First, let me apologize in advance. I have used the Search function (and google, and monodox, and every other tuning site I can find) and my answer is not out there ... yet.

The car is a 95' OBDI Cam-Only car. However it is an oddly spec'd cam. It is a 224*/230* .600/.600 108+2LSA. Car has a mail order PCMforLess Tune.

Car suffers from very weak idle (will bog ALOT if turning the wheels sometimes), bucking, surging, all the way up to around 1800 RPM's. From there it runs pretty well. I have mildly split BLM's (less than 5) in the driving range. But in Cell 16 and Cell 18 (0% Throttle & 0 MPH - 0% Throttle & MPH greater than 0) I have horrific splits nearly to the limits (108 & 156).

Plugs have less than 1000 miles on them. Wires have a few thousand miles now (none are burned or arching.) Car has 30# SVO Fuel Injectors with stock pressure regulator (Injector Flowrate = 32.35 ? Should be 31.68)

My Individual Cylinder Fuel Trim's are as follows:
Cyl. Off Idle At Idle
1 - 1.03 1.06
8 - 0.98 0.95
4 - 1.02 0.95
3 - 1.02 1.00
6 - 0.99 0.98
5 - 0.97 0.95
7 - 0.98 0.94
2 - 1.02 1.08

This raises some eye brows However when measuring my header temperatures with a decent IR Thermometer, there is no large spread. In fact, when measuring each of them (From 6" away, at non-coated (rust) regions that are bigger than the field of view of the IR Lens) I saw very consistent temperatures.

Cyl.
1 - 275*
8 - 275*
4 - 330*
3 - 300
6 - 350
5 - 300
7 - 275
2 - 275

If I took readings on the Ceramic Coated a few inches down they all ranged from 380*-490*. So still no drastic spread.

I am running 32* timing at idle (and is very smoothly transitioned into Main Spark Tables) and am seeing no KR at idle. MAP readings appear to be consistent Idling - 55kPa, WOT - 100 kPa, letting off throttle at WOT - 15-20 kPa. Cleaned IAC and TB. IAC counts were around 55 (with idle timing at 27*) and now currently sit around 27ish at hot idle (with idle timing now advanced to 32* AND idle speed RAISED from 825 to 875). Ran around the entire Intake Manifold, Injectors, MAF, MAP, TB, etc. with Starting Fluid and shows zero signs of vacuum leak.

I have tried closing the TB Blades to the point that they nearly stick to force all idle air through the IAC - still have Split BLM's. And only at 0% TPS in cells 16 & 18.

Suggestions? Comments?

I am going to replace my O2 Sensors this weekend just to be sure they are FRESH AC Delco sensors.

*****EDIT*****
-Today I noticed I have (1) Bosch O2 Sensor and (1) AC Delco Sensor. Also, in my latest datalog I am picking up unusual O2 feed back that was not there before (or maybe they were still cycling fast, just incorrectly?) When verified against my Wide Band they seem OK reading around 950mV at WOT (11.9 AFR) and idling between 14 and 15 AFR. Crusing around 13.5-15 AFR dependant on throttle, load, RPM, etc.
*****EDIT*****


So there you have it - I think I mentioned everything. Why the heck do I still have these Split BLM issues at 0% Throttle?


Joe

 

After you change your sensors and still have the problem, I would look mechanically.

Based on what you are saying, I would look into the intake idle plenum. This is the plenum that the IAC dumps into. Sadly, this means pulling off your intake but unless you have missed the obvious, you have problems with idle air getting to each bank evenly.

Try this: crack the TB blades open until you have almost 0 IAC count at idle. This allows more of the air into the main plenum and bypassing the idle air plenum. If your BLM's at idle get closer, then you know you have problems with air going through your idle air plenum.

 

95Blackhawk - I work at the garage this weekend so I will order some new AC Delco O2's for it and try them first. Oddly I also noticed watching my datalogs that on a cold, just started engine, where the O2's should be locked at .450mV I am reading:

Left O2 - .53mV
Right O2 - .67mV

This is before it even starts taking readings from the O2's on a just started, cold (not ran in a few days) engine. The numbers slowly climb (evenly) to around .67mV Left and .78mV Right until the sensor is warmed enough for them to start oscillating.

I wonder if part of it is having two different brand O2's...? I will have to swap these out for sure, as one is finally showing intermittent signs of slow switching...

Will try to update on Sunday once I swap my O2's datalog it, and then try (if O2's dont work) backing the TB Stop screw OUT to force idle air through the TB instead of the IAC.

Thanks guys,

Joe

 

you can also try swapping the O2s from one bank to the other to see if the split switches side.

also i read something in the new issues of engine masters about idle tuning with the engine warmed up that may help you out so i'll just throw it out there. in a nutshell it says unplug your iac and cover the passage. then set your timing to about 22 degrees and open your tb blades by adjusting the screw so that the engine idles strongly about 1300 rpm. then increase timing 4 degrees at a time. if your idle speed increases adjust the screw back to get the idle at 1300. once you reach the point where an increase in timing no longer affects the idle speed your tb blade settings are in pretty good shape. now retard the timing until you get your desired idle speed. if you have to retard it by more than 8 degrees to get your desired idle lower the tb blades slightly. then you know your tb blades are set and you can then plug the iac back and uncover the passage.

it seems like this would require you to slot your tps sensor and then reset it as well so that you get a 0% tps reading at idle and the correct voltage. they were using a fast computer on a distributor setup on an engine dyno so they can make the changes way faster than we would be able to. again dont know if doing the above would prove to be beneficial to you but just thought i'd throw it out there. either way the article was a good read. thanks injuneer for the heads up.

