I really hope one of you guys have an idea...

I really have no idea what is wrong with the car at this point. This has been going on for at least a year... Does anyone know what would cause RPM to suddenly drop like this in a scan? I replaced the CKP this morning with NO change at all. The car breaks up at high rpm's especially, but I've felt it at 20% throttle before too. Pretty rare though; 99% of the time, it happens at WOT after like 4.5k rpm. Here are two videos I made of it, you can hear it breaking up if you listen good. It's NOT spark blowout or wires or coils or icm. They've all been replaced. Any votes for PCM? Also, I did the timing chain this past fall and noticed the cam magnet was really loose in the sprocket, is it supposed to be like that?

1_Misfire? - YouTube
2_Misfire? - YouTube

0ad5b443.png
 
Lol a red cunthair... Hey I think I talked to you at Regal Madness last year? Remember I had that misfire issue? LOL same BS still a year later...

Yeah I think it just jiggled around in the bore a tiny bit, it definitely didn't come out though. I could try taking the cps off and rotating the crank till I see the magnet and jiggle it with my finger to see. Do you think it's possible that this is the issue? I really dread taking the front cover off again!
 
That timing advance makes me ponder....

Good point, why didn't the timing change when the rpms did that...

Fireman, I've changed the plugs countless times on this thing trying to figure out this problem. Right now they are XP103's @ roughly .050. I've had them at .030 with no change. The fact that it has done this at like 20% throttle before I'm pretty sure it's not blowout
 

Turbocharged400sbc

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rpm signal dropped out and because it did the PCM calculated a much higher cyl airmass even though the maf freq/gps didnt change.

more than likely your looking at a 7x signal dropout between the ICM and PCM.

first things first confirm you have a good/goodused OEM ICM with the silver circuit board cover and flat aluminum backplate....never had any good experiences with the aftermarket icm's (black circuit covers and sometimes stainless bottom plates (much heavier than OEM)
cam position sensor is only used for misfire diagnostics and for injector sync (cyl1 sync'd to Ivalve on cyl1 open) durring startup... even it dropping out wont affect the rpm signal the pcm see's

that said these things are getting older and im finding intermittent pin contact issues ALL the time.
the ICM uses the 3x and 18x CKPS pulses and outputs a 7x/rpm signal to the PCM, your problem lies somewhere there im guessing.
do you have access to a genuine scantool that can pull up all the PIDs?
youll want something like the mt2500/gensys/tech2/solus/etc where you can see the 3x 18x and 7x signals present as well as ISS/TCC slip speed and go on a test drive to see which one disapears...looks like what you will see is that ISS and TCCslip will cal out to correctish engine rpm durring the dropout, 3x and 18x will stay "ok" and the 7x pid will go to "none" or "not present"

the ICM to icm/cam/crank sens harness pins are often teribly weakened or bent as people constantly intstall and remove em so get a fine sewing needle and bend the banana shaped side of the terminal outward, you should feel nice positive contact as you "fuck it" with a small paper clip (.5mm dia wire) if you dont, bend the terminal back to shape.
the icm connector being boltin and people wiggling em excessivly leads em to more wear and tear than say the 10/12 pin ICM harness to primary engine harness connector but youll wanna check that one too, find a sewing needle about the same thickness as the oem pins and "fuck" each female terminal

its also entirely possible you have a broken or shorting wire between the icm and PCM...if you have a graphing or DSO meter (with glitch capture/trigger is even better) you can backprobe all the circuits and just hit record and go for a drive and youll be able to confirm that (lets just say) you have perfect dignal durring fault at the ICM but when backprobed at the pcm it disapears...in which case you just run a new wire alongside the primary harness.

you can check the CmPS magnet by just removing the cam pos sensor from its hole and looking with a mirror but like i said all the pcm uses it for is initial sequential fuel injection syncing to the crank position of cyl1 TDC...it has no responsability in terms of the rpm signals tothe PCM from the ICM


edit: also since the issue seems to be at wot and over 4k rpm's your gonna be looking at significant rocking rearward and the bottom mounts compressing downward and forward so this is probably whats flexing the engine/icm/pcm harness to the point the connectiong breaks leading further evidence to a weak/int contact or wire that only rears its head when the harness is moved "juuuust right"
 

Turbocharged400sbc

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Lol a red cunthair... Hey I think I talked to you at Regal Madness last year? Remember I had that misfire issue? LOL same BS still a year later...

