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I made a thread a while back about a vibration issue and it went dead due to my funding, but I've put another flywheel and clutch into the car and nothing's changed.
I should mention that the engine in the car is a 400ci dynoed at 450hp from the engine builder.
Now when I step on it, the thing shakes and can't even break tires loose.
I'm thinking maybe the problem is an engine issue? Here's a screenshot from EEHack of a knock analysis and it's everywhere. I think the knock is false because there's no sound even coming from the engine, the events just appear.
So far I've redone the ignition with new plugs and wires, plus a new optispark that came with the engine.
I've tested the injector plugs with a noid light and all is well there. I know it's not the injectors themselves because they were dynoed with the engine builder. Fuel Pressure is 46 pounds.
I installed 2 new O2 sensors.
The cat's been deleted as well.
I'm going to attach two EEHack logs and my PCM's bin file.
I'm super stuck here and any help would be appreciated.
Last edited by Metalface; Jun 7, 2020 at 06:10 PM.
Reason: More info
is the engine balance ? shake at all on dyno
what type of clutch and flywheel did you use ?
Engine is internally balanced on both sides, with no shake on the dyno. The clutch is a stage 3 kit from carolina clutch and an aluminum fidanza flywheel, also neutrally balanced.
As an experiment, you could try setting every single knock retard table in the BIN to 0 and see if that corrects for the false knock. If it does, then the engine should run smoothly and your knock visual shouldn't change. If however you do this and way more knock events appear--especially in PE--then your tune is WAY off and dangerously so.
Note that if your engine is making more noise than whatever the stock PCM you're using was calibrated for, it will absolutely detect false knock and correct for something that isn't actually there. When altering the acoustic profile of the engine, it's on the tuner to listen for real knock and adjust accordingly. The knock module in our PCM is tuned for a very specific noise profile, and if the engine no longer fits that profile, it will be retarding timing like crazy.
As an experiment, you could try setting every single knock retard table in the BIN to 0 and see if that corrects for the false knock. If it does, then the engine should run smoothly and your knock visual shouldn't change. If however you do this and way more knock events appear--especially in PE--then your tune is WAY off and dangerously so.
Note that if your engine is making more noise than whatever the stock PCM you're using was calibrated for, it will absolutely detect false knock and correct for something that isn't actually there. When altering the acoustic profile of the engine, it's on the tuner to listen for real knock and adjust accordingly. The knock module in our PCM is tuned for a very specific noise profile, and if the engine no longer fits that profile, it will be retarding timing like crazy.
It did run through my mind to disable the knock retard but I was worried that it'd actually knock and damage the engine. I'll see what happens.
It did run through my mind to disable the knock retard but I was worried that it'd actually knock and damage the engine. I'll see what happens.
I wouldn't do a dyno run on an untested motor in that condition, but it would be generally safe to just do a normal drive and watch the knock counts in EEHack. I did run for a little while with knock retard disabled just to test false knock from my exhaust.
Just take it easy and stop as soon as you've confirmed whether the poor operation condition changed. If it changed great, you know what's wrong and can start from there. If it didn't, turn the knock retard back to what it was as you could potentially have a real knock issue.
I just came back from a light run with knock retard disabled and of course it's still shaking its guts out, so knock retard could be a problem in the future but isn't my immediate one.
The shaking is worst at low RPMS under load. Oddly enough what gear I'm in makes the shaking worse, but I'm considering it to just be a characteristic of the transmission.
Here's a screenshot at low load, low RPM at low speed. This is in 5th gear.
Notice the O2 Sensor readouts? At RPMs where it's not shaking itself to death the voltages are above 100mv. If the O2 sensor reads "really ******* lean" then maybe there's evidence of a misfire or something else. I really have no clue, low voltages at this RPM could be completely normal. Here's the EEHack log.
A screenshot doesn't tell us much; you're in closed loop, and the BLMs are at 0 with PE disabled, which suggests the computer doesn't think your fuel is off by any margin at all and thus the O2s are fluctuating in their normal range. Could you post the EEDATA log instead? It's better to look at it as a graph over time than a single screenshot. It's a dynamic system, after all.
