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Thread: LT1 swap, start up surging, injector driver error, extreme O2 swing periods

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    LT1 swap, start up surging, injector driver error, extreme O2 swing periods

    Hello fellow gearheads,
    Iím having several issues with my LT1 powered ride. Iíve got a wicked surge during warm up, and also a really weird rich / lean swing at operating temp. Hoping I can lean on some folks here, learn more and get this thing fixed up. Sorry for the long post. Thanks to anyone that reads it, maybe this is too much. Even more thanks to anyone willing to help the lost find their way!

    First, a little background is probably in order.

    I am new to the EFI world, tuning my first injected ride, a 91 Camaro RS with a í93 LT1 / T56 drivetrain. I got the donor 4th gen for 800 bucks, couldnít pass it up. This install required lengthening all the ECM wiring to install ECM in stock 91 Camaro location in the dash. Everything worked the first time, except the tach, which needed the tach mod with potentiometer to fix the busted internal resistor. Iíve been messing with cars a good while, but all carbíd SBCs.
    I rebuilt the engine the poor manís way, this was intended to be a ďjust build it cheap for fun and use it as a dailyĒ kinda deal Ė just honed it up and installed new rings and bearings. Freshened the heads, threw in LT4 valve springs, and a Schneider 224/224 114LSA cam, and LTs, flowmaster exhaust.

    Pretty simple car, been fun to drive so far. Had the original injectors after I built it, which I believe were 22ís. I spent some time learning TunerProRT, bought the stuff from Moates, and started burning chips and learning. Got the car to where I felt decent about the VE maps, timing, etc., but the car still wasnít right. It started fine, warmed up without issue, but just smelled rich, and had split BLMs. The O2s were showing the up/down signal they should, and computer seemed to be acting logically. But the split was bad, so bad that while cruising, the right side would run up to 160 while the left was 130 or so. At idle, right was 135 or so, left was 120 Ė and they would both vary about +-5. Tried several things, and never really figured it out. I turned the max. BLM to 145 and drove it some. The car smelled rich, and was getting about 16mpg. I had pulled plugs expecting to see a dead cylinder or something out of the ordinary, but really didnít. Checked compression on right bank fearing something mechanical, but got 180-185 on those 4, good enough for me. Did try swapping the heated O2 sensors, but the problem remained on the same bank.

    A few things led me down the path of swapping the old injectors (age, possible leakage, Injector bank errors showing up). I pulled the injector plugs one by one and at least 4 of them made little difference when unplugged (leaking I guess?). So, FIC seemed to be a good vendor, and not wanting to limit myself with 24ís, I went the next size they had in stock which was Bosch design III 32lb units. Yes, they are plenty large for what Iím doing, but I donít think they are really that far out there. Opinions welcome however.

    So I get these new injectors installed, and have changed the low PW offset, volts vs. offset, and flow rating in the ECM per excel sheet from FIC. The engine was warm when I did it, so after the install was done I start the motor and all seemed well for the most part. The fueling was way off Ė could be I had 22lb injectors, but tune was 24lb for 94 up cars, not sure. I get the fueling in line enough, and I drive the car a bit, and encounter a strange bog that was concerning Ė like I had something in the FI system failing. I get the car back home and quit for the day.

    The next day I decide to give it another go. I start the engine, it runs fine for a bit, then starts this crazy cyclical surging (700 Ė 1200 RPM or so). Whoa Ė whatís this? So I decide it must be way lean on the start up enrichment Ė never a problem with the old injectors, but maybe they were leaking bad enough that the extra fuel masked the warm up issue? Richened the start up enrichment, and the open loop % change per coolant temp table a little, then little more, then a lot more. Each time I start it I get the same darn thing. Starts up OK, then when it tries to idle down the surging starts, IAC normally runs right at -0 warmed up, but when it surges it maxes out at 160. I have a log of this that Iíll attach (R17 Tune warming up ). So after a bunch more of this, eventually the motor goes into closed loop mode Ė but itís so lean the BLMs shoot up to 160. The surging continues, but gets some better with the additional fuel, IAC starts to relax some. I let it warm all the way up, and now the BLMs are about 115 Ė 120, and the motor acts pretty good for the most part. The BLMs shooting to 160 until it hits 190F is weird because with the old injectors once it hit closed loop the BLMs were stable.

    There is also a strange issue when itís up to temp. and idling Ė the O2s will be cycling what I think is normal, but then it will suddenly go totally lean, start struggling to run for about 6-7 seconds. (see attached log "Idling in garage new injector offset values). Then it will go full rich for 6-7 seconds, and continue this oscillating pattern. I have pics of this and the log. While this is happening, the ECM doesnít seem to be reacting much - the BLMs donít seem to be rising / falling as I would expect they should under such an extreme condition on both sides. I would think the ECM would be all kinds of excited to try to get the AFR in check. I do notice the BPWs are changing more than I would expect Ė from 6 to 13 or 16 ms, but donít seem to be tied to the rich / lean condition from what I can see in the log. Seems like a wide swing. Canít help but think thereís a parameter in the tune somewhere thatís causing this math equation to swing the BPWs too far. Or maybe the ECM is smart enough to know the engine is going to die without more fuel, so it steps in above the tuned parameters to stay alive??

