95 LT1 stumble
05-28-2017, 05:00 PM
#1
Registered User
Thread Starter
Join Date: Aug 2008
Location: CFB Bagotville, QC
Posts: 46
95 LT1 stumble
The car:
95 Caprice Wagon. 83k miles. In the fall I added 3.73 gears, truetrac posi, SLP shorty headers, Pro-magnum 1.6 roller rockers and valvesprings on the stock iron heads. I also did new plug wires and plugs at that time. NGK platinum plugs, AC delco wires, routed the stock routing. The car has a tune from Solomon, tuned for 91 octane.
During the rocker swap, I noticed that the number 8 exhaust valve doesn't close completely: with compressed air in the cylinder I could hear it escaping. It's not staying open by much.
About a year and a half ago, I had a waterpump failure. I replaced the waterpump, and while it was off removed the Opti. I opened it and noticed some buildup around the leads in the cap. I cleaned it with contact cleaner and emory paper, put red loctite on the rotor screws and a thin bead of RTV on the case and put it back on.
Symptoms:
For the last 2 months, the car has had an intermittent irregular idle. It will dip below 500 rpm (per datamaster) while in gear. It is worsened by load (for example it's worse if I put the AC on). Ever since I've had the car (2012) I'd say the idle has never been as smooth as my other LT1s, but it's always been quite subtle. After cleaning the opti as described above it seemed to run better for a while.
On top of the intermittent irregular idle when in gear, when in closed loop the car will occasionally, but not always, stumble at part throttle especially with high load. It seems to be doing it more and more frequently though. It will clear up if I give it more gas. Situations where this happens for example is leaving from a complete stop, gradually accelerating while in 4th/lockup from 40+ mph, or climbing a hill. Datamaster shows the car is pulling up to 12deg timing during the stumble. Moreover, knock counts are increasing when the car is commanding spark retard. this is at 10-20% TPS. If I give it like 30+ it seems to clear up and drive fine.
LTFTs seem low, 112 ish.
No CELs thrown.
diagnostics so far:
Pretty sure the car only stumbles in closed loop. O2s are original, putting in new delcos Friday.
triple checked spark plug routing (no crossed wires). Checked for arcing at night, none seen.
Car still stumbles/pulls timing with MAF unplugged (though this will set the MAF CEL). Seems to have a normal amount of g/s going through it, and it's installed facing in the correct direction.
I unplugged both Knock Sensors (B-body uses 2) and the car threw the appropriate MALF code. Car still pulls timing and stumbles but it's no seeing knock counts increase.
I cleaned the IAC (without touching the pintle), reseated and did the reset procedure. Also cleaned the TB. IAC seems to be in a better position per the IAC counts but no improvement.
I used a multimeter to verify the Knock Sensors per shbox. Volts at the harness (even wiggling it) and ohms at the sensor tested within spec.
MAP: rubber nipple looked great on it, surprisingly. Previous owner has removed the MAP before as the little green harness had the classic broken clip. got 5 volts at the harness even wiggling it. Haven't really heard of these MAPs going bad, but I'll throw on a spare tomorrow from a friend's car for confirmation.
Fuel pressure: per FSM spec. Nothing erratic while driving. Fuel pump is less than a year old.
Vaccum: 20in (steady) idle in park, 18 in drive AC off (steady) , drops to 15 ish with the AC on, slight wobble of the needle.
Put in spare coil, no change. Both coils Ohmed the same per shbox.
TPS: seems ok based on datamaster.
Injectors are stock, with 83k miles. Each confirmed 'ticking' with stethoscope. Also I unplugged them all one by one with the car running, and the idle worsened noticeably at each. Doesn't prove they're great, but proves none of them are dead.
Since this started 2 months ago it seems to be worsening. During that time I found an arcing coil wire (the new ac delco). Replaced, helped for a while but the poor idle/stumble is back. New wire is not arcing. Also went through almost every vac line to find a vac leak. The lines at the TB are new, PCV is new, PCV hoses are new. I did find the vac line that goes to the regulator was cracked. Replaced, no change (there was no fuel leaking out of it, so regulator is not suspect. It's a known good unit from my 50k mi roadmaster)
EGR is deleted, and is deleted in tune.