A screenshot doesn't tell us much; you're in closed loop, and the BLMs are at 0 with PE disabled, which suggests the computer doesn't think your fuel is off by any margin at all and thus the O2s are fluctuating in their normal range. Could you post the EEDATA log instead? It's better to look at it as a graph over time than a single screenshot. It's a dynamic system, after all.
No, I'm just getting blind. My apologies for not seeing that part of the post. Focused too much on the screenshot.
In any case, I've had a look at it. At first glance it seems pretty normal. But if you look around, say, the timestamp for 165.3 seconds, you'll see the integrators suddenly demand an insane amount of additional fuel despite the BLMs requesting less fuel. This is at 22% throttle at about 2500 RPM. Looking at the O2 voltages on the graph, they don't look right for a non-PE situation. The right-side O2 goes dead lean for almost 6 seconds, while the left-side O2 also goes lean but then blips randomly about 4 seconds into the event. Commanded injector pulsewidth looks fine. However, if the car was physically bucking at this point, it points to a mechanical issue. The computer was following its data as best it could, and commanding the best possible fuel for the conditions it saw.
Have you confirmed fuel pressure at the rail? When were the fuel filters last changed? A sudden loss of fuel pressure to the rail could explain the odd dead lean reading as well as the terrible performance.
Does the car viberate in netrual when you just rev the engine? That should answer the balance question. It sounds to me like you have an ignition miss causing a vibration that you feel under load.
Does the car viberate in netrual when you just rev the engine? That should answer the balance question. It sounds to me like you have an ignition miss causing a vibration that you feel under load.
No vibration in neutral just revving the engine. I'm already looking for a miss and I've gone through the ignition system and I didn't find anything wrong with it.
Originally Posted by Nomake Wan
No, I'm just getting blind. My apologies for not seeing that part of the post. Focused too much on the screenshot.
In any case, I've had a look at it. At first glance it seems pretty normal. But if you look around, say, the timestamp for 165.3 seconds, you'll see the integrators suddenly demand an insane amount of additional fuel despite the BLMs requesting less fuel. This is at 22% throttle at about 2500 RPM. Looking at the O2 voltages on the graph, they don't look right for a non-PE situation. The right-side O2 goes dead lean for almost 6 seconds, while the left-side O2 also goes lean but then blips randomly about 4 seconds into the event. Commanded injector pulsewidth looks fine. However, if the car was physically bucking at this point, it points to a mechanical issue. The computer was following its data as best it could, and commanding the best possible fuel for the conditions it saw.
Have you confirmed fuel pressure at the rail? When were the fuel filters last changed? A sudden loss of fuel pressure to the rail could explain the odd dead lean reading as well as the terrible performance.
Sorry about going dark, life got in the way. I think you're on to something because I'm changing the filter and I went to relieve the pressure to the rail and it was already depressurized in the 30 seconds that it took to pop the hood, grab tools and press the valve. If it's not the filter then maybe a leaky injector? I've confirmed pressure at the rail while the engine was running... but not under load.
Sorry about going dark, life got in the way. I think you're on to something because I'm changing the filter and I went to relieve the pressure to the rail and it was already depressurized in the 30 seconds that it took to pop the hood, grab tools and press the valve. If it's not the filter then maybe a leaky injector? I've confirmed pressure at the rail while the engine was running... but not under load.
No worries! Yes, if the filter doesn't resolve it, then you'll want to confirm that the fuel pressure regulator is operating correctly first. The C4 uses a return system, so if the FPR isn't operating correctly, then it can allow fuel pressure to feed back to the tank when it shouldn't. If the FPR checks out, then the next guess is a leaky injector.
