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Thread: problems full throttle 3rd gear 6500-7000 RPM

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Posts: 1-7 of 7
2009-04-10 21:24:27
#1
problems full throttle 3rd gear 6500-7000 RPM
I'm having problems with my '94 DE+T, breaks up/no accel around 6500-7000 in 3rd gear full throttle,
6975 rpm, 4.2v maf, 78% inj duty cycle - 1st & 2nd fine to redline.
3rd gear partial throttle fine to redline.

It was running good before the Chicago convention, until the day at the drag strip - 4th didn't engage, broke 3 rockers. Wes helped me put new rockers in, found all the shims, all the broken rocker parts.
Last fall the wastegate pipe weld cracked, no more boost, so it sat until this week. All welded up and good to go, other than this break up issue.

Setup:
94 SR20DE stock compression
JWT ECU & S3 cams
O2 induction intake manifold with IACV-AAC & air regulator installed
50 lb MSD @ 3 bar
Stock FPR - fuel pressure about 39psi @ idle (a bit too high)
AirResearch turbo @ 9psi, T3 .60 a/r, .63 wheel
unknown, probably rwd det exhaust manifold
2-1/2" crush bent downpipe to 3" side exit
Tial external wastegate
Z32 MAF blow through
Turboxs bov
Newer cap, rotor, OEM wires, NGK BKR7E @ 0.030" then 0.026" now 0.022"
"55" = no error codes
Vacuum @ idle about 12 in Hg


What I've tried so far:
Plugs were @ 0.030", so dropped them to 0.026" - didn't help.

BORNGEARHEAD stopped by and set timing and idle.
Timing was @ 25 degrees!!!
Now @ 15 degrees.
Checked compression - 180 - 180 - 180 - 178.

Made the problem worse! Happens in 2nd gear around 6500 RPM now.

Last fall I had a NISMO FPR on, but thought it was causing problems, so put a stock FPR on.
So, I put the Nismo FPR back on today.
Fuel pressure right on 36psi, 42psi no vacuum.
Dropped plug gap to 0.022".

Even worse yet. Breaks up around 5000 in 2nd gear now.

It ran better until 7000 in 3rd with 25 deg timing, 0.030" gap and 39psi fuel pressure.


Haven't done a boost leak check, need to make a tester, but it idles great.
2009-04-11 13:20:52
#2
Grab another coil, had very similar fault ages ago, any de or det coil will do, dont worry about aftermarket, the stock coil is very good until they die of old age.

Can almost guarantee this is the fault.
2009-04-11 16:46:32
#3
thats very low vac for s3's my s4's vac was about 16hg. is it possible that you have a small leak after the maf. you are probly running threw the gears down low to fast to put a good load on the engine and when you get to a higher gear you can thus getting some spark blow out or possibly running rich. how old is the ignition equipment? plugs, wires, cap rotor? is it possible that when you lost some rockers the timing chain jumped thus screwing with your timing so much? just throwing some ruff ideas out there.
2009-04-11 22:18:56
#4
Originally Posted by Evlnxr
Grab another coil, had very similar fault ages ago, any de or det coil will do, dont worry about aftermarket, the stock coil is very good until they die of old age.
Can almost guarantee this is the fault.

Good idea to check the coil.
I have an MSD coil I can try, have to figure out how to wire it up.
The car has 101k on it, but the stock coil looks to be in good shape.

Originally Posted by Mr.sentra_specv
thats very low vac for s3's my s4's vac was about 16hg. is it possible that you have a small leak after the maf. you are probly running threw the gears down low to fast to put a good load on the engine and when you get to a higher gear you can thus getting some spark blow out or possibly running rich. how old is the ignition equipment? plugs, wires, cap rotor? is it possible that when you lost some rockers the timing chain jumped thus screwing with your timing so much? just throwing some ruff ideas out there.

Yeah, I thought the vacuum was low. The O2 induction was warped pretty bad when I got it, by the coolant sensors.
So I had it machined flat, and put a new gasket on.
I need to make a leak tester - maybe the IACV, air regulator or some other component is leaking.

Newer cap, rotor, wires & plugs - less than 1k miles on them.

I thought it was blowing out the spark, but thought 0.022" would take care of that.
The last time I had it running good, 0.028" was good enough to prevent the spark blow out.

I searched some other threads last night, and found one similar to what you're saying about the timing, skipping a tooth.
Their solution was to put the engine at TDC cyl 1, cams at 10 & 2, and reset the distributor, and adjust timing.

Since all the ignition components are newer, except 101k mile coil (although looks to be in great shape), I'm leaning towards
a timing issue, and also a vacuum leak - especially since it ran better at 25 degrees advanced vs 15.

Thanks for the ideas!
2009-04-11 23:10:40
#5
i think running the plugs down to .022 is to small any way bump them back to 28-30. at 022 you might not be getting a good burn and might be making the problem worse down the road.
2009-04-16 14:11:04
#6
Originally Posted by Mr.sentra_specv
i think running the plugs down to .022 is to small any way bump them back to 28-30. at 022 you might not be getting a good burn and might be making the problem worse down the road.


Yes, I agree. I forgot to mention that I bumped the gap up to 0.026", after none of the other stuff we tried helped.


*Problem solved*
I swapped coils this morning.
Pulled fine full throttle through 2nd gear to redline,
again until near redline in 3rd, shifted to 4th and
nothing there...

it blew...




...a coupler off.
Scared the crap out of me - thought something major broke.
Quite the difference in acceleration in 4th boost vs. n/a, lol.

Time to put the MSD coil on.

Still have low vacuum at idle, gotta get a pressure tester on it.
2009-04-21 22:28:31
#7
Originally Posted by jp314

*Problem solved*
I swapped coils this morning.


Correction, maybe...

I didn't have a spare coil, just swapped them between my N/A & turbo car.
Both seem to be running fine now.
I thought about it some more, and remember tightening the throttle cable bracket on the O2 induction manifold, on the turbo car, when I swapped the coil.
All the wires grounded to the intake are on the throttle bracket, with my O2 induction setup.
I think the problem was with a loose/bad MAF ground.
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