The intake manifold has a surprising amount of oil around the front (opti is shiny with oil, as seen from underneath). I gave the front intake manifold bolts half a turn to snug them. Maybe an intake vacuum leak ?
Loaded the stock tune (for 87 octane), and car does the same, even with 91oct fuel.
Last piece of info, I brought the car to a shop for a motorvac treatment about a month ago, right after I found the bad coil wire. I've had good success in the past and guys on the Impala SS board used to swear by it. Gets rid of soft carbon and can cure mystery drivability problems sometimes. Well, it turns out the machine at the place I brought it too was U/S so without asking they just did a seafoam treatment. I noticed the machine wasn't hooked up from the window and went to see what was going on. The mechanic had the air filter off and was spraying carb cleaner directly into the MAF with the car running. Unloaded an entire bottle in there. Not sure if that stuff could have damaged any sensors (MAF, MAP, O2s).
I requested that the tuner desensitise the KS for the pro-magnum rockers since I don't have an LT4 KM in this car. he seems to have done it, as the stock tune seems to pick up a bit more knock at idle. Could it be something as simple as false knock from the rockers ? I had read that the LT4 KM isn't really needed anymore with appropriate tuning.
Not too sure where to go from here. O2s ? KS ? MAP ? opti (since it had some accumulated metal around the leads inside, and I have a known good spare) ? reseat/reseal the intake manifold ? Any insight would be greatly appreciated.
Attached are 3 scans of the car using datamaster (had to zip them as the forum doesn't like the .uni extension). The one called 'stock' is a scan of the car using the stock tune, still showing the problem.
95 Caprice Wagon. 83k miles. In the fall I added 3.73 gears, truetrac posi, SLP shorty headers, Pro-magnum 1.6 roller rockers and valvesprings on the stock iron heads. I also did new plug wires and plugs at that time. NGK platinum plugs, AC delco wires, routed the stock routing. The car has a tune from Solomon, tuned for 91 octane.
During the rocker swap, I noticed that the number 8 exhaust valve doesn't close completely: with compressed air in the cylinder I could hear it escaping. It's not staying open by much.
About a year and a half ago, I had a waterpump failure. I replaced the waterpump, and while it was off removed the Opti. I opened it and noticed some buildup around the leads in the cap. I cleaned it with contact cleaner and emory paper, put red loctite on the rotor screws and a thin bead of RTV on the case and put it back on.
Symptoms:
For the last 2 months, the car has had an intermittent irregular idle. It will dip below 500 rpm (per datamaster) while in gear. It is worsened by load (for example it's worse if I put the AC on). Ever since I've had the car (2012) I'd say the idle has never been as smooth as my other LT1s, but it's always been quite subtle. After cleaning the opti as described above it seemed to run better for a while.
On top of the intermittent irregular idle when in gear, when in closed loop the car will occasionally, but not always, stumble at part throttle especially with high load. It seems to be doing it more and more frequently though. It will clear up if I give it more gas. Situations where this happens for example is leaving from a complete stop, gradually accelerating while in 4th/lockup from 40+ mph, or climbing a hill. Datamaster shows the car is pulling up to 12deg timing during the stumble. Moreover, knock counts are increasing when the car is commanding spark retard. this is at 10-20% TPS. If I give it like 30+ it seems to clear up and drive fine.
LTFTs seem low, 112 ish.
No CELs thrown.
diagnostics so far:
Pretty sure the car only stumbles in closed loop. O2s are original, putting in new delcos Friday.
triple checked spark plug routing (no crossed wires). Checked for arcing at night, none seen.
Car still stumbles/pulls timing with MAF unplugged (though this will set the MAF CEL). Seems to have a normal amount of g/s going through it, and it's installed facing in the correct direction.
I unplugged both Knock Sensors (B-body uses 2) and the car threw the appropriate MALF code. Car still pulls timing and stumbles but it's no seeing knock counts increase.
I cleaned the IAC (without touching the pintle), reseated and did the reset procedure. Also cleaned the TB. IAC seems to be in a better position per the IAC counts but no improvement.
I used a multimeter to verify the Knock Sensors per shbox. Volts at the harness (even wiggling it) and ohms at the sensor tested within spec.