Alright, I'm back with some more information and likely more questions. I've replaced the filter and the fuel pressure regulator. The fuel pressure now stays at a steady 48, so no leaky injectors. I'm still unsure about the problem and then I started thinking about the Optispark, which we had to get a new one with the new engine. The old one didn't fit on the timing cover? I don't know the difference between the optisparks over the years except on one stray thread someone said that they changed the way that the optispark is driven. Would there be a possible incompatibility there with the ECM and possibly a newer model optispark? The old engine was stock 94, so I don't know what changed with the new one. There could be a way to just check the optispark though.
Also the RPM's shown on the dash are inaccurate to what's shown on the computer but at first I thought this was just some calibration error on the dash.
No optispark errors show up in my logs, so this might be the end of the road for me.
One more thing, when the engine was room temp cold I thought I had fixed the problem completely and all of the trans noise went away.
Last edited by Metalface; Jun 20, 2020 at 11:56 PM.
Alright, I'm back with some more information and likely more questions. I've replaced the filter and the fuel pressure regulator. The fuel pressure now stays at a steady 48, so no leaky injectors. I'm still unsure about the problem and then I started thinking about the Optispark, which we had to get a new one with the new engine. The old one didn't fit on the timing cover? I don't know the difference between the optisparks over the years except on one stray thread someone said that they changed the way that the optispark is driven. Would there be a possible incompatibility there with the ECM and possibly a newer model optispark? The old engine was stock 94, so I don't know what changed with the new one. There could be a way to just check the optispark though.
Also the RPM's shown on the dash are inaccurate to what's shown on the computer but at first I thought this was just some calibration error on the dash.
No optispark errors show up in my logs, so this might be the end of the road for me.
One more thing, when the engine was room temp cold I thought I had fixed the problem completely and all of the trans noise went away.
For one thing, the dash gauge is always wildly inaccurate. It can be off by 500 RPM or more versus the PCM. Totally normal for our cars.
As for the differences in Optisparks, they're physical; you wouldn't be able to fit a newer model onto an older car because the actual drive is incorrect. Here are photos of both:
As you can see, it's not possible to put one onto the other. The actual pinouts, however, are the same--as is how they interface with the PCM. If you have no codes for the opti, then the opti is probably fine--but the spark may not be, if it's been leaked on. The PCM can only talk to the optical sensor. If the optical sensor isn't sending a proper signal, it'll throw a code. If however there is a physical problem like the spark interface degrading, it has no way of detecting that.
Anyway, you say that now your fuel pressure is holding steady. Do your logs look exactly the same? That is, are they doing the same sudden dead lean thing? Or has the symptom changed in the logs?
For one thing, the dash gauge is always wildly inaccurate. It can be off by 500 RPM or more versus the PCM. Totally normal for our cars.
As for the differences in Optisparks, they're physical; you wouldn't be able to fit a newer model onto an older car because the actual drive is incorrect. Here are photos of both:
As you can see, it's not possible to put one onto the other. The actual pinouts, however, are the same--as is how they interface with the PCM. If you have no codes for the opti, then the opti is probably fine--but the spark may not be, if it's been leaked on. The PCM can only talk to the optical sensor. If the optical sensor isn't sending a proper signal, it'll throw a code. If however there is a physical problem like the spark interface degrading, it has no way of detecting that.
Anyway, you say that now your fuel pressure is holding steady. Do your logs look exactly the same? That is, are they doing the same sudden dead lean thing? Or has the symptom changed in the logs?
Some points of interest, #2075 was my initial acceleration to the on-ramp. At 20% throttle the integrators demand a ton of fuel randomly mostly on the right side.
I stepped on it at #2223 and my fueling suddenly stays consistent.
From #2274 the computer suddenly decided that the AFR needs to be 12.20. I looked through my tune and my guess is that this is the CAT protect mode but I don't have any cats so this is turned off. It's still doing it though?
At #5955 I pull out from a left turn, during acceleration at #6077 fueling does the same thing.
Fuel pressure didn't change anything in the logs unfortunately. My next step is injector testing then plugs and wires, then optispark.
False Knock and possible misfire