    I am also getting intermittent ďInjector driver ERRORĒ, and steady Injector bank 1 and 2 ERRORs at all times (cold, warming up, warm). These errors were about the same before and after the injectors. I have removed the plugs at the ECM and checked all the ground wires, and all seemed to read good with DVM. Several of them are tied together at the rear of the block, but I canít say that I have every ground at the same place it was on the 4th gen car. Does the placement mean that much? I donít have a scope, so havenít been able to scope the circuit while the car runs Ė is this the next step for this item?

    So I have two big issues: the Warm up surging, and also the rich / lean swing. Just odd, cause it behaved pretty well with the old injectors. Not sure what Iím missing. Thought about going back to the old injectors for baseline, but not sure what it would really tell me.

    Alright then, if you made it this far you are dedicated. My sincere thanks to anyone willing to lend a hand. I'm really not sure where to go next. Maybe to Holley 4 barrel.
    Need more of those.
    Attached Images Attached Images
    Attached Files Attached Files
    J. Moen
    91 Camaro - NASA American Iron Road Racer #91 "The Menace", carb'd 350, FloTek heads, "because racecar"
    91 Camaro RS - '93 LT1 /T56 swap, 224/224, 60lb Siemens, garage ported heads, VS racing 78/75 turbo, Intercooled

  2. #2
    Fuel Injected! steveo's Avatar
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    Several of them are tied together at the rear of the block, but I can’t say that I have every ground at the same place it was on the 4th gen car. Does the placement mean that much?
    not really. anything that went to chassis or engine block is safe to relocate.

    the one thing you don't want to do is take 'sensor grounds' that were attached to a 'sensor ground' terminal on the ecm and ground them to chassis
    ...or ground other new things to 'sensor grounds' at the ecm
    ...or ground those sensor ground lines to a chassis ground.

    reason being the ecm sometimes has filters on those sensor ground lines

    eventually the motor goes into closed loop mode – but it’s so lean the BLMs shoot up to 160. The surging continues, but gets some better with the additional fuel, IAC starts to relax some. I let it warm all the way up, and now the BLMs are about 115 – 120, and the motor acts pretty good for the most part. The BLMs shooting to 160 until it hits 190F is weird because with the old injectors once it hit closed loop the BLMs were stable.
    if you change injectors and suddenly it runs like crap and your BLMs are pegged, you probably haven't got the right injector flow constant or offsets, do you have a data sheet for the injectors?

  3. #3
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    Quote Originally Posted by steveo View Post
    not really. anything that went to chassis or engine block is safe to relocate.

    the one thing you don't want to do is take 'sensor grounds' that were attached to a 'sensor ground' terminal on the ecm and ground them to chassis
    ...or ground other new things to 'sensor grounds' at the ecm
    ...or ground those sensor ground lines to a chassis ground.

    reason being the ecm sometimes has filters on those sensor ground lines
    I'll go back and double check, but I know I didn't change the way the sensors were wired. If they had 2 or 3 wires straight to the ECM, one of them presumably a sensor ground, then that's how I kept it. I think there were several grounds on the ECM, maybe 5 or so. I know one went to the dash, several others at rear of the block. I'll see where I landed them. Can't recall if any of those were called out as sensor grounds or what. I printed all my wiring stuff as I came across it, so I'll have to do a little digging through the binder.


    Quote Originally Posted by steveo View Post
    if you change injectors and suddenly it runs like crap and your BLMs are pegged, you probably haven't got the right injector flow constant or offsets, do you have a data sheet for the injectors?
    Couple things perhaps threw me off: leaky injectors and 22lb injectors with a tune that had the constant set to 24. I should have changed it right away but didn't. Anyhow, I have the excel sheet that FIC sent to me. I'll post that up here. The values were certainly quite different than what was in the ECM stock. I used the rows called "Min Puls and Def pulse. There were several more values in the excel file than would go into the LT1 ECU. For battery V offset, I used the first column.

    I've also attached the last Bin file too, in case that would help at all.
    Attached Files Attached Files
    Last edited by hotrodf1; 06-01-2017 at 08:09 PM.
    J. Moen
    91 Camaro - NASA American Iron Road Racer #91 "The Menace", carb'd 350, FloTek heads, "because racecar"
    91 Camaro RS - '93 LT1 /T56 swap, 224/224, 60lb Siemens, garage ported heads, VS racing 78/75 turbo, Intercooled

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    I thought a little more about the injector offsets like you said. When I put the info I got from FIC into the tune, the offsets were a LOT less than the stock (in both tables). Then I'm reading in my binder tonight, and ran across a nice article I had printed a while ago from LT1PCMTUNING.com. He had said that not enough offset could result in lean at idle and rich at WOT or part throttle (sounds familiar). And also mentioned that the typical Bosch injectors used on LT1s are actually slower acting than the stockers. The values I had input would be if the Bosch were about 4x faster than the stock units! So maybe that's the deal. So I put the offsets back to stock and I'll try to start the car tomorrow evening and see what that does.