MAP: rubber nipple looked great on it, surprisingly. Previous owner has removed the MAP before as the little green harness had the classic broken clip. got 5 volts at the harness even wiggling it. Haven't really heard of these MAPs going bad, but I'll throw on a spare tomorrow from a friend's car for confirmation.
Fuel pressure: per FSM spec. Nothing erratic while driving. Fuel pump is less than a year old.
Vaccum: 20in (steady) idle in park, 18 in drive AC off (steady) , drops to 15 ish with the AC on, slight wobble of the needle.
Put in spare coil, no change. Both coils Ohmed the same per shbox.
TPS: seems ok based on datamaster.
Injectors are stock, with 83k miles. Each confirmed 'ticking' with stethoscope. Also I unplugged them all one by one with the car running, and the idle worsened noticeably at each. Doesn't prove they're great, but proves none of them are dead.
Since this started 2 months ago it seems to be worsening. During that time I found an arcing coil wire (the new ac delco). Replaced, helped for a while but the poor idle/stumble is back. New wire is not arcing. Also went through almost every vac line to find a vac leak. The lines at the TB are new, PCV is new, PCV hoses are new. I did find the vac line that goes to the regulator was cracked. Replaced, no change (there was no fuel leaking out of it, so regulator is not suspect. It's a known good unit from my 50k mi roadmaster)
EGR is deleted, and is deleted in tune.
The intake manifold has a surprising amount of oil around the front (opti is shiny with oil, as seen from underneath). I gave the front intake manifold bolts half a turn to snug them. Maybe an intake vacuum leak ?
Loaded the stock tune (for 87 octane), and car does the same, even with 91oct fuel.
Last piece of info, I brought the car to a shop for a motorvac treatment about a month ago, right after I found the bad coil wire. I've had good success in the past and guys on the Impala SS board used to swear by it. Gets rid of soft carbon and can cure mystery drivability problems sometimes. Well, it turns out the machine at the place I brought it too was U/S so without asking they just did a seafoam treatment. I noticed the machine wasn't hooked up from the window and went to see what was going on. The mechanic had the air filter off and was spraying carb cleaner directly into the MAF with the car running. Unloaded an entire bottle in there. Not sure if that stuff could have damaged any sensors (MAF, MAP, O2s).
I requested that the tuner desensitise the KS for the pro-magnum rockers since I don't have an LT4 KM in this car. he seems to have done it, as the stock tune seems to pick up a bit more knock at idle. Could it be something as simple as false knock from the rockers ? I had read that the LT4 KM isn't really needed anymore with appropriate tuning.
Not too sure where to go from here. O2s ? KS ? MAP ? opti (since it had some accumulated metal around the leads inside, and I have a known good spare) ? reseat/reseal the intake manifold ? Any insight would be greatly appreciated.
Attached are 3 scans of the car using datamaster (had to zip them as the forum doesn't like the .uni extension). The one called 'stock' is a scan of the car using the stock tune, still showing the problem.
Last edited by jasonlachapelle; 05-28-2017 at 05:14 PM.
05-28-2017, 08:07 PM
#2
Administrator
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,647
Re: 95 LT1 stumble
If you can do a DataMaster export as .csv, I'll review the files. I can give you my preferred sequence of data for the export setup in the morning when I can access my PC. I have DataMaster, but I prefer the ability to manipulate the data in Excel, and would prefer not to have to spend the time to convert the .uni file to .csv.
Let me know if you are interested.
Let me know if you are interested.
05-29-2017, 08:20 AM
#4
Registered User
Thread Starter
Join Date: Aug 2008
Location: CFB Bagotville, QC
Posts: 46
Re: 95 LT1 stumble
Monitored datamaster on the drive to work today. Definitely no issue in open loop.
Oddly, I noticed that when I come to a stop at a light, the spark advance will read 1, then inevitably the car will sense knock and pull timing when I leave the light or stop sign. If I pop the gear selector in N, spark advance will reset to 26-27 and I can accelerate no problem (the car doesn't sense knock or pull timing). I hit about 5 stops within 100m of each other, and it did it on 4 of them. I can only get to 15mph between them. Putting it in N always solves the prolem.
