I did the water test again, and this time #2 was the same...water slowly evaporated, but #4 and #1 were not much better....on all the others it came off pretty quickly.

And the logs....it shows super lean like bank 1 +17% fuel bank 2 will be +3.9, then if you wait long enough they'll swap sides and Bank 2 will be super lean.

But the tailpipe emissions are incredibly rich, it will burn your eyes. So I had a new theory..if it is so rich it missfires, that would show up as lean to the 02 sensors because of all the unburned oxygen. I leaned it up a whole pound on the injector constant....no change in fuel trims.

I dunno.....at this point I am thinking maybe it is the fuel pump? If the engine was starving for fuel, wouldn't the cylinders toward the front go lean first since they are the farthest from the regulator on the fuel rails?

Half tempted to just go ahead and order a Walbro 255 and new regulator just to rule them out.

Its getting spark....every cylinder is getting spark and plenty of it....I can 100% rule that out. General electrical issues have let me nowhere...and since I know its getting plenty of spark anything electrical related is sort of ruled out by default......

 

I suggested you check fuel pressure in my last post. Do you have a gauge to check it? I would not go to the trouble of putting in a fuel pump without some real reason to do so.

 

I do have a gauge, and I have checked it and it was fine, but that was not recently, it was several months ago.

So yeah, I should check it again. I kind of blew that suggestion off because I was pretty sure that wasn't it, but with the water test it has pushed it back to the front of the list. Thanks for trying to get me to take it step by step though. (I have a tendency to skip to what I think it is rather than test the options methodically)

 

Fuel pressure checks out perfectly fine both at idle and full throttle. Changed fuel filter too.

Still the same.

What about fuel rails, could there be a restriction?

Or what about cylinder balance..could the front cyls be starving for air and therefore running rich?

 

I'm going to see if I can find a way to test the injector harnesses, seems like I've seen a diagnostic tool for that which plugs in between the injector and the plug.

Also wondering about a bad PCM? I froze it up doing a re-program a year or more ago and had to send it to Andrew Mattei to unlock it.

 

The idea of the front cylinders, both left and right being starved for fuel because they are farthest from the regulator doesn't work. The fuel doesn't go into the back of both rails, it goes in the back of the passenger side rail, loops around the front of the engine, and flows out the back end of the drivers side rail at the regulator. In effect, #8 is farthest from the regulator, and #2 and #1 are "in the middle". I'm assuming you haven't modified the fuel rails.

Have you checked the two Opti conectors for cleanliness, and freedom from corrosion? The one at the Opti, and the grey "test" connector on the bracket in the middle of the passenger side of the intake manifold.

Any chance you have a plug wire or the coil wire running very close to the Opti harness wire? Electronic interference from a high voltage wire can mess up the Opti pulse patterns.

 

Thanks, I was not sure how the fuel was distributed in the rails.

All the wire routing is fine, its all been double checked plus its all changed with no difference in the miss.

I ordered a new PCM from Bryan Herter....$40 shipped plus core, just to rule that out...if that doesn't fix I'll send it back.

The last thing I can think of is perhaps the lifters, which are stock with 70K miles now, are collapsing...not too common to hear of it at idle though. I'll check the valve adjustment again before tearing anything open, however.

 

Well guys I wanted to bring this back up again.

Since the last time I've tested another PCM, yet another new Opti, removed the LTCC, yet another set of plug wires, new lifters, new IAT, MAP and a borrowed MAF. Checked injector harness with noid light.

#7 cyl is barely firing, almost totally dead. the water on the primaries test reveals it is barely above ambient block temperature. Other cylinders are in various stages of heat, but #7 is the worst, pulling the plug wire on that cyl does not affect the miss at all. Re-adjusted rockers on that cylinder today, swapped the plug with #1 and even tested spark to the block with a used plug w/o electrode.

I am still seeing "Hi Res: No" on my scan software. The opti harness checks out .4 ohms from the PCM all the way to the opti plug...I've checked all the relevant weatherpack connectors too.
However, I do not have any codes for anything opti or otherwise except for the P0300 random miss (which has actually been turned off in the PCM)


So I am left here w/o any additional options. Myself and several other knowledgeable LT1 guys are all stumped.

 

Have you contacted Jeff Creech? You can go to
www.carolinaautomasters.com

He knows a lot about LT1s, like you wouldn't believe. Try emailing him and sending him this link. I think he could help you out

Good luck, and I couldn't imagine having such a frustrating problem

 

ok i didnt read all the replies but my situation was similar to yours.i had a miss at idle that wasnt constant kind of all over the place.i replaced new otvc wires,new ngk tr55,new opti,good ICM goo fuel pressure,accel coil.i had bosch o2's and swapped in ac delco o2 sensors.my pass side harness was severly burned so i had to cut the harneses and heat wrap the wires together.on thurs i freescaned it and hes what we uncovered:

i have 7degrees of false knock at wot so i have a lt4km on the way.i have a backed out header bolt that isnt helping the knock situation too.
my right bank was running crazy lean also b/c of this.
i threw two codes one was a fan#1code which was odd b/c i dont have a fan switch.so im gonna get the header bolt in and lt4km in and freescan it again and see what problems go away.PM me and i ll explain in a little more detail my "Mystery Miss"

since the install of o2 the car is running pretty sweet.

 

Yeah, I was going to ask about O2's since you're seeing a big split that moves from side to side. I've seen these hard to track misses be O2's before, but I've also seen them be Fuel pump (grounding issues sometimes!) PCM (injector drivers) and voltage regulator in the alternator.

Now, the one question about what does unburt fuel look like on the scanner, well, it looks lean. Seems like it would be really rich, but totally unburned and the sensor don't even detect it, it just detects the air.

Thanks for the props Angela, but this isn't one of those AH HA things, sounds like lots of people have been all up in this one and not found it, so the smoking gun is going to be a mess to find. If you're in the Triangle Area of NC, then pop on by and let's look at some ideas....

take care gang,
-jeff

 

Things checked last night:

Ground strap resistance tested nearly zero ohms

Fuel pressure 44 psi at idle with vacuum hose off, 39.5 with it on

compression test on #7 195 psi throttle closed, 210 open.

Tried a different brand spark plug, also tried a .035 gap rather than .050. That seemed to help it out a small amount...#7 burned hotter but still incomplete or mostly missing compared to others.

I have borrowed a set of spare Taylor wires I'll try tonight, these are not cut to fit but pre-made. Ohms tested similar to mine this morning except the coil wire which tested 34 ohms vs. mine at 204.

 

Just on a lark, swap the O2's from side to side and see if they measure the same thing in terms of splits, or if the split moves sides with the sensors.

And I'll throw another weird one out there, pull the oil cap while the motor's running and look for blowby for me. (The chugga chugga of death.)

Since most every PART has been changed, it's got to be how those parts are hooked together, like wiring/grounds.

I know this has to be frustrating as hell.....
-jeff

 

Also tested the lo and hi res wires from PCM to opti for the 5v reference signal with key on, checked out OK on both.

 

Guys, what about the ignition switch in the steering column? Could it cause odd behavior such as flickering lights and intermittent weak/no spark? This would explain the bad miss at idle plus the cutting out at higher RPMs.

I don't relish the idea of stripping the column down but if all else has been ruled out it is the only part of the ignition I haven't either checked or replaced.