    I do notice that the values in the spreadsheet are for LS computers. Are the LT1 and LS offset computed differently perhaps?

    Also searched a little harder for the offset values, and pulled some threads that said I should zero out the low PW adder table, since the Design III actually flow MORE at low PW not less. So I'll try doing that too. I see several sets of offset data, but nothing yet for 32lbs.

    One thread showed this for 30lb Bosch
    ------------------------------
    The M-9593-BB302 calibration sheet matches 30#/hr injectors. Maybe check for a Bosch number on them and run the 'net for it.

    Here is the PW offset vs. Bat for the 'BB302 injectors:

    @44 psi
    Value found in thread on left vs. value in my spreadsheet on right
    6.4 V: 3.01787012 vs 2.5733
    8.0 V: 2.04425964 vs 1.3091
    9.6 V: 1.52886932 vs 0.8279
    11.2 V: 1.20760185 vs 0.5500 or so
    12.8 V: 0.97447267 vs 0.35xx or so
    14.4 V: 0.77577132 vs 0.2129
    15.0 V: 0.74079391* vs 0.1769
    -----------------------------------

    Hmmm. That seems a little different.


    The min. PW is supposed to be .853. Where do I put that guy in the tune?

    Why wouldn't the data in the spreadsheet be correct??
    Last edited by hotrodf1; 06-01-2017 at 08:48 PM.
    J. Moen
    91 Camaro - NASA American Iron Road Racer #91 "The Menace", carb'd 350, FloTek heads, "because racecar"
    91 Camaro RS - '93 LT1 /T56 swap, 224/224, 60lb Siemens, garage ported heads, VS racing 78/75 turbo, Intercooled

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    Update: She sings again!

    Update:

    As of yesterday, the car is running much much better. Thank you Steveo for the suggestion on the injector offset values. I never would have thought I had bad info. I used the offsets that I posted above, and extrapolated as best I could to fill in the other values in the LT1 tune file using an excel generated equation. Also zeroed out the low PW offset table as suggested on Thirdgen.org. Having these two tables right has enabled me to continue on with the tune. The low MAP / low RPM areas were still lean, I believe due to the leaky injectors previously adding fuel unknown to the ECM. The car now warms up fine with no surging. Runs better than it ever did, hopefully some sort of fuel mileage will come about as well.

    Is there any way to "verify" that the offsets I have used are in fact the correct ones? Since this is '93 batch fire injection maybe I won't be able to tell that much?

    I do still see the injector driver errors popping up, and the ERROR still shows on injector banks 1 and 2. I'm not sure I feel any effects from that.

    I have attached the excel file I used, if that helps anyone out there. The equation I used to extrapolate was :
    y = 62.993x^(-1.638)
    Put the volts in as x, and it turns out a value that fits pretty decent.
    Attached Files Attached Files
    J. Moen
    91 Camaro - NASA American Iron Road Racer #91 "The Menace", carb'd 350, FloTek heads, "because racecar"
    91 Camaro RS - '93 LT1 /T56 swap, 224/224, 60lb Siemens, garage ported heads, VS racing 78/75 turbo, Intercooled

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    Fuel Injected! steveo's Avatar
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    Is there any way to "verify" that the offsets I have used are in fact the correct ones? Since this is '93 batch fire injection maybe I won't be able to tell that much?
    for a car like yours if it runs good enough now, your offsets are probably good enough to continue tuning. just go with it.

    I do still see the injector driver errors popping up, and the ERROR still shows on injector banks 1 and 2. I'm not sure I feel any effects from that.
    are you sure about that error code? what scan tool gives you the error? what are the error numbers

  7. #7
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    Quote Originally Posted by steveo View Post
    for a car like yours if it runs good enough now, your offsets are probably good enough to continue tuning. just go with it.



    are you sure about that error code? what scan tool gives you the error? what are the error numbers
    Not totally sure about much LOL. Just the laptop running TunerproRT 5. Using the files I posted in the first post. I've not used a scan tool on this thing ever. How does that differ from seeing it in TunerPro? I guess I could try scanning and see if the same error is popping up. What kind of scanner would you recommend?

    I guess I don't know what the error number is. I see this in the "item lists" tab while live with the ECU. You can see it in the logs as well playing it back. I have DTC 1 - 72 shown, then there's a bunch of other stuff listed, then the Warm start A/C logic, and right after that is the two injector banks, and two injector drivers. This is in the $DA3-16159278-V2.adx. I don't know much about these details - I downloaded this from perhaps someone on this forum. But I didn't set it up. If I double click on the "Injector bank 1" it says the following:
    Unique ID is 85. Packet offset is 0x0E 14
    8 bit data size
    Operand is 0x08
    Result to test 0x08.
    Honestly don't know much about the hex values etc.. I certainly respect all of you that can dig into this stuff so far.

    Maybe that ADX is for the 94-96 cars, and it's picking up something else in my '93?
    J. Moen
    91 Camaro - NASA American Iron Road Racer #91 "The Menace", carb'd 350, FloTek heads, "because racecar"
    91 Camaro RS - '93 LT1 /T56 swap, 224/224, 60lb Siemens, garage ported heads, VS racing 78/75 turbo, Intercooled

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