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Registered User
Join Date: Jan 2013
Posts: 5
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Intermittent Ignition Problems - 911 (1988)
Hi,
Ok, I have been searching the forums for help. Symptoms: Start the car Drive 20 minutes - Perfect Stop the car Car will not start again Wait 30 minutes - No really every time its 30 mins.. and it starts. Spark and ignition is perfect when working (Confirmed with Strobe) No Ignition when the car will not start (Confirmed with Strobe) Car Specs: 1988 911 Targa Super Sport Sigma Sector S Alarm Work so far: New DME Relay Checked the DME Harness pins 25/26 - 1155 Ohms drops to 1127 when not working Checked the DME Harness pins 8/27 - 1170 Ohms increases to 1245 when not working Questions: Some forums say when I turn the key I should get a voltage on 25/26 pins and 8/27.. I do not.. is this normal? What on earth could be stopping the ignition. Please help me... |
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wild guess
aloha, i'm not sure if 88 3,2 has a crank position sensor but on a 89 3.6 motronic it was the solution to an oddball intermittent issue I worked on. easy to check with a noid light for a fuel injector (cheap at any parts store) as the sensor generates a volt and a half or so. if it doesn't, no fuel pump, spark etc as it tells the dme when the engine is turning, cheers
geoff Last edited by c2kid; 01-31-2013 at 09:56 PM.. |
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vince_wa
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Just finished resolving the exact problem on my 87
Reference sensors were too far away from flywheel - problem happened after replacement of both reference sensors and 3 months of driving - my symptom was same as yours but I also did not get full range in revs - after 5500 rpm engine simply starved for fuel. Easy fix after working out problem Remove left rear wheel whilst jacked up. Loosen 2x 10mm bolts and move reference sensor till it touches flywheel then move back a very small amount and slightly tighten all bolts. Once you think in right position use fan pulley bolt to rotate engine to confirm reference sensor does not hit flywheel. Tighten all bolts to required torque. Happy driving
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Garage - 1987 911 widebody |
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Join Date: Jan 2009
Location: Norcross, GA
Posts: 627
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I agree with above - I changed out both sensors, speed and reference as they sit right next to each other. No more problems.
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'85 RoW 911 Coupe '65 356 SC '72 BMW 2002Tii '10 Cayenne '20 Ram Longhorn |
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I recently had an intermittent problem too on my 85. It was the electronic portion of the ignition switch. The contacts get worn and sometimes everything is fine and sometimes not ... worth consideration.
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Dave 1985 Factory Turbo-Look Coupe 2011 Cayman S 2012 Audi S4 |
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Registered User
Join Date: Jan 2013
Posts: 5
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Guys. Thanks so much. I will try those things..
A slight update. I have a multimeter on pins 25/26 and there is no voltage on cranking the engine. The voltage from 8/27 is 0.9v. |
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Registered User
Join Date: Jan 2013
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Oh well.. I thought it was the sensor.. but the results from the multimeter are inconclusive:
TDC - Pins 25/26 0hms / Volts 1155 / 0 - Non Start 1125 / 0.125 - Starts 1058 / 0.143 - Starts 1233 / 0.124 - Non Start RPM - Pins 8/27 0hms / Volts 1147 / 1.7 - Starts 1086 / 1.9 - Starts 1247 / 1.8 - Non Start 1226 / 1.8 - Non Start |
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I had an issue like this on my '88. It turned out to be not the reference sensors, but a bad connection on the CHT sensor. Make sure the plugs on all three sensors are locked in and secure. I had to take mine out of the bracket, and ran it that way until I could replace the broken connector.
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Alan Past: '74 914 2.0, '82 911 SC Targa, '88 911 Cabriolet, '88 911 Cabriolet again Present: '00 Boxster S "Happiness is not around the next corner......happiness IS the next corner." |
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Join Date: May 2002
Location: St Louis
Posts: 4,211
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If you can verify the injectors are pulsing you could rule out the variable reluctance sensors. If you short the Cylinder Head Temperature sensor mating connector you can rule that out.
