place.
Coils - stock '99 ls1 coils - not check or tested in any way
Plugs - Stock spec TR-55's? (600 miles from new) not yet pulled or checked
Grounds checked all, and added an additional ground strap
In the PCM data, the TPS reads 100% at WOT
Coolant temperature reads normally
Cleaned the stock MAF
Can't find any vacuum leaks

What should I check, in order of relevance.
Someone told me the MAF may be reaching it's limit's of measuring airflow.??

Thanks for any input,
T

BigBadWolf

Check your MAF sensor. Your MAF is descreened and if you use a K&N (or any oiled filter for that matter) you could have over-oiled and dirtied the MAF sensor.

I went through hell trying to figure out a similar problem and it turned out to be the above.

crainholio

iTrader: (2)

Sounds like a broken valve spring...

topfuelman

iTrader: (6)

I sprayed the wires with Brake cleaner to clean them already. Do I need to clean this some other way?

I will check into this to be sure, but wouldn't there be some sort of telltale sound or other issues. If I rev without without WOT the engine will still pull /rev to redline. Only stumbles specifically under WOT/load

Thanks,

Trev

BigBadWolf

I don't know that I would have used Brake Cleaner. They sell spray specifically for electronics. I read where several people used this and GENTLE touching with a Q-tip and have been successful.

BigBadWolf

https://ls1tech.com/forums/generation-iii-external-engine/349054-maf-cleaning.html

Cleaning the MAF is easy which is why I bothered to mention it. A lot easier than checking for a broken spring which I doubt it is. As you said, there would be more telltale signs.

topfuelman

iTrader: (6)

Any other suggestions?????


Thanks,

T

crainholio

iTrader: (2)

Given that it ran OK previously and this is a new condition, and assuming you didn't change anything, that means something changed by itself.

If you're running dual valvesprings instead of singles, it's possible for the valve to be somewhat controllable at gradual acceleration but not at sharp spikes.

Now quit typing go pull your valvecovers.

topfuelman

iTrader: (6)

Will do! As soon as i am off work.
BTW, They are dual PP Gold springs, with low mileage.

Thanks,

T

crainholio

iTrader: (2)

Patriot springs have a great reputation so it's unlikely they're the cause, but still the right next step to check off the list. Let us know what you find, look really closely at each one and the surrounding area for piece(s) of spring where not appropriate.

topfuelman

iTrader: (6)

Found a unclipped spark plug wire (at the end that snaps onto the plug)

Couldn't check this easily as the hybrid I have the LS1 installed in makes accessing the DS rear plug very difficult.

Thanks to all for the suggestions!

Cheers