The car seems to go to 1 spark advance on deceleration. Not sure if that's in the tune or what... it seemed to be doing on the stock tune.
Oddly, I noticed that when I come to a stop at a light, the spark advance will read 1, then inevitably the car will sense knock and pull timing when I leave the light or stop sign. If I pop the gear selector in N, spark advance will reset to 26-27 and I can accelerate no problem (the car doesn't sense knock or pull timing). I hit about 5 stops within 100m of each other, and it did it on 4 of them. I can only get to 15mph between them. Putting it in N always solves the prolem.
The car seems to go to 1 spark advance on deceleration. Not sure if that's in the tune or what... it seemed to be doing on the stock tune.
Last edited by jasonlachapelle; 05-29-2017 at 09:47 AM.
05-29-2017, 10:34 AM
#5
Administrator
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,647
Re: 95 LT1 stumble
Here's the list of data to set up in the tables. If you haven't done this before (this is a copy & paste):
Click on "File"
Click on "Export Engine Data"
Enter number of last record in "Count" field
Click on first vacant field starting from the left
Select "Engine Export Items" from popup and "Apply"
Work your way left to right until all columns are filled
Click on "File" on Export Engine Data screen
Click on "Save as....... CSV"
1 - Runtime
2 - RPM
3 – Speed (MPH)
4 - TPS – Volts
5 - TPS - %
6 - MAP (kPa)
7 - CLT Temp (Degrees F)
8 - IA Temp (Degrees F)
9 - IGN Volts
10 - IAC Position
11 - AFGS
12 - SPARK ADV
13 - SPARK RETARD
14 - KNOCK COUNT
15 - Injector BPW – Left
16 - Injector BPW – Right
16 - Fuel Trim Cell
18 - Left O2
19 - Right O2
20 - Long Term – L
21 - Long Term – R
22 - Short Term – L
23 - Short Term – R
24 - CCP Duty Cycle
25 - EGR Duty Cycle
26 - Barometer
27 - IAC Target
28 - Idle RPM
29 - Injector Duty Cycle – L
30 - Injector Duty Cycle - R
Click on "File"
Click on "Export Engine Data"
Enter number of last record in "Count" field
Click on first vacant field starting from the left
Select "Engine Export Items" from popup and "Apply"
Work your way left to right until all columns are filled
Click on "File" on Export Engine Data screen
Click on "Save as....... CSV"
1 - Runtime
2 - RPM
3 – Speed (MPH)
4 - TPS – Volts
5 - TPS - %
6 - MAP (kPa)
7 - CLT Temp (Degrees F)
8 - IA Temp (Degrees F)
9 - IGN Volts
10 - IAC Position
11 - AFGS
12 - SPARK ADV
13 - SPARK RETARD
14 - KNOCK COUNT
15 - Injector BPW – Left
16 - Injector BPW – Right
16 - Fuel Trim Cell
18 - Left O2
19 - Right O2
20 - Long Term – L
21 - Long Term – R
22 - Short Term – L
23 - Short Term – R
24 - CCP Duty Cycle
25 - EGR Duty Cycle
26 - Barometer
27 - IAC Target
28 - Idle RPM
29 - Injector Duty Cycle – L
30 - Injector Duty Cycle - R
05-31-2017, 07:18 PM
#6
Registered User
Thread Starter
Join Date: Aug 2008
Location: CFB Bagotville, QC
Posts: 46
Re: 95 LT1 stumble
Issue is resolved. Optispark (83k mi original) was causing an intermittent and weak spark on cyl 2. I used a laser heat gun to measure the primaries and found number 2 was much cooler. Changed the plug, no joy. Changed the wire, no joy. Put a good wire and plug to ground and it had occasional weak spark.
Changed out the opti and WP/Opti seals and now the car runs great.
I hadn't read about optis causing single cylinder issues, but I guess it happens. I'll post a pic of the cap later. One of the leads has significant damage around it (large rotor trace, seems burnt).
Changed out the opti and WP/Opti seals and now the car runs great.
I hadn't read about optis causing single cylinder issues, but I guess it happens. I'll post a pic of the cap later. One of the leads has significant damage around it (large rotor trace, seems burnt).