 

C Rules - Thought about swapping the O2's but here is my issue:

(1) Sensor is a factory original from 1995. Has 20,000 Miles on it. Sat for 9 years from 1995 to 2004 while the car sat in a garage totalled. Then I got it.

(1) Sensor was replaced shortly after I rebuilt the car as it would develop an intermittant misfire and the O2 would lag badly. Sensor was replaced with a Bosch (This was BEFORE everyone hated Bosch) and is currently in the car.

Since then I have installed coated headers, and ran on a somewhat rich tune. I figure it best to just replace them both and have peace of mind and a fresh start to try to work my tune issues out. Also, I have noticed a few off-the-wall readings from my O2's and I want to replace them to confirm they are not the problem...

And on a very gay note - no where near me has AC Delco's in stock so I had to order them online and wont have them until sometime next week. In the mean time, I may swap sensors, datalog it, and watch my BLM's.

Also, thanks for posting the idle tuning thing. I will give it a try. It may take a while, but it cant hurt to try!

Joe

 

Your O2's will not provide a correct reading until they are hot. This could take a few minutes.

Remember 0.45V is at 14.7 AFR when they are hot. A cold engine will generally be rich because they are tuned that way from the factory but don't trust the O2's until the computer starts adjusting fueling.

Further as an FYI, if you have not modified your tune, the PCM will oscillate around 0.425V not 0.450. It is just what GM did.

Ben

 

The issue I see with this is the lack of idle air plenum. I am not familiar with the manifold they used but assume they didn't have this plenum.

in our plenums, they objective is to get everything to go through the idle plenum during idle. Doing otherwise on larger cammed cars will cause split BLM's.

Remember most manifolds intakes are up top and the air intake is spaced evenly from all cylinders (well at least closer than an LT1). Our intakes have the opening at one end. This leaves an opportunity for improper air distribution if air goes through the TB blades and not the idle plenum during idle.

 

Pull the intake off and remove the sheet metal guard on the bottom of it. There will be a bunch of threaded pipe plugs under there. Those go into your idle air plenum. Take all the plugs out and clean out all those passage ways. Get a dremel tool and smooth/debur anyplace you can reach with it on those passages. reassemble everything and see if that fixes your problem. If your intake was ever hot tanked or media blasted or cleaned in any way those passages usually end up full of crap. Most of the time no one takes the intake apart to clean them properly.

 

LearJet - I will do this if the new O2's don't fix my issue.

95Blackhawk - I was under the impression that the O2's should read .450mV at a cold idle until the car warms up, then oscillate. Mine start out a good bit higher (leaner - which is False, my Wideband confirms it but sensors are still cold anyways...) and creep up.

I thought they were to be locked at .450mV until the point where it enters Closed Loop?

Either way, one of my sensors is a Bosch, both have been through a header install, and one (intermittently) lags and wont oscillate for a couple seconds ...!?!? I noticed this after spending about an hour scrolling through my Datalogs ... Sometimes their fine, other times it ****s up. So we shall see ...

If this doesn't fix it, I will be pulling the intake off, and blowing the passages out with a dremel and compressed air. See what that does...

Joe

 

Everything else you mentioned is interesting as well because I always wondered why stock idle timing is so retarded! Maybe that explains why. Anyway, the stock PCM learns 0% from something like key on TPS voltage, and it can vary, to prove this shut your car off, open the throttle roughly 2% then turn key on and start it, if it shows 2% still then shut if back off, and re-start it, eventually it will show 0% but your voltage will stay linked to actual throttle position.

 

Bad plug wires caused a very similar problem on my car. Even if yours are new and look OK they could be the cause... my old logs had ~150/108 L/R split BLMs and my plug would foul out after only a few minutes of idling. After new wires and cleaning the plugs my BLMs now look pretty good...

Good luck man.

 

Hmmm ... well ... I know NONE of my wires are burned. They have dielectric grease on both ends. At night I see no arching. Maybe I should unplug plug wires one at a time and put an old plug in to ensure consistent spark ... I could always Ohm Test them too ...

Call me out of the loop but I don't even know who else makes OTVC Wire Kits for LT1's anymore. I bought a set from Elite Spark Plug a few years back, and sat on them until I burned up my stock wires with the long tubes ...

Joe

 

Those were the wires I had. My car started running like crap as soon as I put them on. I could be wrong and I just got a bad set, but I'd try different wires before anything else if I were you.

Little wonder they're out of business...

 

Yea ... was I ultra pissed when I found out they went out of business. Seemed like a lot of guys on this board were buying them up, I was surprised to hear they went under so fast ...

Joe

 

UPDATE :

Changed spark plug wires (switched to MSD Super Conductors and nice MadeForYou OTVC Looms ) and replaced both my Oxygen Sensors with brand new AC Delco O2's.

I found that my #7 wire was VERY corroded on the Opti end but was connected firmly . The car does run smoother with new wires and O2's.

However, I still have my extreme split BLM's.

Here is what I now KNOW for fact:

- O2's are brand new
- Plug wires brand new
- No vacuum leaks (tested with starter fluid - EVERYWHERE)
- No exhaust leaks prior to the O2's




From what I know, that leaves me with an Opti that could suck (which is possible, the split BLM's are becoming worse, the more stuff I fix lol - and it sometimes pulls much harder through to redline than other times?) - or a bad injector. They are Ford SVO #30's with relatively low miles on them. When installed (bought used) they did each spray an even cone spray. Currently, listening to them with a mechanics stethascope - they all tick consistantly.



Ideas? Suggestions?


Thanks again ... frustrated ...

Joe