If the injectors are working you will have to look into the DME itself.
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Rick 88 Cab |
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Join Date: Jan 2006
Location: Santa Barbara, CA
Posts: 2,307
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Had a very similar problem on a 74. A several pin connector carrying electricity fore and aft thru the front "firewall" had a bit of corrosion at one or two of the pins. Unplugging and cleaning fixed the issue.
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jhtaylor santa barbara 74 911 coupe. 2.7 motor by Schneider Auto Santa Barbara. Case blueprinted, shuffle-pinned, boat-tailed by Competition Engineering. Elgin mod-S cams. J&E 9.5's. PMO's. 73 Targa (gone but not forgotten) |
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muck-raker
Join Date: Jan 2009
Location: Coastal PNW
Posts: 3,059
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crank position sensor or cylinder head temp sensor.
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STONE '88 Cabriolet, using EP Slick 20w50 partial synthetic Snake Oil...just as Rommel intended. ![]() Deny Everything; Admit Nothing; and Always Make Counter-accusations ![]() |
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Registered User
Join Date: Jan 2013
Posts: 5
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Cylinder Head Sensor (CHT).. Pins 13/5 on DME Harness.
Cold Start (Working) - 4.66 KOhms on DME Took for a drive and took over 5000 RPM to make sure there was no loss of power.. There wasn't and it was as always a lot of fun.. Until I hit a puddle! Returned > Turned engine off > Start up.. No Problem Waited 5 minutes > Attempt Start up.. No Start! (179.6 Ohms) I am now just using this as a Diary.. Are we still thinking Sensors, they seem to be working correctly??? |
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Should those noted pins for your resistance checks of the ref/speed sensors correlate to terminals 1 and 2 at the connector up top (engine bay) looks like the range should be 864 ohms - 1056 ohms (at ~77 degrees F) . Is she going high when warm?..?..///
Terms 1-3 and 2-3 should be >100K Per Bentley. Best! Doyle
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Recording Engineer, Administrator and Entrepeneur Designer of Fine Studios, Tube Amplifier Guru 1989 Porsche 911 Carrera Coupe 25th Anniversary Special Edition Middle Georgia |
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Join Date: May 2002
Location: St Louis
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Ooops brain fart.
The CHT sensor has nothing to do with spark delivery. You should however see if you have injector pulses to see the DME is getting reference signals. There have been cases of the ignition transistor in the DME having bad solder joints. EDIT the cht will not inhibit spark.
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Rick 88 Cab Last edited by rick-l; 02-02-2013 at 09:57 AM.. |
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CHT numbers look to be ok.....knowing:
(from the Porsche manual) CHT and sensor temp is ~ 265 degrees F with an oil temp of 194 degrees F. This would give you 90 ohms. 212 degrees F gives you 160-210 ohms. On the other side,....32 degrees F will give you 4.4k-ohms to 6.8 k-ohms.
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Recording Engineer, Administrator and Entrepeneur Designer of Fine Studios, Tube Amplifier Guru 1989 Porsche 911 Carrera Coupe 25th Anniversary Special Edition Middle Georgia |
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Have you checked the DME for cracked solder joints? On mine that caused similar problems - runs GREAT then bam, no spark. Cool down a little and runs again as if nothing happened. The coil is driven by transistors that stand up off the board, so they are subject to vibration and easily crack the solder over time.
Chuck.H '89 TurboLookTarga, 346k miles |
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Registered User
Join Date: Jan 2013
Posts: 5
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Hi, I resolved it. It was simply the connection to the DME Relay. The connections looked good but they weren't making 100% contact.
Thanks everyone for your help! |
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The Dude abides...
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So what'd you do to make good contact? Just remove and replace a bunch of times?
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Steve '03 Carrera 4S |
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Tags |
1988 , 911 , ignition , no spark , targa |