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| 3800SC stumble and miss after 4000rpm (Page 1/2) |
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Additivewalnut
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NOV 04, 08:54 PM
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04 3800sc 4spd manual - bone stock, no emissions, CAI
Okay so I had another post about maybe needing a CASE learn on my 3800sc or maybe my PCM being corrupted, but everyone said it wasn't that. I got a retuned PCM and put it and now the car seems noticeably more powerful and seems to run better, I don't have any check engine lights yet, but I still can't go past 4000rpm while in boost without the car bucking. Sometimes I can take my foot out and get back in and it'll rev out just fine. When hooked to a scan tool, when it bucks, timing goes to -37 +/- 5 degrees. There are other posts here about this exact issue but they all end up dead threads with no solution, so hopefully someone can point me in the right direction.
Symptoms include:
Long cold start times
What sounds like a miss at idle and some shuddering
when revved in neutral it'll hang a bit at 1500 then go down to a 900rpm idle,
1/2 throttle and up in any gear causes it to buck similar to hitting a rev limiter
Things tested or replaced:
New plug wires from when it was swapped 6 months ago, haven't changed since issue started
New coils
New plugs, autolite 104 .050 gap
Lower intake gasket was replaced during swap
New PCM
Fuel pressure within spec
O2 readings within spec from what I can tell
LTFTs are kinda all over the place, sometimes being in the +teens and sometimes in the -teens
TPS voltage reads correct throughout range
MAF sensor has been cleaned
I will post a video what it sounds like and looks like tomorrow[This message has been edited by Additivewalnut (edited 11-04-2023).]
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Additivewalnut
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NOV 05, 08:58 PM
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bump, but also would changing the plug gap be a possible solution? Send it down to .040?
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Darth Fiero
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NOV 06, 12:51 AM
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Sorry for not following up on your issue sooner, I've been busy. Sounds ignition system-related to me.
Have you tried a different ignition module?------------------
More is more. Less is not enough.
Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com
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Additivewalnut
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NOV 06, 09:24 AM
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| quote | Originally posted by Darth Fiero:
Sorry for not following up on your issue sooner, I've been busy. Sounds ignition system-related to me.
Have you tried a different ignition module?
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I haven't, I'll have to run to the junkyard. Those icms are going for like 250 around here now. I did notice that my ICM bracket is mounted on the trunk wall, there's no ground wire or anything coming from it. Should there be a bracket to engine ground?
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ericjon262
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NOV 06, 06:11 PM
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I doubt the ICM is the problem if the PCM is commanding negative timing, the PCM commanding negative timing sounds alot like a rev limiter.
your other problem related to RPM hangup sounds alot like the PCM is tuned for an automatic trans and not a manual, as I said in your other thread. ------------------
"I am not what you so glibly call to be a civilized man. I have broken with society for reasons which I alone am able to appreciate. I am therefore not subject to it's stupid laws, and I ask you to never allude to them in my presence again."
I invited Lou Dias to trash me in my own thread, he refused. sorry. if he trashes your thread going after me. I tried.
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Additivewalnut
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NOV 06, 07:44 PM
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| quote | Originally posted by ericjon262:
I doubt the ICM is the problem if the PCM is commanding negative timing, the PCM commanding negative timing sounds alot like a rev limiter.
your other problem related to RPM hangup sounds alot like the PCM is tuned for an automatic trans and not a manual, as I said in your other thread.
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The PCM says it's in drive according to my scanner.
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Darth Fiero
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NOV 08, 12:59 AM
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The -37 degrees of timing advance you are seeing on the scan tool is troubling. The only thing in the PCM that could retard timing that much is Abuse Mode. However, this should have been turned off in a custom tune for a manual trans application by whoever tuned your PCM.
Who tuned your PCM, OP?[This message has been edited by Darth Fiero (edited 11-08-2023).]
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lateFormula
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NOV 08, 09:31 AM
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These engines all came mated to an auto trans. With the electronically controlled transmissions, the ECU pulls timing on upshifts momentarily to reduce the torque load on the trans. If you are running it with a manual, I would expect the ECU needs a custom tune to address this.
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Additivewalnut
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NOV 08, 09:48 AM
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| quote | Originally posted by Darth Fiero:
The -37 degrees of timing advance you are seeing on the scan tool is troubling. The only thing in the PCM that could retard timing that much is Abuse Mode. However, this should have been turned off in a custom tune for a manual trans application by whoever tuned your PCM.
Who tuned your PCM, OP?
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Same guy who made the harness, Danny Mcllmoyle or something close to that. Great reputation on Facebook, does this all the time with no complaints. So idk if he's dropping the ball or what. I'd be willing to get a PCM from you but then I run into the problems of not having wires in my harness for doing a CASE learn
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Additivewalnut
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NOV 08, 09:54 AM
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| quote | Originally posted by Darth Fiero:
The -37 degrees of timing advance you are seeing on the scan tool is troubling. The only thing in the PCM that could retard timing that much is Abuse Mode. However, this should have been turned off in a custom tune for a manual trans application by whoever tuned your PCM.
Who tuned your PCM, OP?
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Whatre the chances I could just send you my PCM and you check and see what he screwed up?
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