PDA

View Full Version : Calling on ~ Best of the Best~ for help with this



compression
06-23-2005, 12:09 PM
I am getting very deparate. I need the help from the Best-of-The-Best Nissan Gurus out there.

The car:
1973 Datsun 510
S13 SR20DET(fresh rebuild, forged pistons, bearings, head work, head gasket, etc)
AEM Engine Management System
Custom everything
Running a speed density system (no MAF sensor)
T28 Turbo from an S15 Silvia
AEM CDI


The Problem:
The engine is bogging above 6000RPM. At lower boost levels (9psi or so) it is not as noticeable, but shows up on the dyno that after 6000rpm it loses about 20hp, but it still makes it to the rev limiter (7600RPM). At higher boost levels, 13-14 psi, it bogs much worse, it wont rev past 6500 power drops way off. After a hi-boost bog, it goes into a loping 3-cylinder idle(I call it "limp mode") with the #2 cylinder dead. It hardly responds to throttle inputs at this point and it is stumbling and making bogging sounds. I pull over, let it stumble for a minute or two, feather the gas a little, and after about a minute, it is back to normal...until I try to take it past 6000 again. It does NOT go into "limp mode" when boosting under 10psi.
I have had it looked at by professional AEM tuners (very good shop) and they do not believe it is EMS related.
Here is what has been ruled out already:
-It is not the coils
-Injectors are fine(and the correct impedence)
-it is not software/EMS related
-it is not the spark plugs, or the gap
-compression test revealed good compression in all cylinders
- it is not the fuel supply system

Additional notes:
system goes rich (wideband oxygen sensor shows that anyway) just before the bog. But it is not the fault of the AEM system or the calibration it is running (i.e. injectors are not being told to all of the sudden dump a lot of fuel)
Head was rebuilt and ported, possible valve problem?
During "limp mode" stabbing the throttle will make the boost increase, but the RPMs dont go up, and therefore the car does not go any faster.
We have held a fuel injector probe to the wires of the #2 injector and it is getting a good pulse signal all the way to up the rpm's(aka not the injector wiring).
We know it is #2 because when it is in "limp mode" and we unplug the #2 injector, it does not sound any different, unplugging any other injector causes it to die.

Please pipe up if you have had a similar experience or you can offer any feedback that (no matter how simple it seems) could be useful.
Thanks in advance! I am very desparate to solve this!!!

YumGTR
06-23-2005, 12:30 PM
ignitor chip?

Enthalpy
06-23-2005, 12:31 PM
bad CAS?

compression
06-23-2005, 01:05 PM
ignitor chip?


I am not using and ignitor chip, the coil firing signals from the EMS are sent directly to the CDI, it ups' the voltage and fires the appropriate coil.

I am able to log my signals from the CAS, so far from what I have seen they look good. That was also checked by the AEM tuning technician.

Keep it up guys, this is a good start!

TS4l
06-23-2005, 01:06 PM
Does #2 change if you pull the coilpack?

compression
06-23-2005, 01:29 PM
we have tried switching coil packs from cylinder to cylinder, but the #2 cylinder is always the dead one.

SRFiveTen
06-23-2005, 01:49 PM
Does #2 change if you pull the coilpack?




we have tried switching coil packs from cylinder to cylinder, but the #2 cylinder is always the dead one.



i think what you were being asked was,
"is your #2 plug throwing sparks while in the limp mode?"
no fuel or no spark?

compression
06-23-2005, 02:19 PM
I can pull the plug off of the injector, or the plug off of the coil, either way #2 is still dead. What I have not done is pulled the coil off of the plug to see if it is still sparking during limp mode.
I am kind of under the impression that the #2 plug is fouling and it takes a few minutes to clean off.

What I can do is get it into limp mode, and then pull the spark plug out and check to see if it is fouled, and at the same time check the coil to make sure it is firing.

any other suggestions? keep em coming!

TS4l
06-23-2005, 03:20 PM
How about the injector grounding out, causing it to dump fuel. Seen that happen before!

Dcell
06-23-2005, 04:59 PM
Have you swapped injectors with another known good cylinder? What injectors are you running? If the injector is somehow failing, unplugging it will not change anything. Do you have a way to measure EGT's? What wideband are you using?

compression
06-23-2005, 05:29 PM
The injectors are nismo 740cc high impedence, basically brand new (about 1000 miles on them). I had this same problem with the stock 370's, so I am pretty sure I can rule out injectors.
I am using the AEM wideband that came with the EMS.
I am running an EGT sensor, it is on the downpipe. I have datalogged its values, but nothing really obvious came up.

compression
06-23-2005, 05:34 PM
How about the injector grounding out, causing it to dump fuel. Seen that happen before!



