1994 LT1 tuning Issue

[Caleditor]

I need a hand with a 1994 LT1. This is the first OBD1 LT1 that I have ever touched. I wish N0dih was down here to tune this one. The guy contacted me over a year ago.

This is the story (1994 Camaro 6spd). The guy had heads and a cam installed a year ago or more. It has long tubes on it also, but I am not sure if they were already on the car. When I got (12/31/13) it the car was a dog. I drove it 2 days to get a feel for it and that I parked it until the weekend. I threw a tune in it the Friday night before leaving the shop that should have been close. It was based off of the 97 LT4 tune. The car ran great that night. Cold start in the morning acted like it was loaded up with fuel and then lean when tip in. The SES had been on since he dropped it off, but I just figured it was for the skip shift. The MAP sensor was unplugged. I plugged in the MAP sensor and monitored the data. I found that the right O2 was lean. I checked the AIR check valves and found the right side was leaking and had even melted the hose. I removed the AIR system and capped the ports. Test drove and it broke the tires loose into 3rd. Now the timing wasn't fixed (locked usually at 10 deg) it ran great. It had the same cold start issue. I also noticed it took about 5 minutes of driving to go into closed loop. The car was parked again all week until I had time to get my wide band installed. I installed a set of poly engine mounts and the wide-band. It rained all weekend so I was unable to tune it. The car sat all week again and got to it Yesterday

Yesterday I installed a set of used O2 sensors. The car gets into closed loop within 2 minutes. Now it is pulling a ton of fuel.

I put the car in Speed Density Mode. Still a pulling fuel -- The max amount
Next I disable Closed Loop by the temp setting and set the Open Loop AFR Table to 14.7
PARTIALLY PINCHED OFF THE UPPER RADIATOR HOSE TO MAINTAIN 185 TO 200. ONLY LOGGED WHEN ABOVE 185
Next I data log it with the wide band. I pull about 25% off of the low end VE table
Then I pull about another 25% off. I cut that table by about 40% and it was still rich. Both the wide band and the narrow band O2's still show rich. I tuned the first couple of rows on the extended VE table and pulled about the same amount.

I have a tune they I am very close to that is labeled Comp Cam.

I test drove the car and had to pull over and put it back to the LT4 VE settings. The wide band shows 11's and the narrows are 800 to 900mv

I tested it in closed loop one more time and changed the min BLM to 90. The data logs reflex the change. The BLM just max out

Comp Cams LT1 Extreme
LT1 3315/3316 HR112.0
INT: Adv Dur - 281, Dur @ .050: 230
EXH: Adv Dur - 287, Dur @ .050: 236
Valve Lift: INT .510, EXH .520
Lobe Sep: 112.0

In the shop in Neutral This was the tune after the first 25%. Then I pulled another 25% and test drove. You can see it was rich.

RPM

'MAP'

WIDEBAND

965	67	11.48
949	66	11.32
967	67	11.2
928	68	11.4
955	66	10.96
903	69	11.16

982	68	11.32
988	67	11.28
959	68	10.96
973	66	11.4
996	67	10.96
992	66	11.08
973	67	10.88
980	67	11.12
983	67	11
998	68	11.12

1539	49	10.48
1678	44	10.6
1715	41	11.44
1732	40	11.88
1712	40	11.8
1706	40	11.68
1709	40	11.64
1697	40	11.84
1689	39	11.8
1698	40	11.88
1707	40	11.68
1705	39	11.68
1688	41	11.8
1705	40	11.88
1686	40	11.8
1715	39	11.88

1308	50	12.36
1280	50	12.2
1281	50	12.4
1273	50	12.32
1272	50	12.32
1263	50	12.4
1285	50	12.52
1290	49	12.52
1282	50	12.76
1266	50	12.52
1295	50	12.4
1303	50	12.44
1281	50	12.6
1289	49	12.52
1298	49	12.52
1283	49	12.52
1292	49	12.52
1278	49	12.52
1281	49	12.6
1272	49	12.56
1257	49	12.6
1268	49	12.6
1277	49	12.72
1259	49	12.72
1278	50	12.72

1826	39	11.68
1898	38	11.4
1908	37	11.8
1905	36	12.32
1913	36	12.6
1894	37	12.72
1903	37	12.72
1891	37	12.8
1903	37	12.72
1906	36	12.8
1892	36	12.92
1915	36	13
1894	36	12.92
1882	36	13
1859	37	12.92
1845	37	13
1829	37	13.16
1797	37	13.32

[Caleditor]

The 1994 LT1 file is the original file I read out
The 1994 LT1 MOD is the file I was using. I am not sure what combo it has
The OL SD is the file was running in it at one point. I think it is the one with 25% and then another 25%.
The CL SD is one that I used to just check to make sure the wide-band was still OK

the other 3 are just reference file I pulled. The Cower Cam VE table were very close to one of the OL SD tunes I had. I was surprised at that

The file I read out was corrupt I removed these files

[dave w]

I think the LT1 computer is smart enough to maintain Closed Loop idle. I think I would start with adjusting the parameters pictured below to get CL idle working.

dave w

[EagleMark]

With that cam I would not even try and run CL... tune from the WB in S/D first then do the MAF. Leave it OL.

Big issue with moving O2 sensor in long tube is the $EE mask has never had INT delay vs airflow to change location of O2 sensor.

We were testing an OL idle only setting in another thread (smaller cam) by adjust the WOT to enter PE, seems the settings even at idle RPM = under 1200 can do this.

Grab a copy of the latest mask/XDF that steveo has been working on as it has some more needed parameters we needed. It's in this post, aloso other stuff for LT1 in that thread.
http://www.gearhead-efi.com/Fuel-Inj...ull=1#post3131

[Caleditor]

I had it in SD and removed the oil fill cap. No change, so the oil is not contaminated
to the point of causing my issue.
The opti-spark is new and it has some type of new system. I am not sure what that means.

