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Registered
Join Date: Dec 2006
Location: South Africa
Posts: 76
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Help!!! Bananas with Tach etc
This all started with a Tach which was showing to cut out at 5800 consistently (instead of 6500 - the engine went a bit higher than 5,8K, though, I could feel).
Following the advise from this forum, I replaced the points (now set at 0.35mm), 5º BTDC at idling (and happy), dwell at 35º and ok, replaced the rotor, rebuild the distributor, then replaced the majority of other ignition parts whilst burning some wires with the timing gun... Finally, I apparently broke the Tach itself by taking it out of housing a clipping a wire while "inspecting". Anyhow, the Tach is fixed now and was put back in again.. it works. I tested slowly... Dwell meter vs Tach - both at idling. Tach was ca. 200rpm up (vs dwell) at idling. According to the VDO guy, I could bend the Tach needle (down-wards) gently to come in line with the dwell meter. This I did and now came within 100rpm with the dwell meter at idling. When engine real hot, though, Tach goes up to 1150 rpm when stopped (haven't seen actual dwell as this was during a good drive). The Problem: Took it high and the Tach shows the engine is cutting out at 5000! (it does feel I am going a bit higher but nothing like 6500). The car pulls fine until it cuts out. What is the issue?? I need knowledgeable advise, please. E.g. what is a good way to find out real revs - vs Tach revs? Motor: 2.7s (recently rebuild) 901 tranny (recently rebuild) Tach: comes from a 912 (red-line - 6200) Regards
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_________________ Jacob 911 2.7s - 911 SC - 911 3.2 Carrera |
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06-02-2009, 06:02 AM
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Moderator
Join Date: Dec 2001
Posts: 9,569
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Jacob, your four cylinder tach will NEVER read correctly with three ignition pulses per revolution.
When your engine is running at 6000 rpm, there are three ignition pulses per revolution, or 300 per second. A 911 tach correctly reads this. A four cylinder tach expects two pulses per revolution- and will read 9,000 rpm at the same 300Hz pulse rate. Get yourself a good six cylinder tach from the classifieds.
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'66 911 #304065 Irischgruen ‘96 993 Carrera 2 Polarsilber '81 R65 Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13) Ex-'88 Carrera (Sold 3/29/02) Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04) Ex-'89 944 Turbo S (Sold 8/21/20) |
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06-02-2009, 06:10 AM
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Registered
Join Date: Dec 2006
Location: South Africa
Posts: 76
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Valued point John, thanks, but the Tach has been "calibrated" for a 6 cyl some while ago, according by the local VDO.
Anyhow, why the sudden drop from 5,8 yo 5,0? Regards
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_________________ Jacob 911 2.7s - 911 SC - 911 3.2 Carrera |
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06-02-2009, 06:15 AM
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Registered
Join Date: Dec 2006
Location: South Africa
Posts: 76
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Anyone else to add?
I now also realized that I get 120km/h at 3400rpm. Before it was 120km/h at ca. 3800rpm. Is it my Tach?
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_________________ Jacob 911 2.7s - 911 SC - 911 3.2 Carrera |
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06-03-2009, 10:05 PM
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