Hello,

Im a new poster, however I've read about every single post related to LT1 PCM manipulating, modifying, tuning, etc...

I'll get right to the point, I need major help or a simple answer with my programming project... problem is I cant find much info from people with 83lb High Impedance injectors.

Got the car running pretty good with the following:
Running Pretty Good:
LT1 383
Stock PCM
Cam 230/234 110LSA
AEM High Impedance Driver with 42lb Ford SVO Green Tops
58mm Throttle Body
MSD Pro Billet Distributor (after destroying 2 Accel stockers)

Then I put the 83lb injectors in (using the AEM driver that worked good with the 42lb SVO's), it runs good until it goes into closed loop resulting in major Lean spikes on tip in, almost like the shooter in a carb is not working... stumbles bad at tip-in then recovers but not 100%, and strange thing is when it recovers after tip in it still runs very lean - some times the Lterms show lean as well only during tip in stumble.. then they go back to normal even with slight stumble. The instant the throttle reaches PE mode it is instantly smooth and normal.

I've done everything to try and fix this including:
1) Unplugged one 02 making it run total open loop - this is the only thing that makes it run good, and it runs PERFECT in open loop!! (but I cant change the PE Enrichment in open loop... so this is no good.

2) Messed with MAF - just richens up the LTerms and the Tip-In lean is still there, and eventually it Lterms it right back to the original all over lean condition.

3) Messed with the "MAT to enter Closed Loop", but still enteres Closed Loop

4) Disabled BLM, but still the tip in and lean stumples are there... only runs good in true Open Loop (either during warm up or with 02 unplugged)

Seems to me like the 83's will not work with the stock PCM...
Or if I can get LT1_Edit to not use the 02's at all but still reference the PE tables, WOT tabels, and VE tables, this would be great too!

Please help if you can!!! I've about reached the end of hope for the stock PCM on this one.

 

You say you are running 83lbs High Impedance injectors, I guess that was a typo and you mean LOW Impedance Injectors with an AEM box

According to the symptoms you have described, you need to modify the Injector Offset vs. Battery Voltage tables. Scale up 20% and the lean tip in should go away.

The next step is to go back to stock MAF tables and tune the Low Injector Pulse Width Adder vs. BPW table, that should take care of the reach/lean condition.

 

I use lt1 edit version 2.2 on a 1997SS obd2 PCM. Running 72# Seimens with an Acceleronics driver. I raised the Inj vs. volt value about 10 to 15% in the 12 to 14 volt range. Also, I had the reverse condition. Ran rich in closed loop. I dropped the MAF cal 2% and adjusted the BLM update trigger @ a higher MAP value (ie... 60kpa). Low range blms then would not change. I zeroed alot of the PCM tables as I do not need them. Hope this helps. My application... 383 LT1 AFR heads w/ obd2 PCM and Procharger D1 (7.6 --> 3.4 pulley)/ 72# Seimens injectors/ plus other mods. B.

 

mzgp5x and HungryT/A - Thank you VERY much for the advice, yes these are actually Siemens Deka 83lbs LOW impedance. Whoops. I'll try everything you guys suggest as soon as I can.

I also thought the injector offsets could be causing problems but couldnt find anything anywhere about what low impedance 83lb injectors should be. Good place to start. I found one guy with low impedance that ran stock offsets but I think he was talking up the AEM driver box.

Couple questions though...
Hungry T/A: "Low Injector Pulse Width Adder vs. BPW table, that should take care of the reach/lean condition" I dont believe I've seen this anywhere in LT1_Edit for OBD1. What are you using to modify this? (at least not in my version LT1_Edit OBD1 v2.2)

mzgp5x: "I zeroed alot of the PCM tables as I do not need them". do you know off hand what tables you zero'd? I feel this is the easiest way to determine what tables work - I Zero'd my VE tables while the O2 is unplugged and it runs exactly the same, making me realize I cannot tune True Open Loop like I wanted to.

Thank you thank you! Once I try this I'll post results.

 

I'm using Tunercat, I'm not so familiar with LT1edit... last time I was shown LT1edit, it had half the features and tables Tunercat has.

 

Zeroed the following...
PE vs. temp. (Use PE vs rpm only for wot tune)
Knock table. (ALot of noise and RR's were cause of false knock)
Also, look @ burst knock table. This table can be a cause for you lean condition when you transition with large throttle input. This may help.

