OK guys - I REALLY need your help! I am stumped - please read and see if you have any ideas.

I have got my new motor and supercharger in - here is what I have so far....

94 z28 - 6 speed

383 Stroker - Done right
Hooker L/T headers
EGR block offs
52 mm t/b
30# injectors accel
MSD ignition system
AFPR
G-maf - Installed on the Pressure side of the s/c
Vortech S-trim supercharger - with approx 8lbs of boost.
All the other toys that go along with it -

Here is the problem:

At low rpms - or less than 1/4 to 1/2 throttle - it loads up - but if you just crack the throttle a little more 1/2 or more - it runs awesome! If you let it idle, it will eventually kill it's self from overfueling.....I hooked up the scanner and get this - ZERO codes - nothing!!!! All the components that the scanner can read - seem to be doing great. The only thing that I could see that may be a possible concern - was that one 02 was reading like 1200 and the other was like 580. It has not set a Check engine light or anything - so I don't know if that could possibly be the problem or not.

I really don't know where to start - I did check the msd system - disabled it, and re-connected the OE stuff and the the same thing. The only other thing I can think could possibly suspect would be the PCM - I had it tuned, but That is the only other thing I can think would be controlling the air/fuel mixture and making it run poorly.

I am basically ready to jerk this system off the car, and go N/A - I love the supercharger and it runs awesome - but damn - it's been hell to get it right - and I'm still not there.

Please Help me out!

Paul

 

Sounds like the tune all the way. Take it to have it tuned on the dyno if you can. Sounds like the fuel tables at low rpm and load are way off. Almost like the tuner is hanging the injectors open to long. Check and see if you can have somebody wideband the car. That will tell you all you need.

Jose

 

OK -

Here's the thing - I live ont the outskirts of BFE - there is no dyno for about 200 miles round me - and as poorly as it is running - I am not sure it would make it 200 miles it drive it there - Do you know anyone who I could get hooked up with that could possibly
sell me the stuff I need to record the data - or - program a pcm that I could swap out for mine and try it?

I had Ion from madz28 do the "custom tune" on this one - but I have had a hell of a time getting in touch with him - trying to get this straightened out........


help....Thanks for the info though.....

Paul

 

I doubt this is the "tune" per se, though it's hard to even guess from the data you have available. I suspicious of the MAF. Do you have the stock one you can swap in?

Rich Krause

 

A couple of crossed spark plug wires can cause your low speed symptoms. Massively split BLM's and poor low speed performance. You should definitely check your wires for integrity and correctness.

Not sure how big your cam is, but most will idle good enough if the idle is set at 800 - 900 rpm.

Your injectors ... 30# MSD??? Aren't they a little on the small side. I have SVO 42# injectors and an FMU to boost the fuel pressure, and they are running at 85% duty cycle at 6,000 rpm.

You may want to consider LT1 editor or Tuner cat and a Laptop computer for your tuning needs. Saves a lot of agravation.

Hope this helps

LWM

 

whats exhaust system are you running? I had a serious problem with split BLM's and it turned out to be as simple as a small exhaust leak near the side with the rich condition. fixing the leak cured the situation and brought the BLM's back together and the car ran significantly better throughout. just something to take a look at!

Chris

 

Rich - one of my first guesses was the maf sensor also- but I monitered it with the scanner while it was running, and it seems to be working great - I don't have the old one either - sold it on ebay like 2 years ago

LMW - I have considered going bigger on the injectors, but I have not really got a chance to see it run on these yet - seems to run great so far, and right now I am trying to get less fuel in there, so I think I may wait until later to upgrade to bigger ones. The probelm isn't really a "miss" but more a "overfueling" problem when it gets warm, It's hitting on all 8 most all of the time, except when this starts - then I get the black smoke exc....and it has not tripped a Check engine light or missfire code yet- so I kind of thing the sparkplug wires are ok....I don't know for sure- but the seem to be. Also- where would I buy the lt1 edit or somekind of data reading program?

