Daveinet

I have an intermitten problem. On a good day, All my BLMs will look pretty good everywhere, not perfect, but <+/- 10. However sometimes the BLMs stay way rich - like 112 below 2500 RPM. They get a little more typical and then go slightly lean in the top end or near full throttle. The engine seams lean, slightly down on power and just has a dirty/wimpy sound - kindo of like a misfire, but not random. Even in the top end where the BLMs are fairly normal or slightly lean, it is still down on power and runs weak. Sometimes after driving for several hours, I may hear a pop and all of a sudden everything is normal. Power is normal, BLMs look good everywhere, and everyone is happy. I've given it a complete tune up, new wires, plugs cap and rotor. No change.

I'm wondering if I have an injector sticking open, fooling the ECM but the weird thing is I would have thought that once the throttle got open or the RPM got high enough (where the BLMs are normal) that is should run normal, but it doesn't. It still seams lean even at WOT when it chooses to run poorly. The other thing is the pop at the start of running correctly. The pop happens every time it changes to running correctly.

Any thoughts?

ULTM8Z

Could be an ignition problem on one of your cylinders. If your "pop" is through the intake manifold, check your ignition system first (plugs, wires, distributor). I had been battling a "rich" problem years ago, complete with popping out the intake. Turned out one of my spark plug wires went south. It was wreaking havoc with my BLM's.

Since thirdgens I believe have the O2 sensor on the drivers side and you're noticing the ECM reacting to whatever the malfunction is, I'd start on the driver side.

RBob

iTrader: (1)

A silicone poisoned O2 sensor will report rich and drive the BLMs down to the point that the engine will cut off. BTDT, and it was easy to poison too.

The '7427 PCM code has a lot of 'stuff' in it. Many that are difficult to understand. Which causes funny issues. Like the cat-con arson mode (affects TCC lockup, fueling and SA), torque management for the transmission (affects SA), low octane routine and so on.

RBob.

doc

Daveinet: Do you realize that you have 16 different BLM values, one BLM unique value to each of the 16 Fuel Trim Cells (FTC). Therefore, depending on the FTC RPM boundaries, you can be in FTC #14 while you are above 2,500 RPM with one BLM value, and be in FTC #6 while around 2,000RPM with a different BLM value. It is typical to see a BLM value of 132, and change your cruising speed and then suddenly see 112 BLM. If you have a MAP car, then you "fix" this issue with the VE table. If its a MAF car, then you fix this issue by tuning the MAF table.

Recently, while at idle, I had a BLM value of 108 (FTC 0), and had BLM value of 126 while cruising at 55 mph. I had changed the MAF sensor. So I tuned the MAF table, and all is good now.

Daveinet

Yes, I do realize there are 100+ cells (16197427 ECM). Running TPV5 so taking readings that are averaged over driving long periods. For the first year since install, it has been pretty close. its only been around the last 8 months or so. I starting doing some programing, just to try to perfect some areas. Things were going very well, and then all of a sudden it got real ornery without making any more changes. I'm running a Moates G3 switcher, so I can switch between 8 different programs. I always keep the original in the 0 position, so I can always go back to square one. It doesn't seem to matter what setup I use, it always has this problem, although at random it will run perfectly fine. I have had where switching programs made it run fine, and then switch back and it continues to run fine, but that rarely works.

As was mentioned above, I did change cap rotor and wires, and plugs with no change in the problem - still as it was before. When it pops, its not through intake. It does not spit, you just hear a pop as it immediately takes off and then runs sweet from then on. Usually once it decides to run, it will run fine until I shut it off.

I do think its something on driver's side, as the O2 is on that side. I've though about swapping injectors from side to side, but because the problem is intermittent, I'd be hard pressed to tell if it changed anything. This is MPFI, so its not like I can see anything like a drip.

Daveinet

I finally had some time to do some more trouble shooting and have learned nothing. This is a multi-port setup. I swapped injectors from one side to the other. Now I have a miss all the time, although I think once or twice it did run clean momentarily. You can only hear the miss under load, otherwise it is random misfire that is hard to identify.
This MPFI is so bizzar. I thought I should be able to just start unplugging injectors until I found one that made no difference - try to isolate which cylinder. Cranked the idle up so I could hear the mis better. Started unplugging injectors, and it seemed to make NO difference. I actually had 3 injectors unplgged on one side and it ran the same unless you snapped the throttle. Finally unplugging the 4th injector, the mis would get worse. Not even sure what to try next. It seems the only way to hear the misfire is under moderate to heavy load.

DENN_SHAH

iTrader: (1)

what injectors do you have?
i ask because the factory GM multec port fuel injectors aren't the greatest around.
flaky injectors can cause some strange things when they are starting to go bad.

check the cold and hot resistance of all the injectors.

Daveinet

The injectors are pico injectors that were part of the Edelbrock kit. I have no idea whose injectors they are using.

If an injector does not fire, can you see it on an oscilloscope?

transplant

Sounds like you have some dirty injectors. Try a can of seafoam in the fuel tak & drive it for a few days.

DENN_SHAH

iTrader: (1)

yes, if the injector is not firing you can see it on a scope.
a scope can tell you a good bit about how an injector is behaving if you understand what the patterns are telling you.

if you need it, there is some info on scope patterns at the following links,

http://www.automotivetestsolutions.c...rWaveforms.htm

http://motorage.search-autoparts.com...ategoryId=1079

http://www.240edge.com/manuals/89-90_240sx/waveform.pdf