We checked the injector with a probe and it checked out fine. This is where you jam an electronic probe on the injector wire pin from the back side and a little LED blinks with every injector pulse. As the car revs up, the LED changes from red to green indidcating it is fine.
If there is another way I can check that, let me know.

240sxTurbo
06-24-2005, 06:32 AM
I can pull the plug off of the injector, or the plug off of the coil, either way #2 is still dead. What I have not done is pulled the coil off of the plug to see if it is still sparking during limp mode.
I am kind of under the impression that the #2 plug is fouling and it takes a few minutes to clean off.

What I can do is get it into limp mode, and then pull the spark plug out and check to see if it is fouled, and at the same time check the coil to make sure it is firing.

any other suggestions? keep em coming!


Have you pulled the plug after it went into limp mode to see if it was indeed fouled with fuel ? If you can get into limp mode again and have time pull the coil pak for #2 and plug in another plug and see if you are getting spark at the moment its in limp mode. This "might" help determine if its fuel or fire related.

Enthalpy
06-24-2005, 07:41 AM
The injectors are nismo 740cc high impedence, basically brand new (about 1000 miles on them). I had this same problem with the stock 370's, so I am pretty sure I can rule out injectors.
I am using the AEM wideband that came with the EMS.
I am running an EGT sensor, it is on the downpipe. I have datalogged its values, but nothing really obvious came up.





bad injector o-ring?

heres the weird thing. if it is misfiring #2 then you should see the AFR go either lean or rich. if not...then your tune might be masking the problem AFR wise. i.e. you are leaning out the other 3 to compensate for one 1 rich cyl.

a2low240
06-24-2005, 08:38 AM
I'm going to go with the exhaust valves have too big of a shim in there and when heated up expand and leave the exhaust valve open a bit ......or.... the head / block has a hairline crack in it allowing coolant to get in when hot and is fouling the plug out. Have you done a leakdown while warm yet?

compression
06-27-2005, 01:52 PM
I am back, had to camping for a few days and forget about my car(s).
Anyway, yes it does go rich right before it happens. What makes you think it is the O-ring? wouldnt that leak under almost all conditions? I can pressurize the fuel rail and see if any gas is leaking by the injectors. that is easy enough.

It is very likely that the tune is masking the problem, but there is no easy way I can tell.Unless you can think of something.
When I stay under the boggin limt, the car drives perfectly, it idles smooth all the time, it starts up cold without any trouble, throttle response is crisp, etc, etc...

compression
06-27-2005, 01:57 PM
I'm going to go with the exhaust valves have too big of a shim in there and when heated up expand and leave the exhaust valve open a bit ......or.... the head / block has a hairline crack in it allowing coolant to get in when hot and is fouling the plug out. Have you done a leakdown while warm yet?




no, i have not done a leakdown yet, it is on my list. I am not loosing coolant, and there is no indication out the exhaust pipe that it is burning coolant. THe head was completely disassembled, a valve job was performed and the it was decked also. I cannot say for sure that it is not cracked, but it is unlikely.
One other thing matt, the problem seems to be RPM dependant (gettting worse as engine load is increased) not water temperature dependant.

Monster240
06-30-2005, 10:38 AM
Perhaps a fuel injector is temporarily sticking open due to the higher dynamic fuel pressure offset (assuming you have a 1:1 regulator) by the rise in boost pressure?
Try swapping the #2 injector with one from a different cylinder position.
If the temporary high boost misfire condition transfers to the other cylinder, then replace that injector.

Also, do a compression/leakdown test and compare with other cylinders to rule out any possible engine damage from the fuel wash.


Simonizer.

compression
07-01-2005, 10:18 AM
thanks for the reply. It did the exact same thing with the 370cc injectors, same cylinder,and these are brand new 740's.
But I can swap them, it is easy enough.
I have done compression checks, they are fine, I am going to have a shop do a leakdown this weekend (I dont have a comprssor).
I will update if I find anything.

Monster240
07-01-2005, 12:41 PM
Also, check the valve spring tension of that cylinder.

Simonizer.

Rhombus
07-01-2005, 02:22 PM
If you are sure the injector, coil and plug are good then and the problem always stays with #2, that would lead me to think that you have a problem in the wiring. It could be the wiring, it could be a bad channel on the CDI, could be a problem with the signal sent from the EMS. But logic says that if it isnt the injector or coil, it must be in the wiring or another component. You are loosing either spark or fuel because of somthing. I would probably look into the CDI and its wiring. Higher boost/load will requre more spark energy and could be causing a problem to appear. Perhaps you should switch channels around on the CDI and see if the problem stays on #2 or moves to another cylinder.