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View Full Version : Hesitation during warm operation (Knowledgeable SR owners please read)


MikeySand
09-13-2011, 09:12 PM
Engine background:
Redtop SR w/ 9.0:1 compression bottom end
Stock Head
Stock Intake/Exhaust Manifold
FMIC
SOHC MAF
Stock SR T25 w/ stock internal wastegate
Adjustable FPR w/ gauge (Aeromotive)
Tial 50mm BOV
Stock #62 ECU (un-chipped)


Un-resolved running issue:
As the car progressively warms up from normal operation I start to experience hesitation while idling and when building boost.



Scenario:
Car is able to initially crank and start (cold start). I can begin to drive the car without any trace of hesitation; AF ratios seem to be normal at around 14.7 when throttle is kept constant, and modulate accordingly upon acceleration and deceleration. As the car warms up and ultimately gets to operating temperatures it begins to hesitate as I build boost under moderate throttle. For instance, as throttle is applied, boost builds accordingly until a random point in which the motor seems to hit some sort of fuel cut/bucking as it tries to continue to build boost. The AF ratios go full lean (unreadable by the AEM wideband), come back to rich (around 12 or so) then back to full lean (>16). This doesn’t happen at one given point but at random RPM levels and boost levels. From what I can see, I am not reaching anything above 6 lbs of boost in any gear (read via AEM TRU boost).
Also, I drove the car from Jacksonville FL to Tallahassee FL, which is approximately 180 miles. During this trip, the car started out fine, over the course of the trip the car would randomly go full lean then stabilize itself back to stoich with little to no throttle modulation. When I finally got into town, at the second stop light reached, the car stalled when placed under load from my electric fans. At this point I would try to crank the car but I would not start. Only after I let the car cool down for 30-45 minutes would it start again, at which point I was able to drive the car home and park it.
This is where I sit, at a loss. My father and I have diagnosed the car a dozen times and have come up with no real solution to this issue. Any input by those highly knowledgeable with SR’s would be greatly appreciated.



Thank you for your time.

MikeySand
09-13-2011, 09:13 PM
I will be adding a few videos tomorrow for reference.

blksylv
09-13-2011, 09:18 PM
my car does the exact opposite lol, i believe my issue to be maf/wiring related though

s13silvia123
09-13-2011, 09:34 PM
maf problem

fliprayzin240sx
09-14-2011, 01:27 AM
Start by double checking your spark plugs, make sure they're gapped properly. Actually what plugs are you running? Also, double check the timing. If everything checks out, only other thing I can think of is water temp sensor going bad.

KiLLeR2001
09-14-2011, 08:07 AM
Coolant temperature sensor. Replace it. If problem exists come back to this thread.

MikeySand
09-14-2011, 08:14 AM
Coolant temperature sensor. Replace it. If problem exists come back to this thread.

The coolant temp sensor for the ecu has been replaced with a new one from Nissan, twice.

MikeySand
09-14-2011, 08:17 AM
Start by double checking your spark plugs, make sure they're gapped properly. Actually what plugs are you running? Also, double check the timing. If everything checks out, only other thing I can think of is water temp sensor going bad.

The plugs that are on the car are BKR7ES and gapped to 28 thousandths iirc. I'll take each out and double check them.

Would switching them out with BKR6's change anything?

Sileighty_85
09-14-2011, 10:56 AM
Check Wiring and ECU for codes

KiLLeR2001
09-14-2011, 05:30 PM
The plugs that are on the car are BKR7ES and gapped to 28 thousandths iirc. I'll take each out and double check them.

Would switching them out with BKR6's change anything?

Stock SR20DET gap is 0.036".

After you check for ECU codes and everything is copacetic, check the coilpacks. Inspect them thoroughly for cracks and make sure the spring is making good contact. Sometimes they just go bad and will stop functioning properly when heat builds up. I had one go bad and the car ran fine until I hit around 4500 rpms.