914 2.0L Missing |
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914 2.0L Missing |
hmssaab |
May 7 2015, 06:33 PM
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#1
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hmssaab Group: Members Posts: 36 Joined: 22-February 15 From: Connecticut Member No.: 18,460 Region Association: None |
Chasing down a miss I get when the car is warmed up and under load. Car starts, idles and runs fine when cold. Idles fine when warm. All at once, after driving 1/2 hour, it starts to miss strongly every 10-20 seconds. No backfiring. If I drive with the revs below 2000 it misses gently. I have a Petronix.
I am first checking for loose connections. I changed the cap and rotor. I swapped in a new Bosch Blue Coil. Just how loose should the insulators be on the plugs? Three of the four insulators sway 5 to 10 degrees on the plug but the insulator on #4 sways 30 degrees (I still feel the spark plug threads when putting the insulator on the plug). Is there supposed to be a vacuum advance / vacuum line on the distributor? I see none. |
KELTY360 |
May 7 2015, 06:37 PM
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#2
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914 Neferati Group: Members Posts: 5,031 Joined: 31-December 05 From: Pt. Townsend, WA Member No.: 5,344 Region Association: Pacific Northwest |
I read the title to this thread and thought I'd be reading a sad story about how you parked the car in the WalMart lot and couldn't find it when you came back out. (IMG:style_emoticons/default/biggrin.gif)
Can't really help with your problem except to say...check your grounds. Good luck. |
Mblizzard |
May 7 2015, 07:02 PM
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#3
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Advanced Member Group: Members Posts: 3,033 Joined: 28-January 13 From: Knoxville Tn Member No.: 15,438 Region Association: South East States |
Carbs or FI?
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hmssaab |
May 7 2015, 07:17 PM
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#4
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hmssaab Group: Members Posts: 36 Joined: 22-February 15 From: Connecticut Member No.: 18,460 Region Association: None |
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earossi |
May 7 2015, 07:31 PM
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#5
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Member Group: Members Posts: 210 Joined: 8-December 11 From: Chicago, Il Member No.: 13,878 Region Association: Upper MidWest |
I think that you are on the right track. You mentioned just about every ignition component except the plug wires and plugs. The spark plug connectors should snap firmly in place. Im not that concerned whether they flop around or not, but there should be some force required to push the connectors on the plugs or to remove them. Also, since your issue is related to a hot engine, the insulation on the wires may be breaking down and may open up cracking with heat.
So, since you are new to the car, spend the money to replace the wire set to eliminate that as an item causing your issue. Also, when were the spark plugs last changed out? The little engine is really inexpensive to rune up. So, good time to renew. INcidentally, the miss sounds like ignition, not fuel related. |
stugray |
May 7 2015, 07:55 PM
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#6
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Advanced Member Group: Members Posts: 3,824 Joined: 17-September 09 From: Longmont, CO Member No.: 10,819 Region Association: None |
Is your voltage drooping?
Sounds like your pertronix is cutting out. Maybe your alt is not charging. Does it get worse if you turn on the headlights? |
somd914 |
May 7 2015, 08:27 PM
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#7
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Member Group: Members Posts: 1,171 Joined: 21-February 11 From: Southern Maryland Member No.: 12,741 Region Association: MidAtlantic Region |
Not having a vacuum advance is not uncommon with carbs - depends on the dizzy you are running. You can always throw points and condenser back on it, but I'd suspect wires first.
When it's missing, does it get to the point of being regular and increasing with RPM, i.e. does it appear to be one plug is cutting out? If so, disconnect one plug wire at a time and see if anything changes. Also move the wires around when missing to try to determine if they are arcing. |
hmssaab |
May 7 2015, 08:45 PM
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#8
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hmssaab Group: Members Posts: 36 Joined: 22-February 15 From: Connecticut Member No.: 18,460 Region Association: None |
Not having a vacuum advance is not uncommon with carbs - depends on the dizzy you are running. You can always throw points and condenser back on it, but I'd suspect wires first. When it's missing, does it get to the point of being regular and increasing with RPM, i.e. does it appear to be one plug is cutting out? If so, disconnect one plug wire at a time and see if anything changes. Also move the wires around when missing to try to determine if they are arcing. It is not regular. Let me try new wires. |
r3dplanet |
May 7 2015, 09:02 PM
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#9
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Senior Member Group: Members Posts: 679 Joined: 3-September 05 From: Portland, Oregon Member No.: 4,741 Region Association: None |
I doubt that it's the Pertronix. When they fail they just stop working instead of limping along. Is the timing set correctly? Valves adjusted? Which carbs do you have? Can you post a larger image showing more of the engine bay?
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Johny Blackstain |
May 7 2015, 09:16 PM
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#10
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Walnut Elite Stratocaster player Group: Members Posts: 3,434 Joined: 5-December 06 From: The Shenandoah River Member No.: 7,318 Region Association: MidAtlantic Region |
Off Topic: I would not run a Pertronix w/ a Bosch Blue Coil. I read many horror stories about how they are really not compatible with each other & can be prone to failure when combined. I believe the instructions for the Pertronix even specify what output the coil should have & the Bosch Blue does not match that. When I installed my Pertronix II I also purchased the matching coil that goes with it to insure compatibility & have had no issues.