TPS was 0 to 4% in my logs from idle to 2000 at a stop.

I have not checked the fuel pressure yet. I have a digital gauge with a min/max record option. Kent Moore tool

I guess I will do that on Monday

I guess I was thinking about it too hard. It should be Air Flow vs fuel Flow. The injectors are OE. I will check the fuel pressure next.

I am using the Tech II for the Data-logger and it does not give me the Target or Commanded AFR.
How can I scan for target AFR. If I knew for sure the PCM is commanding 14.7 then I would feel better about chopping the VE table

[dave w]

I would not hesitate removing 0.5 AFR ~ 1.0 AFR from an entire table to see how much change, if any, the leaner AFR setting has.

dave w

[Caleditor]

Looking at this file something does not look right. If you compare the wide-band and the narrows they do not look like they are the same AFR.

I will go out and log it again today


attached is the first SD tune log

[EagleMark]

Stock LT1 injectors let alone pump without a hotwire kit are not going to keep up when you hit WOT and high RPM, your going to go lean!

There's is no Commanded AFR in OBDI datastream, or not one yet found? Best you can do is assume the * Open Loop AFR Target is correct. Again with that cam I'd run OL, adjust the * Open Loop AFR Target table but for the low RPM and Idle I doubt the car will ever be happy at Stoich even though the stock Corvette table is 14.3 AFR in that area. Lower would be better. Actually a flat table at 14.1 would be better with a little richer at idle or whatever makes it happy. Along with more timing at idle then stock.

[steveo]

the PE mode @ idle trick (just go 0% tps for PE below 1200 rpm, and make sure min. map is in range) is working well for me, i'm just playing with it right now. you can zero the PE fuel trims out and work from there.

this is pretty cool, since you can leverage it to specify a band (within reason) where closed loop will live, below and above it, it will be open loop.

the integrator delays that roberisarr found (that are in my XDF now) do the trick to fix the blm splits and a lot of the corrupted data, giving it a bit more realistic trims, but it doesn't get around the fact that higher overlap cams seem to want closer to 14.0 at idle, and the closest you can get in closed loop with a NB seems to be more like 14.5.

go maf open loop and just play with your wideband, its so stupid easy to tune compared to open loop with SD, imo. maybe once you nail that, you can try turning closed loop back on with that hacky open loop idle trick, and just crank the integrator delays through the roof and slow down CORRCL, to see if it starts behaving again. i doubt it will.

[EagleMark]

I was playing with your updated TP XDF for $EE and have to say...

and



Not only things we have needed a long time, but the re-organization and descriptions is sweet!

This also applies to RobertISaar for his disassembly contributions! This is going to be a major ground breaking change to LT1 tuning!

[Caleditor]

Maybe I have been doing it wrong. When I start out I disable the MAF, Lock it in Open Loop, Remove all modifiers to the fuel and lock the open Loop to an EQ of 1. I run this on a engine that is up to temp. After I dial in the VE I then move to the MAF. After I am done I then dial in the PE. After that I do closed loop. Some times I will do Closed loop before PE. My closed loop tuning is usually very minor


On the 512kb PCM's (0411) that have issues with big cams and long tube I have found that the 1 meg PCM and the 2004 O2 sensors fix the surging issue. It is like night and day. The 1 meg is soooooooo much faster and can keep up much better.


I have a data-log to pull out of the Tech II. If I am at a steady speed in Open Loop with no adders and PE locked out, I should be able to dial in the VE tables. The problem I have is that I am chopping the crap out of them.

I was doing the VE table and my error factor was .76x to .80x. I said screw this and took 25% off of the table. I ran the car again and I had better throttle control, but it was still way off.
The 3 & 4 data-logs ran between 10.48 to the mid to high 11's
After the 25% removed mainly in the mid 12's, but I had an area of mid 11's. My correction factor was .735 to .842

Thats just too much removing from the stock table. I have to have something wrong.

[steveo]

I was playing with your updated TP XDF for $EE and have to say...

and



Not only things we have needed a long time, but the re-organization and descriptions is sweet!

This also applies to RobertISaar for his disassembly contributions! This is going to be a major ground breaking change to LT1 tuning!

cheers man its fun to work with

I drive one of these cars daily and I love helping people with them

next up is an lt1 tuning guide to match the xdf

[steveo]

thing is though, some of my comments/descriptons are incomplete or based on logical assumptions, I'm hoping someone eventually calls me on it and says "oh that's wrong". I just did my best based on what I've learned

[Caleditor]

I checked the fuel pressure. The engine was cold, so it did not have much vacuum

@ idle I had 41 psi. I am thinking is was 9" or less
@ 2000 I had 36 psi. The engine was smooth, so it should have been around 18". This is whatI had on previous data-logs

Since this calibration has 1 injector setting for flow rate I can see how this could be compounding my issue. Later calibrations have a table for Flow Rate Vs KPA

KOEO was 41psi, but I did not check it after I ran the car. I thought it might be on the low side, so I headed in to check the spec.

I will go ahead and proceed with my tuning method.

[RobertISaar]

with the OBD1 LT1s, there was never a need from the factory for the IFR vs kPa table because of the vacuum-referenced regulator. if that were to disappear or be modified so that the delta pressure from the fuel side to the air side of the injectors were to change, then problems will certainly pop up that are dependant on manifold pressure. a returnless(or any constant pressure) system that shoots into a vacuum is the same, they need IFR vs kPa or some other code trick to account for the injector flowrate change due to delta-pressure changing the flowrate of the injector. if you dig really far in, this will effect voltage offset and dead-time offsets as well.