Yeah I think it just jiggled around in the bore a tiny bit, it definitely didn't come out though. I could try taking the cps off and rotating the crank till I see the magnet and jiggle it with my finger to see. Do you think it's possible that this is the issue? I really dread taking the front cover off again!

i thought that heap looked familiar so its still happening? with no changes? slowly geting worse?

your gonna wanna lay out a history for me here, what work was done just prior to the issue rearing its head and all of your post issue parts swapping/diagnostics listed. e.g. you replaced the icm hanress, ckp, etc etc

PS none of us have any idea what we are talking about :mamoru:
 
Lol! yes, that is definitely the same James I talked to. IIRC, this all started happening, or at least I started noticing it, when I put the new front mount HE on the front with the new pump. It's on it's own relay and everything (and always has been) so I can't draw any connection there...

The ICM harness is a new/used one from Morad. I cleaned it up and re-loomed and taped it before I put it on the car. I had another set of coils from another L67 that I tried. I bought a fellow GP owner's ICM that was known to work good. (Both of my ICM's are OEM) Tried many different plug gaps and plug sets. Plug wires are brand new as of like 10k miles ago. Tested them last night and ohms stay consistent while jiggling the wires so I can say they are probably still fine. I changed the CKP last night. Front cover was off over the winter to put a new timing chain and tensioner on. This is all after the fact though, nothing seems to have caused it or made it any better/worse.

About 2 years ago, the car started randomly stalling while I was driving. I eventually found it was because the (old) ICM harness I had was chewed through by the accessory belt and was grounding out on the block. IDK if that took something out with it. But I don't think the car had the misfires after that until at least a year later.

I'm going to untape the whole wireloom and physically inspect each wire from the ICM to PCM

James, what connection should I be focusing most on here? PS THANK YOU for all the information and your help!
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Post a copy of your tune and any current logs for said tune and I will take a look at it. It could be hardware related but it could also be in your software instead.

I put the tune I've been using (and the .bin that I make it from it's the .zip). I put two scans up that have the car loosing RPM like that too. Thanks man!!
 

Attachments

  • 5-10_moarTiming.hpt
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  • lapeer02.hpl
    69.7 KB · Views: 47
  • ugh.hpl
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  • 5-10_baselineWith34.zip
    228.5 KB · Views: 9
So the PCM - ICM wire harness is in perfect condition. I literally inspected the entire length of each wire.

I'm going to Marchi's on Thursday and we are going to try swapping a couple things with his parts. If that doesn't work, I'm afraid I will have to succumb to a local mechanic that seems pretty knowledgeable with electrical issues.

I have a 98 PCM I've been dying to try using but I need someone with DHP to put my bin onto it because the serial number got cleared somehow and now HPT won't write to it >.> Anyone? :)
 
And the plot thickens.... it does NOT do it with the supercharger belt off. IDK why I didn't try this earlier. Something near the torque converter was making a horrible racket last year and it went away over the winter. Would a failing TC do anything similar to this? I wonder if it can't hold the torque from all the b000000st?

Just in case it IS ignition somehow, I have some AR103's on order from Murrays as that's what I KNOW worked at one time. Also, I will be trying Marchi's ICM on Thursday
 

Turbocharged400sbc

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i forgot about this but i believe his issue directly relates to PCM engine rpm input dropout.

my guess is that after the sc belt was removed the harness is no longer being tugged as hard causing the intermittent failure.

just yesterday i was working on dave norris' old l67 swapped 95 gtp and found a rad cooling fan control wire from the pcm that had continuity but couldnt flow enough current to pull in the contactor on the fan2 relay.
and thats a pcm ground controlled low current 12v circuit on the primary side of a relay.
hell even angus' car may have this issue with his iss input....if a low voltage hall effect sensor has damn near any resistance on its circuit you can kill the votage peak and the pcm wont pick up on it since its below trigger level, that car has had so many hands on her through several major reworkings that it is a possibility.
half the time you need a DSO that will let you check signal outputs and compare to known good signals.

