Still hunting for my stumble/miss problem.

BLM's are high which, as I've read, means the ECU is seeing a lean condition that doesn't exist and richens up the mixture to compensate, resulting in a rich running engine.

Attached is my latest data file in csv. Couldn't get TGO to accept my xlsx format.

I blocked off the secondary air injection into the headers. From a cold start, it did not start to miss right away. Went into closed loop right on time.

I am hoping an experienced eye can pick out something that is wrong.

I pulled back home and popped the hood. I let it idle and then one by one I removed all vacuum lines and plugged them. The BLMs did not budge, nor did the stumble go away.

I have logged everything I have done to date which is pretty much everything. Timing set, seals, plugs, wires, module, pickup, gaskets, sensors, etc. Fuel system is fine (tested at idle, full throttle, and bleed down).

This is a link to more detailed info: https://www.thirdgen.org/forums/tech...e-stumble.html

 

Have you changed out the injectors? If so with what?

Listened to the injectors with a stethoscope? Tried unplugging them one at a time to determine which one is misfiring?

GD

 

Yes, Bosch D3's 19 lb from South Bay.

I don't think its one injector. On acceleration, even at higher RPM (like in a held gear) sometimes the engine can just "go flat" for a second or two, that's gotta be more than one.

 

It is not uncommon for Bosch D3 to cause TPI to run lean.

 

The symptoms sound like a bad EGR. I just replaced mine, and it runs perfectly.

 

Are they flow rated at the same pressure as the Multecs? I spoke with SouthBay and they said they should be just fine.

Update: Well I'll be! Fred, you might be onto something and this would be a big thing to get cleared up once and for all on these boards...

https://www.thirdgen.org/forums/diy-...ctors-not.html

Looks like the D3s are NOT the same as Multecs....

 

I wouldn't think a stuck open EGR would cause stumbling at mid rpm or higher. But I am not totally certain about that. Idle for sure.

 

The EGR could be stuck, or the diaphragm could have little holes in it. I suggest disconnecting the vacuum line, and plugging it with a screw, and see how it runs.

 

I have the same problem, right at 2000-2400, when it happens the blm goes from 140 to 118 and back.

It's not the EGR, I disconnected it.

When I find it I will let you know.

 

I pulled a vac on it and heard it open and close. I also tested the solenoid. I think its all good. I did block ALL the vac lines and the BLMs and miss didn't change.

 

The EGR could leak even if it opens and closes. Just because the vacuum side of the valve works does not mean the exhaust side is sealing properly.

It's worth ruling out the injectors. Check them with a stethoscope and by unplugging them one at a time to see effect on misfire condition.

Some people do have "tuning" issues with the Bosch injectors but a lot more people do not. I run a performance shop and I've seen the variations between different cars that *should* be the same but aren't for some unknown reason. Usually we try to find that reason, but there are times when the customers budget and our sanity is better served by a custom MAF rescale, etc

That said, I did retune mine but because I went with larger 24 lb injectors on my LB9. But ultimately most of the tables I left stock. I changed the injector size constant and some of the startup enrichment but otherwise pretty much left the rest stock.

GD

 

Yeah, that seems to be the consensus, some love them as-is, some need a tune. I wonder (and its just wondering over a beer) if some that install the D3's are to fix a symptom- the cause of which may include vacuum leak(s) of some sort, and the richer mix just works well to compensate, hence the "eureka!" moment.

From what I've read, I probably shouldn't reinstall my Multecs (I was even thinking of having them cleaned and balanced). I think I want to go after my Prom.

As a cheap way out, maybe I could reinstall them temporarily and see if that fixed my BLMs, then make a decision.

 

It is easy to remove the vacuum line that is attached to the EGR, and plug it. At least if nothing changes, you can rule it out. They're not too pricey, and are easy to replace, and some guys just leave it. You will throw a code 32 with it off. I didn't get a code when mine was bad, but I did with the vac line removed. Go figure.

 

You can't rule out an EGR valve by plugging the vacuum line. If it's stuck open or partially open then manipulating the vacuum signal won't do anything.

 

It worked for me, The only thing I can say is just try it.

 

I understand but that means the EGR solenoid is likely at fault in your case. It was getting a vacuum signal when it shouldn't have been. Replacing the solenoid valve would likely restore your system to operational.

GD

 

I swapped in my original Multecs. Will report back in a short while after driving.

 

Well, well, well. Looks like I need to try to get a refund from SouthBay. All I did was swap out the D3s for my original multecs. Car drives great except for high load miss. (I will be checking my Iridium plugs for fouling).

Data file attached. BLMS are LOW to normal now.

D3s are NOT drop-in compatible in my case.

 

Talk to SouthBay about it. Perhaps you got the wrong injectors. Also you should verify what PROM you are running, and that it indeed is programmed for that injector size, etc. The 305 uses 19 lb injectors, while the 350 uses 22 lb injectors. And check the part number on the Bosch injectors and make sure they match what your PROM is expecting.

GD

 

I didn't replace the EGR solenoid, I replaced the EGR valve attached to the intake. When I removed it, it was stuck, and full or carbon. I replaced it, and no SES, no stumble, and it runs very smooth.
It ran smooth after I disconnected the vac line to the original EGR, and plugged it with a small screw. That's how I knew the EGR wasn't working.
It might not be the gremlin in your case, but it's simple enough to rule EGR out.

 

So I found out I had broken insulation in four places in two of my cylinder spark wires. Cylinders 2 and 4. Pinched and heated. Temporarily patched them up and engine is solid smooth idle and clean revving. Though it still misses at the top, I will take care of that with new wires and follow back up.

This thread continues here...https://www.thirdgen.org/forums/tech...inside-my.html