Chris - I have Hooker L/T headers with True dual 3" pipes and dynomax bullets with a x pipe. I think the reason why my 02's are reading so far off is due to the fact that on the driver's side (left) header, where they have the "bung" for the 02 is in the front of the collector tube - therefore it's only really reading off of 1 cylinder - instaed of all 4 like it should - could this be causing the problem? Could I just send my pcm off and have it re-tuned for a "closed" loop on the 02's - because it seens like when it's cold - it runs awesome......

Thanks for all the help fellas - I a really desperate at this point....

Paul

 

ttt?

 

Well - after a lot of testing today I have come up with several things that might help.

everything I scanned appeared to be operating properly except the 02's the right bank was reading at 1093 constant the left bank would show anywhere from 130 to 900 - and woud just change almost immeadiatly. I am not sure how they are supposed to read, but this seems odd to me.

the map was reading between 34 and 37 depending on request for throttle - seems ok - all the other sensors seemed to be fine - I checked for a vacuum leac around the intake manifold and intake tubes - none.

When I first started it, it ran awesome - for the first 5 miles, never missed or overloaded at all. Then when the temp got to about 180 degrees, started loading up - almost like when the pcm went into "closed loop" - at idle - it would load up, then idle fine, and intermittently miss, whne it would get to the point of almost dying like 300 rpms, it would correct it's self and clean up instantly. This leads me to believe it's in the pcm and the fuel curves are most likely off - unless the o2's are soo far out of wack, it's reading lean and totally dumping fuel, killing one bank of the engine, until i manually override it. by opening it up and forcing more air into the engine - I dont know.....Help!

 

Well - after a lot of testing today I have come up with several things that might help.

everything I scanned appeared to be operating properly except the 02's the right bank was reading at 1093 constant the left bank would show anywhere from 130 to 900 - and woud just change almost immeadiatly. I am not sure how they are supposed to read, but this seems odd to me.

the map was reading between 34 and 37 depending on request for throttle - seems ok - all the other sensors seemed to be fine - I checked for a vacuum leac around the intake manifold and intake tubes - none.

When I first started it, it ran awesome - for the first 5 miles, never missed or overloaded at all. Then when the temp got to about 180 degrees, started loading up - almost like when the pcm went into "closed loop" - at idle - it would load up, then idle fine, and intermittently miss, whne it would get to the point of almost dying like 300 rpms, it would correct it's self and clean up instantly. This leads me to believe it's in the pcm and the fuel curves are most likely off - unless the o2's are soo far out of wack, it's reading lean and totally dumping fuel, killing one bank of the engine, until i manually override it. by opening it up and forcing more air into the engine - I dont know.....Help!

 

That does not sound like PCM or tuning...

Looks to me like: a bad right o2(or wiring), possible stuck injector on the right side, crossed plug wires.....

 

I agree with CJ, looks like the O2 could be fried, wiring is faulty or exhaust leak. either way it looks like the PCM is dumping fuel in for what it thinks is a lean condition. As for injectors hanging, I would have them flow tested. Or if you have no way of doing this, then just simply swap them over from the right bank to the left and idle the car. See if it loads up on left side, if so at least that will tell you, you have a bad injector. That will at least keep you from chasing down other problems that aren't their. As for the 130-900, that is just the millivolts of the O2 as it cycles in closed loop. That is totally normal.

Jose

 

bad,

I know most say to run the O2's off all 4 primaries in the collector, but to resolve my issue, i ran both my O2's of single primaries..left side off number 5, and right side of numver 4.. this cured my loading up issue and got my O2 sensors reading right where they needed to be..carbon buildup on rear bumper is gone now, and the car picked up tremendously on fuel economy!

hope this helps!

Chris

 

Just a update - picked up a new o2 sensor today, I'll be putting it in shortly - hope it works. I think it's the best place to start though.

PS - thanks for all the help.

Later

 

Well, I changed the 02 and it still runs like **** - unless I am full throttle - any suggestions?