these cars are getting older more and more electrical issues are raising their head and predominatly on the most used/disconnected sensors/connectors...but realize that even the smallest nick will seep in salt water and start to go to town on the copper, it also work hardens/fractures strands, so even with the outside seemingly intact.
gm finally released a tsb a year or so back on terminal fretting being found on the metripack connector terminals. with electrical issues suddently being fixed by just disconnecting and reconnecting the connector.
ive also taken to testing pins and tightening up the female terminals by bending the banana spring outward with a small sewing needle. i screw with the icm connectors al the time cause its so easy for them to come off crooked/excessive force used which leads to the terminals no longer grabbing as tightly as they should.
i searched for it and found it, dec 2010, dielectric grease application (likely to dampen movement/shield connection point from oxygen
Electrical - MIL ON/DTC's Set By Various Control Modules TECHNICAL
Bulletin No.: 09-06-03-004D
Date: December 08, 2010
Subject: Intermittent No Crank/No Start, No Module Communication, MIL, Warning Lights, Vehicle Messages or DTCs Set by Various Control Modules - Diagnosing and Repairing Fretting Corrosion (Disconnect Affected Connector and Apply Dielectric Lubricant)
Models:
2011 and Prior GM Passenger Cars and Trucks Attention:
This repair can be applied to ANY electrical connection including, but not limited to: lighting, body electrical, in-line connections, powertrain control sensors, etc. DO NOT over apply lubricant to the point where it prevents the full engagement of sealed connectors. A light coating on the terminal surfaces is sufficient to correct the condition. Supercede:
This bulletin is being revised to update the Attention statement and add the 2011 model year. Please discard Corporate Bulletin Number 09-06-03-004C (Section 06 - Engine/Propulsion System). Condition
Some customers may comment on any of the following conditions:
- An intermittent no crank/no start - Intermittent malfunction indicator lamp (MIL) illumination - Intermittent service lamp illumination - Intermittent service message(s) being displayed The technician may determine that he is unable to duplicate the intermittent condition.
Cause
This condition may be caused by a buildup of nonconductive insulating oxidized debris known as fretting corrosion, occurring between two electrical contact surfaces of the connection or connector. This may be caused by any of the following conditions:
- Vibration - Thermal cycling - Poor connection/terminal retention - Micro motion - A connector, component or wiring harness not properly secured resulting in movement On low current signal circuits this condition may cause high resistance, resulting in intermittent connections.
On high current power circuits this condition may cause permanent increases in the resistance and may cause a device to become inoperative.
Representative List of Control Modules and Components
The following is only a representative list of control modules and components that may be affected by this connection or connector condition and DOES NOT include every possible module or component for every vehicle.
- Blower Control Module - Body Control Module (BCM) - Communication Interface Module (CIM) - Cooling Fan Control Module - Electronic Brake Control Module (EBCM) - Electronic Brake and Traction Control Module (EBTCM) - Electronic Suspension Control (ESC) Module - Engine Control Module (ECM) - Heating, Ventilation and Air Conditioning (HVAC) Control Module - HVAC Actuator - Inflatable Restraint Sensing and Diagnostic Module (SDM) - Any AIR BAG module - Seatbelt Lap Anchor Pretensioner - Seatbelt Retractor Pretensioner - An SIR system connection or connector condition resulting in the following DTCs being set: B0015, B0016, B0019, B0020, B0022, or B0023 - Powertrain Control Module (PCM) - Remote Control Door Lock Receiver (RCDLR) - Transmission Control Module (TCM) Correction
Important
DO NOT replace the control module, wiring or component for the following conditions: - The condition is intermittent and cannot be duplicated. - The condition is present and by disconnecting and reconnecting the connector the condition can no longer be duplicated. Use the following procedure to correct the conditions listed above.
1. Install a scan tool and perform the Diagnostic System Check - Vehicle. Retrieve and record any existing history or current DTCs from all of the control modules (refer to SI). ¤ If any DTC(s) are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle to identify the connector(s) of the control module/component which may be causing the condition (refer to SI). ¤ If DTCs are not set, refer to Symptoms - Vehicle to identify the connector(s) of the control module/component which may be causing the condition (refer to SI). 2. When identified, use the appropriate DTC Diagnostics, Symptoms, Schematics, Component Connector End Views and Component Locator documents to locate and disconnect the affected harness connector(s) which are causing the condition. Note
Fretting corrosion looks like little dark smudges on electrical terminals and appear where the actual electrical contact is being made. In less severe cases it may be unable to be seen or identified without the use of a magnifying glass.
166809927