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somd914 |
May 8 2015, 03:48 AM
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#11
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Member Group: Members Posts: 1,171 Joined: 21-February 11 From: Southern Maryland Member No.: 12,741 Region Association: MidAtlantic Region |
Off Topic: I would not run a Pertronix w/ a Bosch Blue Coil. I read many horror stories about how they are really not compatible with each other & can be prone to failure when combined. I believe the instructions for the Pertronix even specify what output the coil should have & the Bosch Blue does not match that. When I installed my Pertronix II I also purchased the matching coil that goes with it to insure compatibility & have had no issues. Hmmm, mine was installed by the PO and has ran several years sans problems with Pertronix and Blue coil. I've never dug into the documentation, but if this is the case, thanks for the heads up. |
Dave_Darling |
May 8 2015, 10:08 AM
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#12
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914 Idiot Group: Members Posts: 14,985 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California |
Check your valve clearances, and try a compression test. I hope I'm wrong, but my car exhibited similar symptoms the last time it dropped a valve seat.
--DD |
hmssaab |
May 8 2015, 01:13 PM
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#13
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hmssaab Group: Members Posts: 36 Joined: 22-February 15 From: Connecticut Member No.: 18,460 Region Association: None |
Another item I forgot to mention, the tach dips and bounces quite a bit at the same time as the miss. The miss always starts the same time after I start from cold (I drive the same test loop) at about 190 on the console oil temp gage. I will be receiving the plugs (WR7CC) the wires, the points and the condenser shortly. I noticed I have WR7DC plugs (longer electrodes) that are not recommended, however that figures into the equation (I will swap out plugs first by themselves out of curiosity).
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stugray |
May 8 2015, 01:27 PM
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#14
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Advanced Member Group: Members Posts: 3,824 Joined: 17-September 09 From: Longmont, CO Member No.: 10,819 Region Association: None |
Another item I forgot to mention, the tach dips and bounces quite a bit at the same time as the miss. The miss always starts the same time after I start from cold (I drive the same test loop) at about 190 on the console oil temp gage. I will be receiving the plugs (WR7CC) the wires, the points and the condenser shortly. I noticed I have WR7DC plugs (longer electrodes) that are not recommended, however that figures into the equation (I will swap out plugs first by themselves out of curiosity). My next question (if you verified that you have good voltage) was "Is the Dist getting very hot?" In addition to low voltage, high temps could make a questionable pertronix start acting up. You DEFINITELY have an electrical issue (Pertronix dropping out). |
Porschef |
May 8 2015, 02:32 PM
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#15
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How you doin' Group: Members Posts: 2,165 Joined: 7-September 10 From: LawnGuyland Member No.: 12,152 Region Association: North East States |
No problems with Pertronix and the blue coil in almost 4 years.
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hmssaab |
May 8 2015, 03:22 PM
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#16
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hmssaab Group: Members Posts: 36 Joined: 22-February 15 From: Connecticut Member No.: 18,460 Region Association: None |
Another item I forgot to mention, the tach dips and bounces quite a bit at the same time as the miss. The miss always starts the same time after I start from cold (I drive the same test loop) at about 190 on the console oil temp gage. I will be receiving the plugs (WR7CC) the wires, the points and the condenser shortly. I noticed I have WR7DC plugs (longer electrodes) that are not recommended, however that figures into the equation (I will swap out plugs first by themselves out of curiosity). My next question (if you verified that you have good voltage) was "Is the Dist getting very hot?" In addition to low voltage, high temps could make a questionable pertronix start acting up. You DEFINITELY have an electrical issue (Pertronix dropping out). Yes, the distributor cap is very hot. |
Dave_Darling |
May 8 2015, 05:27 PM
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#17
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914 Idiot Group: Members Posts: 14,985 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California |
Another item I forgot to mention, the tach dips and bounces quite a bit at the same time as the miss.... Definitely an ignition problem then. Unplug the black/purple tach signal wire from the coil and see if that fixes the misfire. If so, then your tach is shorting internally and needs to be rebuilt. --DD |
OU8AVW |
May 8 2015, 08:28 PM
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#18
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Yacht Rigger Group: Members Posts: 1,803 Joined: 1-October 08 From: Granbury, TX Member No.: 9,601 Region Association: Southwest Region |
Another item I forgot to mention, the tach dips and bounces quite a bit at the same time as the miss.... Definitely an ignition problem then. Unplug the black/purple tach signal wire from the coil and see if that fixes the misfire. If so, then your tach is shorting internally and needs to be rebuilt. --DD Wow, that's outa left field. Never would I think to check the tach like that. |
hmssaab |
May 11 2015, 09:05 AM
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#19
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hmssaab Group: Members Posts: 36 Joined: 22-February 15 From: Connecticut Member No.: 18,460 Region Association: None |
Not the tach shorting. Waiting for the condenser and points to arrive and will update.
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Dave_Darling |
May 11 2015, 05:35 PM
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#20
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914 Idiot Group: Members Posts: 14,985 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California |
Rats. At least it was an easy test!
Double-check everything that connects to the coil's (-) terminal. Make sure none of it can short to ground. --DD |
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