Hello fellow gearheads,
I’m having several issues with my LT1 powered ride. I’ve 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 ’93 LT1 / T56 drivetrain. I got the donor 4th gen for 800 bucks, couldn’t 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. I’ve been messing with cars a good while, but all carb’d SBCs.
I rebuilt the engine the poor man’s way, this was intended to be a “just build it cheap for fun and use it as a daily” kinda deal – 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 22’s. 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 wasn’t 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 – 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 didn’t. 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 24’s, I went the next size they had in stock which was Bosch design III 32lb units. Yes, they are plenty large for what I’m doing, but I don’t 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 – 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 – 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 – 1200 RPM or so). Whoa – what’s this? So I decide it must be way lean on the start up enrichment – 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 I’ll attach (R17 Tune warming up ). So after a bunch more of this, 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.
There is also a strange issue when it’s up to temp. and idling – 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 doesn’t seem to be reacting much - the BLMs don’t 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 – from 6 to 13 or 16 ms, but don’t seem to be tied to the rich / lean condition from what I can see in the log. Seems like a wide swing. Can’t help but think there’s a parameter in the tune somewhere that’s 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 “Injector driver ERROR”, 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 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? I don’t have a scope, so haven’t been able to scope the circuit while the car runs – 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 I’m 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.
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