Important
DO NOT apply an excessive amount of dielectric lubricant to the connectors as shown, as hydrolock may result when attempting to mate the connectors. Use ONLY a clean nylon brush that is dedicated to the repair of the conditions in this bulletin.
3. With a one-inch nylon bristle brush, apply dielectric lubricant to both the module/component side and the harness side of the affected connector(s). 4. Reconnect the affected connector(s) and wipe away any excess lubricant that may be present. 5. Attempt to duplicate the condition by using the following information: - DTC Diagnostic Procedure - Circuit/System Description - Conditions for Running the DTC - Conditions for Setting the DTC - Diagnostic Aids - Circuit/System Verification ¤ If the condition cannot be duplicated, the repair is complete. ¤ If the condition can be duplicated, then follow the appropriate DTC, Symptom or Circuit/System Testing procedure (refer to SI). Repair Order Documentation
Important
The following information MUST be documented on the repair order. Failure to do so may result in a chargeback.
- Customer vehicle condition. - Was a Service Lamp or Service Message illuminated? If yes, specify which Service Lamp or Service Message. - Was a DTC(s) set? If yes, specify which DTC(s) were set. - After following the procedure contained within this bulletin, could the condition be duplicated? ¤ If the condition was not duplicated, then document the affected module/component connector name and number on the repair order. - If the condition was duplicated after the procedure contained within this bulletin was followed, and additional diagnosis led to the replacement of a module or component, the SI Document ID Number MUST be written on the repair order. Parts Information
166809928

Alternate Distributor For All of North America
Note
NyoGel(R) 760G Lubricant* is equivalent to GMSPO P/N 12377900, and P/N 10953529 (Canada), specified for use to correct the condition in this bulletin.
*We believe this source and their products to be reliable. There may be additional manufacturers of such products/materials. General Motors does not endorse, indicate any preference for, or assume any responsibility for the products or material from this firm or for any such items that may be available from other sources.
i swear we need this crap i spew put in a "random 3800 BS" sticky thread (yes i realize that this affects all gm's and prob other manufacturers)
 

TommyGloves

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Aug 23, 2007
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i forgot about this but i believe his issue directly relates to PCM engine rpm input dropout.

my guess is that after the sc belt was removed the harness is no longer being tugged as hard causing the intermittent failure.

just yesterday i was working on dave norris' old l67 swapped 95 gtp and found a rad cooling fan control wire from the pcm that had continuity but couldnt flow enough current to pull in the contactor on the fan2 relay.
and thats a pcm ground controlled low current 12v circuit on the primary side of a relay.
hell even angus' car may have this issue with his iss input....if a low voltage hall effect sensor has damn near any resistance on its circuit you can kill the votage peak and the pcm wont pick up on it since its below trigger level, that car has had so many hands on her through several major reworkings that it is a possibility.
half the time you need a DSO that will let you check signal outputs and compare to known good signals.

these cars are getting older more and more electrical issues are raising their head and predominatly on the most used/disconnected sensors/connectors...but realize that even the smallest nick will seep in salt water and start to go to town on the copper, it also work hardens/fractures strands, so even with the outside seemingly intact.
gm finally released a tsb a year or so back on terminal fretting being found on the metripack connector terminals. with electrical issues suddently being fixed by just disconnecting and reconnecting the connector.
ive also taken to testing pins and tightening up the female terminals by bending the banana spring outward with a small sewing needle. i screw with the icm connectors al the time cause its so easy for them to come off crooked/excessive force used which leads to the terminals no longer grabbing as tightly as they should.
i searched for it and found it, dec 2010, dielectric grease application (likely to dampen movement/shield connection point from oxygen
i swear we need this crap i spew put in a "random 3800 BS" sticky thread (yes i realize that this affects all gm's and prob other manufacturers)

Yup...then turned into a novelty bathroom book of random 3800 tidbits. :likes:
 
So I think I've been tuning around a dying fuel pump or jacked FPR this whole time. I noticed my wideband tuned MAF table reads about 1.20 lb/min at idle, when a stock car reads .75 ish. That explains the high PCS duty cycle at idle and surging with gear changes. I have my IFR table set to all 64.5 (I have Siemens Deka 60#'ers) which I was under the impression was correct. Last I checked, fuel pressure was 51ish with engine running and vac line unplugged so IDK what the deal is....

I'm replacing the FPR and pump. I wanted to replace the pump so that I could run e85 without running out of fuel after 5 grand anyway.

I will let you guys know how it goes afterwards.
 
01abboud, they are brand new MSD wires and all of them test a constant resistance while jiggling the wires and tugging on the boots so they are all good unfortunately.

Thanks for all your help James, I will keep you updated on whether or not this does it. I went to Marchi's house a couple weeks ago and swapped his ICM and coil packs onto my car (knowing that his car ran perfect) and it still did it.

I did a few runs with him riding shotgun and we noticed that EVERY time I could feel the mising, it would show a little KR. I figure maybe the fp is cavitating and putting air in the line? It might be lean for such a short time that the wideband doesn't pick it up?
 
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