I run alot of timing advance with my set-up even though it is a blower car heavy modified (9.5:1 compression). I tried reduction of timing, but went to the stock map and reduced timing to 32 degrees @ 90 and 100kpa maximum rpm. LT1_edit ver 2.2 is a great tool for tuning. Version 2.2 had a blm lock=1 @ wot (useing that), and a MAF high threshhold feature (reason why I upgraded to v2.2). The stock MAF cal frequency output cannot handle closed loop flow with a D1. LT1 edit ver2.2 has a table that allows you to raise the max high threshold to 60K+ from 10.7k. This can be a problem on FI applications running OBD2. Christian Millard speculated that exceeding MAF freq would drive injector pulse in half. My data indicates this is true.

Also, a boost ref fuel regulator can help with trasition from closed loop part throttle to WOT. The fuel pressure spikes from 43psi to 52psi avoiding a low pressure transient starve. Possibly a momentary fuel starve could be a problem.

I also have tried OBD1 conversion. I like my OBD2 PCM tune much better. ALot of flexibility with LT1_edit.
Good luck and hope this helps. B. (97SS 383 D1 M6)

 

figures about the tables not being in LT1_Edit.

I increased Injector Voltage Offsets by about 15% at first, noticed the Lterms seemed to pull a little more fuel out, same symptoms...

I then added about 150% more time in the Injector voltage offsets... this added tons more fuel especially during cold startup open loop as expected... once Closed loop hit, Lterms quickly ended up bottomed out at -15% under most conditions, and still Tip In Stumble with continuous lean acceleration similar to before. Once throttle hit WOT then smooth power and rich (this is probably only around 1-2psi boost)

Strange part - the worst continuous stumble/lean area (~20% Throttle and accelerating below 2000rpm), While stumbling the Lterms are bottomed out -15.6% and Sterms are also mostly subtracting fuel (-20% and one very small timeframe of +2%). One would think it's actually rich stumble but it's not... this also shows usually around 14.7-16:1 on the wideband while all this is happening.

Tip In stumble also shows 15-17:1 on the wideband... mostly Lterms show it's trying to add fuel but after the Tip In then holding throttle the Lterms start subtracting fuel even if the Wideband shows it's either 14.7 or leaner.

To me it seems the 02's are reporting richer than actual conditions, creating a lean condition. I checked for exhaust leaks but I thought exhaust leaks cause the engine to run richer than it should?

None of this happened with the 42lb injectors + Aem Box. I may try to revert back to the 42lbs to verify 02's are working and exhaust leaks or other problems arent causing this? (if the problems did carry over to the 42lbs this would be a good thing)

 

For those interested I accidently fixed/discovered the problem.. (lean tip in stumble)... Runs perfectly now.

While converting to a 2 bar tune (stock PCM - getting ready to change pullies and ramp to 15psi on a 383 running at 6 psi) I was scaling some tables and other MAP related tables... once I finally got it running and driveable (back to the 1 bar MAP driving condition/quality but with a 2 bar and SD - no MAF) which included scaling the injector size by 1/2 (from 83 to 40), it still had the Lean tip in stumble and ran better in open loop than closed loop... (everything showing up as lean stumple with rich sustained load)... I decided to lower the injector flow rating from 40lb/hr to 30lb/hr (83lb injectors with a 2 bar MAP and 1/2'd VE tables).................................. and..................................

NO MORE LEAN TIP IN STUMBLE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!

Instantly upon startup after doing this I knew it was gone... I could blip the throttle at any rpm/amount and it was nothing like before.. this was completly consistent smooth.. FIXED!! At this point the overall tune was rich from lowering the injector flow setting by 10 (which drives the injectors more) but a couple VE master logs later everything is absolutely perfect.

Since LT1 Edit and Tunercat do not allow you to adjust the "pump shot" like aftermarket ECU's/80-90's production ECU's I can only conclude:
1) Injectors are either not 83lb injectors (maybe 75?)
2) Injector voltage offsets are incorrect (everything I've tried didnt help or I didnt go far enough - everybody else says stock offsets worked for them)

With a set "pump shot" having artifically high injector flow ratings reduces the actual delivered pump shot, while the 02's VE tables add/correct for the continuous load immediately following tip-in.

Sound right? Keep in mind everyting was fine with the 42lb'ers.